Co-reporter:Zhenxiao Pan, Iván Mora-Seró, Qing Shen, Hua Zhang, Yan Li, Ke Zhao, Jin Wang, Xinhua Zhong, and Juan Bisquert
Journal of the American Chemical Society June 25, 2014 Volume 136(Issue 25) pp:9203-9210
Publication Date(Web):May 30, 2014
DOI:10.1021/ja504310w
Semiconductor quantum dots (QDs) are extremely interesting materials for the development of photovoltaic devices, but currently the present the drawback is that the most efficient devices have been prepared with toxic heavy metals of Cd or Pb. Solar cells based on “green” QDs—totally free of Cd or Pb—present a modest efficiency of 2.52%. Herein we achieve effective surface passivation of the ternary CuInS2 (CIS) QDs that provides high photovoltaic quality core/shell CIS/ZnS (CIS-Z) QDs, leading to the development of high-efficiency green QD solar cells that surpass the performance of those based on the toxic cadmium and lead chalcogenides QDs. Using wide absorption range QDs, CIS-Z-based quantum dot sensitized solar cell (QDSC) configuration with high QD loading and with the benefit of the recombination reduction with type-I core/shell structure, we boost the power conversion efficiency of Cd- and Pb-free QDSC to a record of 7.04% (with certified efficiency of 6.66%) under AM 1.5G one sun irradiation. This efficiency is the best performance to date for QDSCs and also demonstrates that it is possible to obtain comparable or even better photovoltaic performance from green CIS QDs to the toxic cadmium and lead chalcogenides QDs.
Co-reporter:Wenran Wang, Guocan Jiang, Juan Yu, Wei Wang, Zhenxiao Pan, Naoki Nakazawa, Qing Shen, and Xinhua Zhong
ACS Applied Materials & Interfaces July 12, 2017 Volume 9(Issue 27) pp:22549-22549
Publication Date(Web):June 16, 2017
DOI:10.1021/acsami.7b05598
Unambiguously direct adsorption (DA) of initial oil-soluble quantum dots (QDs) on TiO2 film electrode is a convenient and simple approach in the construction of quantum dot sensitized solar cells (QDSCs). Regrettably, low QD loading amount and poor reproducibility shadow the advantages of DA route and constrain its practical application. Herein, the influence of experimental variables in DA process on QD loading amount as well as on the photovoltaic performance of the resultant QDSCs was investigated and optimized systematically, including the choice of solvent, purification of QDs, and sensitization time, as well as QD concentration. Experimental results demonstrated that it is essential to choose appropriate solvent as well as control purification cycles of original QD suspensions so as to realize satisfactory QD loading amount and ensure the high reproducibility. In addition, DA mode renders efficient electron injection from QD to TiO2, yet low QD loading amount and adverse QD agglomeration in comparison with the well-developed capping ligand induced self-assembly (CLIS) deposition approach. Mg2+ treatment on TiO2 photoanodes can promote the QD loading amount in DA mode. The optimized QDSCs based on DA mode exhibited efficiencies of 6.90% and 9.02% for CdSe and Zn–Cu–In–Se QDSCs, respectively, which were comparable to the best results based on CLIS mode (6.88% and 9.56%, respectively).Keywords: direct adsorption; loading amount; photovoltaics; QD agglomeration; quantum dot sensitized solar cells;
Co-reporter:Wenxiang Peng;Zhenxiao Pan;Jun Du;Naoki Nakazawa;Jiankun Sun;Zhonglin Du;Gencai Shen;Juan Yu;Jin-Song Hu;Qing Shen
ACS Applied Materials & Interfaces February 15, 2017 Volume 9(Issue 6) pp:5328-5336
Publication Date(Web):January 17, 2017
DOI:10.1021/acsami.6b14649
I–III–VI2 group “green” quantum dots (QDs) are attracting increasing attention in photoelectronic conversion applications. Herein, on the basis of the “simultaneous nucleation and growth” approach, Cu–In–Ga–Se (CIGSe) QDs with light harvesting range of about 1000 nm were synthesized and used as sensitizer to construct quantum dot sensitized solar cells (QDSCs). Inductively coupled plasma atomic emission spectrometry (ICP-AES), wild-angle X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses demonstrate that the Ga element was alloyed in the Cu–In–Se (CISe) host. Ultraviolet photoelectron spectroscopy (UPS) and femtosecond (fs) resolution transient absorption (TA) measurement results indicate that the alloying strategy could optimize the electronic structure in the obtained CIGSe QD material, thus matching well with TiO2 substrate and favoring the photogenerated electron extraction. Open circuit voltage decay (OCVD) and impedance spectroscopy (IS) tests indicate that the intrinsic recombination in CIGSe QDSCs was well suppressed relative to that in CISe QDSCs. As a result, CIGSe based QDSCs with use of titanium mesh supported mesoporous carbon counter electrode exhibited a champion efficiency of 11.49% (Jsc = 25.01 mA/cm2, Voc = 0.740 V, FF = 0.621) under the irradiation of full one sun in comparison with 9.46% for CISe QDSCs.Keywords: alloying strategy; Cu−In−Ga−Se (CIGSe) QDs; high efficiency; photovoltaic cells; quantum dot sensitized solar cells;
Co-reporter:Juan Yu;Wenran Wang;Zhenxiao Pan;Jun Du;Zhenwei Ren;Weinan Xue
Journal of Materials Chemistry A 2017 vol. 5(Issue 27) pp:14124-14133
Publication Date(Web):2017/07/11
DOI:10.1039/C7TA04344A
The undesired charge recombination loss, occurring at photoanode/electrolyte interfaces, as well as the high redox potential of the currently used polysulfide redox couple electrolyte restrain the photovoltaic performance, particularly the open-circuit potential (Voc), of quantum dot sensitized solar cells (QDSCs). Herein, a valid and facile method to improve the performance of QDSCs is presented by modifying the polysulfide electrolyte with the addition of tetraethyl orthosilicate (TEOS). This approach is effective in a series of QDSC systems including the most commonly studied CdSe, CdSeTe, as well as Zn–Cu–In–Se (ZCISe) QDSCs. Experimental results indicate that with the use of 6 vol% TEOS additive in pristine polysulfide electrolyte at a staying time of 24 h, a remarkable enhancement in the conversion efficiency from 11.75% to 12.34% was obtained in ZCISe QDSCs. This photovoltaic performance is believed to be among the best result for all types of QD-based solar cells. The intrinsic mechanism for the performance improvement by the TEOS additive was verified by electrochemical impedance spectroscopy (EIS) and open-circuit voltage decay (OCVD) measurements.
Co-reporter:Xiaohui Yi;Zhenwei Ren;Ningli Chen;Cheng Li;Shiyong Yang;Jizheng Wang
Advanced Electronic Materials 2017 Volume 3(Issue 11) pp:
Publication Date(Web):2017/11/01
DOI:10.1002/aelm.201700251
AbstractOwing to their attractive performance in photovoltaic devices, organolead halide perovskite materials have attracted enormous interest for photodetector applications. However, current perovskite-based photodetectors mainly rely on high-conductive 2D materials such as graphene or transition metal sulfides to transport photocarriers, which indeed significantly improve the photoresponsivity but seriously weaken other parameters such as on/off ratio or response speed. Achieving a high overall performance remains a challenge. Here, a solution-processed TiO2 nanocrystal (NC) film is employed to transport photocarriers. The designed TiO2 NC/perovskite (CH3NH3PbI3) bilayer device exhibits satisfactory overall performance with on/off ratio of 4000, photodetectivity of 1.85 × 1012 Jones, and rise/decay time of 0.49/0.56 s. The device can also be integrated on flexible polyimide substrate. This work provides a strategy to realize high-performance perovskite-based photodetectors and clearly demonstrates their potential applications in future flexible optoelectronics.
Co-reporter:Shuang Jiao, Jun Du, Zhonglin Du, Donghui LongWuyou Jiang, Zhenxiao Pan, Yan Li, Xinhua Zhong
The Journal of Physical Chemistry Letters 2017 Volume 8(Issue 3) pp:
Publication Date(Web):January 11, 2017
DOI:10.1021/acs.jpclett.6b02864
The exploration of catalyst materials for counter electrodes (CEs) in quantum dot sensitized solar cells (QDSCs) that have both high electrocatalytic activity and low charge transfer resistance is always significant yet challenging. In this work, we report the incorporation of nitrogen heteroatoms into carbon lattices leading to nitrogen-doped mesoporous carbon (N-MC) materials with superior catalytic activity when used as CEs in Zn–Cu–In–Se QDSCs. A series of N-MC materials with different nitrogen contents were synthesized by a colloidal silica nanocasting method. Electrochemical measurements revealed that the N-MC with a nitrogen content of 8.58 wt % exhibited the strongest activity in catalyzing the reduction of a polysulfide redox couple (Sn2–/S2–), and therefore, the corresponding QDSC device showed the best photovoltaic performance with an average power conversion efficiency (PCE) of 12.23% and a certified PCE of 12.07% under one full sun illumination, which is a new PCE record for quantum dot based solar cells.
Co-reporter:Zhenwei Ren;Jiankun Sun;Hui Li;Peng Mao;Yuanzhi Wei;Jinsong Hu;Shiyong Yang;Jizheng Wang
Advanced Materials 2017 Volume 29(Issue 33) pp:
Publication Date(Web):2017/09/01
DOI:10.1002/adma.201702055
Due to their wide tunable bandgaps, high absorption coefficients, easy solution processabilities, and high stabilities in air, lead sulfide (PbS) quantum dots (QDs) are increasingly regarded as promising material candidates for next-generation light, low-cost, and flexible photodetectors. Current single-layer PbS-QD photodetectors suffer from shortcomings of large dark currents, low on–off ratios, and slow light responses. Integration with metal nanoparticles, organics, and high-conducting graphene/nanotube to form hybrid PbS-QD devices are proved capable of enhancing photoresponsivity; but these approaches always bring in other problems that can severely hamper the improvement of the overall device performance. To overcome the hurdles current single-layer and hybrid PbS-QD photodetectors face, here a bilayer QD-only device is designed, which can be integrated on flexible polyimide substrate and significantly outperforms the conventional single-layer devices in response speed, detectivity, linear dynamic range, and signal-to-noise ratio, along with comparable responsivity. The results which are obtained here should be of great values in studying and designing advanced QD-based photodetectors for applications in future flexible optoelectronics.
Co-reporter:Hua Zhang;Cheng Yang;Zhonglin Du;Dengyu Pan
Journal of Materials Chemistry A 2017 vol. 5(Issue 4) pp:1614-1622
Publication Date(Web):2017/01/24
DOI:10.1039/C6TA08443E
Although copper sulfide and/or carbon materials have been utilized in counter electrodes (CEs) due to their good catalytic activity and conductivity, the efficiency of the assembled quantum dot-sensitized solar cells (QDSCs) is still unsatisfactory because of the relatively low photovoltage (Voc), which is commonly less than 0.7 V. In this study, graphene hydrogels (GHs) compressed onto titanium mesh served as the CE and the assembled CdSeTe QDSCs exhibited a photovoltaic conversion efficiency (PCE) of 9.85% and a Voc as high as 0.756 V, which increased by 19.0% and 14.9%, respectively, and are higher than those of the conventional CuS on FTO. By incorporating CuS nanoparticles into GH during gelation, the as-prepared GH–CuS CEs show further improved performance and the maximum PCE and Voc obtained were 10.71% and 0.786 V, respectively. The fill factor of the cells was also continuously increased. The excellent performance of the devices could be attributed to the synergistic effects of the water-rich GH (having a 3D porous structure accompanied by good conductivity) and highly catalytic CuS, reflected from the small series resistance, high catalytic activity, small electron transfer resistance, and stability, which have been confirmed by EIS, Tafel polarization, and CV curves.
Co-reporter:Jun Du; Zhonglin Du; Jin-Song Hu; Zhenxiao Pan; Qing Shen; Jiankun Sun; Donghui Long; Hui Dong; Litao Sun; Xinhua Zhong;Li-Jun Wan
Journal of the American Chemical Society 2016 Volume 138(Issue 12) pp:4201-4209
Publication Date(Web):March 10, 2016
DOI:10.1021/jacs.6b00615
The enhancement of power conversion efficiency (PCE) and the development of toxic Cd-, Pb-free quantum dots (QDs) are critical for the prosperity of QD-based solar cells. It is known that the properties (such as light harvesting range, band gap alignment, density of trap state defects, etc.) of QD light harvesters play a crucial effect on the photovoltaic performance of QD based solar cells. Herein, high quality ∼4 nm Cd-, Pb-free Zn–Cu–In–Se alloyed QDs with an absorption onset extending to ∼1000 nm were developed as effective light harvesters to construct quantum dot sensitized solar cells (QDSCs). Due to the small particle size, the developed QD sensitizer can be efficiently immobilized on TiO2 film electrode in less than 0.5 h. An average PCE of 11.66% and a certified PCE of 11.61% have been demonstrated in the QDSCs based on these Zn–Cu–In–Se QDs. The remarkably improved photovoltaic performance for Zn–Cu–In–Se QDSCs vs Cu–In–Se QDSCs (11.66% vs 9.54% in PCE) is mainly derived from the higher conduction band edge, which favors the photogenerated electron extraction and results in higher photocurrent, and the alloyed structure of Zn–Cu–In–Se QD light harvester, which benefits the suppression of charge recombination at photoanode/electrolyte interfaces and thus improves the photovoltage.
Co-reporter:Zhenwei Ren, Zhiqiang Wang, Rong Wang, Zhenxiao Pan, Xueqing Gong, and Xinhua Zhong
Chemistry of Materials 2016 Volume 28(Issue 7) pp:2323
Publication Date(Web):March 12, 2016
DOI:10.1021/acs.chemmater.6b00434
Exploring facile modifications on photoanode to suppress charge recombination at photoanode/electrolyte interfaces is an efficient way to improve the performance of quantum dot sensitized solar cells (QDSCs). Herein, a series of metal oxyhydroxide gels have been overcoated on CdSeTe QD sensitized photoanodes via a hydrolysis and condensation process from the corresponding metal chloride (NbCl5, ZrOCl2, SnCl4, FeCl3, AlCl3, CoCl2, CuCl2, MgCl2, and ZnCl2) aqueous solutions, and their effects on the photovoltaic performance are systematically investigated. Photovoltaic measurement results indicate that the NbCl5 and ZrOCl2 modifications offer a remarkable enhancement in photovoltaic performance, especially in photovoltage. The SnCl4 AlCl3, MgCl2, and ZnCl2 treatments give a negligible influence, and the FeCl3, CuCl2, and CoCl2 treatments present a negative effect on the performance. DFT calculations suggest that different metal oxyhydroxide coatings bring forward distinct densities of empty states at the surface of TiO2, which correspond to different charge recombination kinetics and therefore different photovoltaic performance. Electrochemical impedance spectroscopy (EIS) and open-circuit voltage decay (OCVD) measurements confirm further the suppressed charge recombination process after coating with the amorphous Zr or Nb oxyhydroxide layer. In all, an impressive power conversion efficiency (PCE) of 9.73% (Jsc = 21.04 mA/cm2, Voc = 0.720 V, FF = 0.642) was obtained for CdSeTe-based QDSCs with ZrOCl2 modification on photoanode.
Co-reporter:Jin Wang, Yan Li, Qing Shen, Takuya Izuishi, Zhenxiao Pan, Ke Zhao and Xinhua Zhong
Journal of Materials Chemistry A 2016 vol. 4(Issue 3) pp:877-886
Publication Date(Web):02 Dec 2015
DOI:10.1039/C5TA09306F
Transition metal ion (especially Mn2+) doping has been proven to be an effective approach to modify the intrinsic photo-electronic properties of semiconductor quantum dots (QDs). However, previous works to directly grow Mn doped QDs on TiO2 film electrodes at room temperature resulted in the potential of the Mn dopant not being fully demonstrated in quantum dot sensitized solar cells (QDSCs). Herein, Mn doped CdSe0.65Te0.35 QDs (simplified as Mn:QD) were pre-synthesized via a “growth doping” strategy at high temperature. A QD-sensitized photoanode with the configuration TiO2/Mn:QD/Mn:ZnS/SiO2 was prepared and corresponding cell devices were constructed using Cu2S/brass counter electrodes and polysulfide electrolyte, together with reference cells with the photoanode configurations TiO2/Mn:QD/ZnS/SiO2, TiO2/QD/Mn:ZnS/SiO2, and TiO2/QD/ZnS/SiO2. The photovoltaic performance results indicate that TiO2/Mn:QD/Mn:ZnS/SiO2 cells exhibit the best photovoltaic performance among all the studied cell devices with a power conversion efficiency (PCE) for the champion cell of 9.40% (Jsc = 20.87 mA cm−2, Voc = 0.688 V, FF = 0.655) under AM 1.5 G one full sun illumination, which is among the best results for QDSCs. The open circuit voltage decay (OCVD), impedance spectroscopy (IS) and transient absorption (TA) measurements confirm that the Mn2+ dopant can suppress charge recombination and improve the photovoltage and PCE of the resulting cells.
Co-reporter:Zhonglin Du, Jing Tong, Wenxia Guo, Hua Zhang and Xinhua Zhong
Journal of Materials Chemistry A 2016 vol. 4(Issue 30) pp:11754-11761
Publication Date(Web):28 Jun 2016
DOI:10.1039/C6TA04934F
The development of a highly efficient stretchable counter electrode (CE) for quantum dot sensitized solar cells (QDSCs) is still challenging. In this work, a flexible Cu/Ni film has been pre-prepared via a novel redox reaction between Ni foam and Cu ions. Further, a flexible Cu2S/Ni CE was fabricated for the first time by sulfidation of the Cu/Ni film. A high photovoltaic conversion efficiency (PCE) of 8.94% for a model CdSeTe QDSC composed of the flexible Cu2S/Ni CE and a glass based photoanode was obtained, with the performance being strongly attributed to the excellent catalytic activity, high conductivity and good adhesion between Cu2S and Ni foam. Furthermore, flexible photovoltaic devices constructed using the as-prepared bendable Cu2S/Ni CE as well as a TiO2 based plastic photoanode have also been assembled with the highest PCE of 3.55%. Satisfactory mechanical properties and stability after repeated bending have also been achieved.
Co-reporter:Shuang Jiao, Jin Wang, Qing Shen, Yan Li and Xinhua Zhong
Journal of Materials Chemistry A 2016 vol. 4(Issue 19) pp:7214-7221
Publication Date(Web):11 Apr 2016
DOI:10.1039/C6TA02465C
The power conversion efficiencies (PCEs) of PbS quantum dot sensitized solar cells (QDSCs) reported are typically below 6%. This poor efficiency is mainly derived from the serious charge recombination in internal QDs and at the interface of QDs/TiO2/electrolyte. In this work, PbS/CdS QDs with a core/shell structure, which were used as the photosensitizer to fabricate sensitized solar cells, were prepared through the ion exchange method. With the reduced trapping state defects on the surface of the PbS QDs and resulting effective suppression of adverse charge recombination, the PbS/CdS QD-based cells have been improved remarkably in comparison with the pristine PbS-based QDSCs. By optimization of the thickness of the CdS shell, a PCE of 7.19% under one full sun illumination was obtained on the fabricated devices, which is among the best performances for liquid-junction PbS QDSCs.
Co-reporter:Wenliang Feng, Yan Li, Jun Du, Wei Wang and Xinhua Zhong
Journal of Materials Chemistry A 2016 vol. 4(Issue 4) pp:1461-1468
Publication Date(Web):23 Dec 2015
DOI:10.1039/C5TA08209A
Limited by the volatilization and leakage of liquid electrolytes, the long-term stability of liquid-junction quantum dot sensitized solar cells (QDSCs) remains a main challenge for the application of QDSCs. Herein, a polyelectrolyte with superior water-absorbing and water-holding capacity, sodium polyacrylate (PAAS), was attempted to gelate conventional aqueous polysulfide electrolytes to construct quasi-solid-state QDSCs. PAAS gel electrolytes have a comparable conductivity with liquid polysulfide electrolytes. Meanwhile, the PAAS gel could penetrate readily into the framework of mesoporous TiO2 film electrodes due to the strong coordination ability of carboxylate groups on PAAS polymer chains with metal ions. Benefited from the high conductivity of the PAAS gel and its perfect contact with the TiO2 surface, an impressive photovoltaic performance with a power conversion efficiency of 8.54% in one full sunlight, which is among the best performance for QDSCs, was achieved for CdSeTe QDSCs. Furthermore, the light-soaking stability of the resulting cell devices is significantly improved in comparison with that of the conventional aqueous polysulfide electrolyte based ones.
Co-reporter:Guocan Jiang, Zhenxiao Pan, Zhenwei Ren, Jun Du, Cheng Yang, Wenran Wang and Xinhua Zhong
Journal of Materials Chemistry A 2016 vol. 4(Issue 29) pp:11416-11421
Publication Date(Web):23 Jun 2016
DOI:10.1039/C6TA04027F
Charge recombination losses are primarily responsible for the modest photovoltaic performance of quantum dot sensitized solar cells (QDSCs). Charge recombination occurring at the photoanode/electrolyte interface contributes significant energy loss in QDSC devices. Herein, a facile method to reduce the recombination loss by modifying the polysulfide electrolyte with the addition of poly(vinyl pyrrolidone) (PVP) as an efficient and general additive was introduced. It was found that the PVP modified polysulfide electrolyte could significantly improve the photovoltaic performance of QDSCs, especially the open-circuit voltage and fill factor. In addition, the PVP modified electrolyte is widely applicable to various QD sensitizer based systems. Impedance spectroscopy and open circuit voltage decay (OCVD) measurements reveal that the charge recombination processes occurring at the TiO2/QDs/electrolyte interfaces were remarkably inhibited using the PVP modified electrolyte. The average power conversion efficiency (PCE) was improved remarkably by 9% and a champion PCE of 9.77% was obtained with 20 wt% PVP in the polysulfide electrolyte for CdSexTe1−x based QDSCs. Moreover, the stability of the constructed QDSCs was also improved by employing the PVP modified polysulfide electrolyte.
Co-reporter:Wenran Wang, Jun Du, Zhenwei Ren, Wenxiang Peng, Zhenxiao Pan, and Xinhua Zhong
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 45) pp:31006
Publication Date(Web):October 31, 2016
DOI:10.1021/acsami.6b11122
Increasing QD loading amount on photoanode and suppressing charge recombination are prerequisite for high-efficiency quantum dot-sensitized solar cells (QDSCs). Herein, a facile technique for enhancing the loading amount of QDs on photoanode and therefore improving the photovoltaic performance of the resultant cell devices is developed by pipetting metal salt aqueous solutions on TiO2 film electrode and then evaporating at elevated temperature. The effect of different metal salt solutions was investigated, and experimental results indicated that the isoelectric point (IEP) of metal ions influenced the loading amount of QDs and consequently the photovoltaic performance of the resultant cell devices. The influence of anions was also investigated, and the results indicated that anions of strong acid made no difference, while acetate anion hampered the performance of solar cells. Infrared spectroscopy confirmed the formation of oxyhydroxides, whose behavior was responsible for QD loading amount and thus solar cell performance. Suppressed charge recombination based on Mg2+ treatment under optimal conditions was confirmed by impedance spectroscopy as well as transient photovoltage decay measurement. Combined with high-QD loading amount and retarded charge recombination, the champion cell based on Mg2+ treatment exhibited an efficiency of 9.73% (Jsc = 27.28 mA/cm2, Voc = 0.609 V, FF = 0.585) under AM 1.5 G full 1 sun irradiation. The obtained efficiency was one of the best performances for liquid-junction QDSCs, which exhibited a 10% improvement over the untreated cells with the highest efficiency of 8.85%.Keywords: charge recombination; loading amount; metal oxyhydroxide; photovoltaics; quantum dot-sensitized solar cells
Co-reporter:Ke Zhao; Zhenxiao Pan
The Journal of Physical Chemistry Letters 2016 Volume 7(Issue 3) pp:406-417
Publication Date(Web):January 13, 2016
DOI:10.1021/acs.jpclett.5b02153
Benefiting from the unique excellent optoelectronic properties of quantum dot light absorbers, quantum dot sensitized solar cell (QDSCs) are a promising candidate for the low-cost third-generation solar cells. Over the past few years, the power conversion efficiency (PCE) of QDSCs presents a rapid evolution from less than 1% to beyond 8%. Charge recombination is regarded as one of the most significant factors in limiting the photovoltaic performance of QDSCs. A significant improvement in the PCE of QDSCs has been obtained by charge recombination control. Some effective routes to suppress charge recombination processes, such as adopting preprepared high-quality QD sensitizers, tailoring the electronic properties of QDs, and interface engineering with the use of organic or inorganic thin layer overcoating the sensitized photoanode have been overviewed in this perspective. Also, the possible accesses to better performance (higher efficiency and stability) of the QDSCs have been proposed on the basis of achievements obtained previously.
Co-reporter:Guoshuai Wang, Huiyun Wei, Yanhong Luo, Huijue Wu, Dongmei Li, Xinhua Zhong, Qingbo Meng
Journal of Power Sources 2016 302() pp: 266-273
Publication Date(Web):20 January 2016
DOI:10.1016/j.jpowsour.2015.10.070
Co-reporter:Hua Zhang, Cong Wang, Wenxiang Peng, Cheng Yang, Xinhua Zhong
Nano Energy 2016 Volume 23() pp:60-69
Publication Date(Web):May 2016
DOI:10.1016/j.nanoen.2016.03.009
•Copper selenides with heavily deficient copper are used as counter electrodes.•The champion efficiencies of 6.49% and 8.72% for CdSe and CdSeTe QDSCs are achieved, respectively.•Copper selenide counter electrodes show high conductivity, stability and activity.Semiconductors such as sulfides have been commonly used as counter electrodes (CEs) in quantum dot sensitized solar cells (QDSCs) with high stability and catalytic activity. But the intrinsic unsatisfactory conductivity has been making researchers find alternative materials for further improving the efficiency. Here nanometer sized copper selenides substrated on F-doped SnO2 (CuxSe/FTO) are used as CE in the construction of QDSCs. Through optimizing the composition and structure variables of the CE materials, including Cu/Se ratio, film thickness, sintering temperature and time, we achieve the power conversion efficiencies up to 6.49% and 8.72% for CdSe and CdSeTe based QDSCs, respectively. Our results show that the excellent photovoltaic performance is strongly associated with the low Cu/Se molar ratio in the range of 1.20–1.38, suggesting the heavily deficient copper in CuxSe. The resultant good conductivity and electrochemical catalytic activity of the CuxSe/FTO CE have been verified by the electrochemical impedance spectroscopy, Tafel polarization and four-probe measurement results.
Co-reporter:Wenxia Guo
The Journal of Physical Chemistry C 2016 Volume 120(Issue 30) pp:16500-16506
Publication Date(Web):July 12, 2016
DOI:10.1021/acs.jpcc.6b05211
Because of their good conductivities and high catalytic activities, carbon materials and copper sulfides have been individually and jointly used as counter electrodes in quantum-dot-sensitized solar cells (QDSCs). However, obtaining a combination of high conversion efficiency and stability is still challenging. In this work, we present a facile method for fabricating Cu1.8S–C hybrid counter electrodes through the sulfidation of a copper–carbon composite synthesized by grinding a mixture of organic binder, commercial copper powder, and carbon material containing activated carbon and carbon black in a designed mass ratio. The assembled CdSeTe-sensitized QDSCs achieved a high PCE of 8.40%, larger than that of pure carbon (5.25%) and comparable to that of conventional CuxS/brass-based QDSCs (8.44%). Significantly, the devices based on Cu1.8S–C showed excellent stability. The improved performance is mainly attributed to the good conductivity and stability of carbon and the high catalytic activity of Cu1.8S.
Co-reporter:Yunfei Ma, Yanan Bai, Hailei Mao, Qunying Hong, Dawei Yang, Honglian Zhang, Fangming Liu, Zhenhua Wu, Qinghui Jin, Hongbo Zhou, Jian Cao, Jianlong Zhao, Xinhua Zhong, Hongju Mao
Biosensors and Bioelectronics 2016 85() pp: 641-648
Publication Date(Web):15 November 2016
DOI:10.1016/j.bios.2016.05.067
•We established a new QDs-based FRET nanosensor technique for the detection of DNA methylation.•The method was able to identify both invasive and noninvasive NSCLC samples from control cases.•The method is proven to be a convenient, sensitive, cost-efficient and reliable method.•The method is expected to be a potential tool for noninvasive early clinical diagnosis of cancers.Non-small-cell lung cancer (NSCLC) leads to a significant proportion of cancer-related deaths, and early detection of NSCLC can significantly increase cancer survival rates. A promising approach has been studied to exploit DNA methylation, which is closely correlated to early cancer diagnosis. Herein, in order to realize the early detection of NSCLC, we utilized the developed quantum dots-based (QDs-based) fluorescence resonance energy transfer (FRET) nanosensor technique to analyze the promoter methylation in early stage NSCLC tissue samples and noninvasive bronchial brushing specimens. Using this method, the methylation levels can be quantitatively determined by measuring the signal amplification during FRET. A panel of three tumor suppressor genes (PCDHGB6, HOXA9 and RASSF1A) was assessed in 50 paired early stage NSCLC and their adjacent nontumorous tissue (NT) samples, and 50 early stage NSCLC bronchial brushing and normal specimens. The combined detection was able to identify not only tissue samples but noninvasive bronchial brushing specimens from control cases with a high degree of sensitivity of 92% (AUC=0.977, P<0.001) and 80% (AUC=0.907, P<0.001) respectively, indicating the versatility of promoter expression in invasive and noninvasive NSCLC samples. Therefore this approach can be used to sensitively analyze the methylation levels of cancer-related genes, which might be a potential tool for noninvasive early clinical diagnosis of cancers.
Co-reporter:Zhonglin Du, Zhenxiao Pan, Francisco Fabregat-Santiago, Ke Zhao, Donghui Long, Hua Zhang, Yixin Zhao, Xinhua Zhong, Jong-Sung Yu, and Juan Bisquert
The Journal of Physical Chemistry Letters 2016 Volume 7(Issue 16) pp:3103-3111
Publication Date(Web):July 25, 2016
DOI:10.1021/acs.jpclett.6b01356
The mean power conversion efficiency (PCE) of quantum-dot-sensitized solar cells (QDSCs) is mainly limited by the low photovoltage and fill factor (FF), which are derived from the high redox potential of polysulfide electrolyte and the poor catalytic activity of the counter electrode (CE), respectively. Herein, we report that this problem is overcome by adopting Ti mesh supported mesoporous carbon (MC/Ti) CE. The confined area in Ti mesh substrate not only offers robust carbon film with submillimeter thickness to ensure high catalytic capacity, but also provides an efficient three-dimension electrical tunnel with better conductivity than state-of-art Cu2S/FTO CE. More importantly, the MC/Ti CE can down shift the redox potential of polysulfide electrolyte to promote high photovoltage. In all, MC/Ti CEs boost PCE of CdSe0.65Te0.35 QDSCs to a certified record of 11.16% (Jsc = 20.68 mA/cm2, Voc = 0.798 V, FF = 0.677), an improvement of 24% related to previous record. This work thus paves a way for further improvement of performance of QDSCs.
Co-reporter:Ke Zhao; Zhenxiao Pan; Iván Mora-Seró; Enrique Cánovas; Hai Wang; Ya Song; Xueqing Gong; Jin Wang; Mischa Bonn; Juan Bisquert
Journal of the American Chemical Society 2015 Volume 137(Issue 16) pp:5602-5609
Publication Date(Web):April 10, 2015
DOI:10.1021/jacs.5b01946
At present, quantum-dot-sensitized solar cells (QDSCs) still exhibit moderate power conversion efficiency (with record efficiency of 6–7%), limited primarily by charge recombination. Therefore, suppressing recombination processes is a mandatory requirement to boost the performance of QDSCs. Herein, we demonstrate the ability of a novel sequential inorganic ZnS/SiO2 double layer treatment onto the QD-sensitized photoanode for strongly inhibiting interfacial recombination processes in QDSCs while providing improved cell stability. Theoretical modeling and impedance spectroscopy reveal that the combined ZnS/SiO2 treatment reduces interfacial recombination and increases charge collection efficiency when compared with conventional ZnS treatment alone. In line with those results, subpicosecond THz spectroscopy demonstrates that while QD to TiO2 electron-transfer rates and yields are insensitive to inorganic photoanode overcoating, back recombination at the oxide surface is strongly suppressed by subsequent inorganic treatments. By exploiting this approach, CdSexTe1–x QDSCs exhibit a certified record efficiency of 8.21% (8.55% for a champion cell), an improvement of 20% over the previous record high efficiency of 6.8%, together with an additional beneficial effect of improved cell stability.
Co-reporter:Zhenwei Ren, Jin Wang, Zhenxiao Pan, Ke Zhao, Hua Zhang, Yan Li, Yixin Zhao, Ivan Mora-Sero, Juan Bisquert, and Xinhua Zhong
Chemistry of Materials 2015 Volume 27(Issue 24) pp:8398
Publication Date(Web):November 25, 2015
DOI:10.1021/acs.chemmater.5b03864
Charge recombination at an electrode/electrolyte interface is the main factor to limit the power conversion efficiency (PCE) of quantum dot sensitized solar cells (QDSCs). Herein, we present a novel and facile strategy based on successive coating of a sensitized electrode with a combination of blocking layers in appropriate sequence for suppressing the charge recombination. In this scenario, modification of the exposed surface of both TiO2 particles and QDs with an amorphous TiO2 (am-TiO2) layer via a classical TiCl4 hydrolysis treatment plays a fundamental role to enhance the effectiveness of a recombination blocking ZnS/SiO2 barrier layer. This strategy allows construction of CdSe0.65Te0.35 QD based champion QDSCs exhibiting a new PCE record of 9.28% and a certified PCE of 9.01% under full one sun illumination. The specific nature and sequence of the layering process is critical for the gain of photovoltaic performance. Control experiments indicate that the am-TiO2 is superior to a crystalline TiO2 layer in serving as the passivation/buffer layer and improving the photovoltaic performance of the cells. Insight from impedance spectroscopy (IS) and open circuit voltage decay (OCVD) measurements demonstrates that when the am-TiO2 layer is located at the interface between the QD sensitized photoanode and the ZnS/SiO2 barrier layer, it inhibits remarkably the charge recombination at the photoanode/electrolyte interface and prolongs the electron lifetime.
Co-reporter:Wenjie Li, Zhenxiao Pan and Xinhua Zhong
Journal of Materials Chemistry A 2015 vol. 3(Issue 4) pp:1649-1655
Publication Date(Web):19 Nov 2014
DOI:10.1039/C4TA05134C
CuInSe2 (CISe) based quantum dots (QDs), are perceived to be promising alternatives to those of cadmium or lead chalcogenide based QDs in serving as light-harvesting sensitizer materials in quantum dot sensitized solar cells (QDSCs) due to their near-infrared (NIR) absorbing capacity and low toxicity. Herein, we have synthesized high quality CISe QDs via the organic phase high temperature route, and then alloying with ZnS to form the CISe–ZnS QDs with higher chemical stability and superior optoelectronic properties. The obtained “green” CISe and CISe–ZnS QD sensitizers were immobilized onto TiO2 film electrodes with high loading amount through the linker molecule assisted post synthesis assembly approach with the use of MPA-capped water-soluble QDs. Hindered charge recombination in the built CISe–ZnS QD based solar cells in comparison with reference CISe cells has been confirmed by impedance spectroscopy, as well as transient photovoltage decay measurements. With the combination of high QD loading and passivated trap-state defects, the resulting regenerative sandwich CISe–ZnS QD based champion solar cells exhibited an efficiency of 6.79% (Jsc = 22.61 mA cm−2, Voc = 0.583 V, FF = 0.515) under AM 1.5 G full one sun irradiation. The obtained efficiency was among the best performances for liquid-junction QDSCs and also demonstrated comparable photovoltaic performance of “green” CISe based QDs to the toxic cadmium and lead chalcogenide QDs.
Co-reporter:Hua Zhang, Huili Bao and Xinhua Zhong
Journal of Materials Chemistry A 2015 vol. 3(Issue 12) pp:6557-6564
Publication Date(Web):17 Feb 2015
DOI:10.1039/C5TA00068H
A mixture composed of CuS and Cu1.8S has been easily fabricated via a solvothermal method followed by screen-printing to form a counter electrode. A highly reproducible record efficiency of 6.28% for the assembled CdSe-sensitized solar cells has been achieved, and the irradiation, as well as conservation stability, have also been greatly improved compared to the brass foil based solar cells. With different size and morphology, the phase of CuS shows a slightly superior performance than Cu1.8S through investigating the influence of S/Cu ratio on the efficiency. The sintering temperature of the counter electrode film has also been studied, and the results show that 400 °C is favorable for good conductivity, high electrochemical activity, low charge transfer resistance in a solid–solid interface and between the catalysts and electrolyte. Because of the low cost, convenient fabrication, easy of sealing, as well as the high efficiency, reproducibility and excellent stability of the devices, the as-prepared copper sulfide could be potentially and extensively utilized in semiconductor-sensitized solar cells.
Co-reporter:Jun Du, Xinxin Meng, Ke Zhao, Yan Li and Xinhua Zhong
Journal of Materials Chemistry A 2015 vol. 3(Issue 33) pp:17091-17097
Publication Date(Web):15 Jul 2015
DOI:10.1039/C5TA04758G
Besides the relatively high redox potential of the adopted S2−/Sn2− polysulfide redox couple electrolyte, the parasitic charge recombination process is another significant factor that limits the open-circuit voltage and consequent power conversion efficiency (PCE) of quantum dot sensitized solar cells (QDSCs). Herein, we report a facile method to modify the polysulfide electrolyte with the addition of polyethylene glycol (PEG) additives to suppress the charge recombination occurring at the TiO2/QDs/electrolyte interfaces. Impedance spectroscopy and open circuit voltage decay (OCVD) measurements reveal that the PEG additive in the polysulfide electrolyte reduces interfacial recombination when compared with the conventional polysulfide electrolyte in the absence of the PEG additive. A dramatic enhancement of PCE from 5.80% to 6.74% was observed with the introduction of 15 wt% PEG in the polysulfide electrolyte in CdSe based QDSCs. Moreover, the PEG additive also improves the photovoltaic performance stability of the resultant cells.
Co-reporter:Wenjie Li
The Journal of Physical Chemistry Letters 2015 Volume 6(Issue 5) pp:796-806
Publication Date(Web):February 11, 2015
DOI:10.1021/acs.jpclett.5b00001
Quantum dot-sensitized solar cells (QDSCs), having the advantages of low-cost assembling process, economically viable materials and intrinsic optoelectronic properties of QD sensitizers, are regarded as attractive candidates for the third-generation solar cells. In spite of the previous unsatisfied performance resulted from poor sensitization, an increasing power conversion efficiency has been experimentally confirmed with the development of effective deposition approaches in the last five years. In this Perspective article, we present an overview on versatile QD deposition methods, regarding mainly the effective loading of QDs and surface chemistry issues. Linker-assisted assembly, a most efficient sensitizer deposition approach to achieve fast, uniform and dense coverage of the sensitizers on mesoporous TiO2 film electrode, will be discussed with emphasis. Recent advances based on this deposition technique in achieving high efficiency are presented. Also, combined efforts regarding the overall improvement of the device have been discussed to provide more possible access to higher power conversion efficiencies of the QDSCs.
Co-reporter:Junwei Yang
The Journal of Physical Chemistry C 2015 Volume 119(Issue 52) pp:28800-28808
Publication Date(Web):December 9, 2015
DOI:10.1021/acs.jpcc.5b10546
Surface trap defects are the limited factor for quantum dots (QDs) application in solar cells. The trapping states can be efficiently suppressed by coating a shell of wider band gap material around the core QDs. We choose CdSe0.65Te0.35 (simplified as CdSeTe) as a model core material, and CdS shell was then overcoated around the CdSeTe core QD to decrease surface defect density and to increase the stability of the core QDs. By optimizing the thickness of the CdS shell, the power conversion efficiency (PCE) of the CdSeTe/CdS quantum dots sensitized solar cells (QDSCs) is enhanced by 13% in comparison with that of plain CdSeTe QDSCs. Transient absorption (TA), incident-photo-to-carrier conversion efficiency (IPCE), open-circuit voltage decay (OVCD), and electrochemical impedance spectroscopy (EIS) measurements confirmed the suppressed charge recombination process in internal QDs and QD/TiO2/electrolyte interfaces with the overcoating of CdS shell around CdSeTe core QDs. With the further overcoating of a-TiO2 and SiO2 barrier layers around the QD-sensitized photoanode, the PCE of champion CdSeTe QDSCs achieved 9.48% (Jsc = 20.82 mA/cm2, Voc = 0.713 V, FF = 0.639) with average PCE 9.39 ± 0.09% under AM 1.5 G one full sun illumination.
Co-reporter:Shuang Jiao, Qing Shen, Iván Mora-Seró, Jin Wang, Zhenxiao Pan, Ke Zhao, Yuki Kuga, Xinhua Zhong, and Juan Bisquert
ACS Nano 2015 Volume 9(Issue 1) pp:908
Publication Date(Web):January 6, 2015
DOI:10.1021/nn506638n
Even though previously reported CdTe/CdSe type-II core/shell QD sensitizers possess intrinsic superior optoelectronic properties (such as wide absorption range, fast charge separation, and slow charge recombination) in serving as light absorbers, the efficiency of the resultant solar cell is still limited by the relatively low photovoltage. To further enhance photovoltage and cell efficiency accordingly, ZnTe/CdSe type-II core/shell QDs with much larger conduction band (CB) offset in comparison with that of CdTe/CdSe (1.22 eV vs 0.27 eV) are adopted as sensitizers in the construction of quantum dot sensitized solar cells (QDSCs). The augment of band offset produces an increase of the charge accumulation across the QD/TiO2 interface under illumination and induces stronger dipole effects, therefore bringing forward an upward shift of the TiO2 CB edge after sensitization and resulting in enhancement of the photovoltage of the resultant cell devices. The variation of relative chemical capacitance, Cμ, between ZnTe/CdSe and reference CdTe/CdSe cells extracted from impedance spectroscopy (IS) characterization under dark and illumination conditions clearly demonstrates that, under light irradiation conditions, the sensitization of ZnTe/CdSe QDs upshifts the CB edge of TiO2 by the level of ∼50 mV related to that in the reference cell and results in the enhancement of Voc of the corresponding cell devices. In addition, charge extraction measurements have also confirmed the photovoltage enhancement in the ZnTe/CdSe cell related to reference CdTe/CdSe cell. Furthermore, transient grating (TG) measurements have revealed a faster electron injection rate for the ZnTe/CdSe-based QDSCs in comparison with the CdSe cells. The resultant ZnTe/CdSe QD-based QDSCs exhibit a champion power conversion efficiency of 7.17% and a certified efficiency of 6.82% under AM 1.5G full one sun illumination, which is, as far as we know, one of the highest efficiencies for liquid-junction QDSCs.Keywords: band gap engineering; high photovoltage and efficiency; quantum dot sensitized solar cells; type-II core/shell structure; ZnTe/CdSe quantum dots;
Co-reporter:Wenjin Zhang, Qing Lou, Wenyu Ji, Jialong Zhao, and Xinhua Zhong
Chemistry of Materials 2014 Volume 26(Issue 2) pp:1204
Publication Date(Web):December 19, 2013
DOI:10.1021/cm403584a
A series of Cu doped Zn–In–S quantum dots (Cu:Zn–In–S d-dots) were synthesized via a one-pot noninjection synthetic approach by heating up a mixture of corresponding metal acetate salts and sulfur powder together with dodecanethiol in oleylamine media. After overcoating the ZnS shell around the Cu:Zn–In–S d-dot cores directly in the crude reaction solution, the resulting Cu:Zn–In–S/ZnS d-dots show composition-tunable photoluminescence (PL) emission over the entire visible spectral window and extending to the near-infrared spectral window (from 450 to 810 nm), with the highest PL quantum yield (QY) up to 85%. Importantly, the initial high PL QY of the obtained Cu:Zn–In–S/ZnS d-dots in organic media can be preserved when transferred into aqueous media via ligand exchange. Furthermore, electroluminescent devices with good performance (with a maximum luminance of 220 cd m–2, low turn-on voltages of 3.6 V) have been fabricated with the use of these Cd-free low toxicity yellow-emission Cu:Zn–In–S/ZnS d-dots as an active layer in these QD-based light-emitting diodes.Keywords: ;
Co-reporter:Junwei Yang, Takuya Oshima, Witoon Yindeesuk, Zhenxiao Pan, Xinhua Zhong and Qing Shen
Journal of Materials Chemistry A 2014 vol. 2(Issue 48) pp:20882-20888
Publication Date(Web):28 Oct 2014
DOI:10.1039/C4TA04353G
The charge transfer rate between QD sensitizer/TiO2 interfaces in quantum dot sensitized solar cells (QDSCs) is one of the most important criteria determining the photovoltaic performance of cells. To investigate the influence of linker molecules on the electron transfer rate at the QD–linker–TiO2 interface and the final performance of the resultant QDSCs, colloidal QDs capped with thioglycolic acid (TGA), 3-mercaptopropionic acid (MPA), and cysteine (Cys), which also serve as molecular linkers between QDs and TiO2 nanoparticles, were self-assembled on a TiO2 mesoporous film electrode from the corresponding QD aqueous dispersions. The influence of the studied linker molecules (TGA, MPA, and Cys) on the loading amount of QD sensitizer on the TiO2 mesoporous film, the electron injection rate from QDs to the TiO2 matrix, the incident photon to charge carrier generation efficiency (IPCE), and the corresponding photovoltaic performance of the resultant QDSCs were systematically studied. CdSe and CdSexTe1−x QD sensitized solar cells were selected as a model cell to evaluate the influence of the adopted linker molecules. Under AM 1.5G full one sun intensity illumination, the power conversion efficiency (PCE) of TGA-capped QDs (5.40% for CdSe, and 6.68% for CdSexTe1−x) was 7–14% greater than those of MPA- and Cys-capped QDs. Similarly, the absorbed photon-to-current efficiency was 8–13% greater. These differences arise from linker molecule-dependent variations of the electron-injection rate. Transient grating measurements indicate that the electron injection rate constant from TGA-capped CdSe (8.0 × 109 s−1) was greater than from MPA- and Cys-capped CdSe (2.6–2.9 × 109 s−1). Thus, TGA-capped QDs are readily attached to the TiO2 substrate and exhibit better electronic properties and desirable electron-transfer rate, and therefore bring forward better photovoltaic performance in the resultant solar cells.
Co-reporter:Zhonglin Du, Hua Zhang, Huili Bao and Xinhua Zhong
Journal of Materials Chemistry A 2014 vol. 2(Issue 32) pp:13033-13040
Publication Date(Web):13 Jun 2014
DOI:10.1039/C4TA02291B
As a fundamental part of quantum dot-sensitized solar cells, the composition and configuration of the TiO2 photoanode film plays an important role in photovoltaic performance. In this work, the preparation and optimization of films have been systematically studied, including the TiCl4 treatment technique, transparent layer and light-scattering layer thickness and composition. Experimental results show that the sole TiCl4 treatment on fluorine doped SnO2 (FTO) glass is sufficient for achieving a high efficiency in the resultant cell devices when compared with the simultaneous treatment on both FTO glass and TiO2 mesoporous films. The thickness and porosity of the transparent layer have been optimized by tuning the number of transparent layers and the ethyl cellulose contents in the paste. Moreover, the influence of the light-scattering layer pastes with different contents of the large-sized TiO2 particles on the performance of the cells has also been explored. The CdSe-sensitized solar cells based on the optimized TiO2 film photoanode exhibits a power conversion efficiency of 5.53% under 1 full sun illumination, which is among the best efficiencies for plain CdSe QD-based solar cells.
Co-reporter:Yunfei Ma, Yan Li, Shijian Ma and Xinhua Zhong
Journal of Materials Chemistry A 2014 vol. 2(Issue 31) pp:5043-5051
Publication Date(Web):05 Jun 2014
DOI:10.1039/C4TB00458B
Silica coating via a Stöber method is an effective route to render luminescent quantum dots (QDs) with great biocompatibility, low toxicity and water-solubility for bioapplications. However, the bottleneck in this route is the access of highly luminescent, colloidally stable QD dispersion in alcoholic solution. Herein, we report a facile route based on the Stöber method for the synthesis of isolated silica coated QDs (QD@SiO2) with high emission efficiencies, tunable small size (less than 30 nm) and excellent stability. Prior to silica coating, the initial oil-soluble QDs were made dispersible in alcohol–water media by replacing the native hydrophobic ligands with adenosine 5′-monophosphate (AMP). Then, 3-mercaptopropyl-trimethoxysilane (MPS) was introduced to serve as silane nucleation primers. Finally, a silica shell with controllable thickness was obtained on the QD surface by hydrolysis/condensation of tetraethyl orthosilicate (TEOS). Remarkably, the resultant QD@SiO2 had nearly the same high luminescent efficiency (50–65%) as that of initial oil-soluble QDs and exhibited excellent long-term photo and colloidal stability in harsh environments (pH range of 3–13, saturated NaCl solution and thermal treatment at 100 °C). It was demonstrated that the cytotoxicity of the resultant QD@SiO2 was significantly diminished. Moreover, the QD@SiO2 conjugated with folic acid exhibits high specific binding toward receptor-positive Hela cells over receptor-negative A549 cells, indicating the potential of our obtained QD@SiO2 as robust biomarkers in cells due to their chemical processibility and low cytotoxicity.
Co-reporter:Qin Mu, Hu Xu, Yan Li, Shijian Ma and Xinhua Zhong
Analyst 2014 vol. 139(Issue 1) pp:93-98
Publication Date(Web):30 Sep 2013
DOI:10.1039/C3AN01592K
Facile detection of dopamine (DA) in biological samples for diagnostics remains a challenge. This paper reported an effective fluorescent sensor based on adenosine capped CdSe/ZnS quantum dots (A-QDs) for highly sensitive detection of DA in human urine samples. In this assay, adenosine serves as a capping ligand or stabilizer for QDs to render high-quality QDs dispersed in water, and as a receptor for DA to attach DA onto the surface of A-QDs. DA molecules can bind to A-QDs via non-covalent bonding, leading to the fluorescence quenching of A-QDs due to electron transfer. The A-QDs based fluorescence probe showed a limit of detection (LOD) of ca. 29.3 nM for DA detection. This facile method exhibited high selectivity and anti-interference in the presence of amino acid, ascorbic acid (AA), uric acid (UA) and glucide with 100-fold higher concentration in PBS solution. Furthermore, it was also successfully used in the detection of DA in the human urine samples with quantitative recoveries (94.80–103.40%).
Co-reporter:Qin Mu, Yan Li, Yunfei Ma and Xinhua Zhong
Analyst 2014 vol. 139(Issue 5) pp:996-999
Publication Date(Web):16 Dec 2013
DOI:10.1039/C3AN01957H
The quenched fluorescence of quantum dots (QDs) attached to TiO2 nanoparticles was selectively switched on by biothiols through ligand replacement, which makes it feasible for facilely sensing biothiols based on the fluorescence turn on mechanism. The present sensor exhibited excellent selectivity and high sensitivity. Furthermore, a novel fluorescent indicating paper was constructed by immobilizing the probe on filter paper to visually detect biothiols in which only a UV lamp was used.
Co-reporter:Xiaochi Liu, Yisheng Xu, Shijian Ma, Yunfei Ma, Ayyaz Ahmad, Yuchuan Tian, Xinhua Zhong, and Xuhong Guo
Industrial & Engineering Chemistry Research 2014 Volume 53(Issue 28) pp:11326-11332
Publication Date(Web):June 26, 2014
DOI:10.1021/ie501035s
Novel fluorescence-labeled spherical polyelectrolyte brushes consisting of a fluorescent polystyrene (PS) nanocomposite core and a poly(acylic acid) (PAA) brush shell were successfully prepared. Quantum dots (QDs) were well confined in the PS core through hybrid emulsion polymerization. PAA chains were then grafted onto the surface of the fluorescent PS core to form a brush structure through photoemulsion polymerization. The obtained fluorescent spherical polyelectrolyte brushes are highly pH sensitive in addition to their excellent dispersibility in water. Fluorescent nanoclusters were introduced into spherical polyelectrolyte brushes to acquire high sensitive detection in the applications of spherical polyelectrolyte brushes as catalyst tracer, as biosensor, and in protein coding.
Co-reporter:Yunfei Ma, Yan Li and Xinhua Zhong
RSC Advances 2014 vol. 4(Issue 85) pp:45473-45480
Publication Date(Web):10 Sep 2014
DOI:10.1039/C4RA08367A
To overcome the low emission efficiency and poor photo and colloidal stability of quantum dots (QDs) prepared in aqueous media, the main challenge is to find suitable capping reagents to obtain stable QD/ligand complexes. Adenosine 5′-monophosphare (AMP) appears very promising for the stabilization and the further functionalization of QDs because AMP has multiple functionalities that can chelate metal cations. Herein, we synthesized high-quality CdTe/CdS core/shell nanostructures in aqueous media, in which AMP and thiopropionic acid (MPA) acting as dual stabilizing agents were introduced directly on the surface of QDs. With the combination of AMP and MPA ligands, it was found that dual ligands could accelerate the reaction kinetics, accompanied by possessing high emission efficiency of QDs. The prepared water-soluble AMP/MPA-QDs exhibit narrow size distribution and nearly spherical morphology. Most importantly, the resultant water-soluble AMP/MPA-QDs exhibit superior photo and colloidal stability, solving the problem of deterioration for biological applications. To demonstrate the targeting capability of QDs, we have used folate-receptor targeting to show good selectivity to tumor cells.
Co-reporter:Qin Mu, Yan Li, Hu Xu, Yunfei Ma, Weihong Zhu, Xinhua Zhong
Talanta 2014 Volume 119() pp:564-571
Publication Date(Web):15 February 2014
DOI:10.1016/j.talanta.2013.11.036
•A dual-emission quantum dots nanocomposite serving as a probe for the visual detection of Hg2+.•The quantum dots-based nanocomposite working in ratiometric fluorescence mode.•The ratiometric fluorescence probe having high sensitivity with detection limit down to 3.1 nM in aqueous media.•The excellent Hg2+ detection performance of this ratiometric probe in biological fluids.Fluorescence analysis by means of a single fluorescence signal output usually leads to the signal fluctuation caused by various external factors. Ratiometric fluorescence probes that can significantly eliminate the external effects by self-calibration of two different emission bands are preferable for the detection of real samples. In this work, we designed a dual-emission quantum dots (QDs) nanocomposite as a ratiometric probe for the visual detection of Hg2+. The dual-emission QDs nanocomposite consists of two differently sized CdTe/CdS QDs. The red-emitting larger sized CdTe/CdS QDs embeded in silica nanoparticles are insensitive to Hg2+, while the green-emitting smaller sized ones are covalently conjugated onto the silica nanoparticles surface and sensitive to Hg2+. The addition of Hg2+ can only quench green fluorescence in the dual-emission QDs nanocomposites, which triggers the change of fluorescence intensity ratio of two different emission wavelengths and hence induces the evolution of fluorescence color of the probe solution with variation of Hg2+ concentration. Based on this feature, the dual-emission QDs nanocomposites can be used to develop a ratiometric fluorescence probe for the visual detection of Hg2+. Under the optimized conditions, the ratiometric fluorescence QDs probe shows a linear relationship between fluorescence intensity ratio and Hg2+ concentration in the range of 5–300 nM. The detection limit of this probe was found to be 3.1 nM. This ratiometric assay also exhibits a high selectivity and it has been successfully used in the determination of Hg2+ content in fetal bovine serum and human urine.A quantum dots-based dual-emission fluorescence probe for the visual detection of Hg2+ has been developed. The proposed probe exhibits a high selectivity and sensitivity for Hg2+. The probe has been used in the determination of Hg2+ in biological fluids with satisfactory results.
Co-reporter:Yunfei Ma, Yan Li, Xinhua Zhong
Materials Research Bulletin 2014 60() pp: 543-551
Publication Date(Web):
DOI:10.1016/j.materresbull.2014.08.033
Co-reporter:Ke Zhao ; Haijing Yu ; Hua Zhang
The Journal of Physical Chemistry C 2014 Volume 118(Issue 11) pp:5683-5690
Publication Date(Web):February 28, 2014
DOI:10.1021/jp4118369
Currently, Cu2S based on brass foil is the most commonly used counter electrode (CE) in high efficiency quantum dot sensitized solar cells (QDSCs) because of its superior catalytic activity to the polysulfide electrolyte redox couple. Regretfully, the brass substrate is limited by the shortcomings of corrosion by polysulfide electrolyte and lack of long-term stability. In order to combine the high catalytic activity of Cu2S and superior tolerance of fluorine doped tin oxide (FTO) glass to polysulfide electrolyte, Cu2S film on the FTO glass substrate (Cu2S/FTO) CE was prepared by electrodeposition of the copper film via a multipotential step technique followed by dipping into polysulfide methanol solution. The Cu2S film was proven to be composed by the interconnected nanoflakes, which ensures the highly catalytic activity to the polysulfide redox couple electrolyte in QDSCs. The CdSe quantum dot (QD) sensitized solar cells with the optimized Cu2S/FTO CE exhibit a power conversion efficiency (PCE) of 5.21%, which is very close to that with the commonly used Cu2S/brass CE (5.41%) and much higher than that of Pt CE (1.68%). Furthermore, the cell device based on the Cu2S/FTO CE shows superior stability at a working state for over 10 h without decrease in PCE, which is a serious challenge for the Cu2S/brass CE.
Co-reporter:Haijing Yu ; Huili Bao ; Ke Zhao ; Zhonglin Du ; Hua Zhang
The Journal of Physical Chemistry C 2014 Volume 118(Issue 30) pp:16602-16610
Publication Date(Web):February 24, 2014
DOI:10.1021/jp4125217
Bi2S3 films consisting of two-dimensional interconnected Bi2S3 single-crystalline nanorod networks have been fabricated on a F:SnO2 (FTO) glass substrate through the formation of intermediate BiOI nanosheets from layer-structured BiI3 by chemical vapor deposition and subsequent hydrothermal transformation into Bi2S3 networks. A continuous lattice and structure-directed topotactic transformation mechanism is supposed for the formation of Bi2S3 network film. The prepared Bi2S3/FTO films were employed as counter electrode (CE) for CdSe quantum dot-sensitized solar cells for the first time and showed better photovoltaic performance than that from the convenient Pt CE. The influence of the preparation conditions for Bi2S3/FTO films on the resulting solar cell performance was systematically investigated and optimized with use of J–V curves, scanning electron microscopy (SEM), UV–vis absorption, and electrochemical impedance spectroscopy. To further improve the cell device efficiency, the modification of the Bi2S3 network CE with metal particles was also studied.
Co-reporter:Jin Wang ; Iván Mora-Seró ; Zhenxiao Pan ; Ke Zhao ; Hua Zhang ; Yaoyu Feng ; Guang Yang ; Xinhua Zhong ;Juan Bisquert
Journal of the American Chemical Society 2013 Volume 135(Issue 42) pp:15913-15922
Publication Date(Web):September 26, 2013
DOI:10.1021/ja4079804
Searching suitable panchromatic QD sensitizers for expanding the light-harvesting range, accelerating charge separation, and retarding charge recombination is an effective way to improve power conversion efficiency (PCE) of quantum-dot-sensitized solar cells (QDSCs). One possible way to obtain a wide absorption range is to use the exciplex state of a type-II core/shell-structured QDs. In addition, this system could also provide a fast charge separation and low charge-recombination rate. Herein, we report on using a CdTe/CdSe type-II core/shell QD sensitizer with an absorption range extending into the infrared region because of its exciplex state, which is covalently linked to TiO2 mesoporous electrodes by dropping a bifunctional linker molecule mercaptopropionic acid (MPA)-capped QD aqueous solution onto the film electrode. High loading and a uniform distribution of QD sensitizer throughout the film electrode thickness have been confirmed by energy dispersive X-ray (EDX) elemental mapping. The accelerated electron injection and retarded charge-recombination pathway in the built CdTe/CdSe QD cells in comparison with reference CdSe QD-based cells have been confirmed by impedance spectroscopy, fluorescence decay, and intensity-modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS) analysis. With the combination of the high QD loading and intrinsically superior optoelectronic properties of type-II core/shell QD (wide absorption range, fast charge separation, and slow charge recombination), the resulting CdTe/CdSe QD-based regenerative sandwich solar cells exhibit a record PCE of 6.76% (Jsc = 19.59 mA cm–2, Voc = 0.606 V, and FF = 0.569) with a mask around the active film under a full 1 sun illumination (simulated AM 1.5), which is the highest reported to date for liquid-junction QDSCs.
Co-reporter:Hu Xu, Zhiping Wang, Yan Li, Shijian Ma, Peiyi Hu and Xinhua Zhong
Analyst 2013 vol. 138(Issue 7) pp:2181-2191
Publication Date(Web):21 Jan 2013
DOI:10.1039/C3AN36742H
Since zinc ions play an important role in various physiological activities, developing a facile detection method for Zn2+ is highly desirable. Owing to their superior optical properties, semiconductor quantum dots (QDs) have been developed as a promising alternative for organic fluorophores in fluorescence analysis. In this study, water soluble di-2-picolylamine-dithiolcarbamate (DPA-DTC)/proline-dithiolcarbamate (P-DTC) co-capped CdSe/ZnS QDs as a sensitive and selective “turn-on” fluorescence probe for Zn2+ was reported. The probe was easily obtained via ligand exchange. The initial bright fluorescence of QDs was effectively quenched by DPA-DTC that acted as an effective hole trapper. Upon complexation with Zn2+, the formation of Zn2+–DPA-DTC complex altered the energetic position of the HOMO for DPA-DTC, which rendered it unfavorable for the hole transfer. Thus the QDs PL was switched on. Under optimal conditions, a good linear relationship between the fluorescence response and Zn2+ concentration could be obtained in the range from 0.9 to 16 μM. The limit of detection for Zn2+ was found to be 0.7 μM. Furthermore, the present probe exhibited a high selectivity for Zn2+ over other common metal ions and was successfully used in the detection of Zn2+ in simulated biological fluids.
Co-reporter:Zhenxiao Pan, Ke Zhao, Jin Wang, Hua Zhang, Yaoyu Feng, and Xinhua Zhong
ACS Nano 2013 Volume 7(Issue 6) pp:5215
Publication Date(Web):May 25, 2013
DOI:10.1021/nn400947e
CdSe0.45Te0.55 alloyed quantum dots (QDs) with excitonic absorption onset at 800 nm and particle size of 5.2 nm were prepared via a noninjection high-temperature pyrolysis route and used as a sensitizer in solar cells. A postsynthesis assembly approach with use of bifunctional linker molecule mercaptopropionic acid (MPA) capped water-soluble QDs, obtained via ex situ ligand exchange from the initial oil-dispersible QDs, was adopted for tethering QDs onto mesoporous TiO2 film. With the combination of high loading of the QD sensitizer and intrinsic superior optoelectronic properties (wide absorption range, high conduction band edge, high chemical stability, etc., relative to their constituents CdSe and CdTe) of the adopted CdSe0.45Te0.55 QD sensitizer, the resulting CdSexTe1–x alloyed QD-based solar cells exhibit a record conversion efficiency of 6.36% (Jsc = 19.35 mA/cm2, Voc = 0.571 V, FF = 0.575) under full 1 sun illumination, which is remarkably better than that of the reference CdSe and CdTe QD based ones. Furthermore, the solar cells with Cu2S counter electrodes based on eletrodeposition of Cu on conductive glass show long-term (more than 500 h) stability.Keywords: alloyed quantum dots; CdSexTe1−x; high efficiency; solar cells
Co-reporter:H. Zhang, K. Cheng, Y. M. Hou, Z. Fang, Z. X. Pan, W. J. Wu, J. L. Hua and X. H. Zhong
Chemical Communications 2012 vol. 48(Issue 91) pp:11235-11237
Publication Date(Web):03 Oct 2012
DOI:10.1039/C2CC36526J
A postsynthesis assembly approach, an ex situ ligand exchange route, was developed for fast (within 2 h) and high loading (34% coverage) deposition of CdSe QDs on TiO2 films. With the combination of high-quality QD sensitizers and the effective deposition technique, a record photovoltaic performance with an efficiency of 5.4% was observed for the resulting cell device.
Co-reporter:Lu Liu and Xinhua Zhong
Chemical Communications 2012 vol. 48(Issue 46) pp:5718-5720
Publication Date(Web):28 Feb 2012
DOI:10.1039/C2CC30444A
We report a facile and general phase transfer strategy using nucleotides or nucleosides as phase transfer reagents to render a wide variety of nanomaterials transferring from organic phase to aqueous phase or vice versa, while preserving their intrinsic physicochemical features.
Co-reporter:Wenjin Zhang, Xinggui Zhou, and Xinhua Zhong
Inorganic Chemistry 2012 Volume 51(Issue 6) pp:3579-3587
Publication Date(Web):February 24, 2012
DOI:10.1021/ic2024023
Unlike Mn doped quantum dots (d-dots), the emission color of Cu dopant in Cu d-dots is dependent on the nature, size, and composition of host nanocrystals (NCs). The tunable Cu dopant emission has been achieved via tuning the particle size of host NCs in previous reports. In this paper, for the first time we doped Cu impurity in ZnxCd1-xS alloyed NCs and tuned the dopant emission in the whole visible spectrum via variation of the stoichiometric ratio of Zn/Cd precursors in the host ZnxCd1-xS alloyed NCs. A facile noninjection and low cost approach for the synthesis of Cu:ZnxCd1-xS d-dots was reported. The optical properties and structure of the obtained Cu:ZnxCd1-xS d-dots have been characterized by UV–vis spectroscopy, photoluminescence (PL) spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD). The influences of various experimental variables, including Zn/Cd ratio, reaction temperature, and Cu dopant concentration, on the optical properties of Cu dopant emission have been systematically investigated. The as-prepared Cu:ZnxCd1-xS d-dots did show PL emission but with quite low quantum yield (QY) (typically below 6%). With the deposition of ZnS shell around the Cu:ZnxCd1-xS core NCs, the PL QY increased substantially with a maximum value of 65%. More importantly, the high PL QY can be preserved when the initial oil-soluble d-dots were transferred into aqueous media via ligand replacement by mercaptoundeconic acid. In addition, these d-dots have thermal stability up to 250 °C.
Co-reporter:Wenjin Zhang, Chan Jin, Yongji Yang, and Xinhua Zhong
Inorganic Chemistry 2012 Volume 51(Issue 1) pp:531-535
Publication Date(Web):December 13, 2011
DOI:10.1021/ic201989w
Nearly all reported approaches for synthesis of high quality CdSe nanocrystals (NCs) involved two steps of preparation of Cd or Se stock solution in advance and then mixing the two reactants via hot-injection in high temperature. In this manuscript, Gram-scale CdSe multipod NCs were facilely synthesized in a noninjection route with the use of CdO and Se powder directly as reactants in paraffin reaction medium containing small amount of oleic acid and trioctylphosphine. The influence of various experimental variables, including reaction temperature, nature and amount of surfactants, Cd-to-Se ratio, and the nature of reactants, on the morphology of the obtained CdSe NCs have been systematically investigated. After deposition of ZnS shell around the CdSe multipod NCs, the PL QY of the obtained CdSe/ZnS can be up to 85%. The reported noninjection preparation approach can satisfy the requirement of industrial production bearing the advantage of low-cost, reproducible, and scalable. Furthermore, this facile noninjection strategy provides a versatile route to large-scale preparation of other semiconductor NCs with multipod or other morphologies.
Co-reporter:Hu Xu, Yiwen Wang, Xiaomei Huang, Yan Li, Hua Zhang and Xinhua Zhong
Analyst 2012 vol. 137(Issue 4) pp:924-931
Publication Date(Web):16 Dec 2011
DOI:10.1039/C2AN15926K
In this work, we report a colorimetric assay for the screening of biothiols including glutathione (GSH), cysteine (Cys), and homocysteine (Hcys) based on Hg2+-mediated aggregation of gold nanoparticles (AuNPs). Hg2+ can induce aggregation of thiol-containing naphthalimide (1) capped AuNPs due to the cross-linking interactions from the resulting “thymine–Hg2+–thymine” (T–Hg2+–T) analogous structure. When Hg2+ is firstly treated with biothiols, followed by mixing with 1-capped AuNPs suspension, AuNPs undergo a transformation from an aggregation to a dispersion state depending on the concentration of biothiols. This anti-aggregation or re-dispersion of AuNPs is due to the higher affinity of Hg2+ for biothiols relative to compound 1. The corresponding color variation in the process of anti-aggregation of AuNPs can be used for the quantitative screening of biothiols through UV-vis spectroscopy or by the naked eye. Under optimized conditions, a good linear relationship in the range of 0.025–2.28 μM is obtained for GSH, 0.035–1.53 μM for Cys, and 0.040–2.20 μM for Hcys. The detection limits of this assay for GSH, Cys, and Hcys are 17, 9, and 18 nM, respectively. This colorimetric assay exhibits a high selectivity and sensitivity with tunable dynamic range. The proposed method has been successfully used in the determination of total biothiol content in human urine samples.
Co-reporter:Yan Li, Bing Shen, Lu Liu, Hu Xu, Xinhua Zhong
Colloids and Surfaces A: Physicochemical and Engineering Aspects 2012 410() pp: 144-152
Publication Date(Web):
DOI:10.1016/j.colsurfa.2012.06.034
Co-reporter:Zhenxiao Pan, Hua Zhang, Kan Cheng, Yumei Hou, Jianli Hua, and Xinhua Zhong
ACS Nano 2012 Volume 6(Issue 5) pp:3982
Publication Date(Web):April 18, 2012
DOI:10.1021/nn300278z
Presynthesized high-quality CdS/CdSe inverted type-I core/shell structure QDs have been deposited onto TiO2 electrodes after first coating with bifunctional linker molecules, mercaptopropionic acid (MPA), and the resulting quantum dot sensitized solar cells (QDSCs) exhibited record conversion efficiency of 5.32% (Voc = 0.527 V, Jsc = 18.02 mA/cm2, FF = 0.56) under simulated AM 1.5, 100 mW cm–2 illumination. CdS/CdSe QDs with different CdSe shell thicknesses and different corresponding absorption onsets were prepared via the well-developed organometallic high-temperature injection method. MPA-capped water-dispersible QDs were then obtained via ligand exchange from the initial organic ligand capped oil-dispersible QDs. The QD-sensitized TiO2 electrodes were facilely prepared by pipetting the MPA-capped CdS/CdSe QD aqueous solution onto the TiO2 film, followed by a covering process with a ZnS layer and a postsintering process at 300 °C. Polysulfide electrolyte and Cu2S counterelectrode were used to provide higher photocurrents and fill factors of the constructed cell devices. The characteristics of these QDSCs were studied in more detail by optical measurements, incidental photo-to-current efficiency measurements, and impedance spectroscopy. With the combination of the modified deposition technique with use of linker molecule MPA-capped water-soluble QDs and well-developed inverted type-I core/shell structure of the sensitizer together with the sintering treatment of QD-bound TiO2 electrodes, the resulting CdS/CdSe-sensitized solar cells show a record photovoltaic performance with a conversion efficiency of 5.32%.Keywords: CdS/CdSe; core/shell structure; high conversion efficiency; quantum dot sensitized solar cells; sintering treatment
Co-reporter:Wenjin Zhang, Hua Zhang, Yaoyu Feng, and Xinhua Zhong
ACS Nano 2012 Volume 6(Issue 12) pp:11066
Publication Date(Web):December 12, 2012
DOI:10.1021/nn304765k
The common two-step “hot-injection” methods are not suitable for reproducible production of core/shell quantum dots (QDs) at large scale for practical applications. Herein we develop a scalable, reproducible, and low-cost synthetic approach for high-quality core/shell QDs (CdS/ZnxCd1–xS, CdSe/ZnxCd1–xS, and CdTe/ZnxCd1–xS) with shell material composed of gradient alloy structure by directly heating commercial available, air-stable CdO, Zn(NO3)2, and chalcogenide elements in octadecene media at air. With simple variation of reaction recipe (reactants and feeding ratio), luminescence color of the resulting QDs can be conveniently tuned from violet to near-infrared (400–820 nm). The emission efficiency of the as-prepared QDs can be up to 80%. Moreover, the high emission efficiency can be preserved after QDs transferred into aqueous media via ligand exchange. The structure, chemical composition, and optical properties of the obtained QDs have been characterized with use of transmission electron microscopy, elemental analysis, and optical spectroscopy. The scalability of the reported approach has been demonstrated by the facile preparation of gram-scaled QD product in one batch reaction.Keywords: one-pot noninjection synthesis; photoluminescence; quantum dots; scalable synthesis
Co-reporter:Hu Xu, Ran Miao, Zheng Fang, Xinhua Zhong
Analytica Chimica Acta 2011 Volume 687(Issue 1) pp:82-88
Publication Date(Web):14 February 2011
DOI:10.1016/j.aca.2010.12.002
Health or environmental issue caused by abnormal level of metal ions like Zn2+ or Cd2+ is a worldwide concern. Developing an inexpensive and facile detection method for Zn2+ and Cd2+ is in urgent demand. Due to their super optical properties, fluorescent quantum dots (QDs) have been developed as a promising alternative for organic dyes in fluorescence analysis. In this study, a CdTe QDs-based sensitive and selective probe for Zn2+ and Cd2+ in aqueous media was reported. The proposed probe worked in fluorescence “turn-on” mode. The initial bright fluorescence of CdTe QDs was effectively quenched by sulfur anions (S2−). The presence of Zn2+ (or Cd2+) can “turn-on” the weak fluorescence of QDs quenched by S2− due to the formation of ZnS (or CdS) passivation shell. Under optimal conditions, a good linear relationship between the fluorescence response and concentration of Zn2+ (or Cd2+) could be obtained in the range from 1.6 to 35 μM (1.3–25 μM for Cd2+). The limit of detection (LOD) for Zn2+ and Cd2+ were found to be 1.2 and 0.5 μM, respectively. Furthermore, the present probe exhibited a high selectivity for Zn2+ and Cd2+ over other metal ions and was successfully used in the detection of Zn2+ or Cd2+ in real water samples.
Co-reporter:Hua Zhang, Jing Huang, Xinggui Zhou, and Xinhua Zhong
Inorganic Chemistry 2011 Volume 50(Issue 16) pp:7729-7734
Publication Date(Web):July 20, 2011
DOI:10.1021/ic201332n
High-quality Bi2S3 discrete single-crystal nanosheets with orthorhombic structure have been synthesized through the thermal decomposition of a single-source precursor, Bi(S2CNEt2)3, in amine media. The morphology evolution reveals that the Bi2S3 nanosheets are developed through the assembly of nanorods, and an attachment–recrystallization growth mechanism is proposed for the formation of nanosheets with the use of nanorods as building blocks. High-resolution transmission electron microscopy studies reveal that the nanosheets have the largest exposed surface of (100) facets. The effects of experimental variables, such as the reaction temperature, time, precursor concentration, and media, on the morphology of the obtained nanocrystals have been systematically investigated in which the amine has served as the solvent, surfactant, and electron donor.
Co-reporter:Wenjin Zhang, Yan Li, Hua Zhang, Xinggui Zhou, and Xinhua Zhong
Inorganic Chemistry 2011 Volume 50(Issue 20) pp:10432-10438
Publication Date(Web):September 19, 2011
DOI:10.1021/ic201547g
Manganese-doped zinc sulfide quantum dots (Mn:ZnS d-dots) with high optical quality, pure dopant emission of 55–65% photoluminescence quantum yield, were synthesized in octadecene media with generic starting materials, namely, zinc (manganese) carboxylic acid salts, S powder, and dodecanethiol (DDT) based on a “nucleation doping” strategy. The optical properties and structure of the obtained Mn:ZnS d-dots have been characterized by UV–vis, photoluminescence (PL) spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD). The resulting nearly monodisperse d-dots were found to be of spherical shape with a zinc-blende crystal structure. The influences of various experimental variables, including the reaction temperature for the MnS core nanocluster and ZnS host material, the amount of octadecene (ODE)-S, DDT, as well as Zn/Mn ratio have been systematically investigated. The use of DDT as capping ligand ensured the reproducible access to a stable small-sized MnS core. This paves the way for reproducibly obtaining highly luminescent d-dots. Programmed overcoating temperature for growth of ZnS shell was employed to realize balanced diffusion of the Mn ions in the d-dots.
Co-reporter:Wenjin Zhang and Xinhua Zhong
Inorganic Chemistry 2011 Volume 50(Issue 9) pp:4065-4072
Publication Date(Web):April 1, 2011
DOI:10.1021/ic102559e
High-quality ZnS−CuInS2 (ZCIS) alloy nanocrystals have been synthesized via reaction between the acetate salts of the corresponding metals and elemental sulfur in the presence of dodecanethiol in octadecene media at 230 °C. The PL emission wavelength can be tuned conveniently via variation of the stoichiometric ratio of their components. The influence of various experimental variables, including Zn/CuIn ratio, amount of sulfur and dodecanethiol, and reaction temperature, on the optical properties and composition of the obtained ZCIS NCs have been systematically investigated. The plain ZCIS NCs did show PL emission but with quite low PL quantum yield (typically below 3%). In order to improve the PL emission efficiency, the ZnS shell was subsequently overcoated around the ZCIS core NCs. With ZnS shell growth, the PL emission wavelength of the resulting ZCIS/ZnS NCs can cover from 518 to 810 nm with the maximum PL quantum efficiency up to 56%. Furthermore, the obtained ZCIS/ZnS NCs show promising photocatalytic activity in the degradation of rhodamine B.
Co-reporter:Yan Li, Ping Wu, Hu Xu, Hua Zhang and Xinhua Zhong
Analyst 2011 vol. 136(Issue 1) pp:196-200
Publication Date(Web):07 Oct 2010
DOI:10.1039/C0AN00452A
For the widely used Au nanoparticles (AuNPs)-based colorimetric probe, AuNPs generally change from the dispersion to the aggregation state and corresponding colors turn from red to blue concomitantly. In previous studies, there are few probes based on the anti-aggregation of AuNPs though anti-aggregation of AuNPs is preferable to aggregation to achieve higher selectivity. In this manuscript, a fast and simple but sensitive and selective sensor suitable for on-site and real-time detection of glutathione (GSH) has been developed based on the anti-aggregation of AuNPs. The sensor has a LOD of 8 nM and excellent selectivity toward GSH by a factor of 200-fold or more relative to natural amino acids as well as homocysteine (Hcys) and glutathione disulfide (GSSG). The dynamic range of the sensor can be tuned simply by adjusting the amount of aggregation agent used.
Co-reporter:Lifang Liao, Hua Zhang, Xinhua Zhong
Journal of Luminescence 2011 Volume 131(Issue 2) pp:322-327
Publication Date(Web):February 2011
DOI:10.1016/j.jlumin.2010.10.023
High-quality CdTeSe colloidal nanocrystals with gradient distribution of components, consisting of Te-rich inner cores and Se-rich outer shells, were synthesized in a “green” solvent paraffin via a noninjection one-pot approach with the use of cadmium oxide (CdO), elemental tellurium, and elemental selenium as Cd, Te, and Se sources, respectively. All of these reactants were loaded at room temperature. This features synthetic reproducibility and large-scale capability. The bandgap engineering of the obtained CdTeSe QDs can be conveniently realized through the variation of growth temperature. Red- to near-infrared-emitting (620–780 nm) QDs with nearly identical particle sizes can be obtained when the reaction temperature was changed from 180 to 280 °C with the fixation of precursor feed ratio at 5Cd–0.5Te–0.5Se. The as-prepared CdTeSe QDs exhibit PL QY as high as 53%. The resulting CdTeSe QDs were characterized by UV–vis and photoluminescence spectroscopy, powder X-ray diffraction, transmission electron microscopy, and inductively coupled plasma atomic emission spectroscopy.
Co-reporter:Yan Li;Feifei Du;Hua Zhang;Xiling Du;Jian Zhu
Journal of Materials Science 2011 Volume 46( Issue 3) pp:670-674
Publication Date(Web):2011 February
DOI:10.1007/s10853-010-4789-5
A surfactant-assisted colloidal chemistry technique for the controllable growth of various PbS architectural nanostructures catalyzed by Ag nanocrystal seeds was reported. The sizes and morphologies of the obtained PbS nanostructures were dependent on the amount of Ag nanocrystal seeds and the ratio of Pb to S precursors. By varying the amount of Ag seed, sphere-, cube- and rod-shaped PbS nanostructures were obtained; while the morphologies changed from nano-scaled sphere to small cube and then to large truncated-cube when decreasing the precursors’ ratio of Pb to S from 5:1 to 2:1 and then to 1:2 with the fixation of the amount of Ag seed. Control of morphology under different conditions has been systematically studied and the mechanism of morphology formation was also primarily discussed.
Co-reporter:Ping Wu, Zheng Fang, Xinhua Zhong, Yong-Ji Yang
Colloids and Surfaces A: Physicochemical and Engineering Aspects 2011 Volume 375(1–3) pp:109-116
Publication Date(Web):5 February 2011
DOI:10.1016/j.colsurfa.2010.11.070
An aqueous-based route has been demonstrated for the preparation of ZnSe/ZnS core/shell nanocrystals via the directly thermal treatment of the crude ZnSe nanocrystals reaction solution in the presence of additional thiol ligand together with Zn source. The obtained ZnSe/ZnS core/shell nanostructures have tunable and narrow photoluminescence emission from ultraviolet to blue window (370–400 nm). Three common thiol ligands (mercaptopropionic acid (MPA), thioglycolic acid (TGA), and glutathione (GSH)) were tested as the sulfur source for ZnS shell deposition. It was found that with the addition of additional MPA or GSH into the ZnSe crude reaction solution, the PL efficiency of the obtained ZnSe/ZnS core/shell nanostructures can be improved significantly compared with the original ZnSe nanocrystals; while TGA has a quenching effect on the PL efficiency. The effects of experimental variables, including the nature of thiol ligand, amount of thiol ligand, reaction temperature, and pH value, on the synthesis and the optical properties of the obtained core/shell nanocrystals were investigated systematically. In comparison with plain ZnSe cores, both the PL emission efficiency and the stability against chemical oxidation of the ZnSe/ZnS core/shell structures have been improved substantially.Graphical abstractResearch highlights▶ ZnSe/ZnS core/shell nanocrystals prepared via the directly thermal treatment. ▶ PL efficiency of ZnSe/ZnS nanostructures improved significantly. ▶ Economic and facile preparative procedure.
Co-reporter:Yan Li, Ping Wu, Hu Xu, Zhongping Zhang, Xinhua Zhong
Talanta 2011 Volume 84(Issue 2) pp:508-512
Publication Date(Web):15 April 2011
DOI:10.1016/j.talanta.2011.01.037
For the widely used gold nanoparticles (AuNPs)-based colorimetric probes, AuNPs generally change from dispersion to aggregation state accompanying with corresponding color turning from red to blue. Although colorimetric probes based on the anti-aggregation of AuNPs show exceptional selectivity and sensitivity, few examples have been reported in literature. A facile but highly sensitive and selective colorimetric probe based on the anti-aggregation of AuNPs transferred from the deactivation of aggregation agent 4,4′-dipyridyl by Hg2+ was developed in this work. This reported probe is suitable for real-time detection of Hg2+ in water with a detection limit of 3.0 ppb for Hg2+, and exhibits a selectivity toward Hg2+ by two orders of magnitude over other metal ions. The dynamic range of this probe can be conveniently tuned by adjusting the amount of 4,4′-dipyridyl used.
Co-reporter:Lu Liu ; Xuhong Guo ; Yan Li
Inorganic Chemistry 2010 Volume 49(Issue 8) pp:3768-3775
Publication Date(Web):March 23, 2010
DOI:10.1021/ic902469d
We have designed and synthesized a multidentate polymer ligand used for water-solubilization of luminescent quantum dots (QDs). The synthesis of the multidentate ligand (PAA-g-MEA) was based on several thiol groups grafted to a linear polymer chain through a simple carboxy-amine coupling reaction between poly(acryl acid) (PAA) and mercaptoethylamine (MEA). Water-soluble QDs capped with these PAA-g-MEA ligands were prepared via ligand exchange from the original hydrophobic ones. The resulting PAA-g-MEA capped water-soluble QDs with relatively small hydrodynamic diameters possess higher photoluminescence quantum yields than the initial hydrophobic QDs, extraordinary stability over extended periods of time and over a broad pH range (3−14), salt concentrations (up to saturated NaCl solution), and thermal treatment at 100 °C.
Co-reporter:Feifei Du, Hua Zhang, Xiling Du, Jian Zhu, Xinhua Zhong
Materials Chemistry and Physics 2010 Volume 121(1–2) pp:118-124
Publication Date(Web):15 May 2010
DOI:10.1016/j.matchemphys.2010.01.013
Inverted type-I CdS/CdSe hetero-nanostructures with various dimensionalities were controlled and synthesized through successive ionic layer adsorption and reaction method by tuning the reaction temperature, core size, and shell thickness. The morphologies and crystal structures were characterized by transmission electron microscopy and X-ray diffraction analyses. Hetero-nanospheres and nanotetrapods were obtained at relative high temperature and low temperature, respectively. The rod- and cone-shaped nanostructures were controlled via using different sized cores at medial growth temperature. All the hetero-nanostructures showed fine absorption and photoluminescence properties attributed to CdSe shell. The morphology evolution mechanism was also discussed.
Co-reporter:Xiang Wang;Zheng Fang;Jinku Liu;Bangce Ye
Chinese Journal of Chemistry 2010 Volume 28( Issue 6) pp:1005-1012
Publication Date(Web):
DOI:10.1002/cjoc.201090158
Abstract
An approach for the sensitive and selective determination of Ag+, Cu2+ and Hg2+ ions was developed based on the fluorescence quenching of mercaptopropionic acid (MPA) capped CdTe quantum dots in the existence of hydroxyapatite (HAP) nanoribbon spherulites. Among various metal ions investigated, it was found that the fluorescence of CdTe QDs was only sensitive to Ag+, Cu2+ and Hg2+ ions. The addition of HAP into the CdTe system could bring forward a sensitivity improvement of about 1 to 2 orders of magnitude in the detection of Ag+ and Cu2+ compared with the plain CdTe system without the existence of HAP; while there was no sensitization effect for Hg2+. Under optimal conditions, the detection limits for Ag+, Cu2+ and Hg2+ were 20, 56 and 3.0 nmol·L−1, respectively, and the linear ranges were 0.02–50, 0.056–54 and 0.003–2.4 µmol·L−1, respectively. Mechanisms of both QDs fluorescence quenching by metal ions and the sensitization effect by HAP were also discussed.
Co-reporter:Dr. Hu Xu;Xiaomei Huang;Wenjin Zhang;Guanjiao Chen; Weihong Zhu ; Xinhua Zhong
ChemPhysChem 2010 Volume 11( Issue 14) pp:3167-3171
Publication Date(Web):
DOI:10.1002/cphc.201000287
Abstract
Quantum dots (QDs) usually act as energy donors in Förster resonant energy transfer (FRET) in various application fields. We report, for the first time, a FRET process from a conventional naphthalimide chromophore 1 to CdSe/ZnS core/shell QDs (acting as energy acceptors) in (1)–QDs hybrid system in solution. This FRET process is supported by various spectroscopies, such as steady-state and time-resolved photoluminescence (PL) as well as PL excitation spectra. The highest energy transfer efficiency is estimated to be about 0.37. Interestingly, the role of QDs in FRET can be specifically reversed (from energy acceptors to energy donors) with the use of QDs with larger band-gaps.
Co-reporter:Tong Wu;Xinggui Zhou;Hua Zhang
Nano Research 2010 Volume 3( Issue 5) pp:379-386
Publication Date(Web):2010 May
DOI:10.1007/s12274-010-1042-0
Co-reporter:Guanjiao Chen;Wenjin Zhang
Frontiers of Chemistry in China 2010 Volume 5( Issue 2) pp:214-220
Publication Date(Web):2010/06/01
DOI:10.1007/s11458-010-0106-8
We reported a facile route for overcoating CdS and ZnS shells around colloidal CdSe core nanocrystals. To synthesize such double shelled core/shell nanocrystals, first, CdSe core nanocrystals were prepared in a much “greener” and cheap route, which did not involve the use of hazardous and expensive trioctylphosphine. Then, a low-cost and labor-saving route was adopted for the CdS and ZnS shell growth with the use of thermal decomposition of commercial available air stable single-source precursors cadmium diethyldithio-carbamate and zinc diethyldithiocarbamate in a non-coordinating solvent at intermediate temperatures. Powder X-ray diffraction patterns and transmission electron microscopy images confirm the epitaxial growth of the shell in the core/shell nanocrystals. The photoluminescence quantum yield of the resulting CdSe/CdS/ZnS core/shell nanocrystals can be as high as 90% in organic media and up to 60% after phase transfer into aqueous media. By varying the size of CdSe cores, the emission wavelength of the obtained core/shell nanostructures can span from 554 to 636 nm.
Co-reporter: Hua Zhang;Ping Wu;Yan Li;Lifang Liao;Zheng Fang ; Xinhua Zhong
ChemCatChem 2010 Volume 2( Issue 9) pp:1115-1121
Publication Date(Web):
DOI:10.1002/cctc.201000090
Abstract
Colloidal oil-soluble Bi2O3 quantum dots (QDs) are synthesized through an alcoholysis route in organic media. Water-soluble Bi2O3 QDs are then obtained from the initial oil-soluble QDs through phase transfer by surface modification with mercaptopropionic acid. X-ray diffraction and transmission electron microscopy studies show that the crystallinity is enhanced and particles grow larger after phase transfer. The water-soluble Bi2O3 QDs exhibit excellent photocatalytic activity for the degradation of methyl orange at a wide range of pH values. After several cycles, the Bi2O3 QDs retain high degradation efficiency. Simulation according to the first-order reaction dynamics indicates that the degradation reaction may follow complicated quasi-homogeneous photocatalysis.
Co-reporter:Wenjin Zhang, Guanjiao Chen, Jian Wang, Bang-Ce Ye and Xinhua Zhong
Inorganic Chemistry 2009 Volume 48(Issue 20) pp:9723-9731
Publication Date(Web):September 22, 2009
DOI:10.1021/ic9010949
Applications of water-dispersible near-infrared (NIR)-emitting quantum dots (QDs) have been hampered by their instability and low photoluminescence (PL) efficiencies. In this paper, water-soluble highly luminescent NIR-emitting QDs were developed through constructing CdTe/CdSe/ZnS core/shell/shell nanostructure. The CdTe/CdSe type-II structure yields the QDs with NIR emission. By varying the size of CdTe cores and the thickness of the CdSe shell, the emission wavelength of the obtained nanostructure can span from 540 to 825 nm. In addition, the passivation of the ZnS shell with a substantially wide bandgap confines the excitons within the CdTe/CdSe interface and isolates them from the solution environment and consequently improves the stability of the nanostructure, especially in aqueous media. An effective shell-coating route was developed for the preparation of CdTe/CdSe core/shell nanostructures by selecting capping reagents with a strong coordinating capacity and adopting a low temperature for shell deposition. An additional ZnS shell was deposited around the outer layer of CdTe/CdSe QDs to form the core/shell/shell nanostructure through the decomposition of single molecular precursor zinc diethyldithiocarbamate in the crude CdTe/CdSe reaction solution. The water solubilization of the initially oil-soluble CdTe/CdSe/ZnS QDs was achieved through ligand replacement by 3-mercaptopropionic acid. The as-prepared water-soluble CdTe/CdSe/ZnS QDs possess PL quantum yields as high as 84% in aqueous media, which is one of the best results for the luminescent semiconductor nanocrystals.
Co-reporter:Lei Zou, Zheng Fang, Zhenyu Gu, Xinhua Zhong
Journal of Luminescence 2009 Volume 129(Issue 5) pp:536-540
Publication Date(Web):May 2009
DOI:10.1016/j.jlumin.2008.12.009
In this manuscript, we present a facile approach for the synthesis of highly luminescent CdS nanocrystals (maximum quantum yield of 36%) by the reaction of Cd2+ and thiourea in the presence of glutathione (GSH) as capping reagent. The influence of various experimental variables, including pH value, S-to-Cd ratio, as well as Cd-to-ligand ratio, on the growth rate and optical properties of the obtained CdS nanocrystals has been systematically investigated. Experimental results indicate that the pH value and Cd-to-ligand molar ratio play a crucial role in determining luminescent properties of the obtained CdS nanocrystals. Furthermore, the luminescence intensity can be enhanced significantly when the nanocrystals sample is illuminated by room light. The mechanism for the resulting high-quality optical properties of the obtained CdS nanocrystals is also elucidated.
Co-reporter:Zheng Fang, Lu Liu, Jian Wang and Xinhua Zhong
The Journal of Physical Chemistry C 2009 Volume 113(Issue 11) pp:4301-4306
Publication Date(Web):2017-2-22
DOI:10.1021/jp809653c
A ZnxCd1−xS shell was deposited around CdSe nanocrystal cores via a noninjection approach in aqueous media. The deposition of the ZnxCd1−xS shell around CdSe cores was carried out at 90 °C in a reaction flask consisting of the shell precursor compounds, together with CdSe nanocrystal cores and the capping reagent glutathione. This newly developed depositing approach uses CdCl2, Zn(OAc)2, and thiourea as Cd, Zn, and S sources, respectively. All of these chemicals were loaded at room temperature. The optical features and structure of the obtained CdSe/ZnxCd1−xS core/shell nanocrystals were characterized by UV−visible and photoluminescence spectroscopy, transmission electron microscopy, X-ray diffraction, and inductively coupled plasma atomic emission spectroscopy. The influences of various experimental variables, including the Cd-to-Zn ratio, amounts of ligand and thiourea, as well as pH value, on the growth rate and luminescent properties of the obtained core/shell nanocrystals have been systematically investigated. Through the optimization of experimental variables, the obtained water-soluble core/shell nanocrystals possess a maximum emission efficiency of 35% and a spectral width of less than 30 nm.
Co-reporter:Jian Wang;Yitao Long ;Yuliang Zhang Dr., ;Linyong Zhu
ChemPhysChem 2009 Volume 10( Issue 4) pp:680-685
Publication Date(Web):
DOI:10.1002/cphc.200800672
Co-reporter:Zheng Fang, Yan Li, Hua Zhang, Xinhua Zhong and Linyong Zhu
The Journal of Physical Chemistry C 2009 Volume 113(Issue 32) pp:14145-14150
Publication Date(Web):July 9, 2009
DOI:10.1021/jp903806b
Unlike that for cadmium based nanocrystals, little research has been found on the synthesis of the UV-blue-emitting ZnSe based QDs with photoluminescence (PL) quantum yield (QY) superior to 50%. In this article, high-quality water-dispersible ZnSe/ZnS core/shell nanocrystals have been prepared in aqueous media. The epitaxial overgrowth of the ZnS shell was carried out at 90 °C in a reaction flask consisting of the shell precursor compounds (zinc acetae as zinc resource and thiourea as sulfur resource), together with the as-prepared ZnSe core nanocrystals and the capping reagent glutathione. The optical features and structure of the obtained ZnSe/ZnS core/shell nanocrystals have been characterized by UV−vis, PL spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy-dispersive X-ray analysis (EDX). The influences of various experimental variables, including amounts of ligand and thiourea as well as pH value, on the growth rate and luminescent properties of the obtained core/shell nanocrystals have been systematically investigated. The PL QY of the as-prepared water-soluble ZnSe/ZnS core/shell QDs is up to 65%, which is one of the best results for the water-soluble UV-blue-emitting semiconductor nanocrystals. In comparison with the plain ZnSe nanocrystals, both the PL QY and the stability against UV irradiation and chemical oxidation of the ZnSe/ZnS core/shell QDs have been greatly improved.
Co-reporter:Lei Zou, Zhenyu Gu, Nan Zhang, Yuliang Zhang, Zheng Fang, Weihong Zhu and Xinhua Zhong
Journal of Materials Chemistry A 2008 vol. 18(Issue 24) pp:2807-2815
Publication Date(Web):30 Apr 2008
DOI:10.1039/B801418C
It is commonly observed that the “traditional” aqueous solution route to prepare CdTe nanocrystals (NCs) using thiol ligands as capping reagents is usually very time-consuming and the luminescent properties are poor in the deep red to near infrared (NIR) emission window. Herein, we present an ultrafast and facile aqueous phase route under atmospheric pressure to prepare high-quality green- to NIR-emitting CdTe NCs with mercaptopropionic acid as capping reagent. In contrast to previous reports, red- to NIR-emitting CdTe NCs with emission efficiency up to 50% can be obtained within 1 h reflux time under the optimized experimental conditions. The growth rate is about 100 times faster than those reported previously. The influences of various experimental variables, including Te-to-Cd ratio, ligand-to-Cd ratio, pH value as well as the precursor concentration, on the growth rate and luminescent properties of the obtained CdTe NCs have been systematically investigated. Experimental results indicate that the combination of high pH value and low Te-to-Cd molar ratio plays a crucial role in determining the fast growth rate and the high-quality optical properties of the obtained CdTe NCs. The mechanism for the fast growth rate and the resulting high-quality optical properties is also elucidated.
Co-reporter:Xinhua Zhong;Yaoyu Feng
Research on Chemical Intermediates 2008 Volume 34( Issue 2-3) pp:287-298
Publication Date(Web):2008 February
DOI:10.1163/156856708783623456
In the last decade, the main efforts have focused on the preparation of different sized binary II–VI group semiconductor nanocrystals to obtain different color-emitting luminescence. However, the tuning of physical and chemical properties by changing the particle size could cause problems in many applications, in particular if unstable small particles are used. Recent advances have led to the exploration of tunable optical properties by changing their constituent stoichiometries in ternary alloy nanocrystals. High-quality ZnxCd1−xSe alloy nanocrystals have been successfully prepared at high temperature by incorporating stoichiometric amounts of Zn and Se into pre-prepared CdSe nanocrystals or embryonic CdSe nuclei. With increasing Zn content, a composition-tunable emission across the whole visible spectrum has been demonstrated by a systematic blue-shift in emission wavelength. High-quality alloy ZnxCd1−xS nanocrystals have been obtained by the conucleation and co-growth of the constituents through the reaction of a mixture of CdO- and ZnO-oleic acid complexes with sulfur at elevated temperatures. The obtained ZnxCd1−xS alloy nanocrystals possess superior optical properties with photoluminescence quantum yields of 25–50%, especially the extremely narrow emission spectral width (fwhm=14 nm).
Co-reporter:Zheng Fang;Yuliang Zhang;Feifei Du
Nano Research 2008 Volume 1( Issue 3) pp:249-257
Publication Date(Web):2008 September
DOI:10.1007/s12274-008-8029-0
This paper reports an effective method for the synthesis of platinum nanostructures with anisotropic morphologies by decomposition of platinum dichloride in oleylamine at intermediate temperatures catalyzed by gold seed nanoparticles. A small quantity of spherical gold nanoparticles formed in situ was used to trigger the nucleation and anisotropic growth of the Pt nanocrystals. By varying the amount of gold seed nanoparticles, porous flower-like, irregular polyhedron-shaped, multi-branched rod shaped, and caterpillar-like Pt nanostructures were produced in high yields at 190–240 °C in reaction times of a few minutes. Control of morphology under different conditions has been systematically studied and a kinetically controlled induced growth mechanism has been proposed.
Co-reporter:Zhenxiao Pan ; Iván Mora-Seró ; Qing Shen ; Hua Zhang ; Yan Li ; Ke Zhao ; Jin Wang ; Xinhua Zhong ;Juan Bisquert
Journal of the American Chemical Society () pp:
Publication Date(Web):May 30, 2014
DOI:10.1021/ja504310w
Semiconductor quantum dots (QDs) are extremely interesting materials for the development of photovoltaic devices, but currently the present the drawback is that the most efficient devices have been prepared with toxic heavy metals of Cd or Pb. Solar cells based on “green” QDs—totally free of Cd or Pb—present a modest efficiency of 2.52%. Herein we achieve effective surface passivation of the ternary CuInS2 (CIS) QDs that provides high photovoltaic quality core/shell CIS/ZnS (CIS-Z) QDs, leading to the development of high-efficiency green QD solar cells that surpass the performance of those based on the toxic cadmium and lead chalcogenides QDs. Using wide absorption range QDs, CIS-Z-based quantum dot sensitized solar cell (QDSC) configuration with high QD loading and with the benefit of the recombination reduction with type-I core/shell structure, we boost the power conversion efficiency of Cd- and Pb-free QDSC to a record of 7.04% (with certified efficiency of 6.66%) under AM 1.5G one sun irradiation. This efficiency is the best performance to date for QDSCs and also demonstrates that it is possible to obtain comparable or even better photovoltaic performance from green CIS QDs to the toxic cadmium and lead chalcogenides QDs.
Co-reporter:Juan Yu, Wenran Wang, Zhenxiao Pan, Jun Du, Zhenwei Ren, Weinan Xue and Xinhua Zhong
Journal of Materials Chemistry A 2017 - vol. 5(Issue 27) pp:NaN14133-14133
Publication Date(Web):2017/06/09
DOI:10.1039/C7TA04344A
The undesired charge recombination loss, occurring at photoanode/electrolyte interfaces, as well as the high redox potential of the currently used polysulfide redox couple electrolyte restrain the photovoltaic performance, particularly the open-circuit potential (Voc), of quantum dot sensitized solar cells (QDSCs). Herein, a valid and facile method to improve the performance of QDSCs is presented by modifying the polysulfide electrolyte with the addition of tetraethyl orthosilicate (TEOS). This approach is effective in a series of QDSC systems including the most commonly studied CdSe, CdSeTe, as well as Zn–Cu–In–Se (ZCISe) QDSCs. Experimental results indicate that with the use of 6 vol% TEOS additive in pristine polysulfide electrolyte at a staying time of 24 h, a remarkable enhancement in the conversion efficiency from 11.75% to 12.34% was obtained in ZCISe QDSCs. This photovoltaic performance is believed to be among the best result for all types of QD-based solar cells. The intrinsic mechanism for the performance improvement by the TEOS additive was verified by electrochemical impedance spectroscopy (EIS) and open-circuit voltage decay (OCVD) measurements.
Co-reporter:Hua Zhang, Cheng Yang, Zhonglin Du, Dengyu Pan and Xinhua Zhong
Journal of Materials Chemistry A 2017 - vol. 5(Issue 4) pp:NaN1622-1622
Publication Date(Web):2016/12/12
DOI:10.1039/C6TA08443E
Although copper sulfide and/or carbon materials have been utilized in counter electrodes (CEs) due to their good catalytic activity and conductivity, the efficiency of the assembled quantum dot-sensitized solar cells (QDSCs) is still unsatisfactory because of the relatively low photovoltage (Voc), which is commonly less than 0.7 V. In this study, graphene hydrogels (GHs) compressed onto titanium mesh served as the CE and the assembled CdSeTe QDSCs exhibited a photovoltaic conversion efficiency (PCE) of 9.85% and a Voc as high as 0.756 V, which increased by 19.0% and 14.9%, respectively, and are higher than those of the conventional CuS on FTO. By incorporating CuS nanoparticles into GH during gelation, the as-prepared GH–CuS CEs show further improved performance and the maximum PCE and Voc obtained were 10.71% and 0.786 V, respectively. The fill factor of the cells was also continuously increased. The excellent performance of the devices could be attributed to the synergistic effects of the water-rich GH (having a 3D porous structure accompanied by good conductivity) and highly catalytic CuS, reflected from the small series resistance, high catalytic activity, small electron transfer resistance, and stability, which have been confirmed by EIS, Tafel polarization, and CV curves.
Co-reporter:Zhonglin Du, Hua Zhang, Huili Bao and Xinhua Zhong
Journal of Materials Chemistry A 2014 - vol. 2(Issue 32) pp:NaN13040-13040
Publication Date(Web):2014/06/13
DOI:10.1039/C4TA02291B
As a fundamental part of quantum dot-sensitized solar cells, the composition and configuration of the TiO2 photoanode film plays an important role in photovoltaic performance. In this work, the preparation and optimization of films have been systematically studied, including the TiCl4 treatment technique, transparent layer and light-scattering layer thickness and composition. Experimental results show that the sole TiCl4 treatment on fluorine doped SnO2 (FTO) glass is sufficient for achieving a high efficiency in the resultant cell devices when compared with the simultaneous treatment on both FTO glass and TiO2 mesoporous films. The thickness and porosity of the transparent layer have been optimized by tuning the number of transparent layers and the ethyl cellulose contents in the paste. Moreover, the influence of the light-scattering layer pastes with different contents of the large-sized TiO2 particles on the performance of the cells has also been explored. The CdSe-sensitized solar cells based on the optimized TiO2 film photoanode exhibits a power conversion efficiency of 5.53% under 1 full sun illumination, which is among the best efficiencies for plain CdSe QD-based solar cells.
Co-reporter:Jin Wang, Yan Li, Qing Shen, Takuya Izuishi, Zhenxiao Pan, Ke Zhao and Xinhua Zhong
Journal of Materials Chemistry A 2016 - vol. 4(Issue 3) pp:NaN886-886
Publication Date(Web):2015/12/02
DOI:10.1039/C5TA09306F
Transition metal ion (especially Mn2+) doping has been proven to be an effective approach to modify the intrinsic photo-electronic properties of semiconductor quantum dots (QDs). However, previous works to directly grow Mn doped QDs on TiO2 film electrodes at room temperature resulted in the potential of the Mn dopant not being fully demonstrated in quantum dot sensitized solar cells (QDSCs). Herein, Mn doped CdSe0.65Te0.35 QDs (simplified as Mn:QD) were pre-synthesized via a “growth doping” strategy at high temperature. A QD-sensitized photoanode with the configuration TiO2/Mn:QD/Mn:ZnS/SiO2 was prepared and corresponding cell devices were constructed using Cu2S/brass counter electrodes and polysulfide electrolyte, together with reference cells with the photoanode configurations TiO2/Mn:QD/ZnS/SiO2, TiO2/QD/Mn:ZnS/SiO2, and TiO2/QD/ZnS/SiO2. The photovoltaic performance results indicate that TiO2/Mn:QD/Mn:ZnS/SiO2 cells exhibit the best photovoltaic performance among all the studied cell devices with a power conversion efficiency (PCE) for the champion cell of 9.40% (Jsc = 20.87 mA cm−2, Voc = 0.688 V, FF = 0.655) under AM 1.5 G one full sun illumination, which is among the best results for QDSCs. The open circuit voltage decay (OCVD), impedance spectroscopy (IS) and transient absorption (TA) measurements confirm that the Mn2+ dopant can suppress charge recombination and improve the photovoltage and PCE of the resulting cells.
Co-reporter:Shuang Jiao, Jin Wang, Qing Shen, Yan Li and Xinhua Zhong
Journal of Materials Chemistry A 2016 - vol. 4(Issue 19) pp:NaN7221-7221
Publication Date(Web):2016/04/11
DOI:10.1039/C6TA02465C
The power conversion efficiencies (PCEs) of PbS quantum dot sensitized solar cells (QDSCs) reported are typically below 6%. This poor efficiency is mainly derived from the serious charge recombination in internal QDs and at the interface of QDs/TiO2/electrolyte. In this work, PbS/CdS QDs with a core/shell structure, which were used as the photosensitizer to fabricate sensitized solar cells, were prepared through the ion exchange method. With the reduced trapping state defects on the surface of the PbS QDs and resulting effective suppression of adverse charge recombination, the PbS/CdS QD-based cells have been improved remarkably in comparison with the pristine PbS-based QDSCs. By optimization of the thickness of the CdS shell, a PCE of 7.19% under one full sun illumination was obtained on the fabricated devices, which is among the best performances for liquid-junction PbS QDSCs.
Co-reporter:Jun Du, Xinxin Meng, Ke Zhao, Yan Li and Xinhua Zhong
Journal of Materials Chemistry A 2015 - vol. 3(Issue 33) pp:NaN17097-17097
Publication Date(Web):2015/07/15
DOI:10.1039/C5TA04758G
Besides the relatively high redox potential of the adopted S2−/Sn2− polysulfide redox couple electrolyte, the parasitic charge recombination process is another significant factor that limits the open-circuit voltage and consequent power conversion efficiency (PCE) of quantum dot sensitized solar cells (QDSCs). Herein, we report a facile method to modify the polysulfide electrolyte with the addition of polyethylene glycol (PEG) additives to suppress the charge recombination occurring at the TiO2/QDs/electrolyte interfaces. Impedance spectroscopy and open circuit voltage decay (OCVD) measurements reveal that the PEG additive in the polysulfide electrolyte reduces interfacial recombination when compared with the conventional polysulfide electrolyte in the absence of the PEG additive. A dramatic enhancement of PCE from 5.80% to 6.74% was observed with the introduction of 15 wt% PEG in the polysulfide electrolyte in CdSe based QDSCs. Moreover, the PEG additive also improves the photovoltaic performance stability of the resultant cells.
Co-reporter:Lu Liu and Xinhua Zhong
Chemical Communications 2012 - vol. 48(Issue 46) pp:NaN5720-5720
Publication Date(Web):2012/02/28
DOI:10.1039/C2CC30444A
We report a facile and general phase transfer strategy using nucleotides or nucleosides as phase transfer reagents to render a wide variety of nanomaterials transferring from organic phase to aqueous phase or vice versa, while preserving their intrinsic physicochemical features.
Co-reporter:H. Zhang, K. Cheng, Y. M. Hou, Z. Fang, Z. X. Pan, W. J. Wu, J. L. Hua and X. H. Zhong
Chemical Communications 2012 - vol. 48(Issue 91) pp:NaN11237-11237
Publication Date(Web):2012/10/03
DOI:10.1039/C2CC36526J
A postsynthesis assembly approach, an ex situ ligand exchange route, was developed for fast (within 2 h) and high loading (34% coverage) deposition of CdSe QDs on TiO2 films. With the combination of high-quality QD sensitizers and the effective deposition technique, a record photovoltaic performance with an efficiency of 5.4% was observed for the resulting cell device.
Co-reporter:Wenjie Li, Zhenxiao Pan and Xinhua Zhong
Journal of Materials Chemistry A 2015 - vol. 3(Issue 4) pp:NaN1655-1655
Publication Date(Web):2014/11/19
DOI:10.1039/C4TA05134C
CuInSe2 (CISe) based quantum dots (QDs), are perceived to be promising alternatives to those of cadmium or lead chalcogenide based QDs in serving as light-harvesting sensitizer materials in quantum dot sensitized solar cells (QDSCs) due to their near-infrared (NIR) absorbing capacity and low toxicity. Herein, we have synthesized high quality CISe QDs via the organic phase high temperature route, and then alloying with ZnS to form the CISe–ZnS QDs with higher chemical stability and superior optoelectronic properties. The obtained “green” CISe and CISe–ZnS QD sensitizers were immobilized onto TiO2 film electrodes with high loading amount through the linker molecule assisted post synthesis assembly approach with the use of MPA-capped water-soluble QDs. Hindered charge recombination in the built CISe–ZnS QD based solar cells in comparison with reference CISe cells has been confirmed by impedance spectroscopy, as well as transient photovoltage decay measurements. With the combination of high QD loading and passivated trap-state defects, the resulting regenerative sandwich CISe–ZnS QD based champion solar cells exhibited an efficiency of 6.79% (Jsc = 22.61 mA cm−2, Voc = 0.583 V, FF = 0.515) under AM 1.5 G full one sun irradiation. The obtained efficiency was among the best performances for liquid-junction QDSCs and also demonstrated comparable photovoltaic performance of “green” CISe based QDs to the toxic cadmium and lead chalcogenide QDs.
Co-reporter:Zhenxiao Pan and Xinhua Zhong
Journal of Materials Chemistry A 2016 - vol. 4(Issue 48) pp:NaN18982-18982
Publication Date(Web):2016/11/08
DOI:10.1039/C6TA08717E
Charge recombination at the photoanode/electrolyte interface is one of the priority factors limiting the photovoltaic performance of quantum dot sensitized solar cells (QDSCs). Exploring interfacial engineering with the use of a proper passivation layer around the photoanode is an efficient way to control the charge recombination process and to promote the performance of the resultant cell devices. Herein, an easily synthesised and effective passivation layer making use of a ZnS and metal hydroxide composite material was developed for suppressing charge recombination and therefore improving the photovoltaic performance of a model CdSeTe QDSC. This novel composite passivation layer was formed by mixing the target metal ion with a Zn(OAc)2 aqueous solution during a successive ionic layer adsorption and reaction (SILAR) procedure for overcoating ZnS layers on photoanodes. The influence of the different metal ions (including Be2+, Mg2+, Ca2+, Al3+, and Ga3+) was investigated and photovoltaic measurement results indicate that the formed ZnS and metal hydroxide composite passivation layer contributed to a considerable improvement in the photovoltage and power conversion efficiency of the resultant cell devices in comparison with a plain ZnS layer. The average efficiency was improved from 8.88% to 9.50% and a champion efficiency of 9.64% (Jsc = 21.20 mA cm−2, Voc = 0.702 V, FF = 0.648) was achieved under AM 1.5G full one sun irradiation for the ZnS/Ga(OH)3 composite passivation layer based cells. Impedance spectroscopy (IS) and open-circuit voltage-decay (OCVD) measurements further confirmed that the ZnS and metal hydroxide composite passivation layer outperforms the reference plain ZnS layer in suppressing charge recombination.
Co-reporter:Junwei Yang and Xinhua Zhong
Journal of Materials Chemistry A 2016 - vol. 4(Issue 42) pp:NaN16561-16561
Publication Date(Web):2016/09/23
DOI:10.1039/C6TA07399A
CdTe quantum dots (QDs) with a narrow band gap and high conduction band (CB) edge provide great potential for the fabrication of QD sensitized solar cells (QDSCs). Herein, a convenient aqueous route was adopted to synthesize CdTe core QDs for the construction of type-II core/shell QD sensitizers. First, mercaptopropionic acid (MPA) capped water-soluble CdTe QDs were synthesized in aqueous media. After tethering the CdTe QDs onto a mesoporous TiO2 photoanode, CdTe/CdS and CdTe/CdSexS1−x type-II core/shell QD sensitizers were formed by post-depositing CdS and CdSexS1−x shell materials over the photoanodes via a successive ionic layer adsorption and reaction processes (SILAR), respectively. A wider light harvesting range together with a wider photoelectronic response range was observed in the resultant CdTe/CdS and CdTe/CdSexS1−x core/shell QD based solar cells relative to plain CdTe cells. Simultaneously, suppressed charge recombination processes has also been confirmed by impedance spectroscopy (IS), and open-circuit voltage decay (OCVD) characterizations. Consequently, compared to the plain CdTe QDSCs, the power conversion efficiencies (PCEs) for CdTe/CdS and CdTe/CdSeS were enhanced by 22 and 35%, respectively. With the optimization of CdSexS1−x shell thickness, a PCE of 7.24% under the illumination of one full sun was obtained.
Co-reporter:Junwei Yang, Takuya Oshima, Witoon Yindeesuk, Zhenxiao Pan, Xinhua Zhong and Qing Shen
Journal of Materials Chemistry A 2014 - vol. 2(Issue 48) pp:NaN20888-20888
Publication Date(Web):2014/10/28
DOI:10.1039/C4TA04353G
The charge transfer rate between QD sensitizer/TiO2 interfaces in quantum dot sensitized solar cells (QDSCs) is one of the most important criteria determining the photovoltaic performance of cells. To investigate the influence of linker molecules on the electron transfer rate at the QD–linker–TiO2 interface and the final performance of the resultant QDSCs, colloidal QDs capped with thioglycolic acid (TGA), 3-mercaptopropionic acid (MPA), and cysteine (Cys), which also serve as molecular linkers between QDs and TiO2 nanoparticles, were self-assembled on a TiO2 mesoporous film electrode from the corresponding QD aqueous dispersions. The influence of the studied linker molecules (TGA, MPA, and Cys) on the loading amount of QD sensitizer on the TiO2 mesoporous film, the electron injection rate from QDs to the TiO2 matrix, the incident photon to charge carrier generation efficiency (IPCE), and the corresponding photovoltaic performance of the resultant QDSCs were systematically studied. CdSe and CdSexTe1−x QD sensitized solar cells were selected as a model cell to evaluate the influence of the adopted linker molecules. Under AM 1.5G full one sun intensity illumination, the power conversion efficiency (PCE) of TGA-capped QDs (5.40% for CdSe, and 6.68% for CdSexTe1−x) was 7–14% greater than those of MPA- and Cys-capped QDs. Similarly, the absorbed photon-to-current efficiency was 8–13% greater. These differences arise from linker molecule-dependent variations of the electron-injection rate. Transient grating measurements indicate that the electron injection rate constant from TGA-capped CdSe (8.0 × 109 s−1) was greater than from MPA- and Cys-capped CdSe (2.6–2.9 × 109 s−1). Thus, TGA-capped QDs are readily attached to the TiO2 substrate and exhibit better electronic properties and desirable electron-transfer rate, and therefore bring forward better photovoltaic performance in the resultant solar cells.
Co-reporter:Lei Zou, Zhenyu Gu, Nan Zhang, Yuliang Zhang, Zheng Fang, Weihong Zhu and Xinhua Zhong
Journal of Materials Chemistry A 2008 - vol. 18(Issue 24) pp:NaN2815-2815
Publication Date(Web):2008/04/30
DOI:10.1039/B801418C
It is commonly observed that the “traditional” aqueous solution route to prepare CdTe nanocrystals (NCs) using thiol ligands as capping reagents is usually very time-consuming and the luminescent properties are poor in the deep red to near infrared (NIR) emission window. Herein, we present an ultrafast and facile aqueous phase route under atmospheric pressure to prepare high-quality green- to NIR-emitting CdTe NCs with mercaptopropionic acid as capping reagent. In contrast to previous reports, red- to NIR-emitting CdTe NCs with emission efficiency up to 50% can be obtained within 1 h reflux time under the optimized experimental conditions. The growth rate is about 100 times faster than those reported previously. The influences of various experimental variables, including Te-to-Cd ratio, ligand-to-Cd ratio, pH value as well as the precursor concentration, on the growth rate and luminescent properties of the obtained CdTe NCs have been systematically investigated. Experimental results indicate that the combination of high pH value and low Te-to-Cd molar ratio plays a crucial role in determining the fast growth rate and the high-quality optical properties of the obtained CdTe NCs. The mechanism for the fast growth rate and the resulting high-quality optical properties is also elucidated.
Co-reporter:Yunfei Ma, Yan Li, Shijian Ma and Xinhua Zhong
Journal of Materials Chemistry A 2014 - vol. 2(Issue 31) pp:NaN5051-5051
Publication Date(Web):2014/06/05
DOI:10.1039/C4TB00458B
Silica coating via a Stöber method is an effective route to render luminescent quantum dots (QDs) with great biocompatibility, low toxicity and water-solubility for bioapplications. However, the bottleneck in this route is the access of highly luminescent, colloidally stable QD dispersion in alcoholic solution. Herein, we report a facile route based on the Stöber method for the synthesis of isolated silica coated QDs (QD@SiO2) with high emission efficiencies, tunable small size (less than 30 nm) and excellent stability. Prior to silica coating, the initial oil-soluble QDs were made dispersible in alcohol–water media by replacing the native hydrophobic ligands with adenosine 5′-monophosphate (AMP). Then, 3-mercaptopropyl-trimethoxysilane (MPS) was introduced to serve as silane nucleation primers. Finally, a silica shell with controllable thickness was obtained on the QD surface by hydrolysis/condensation of tetraethyl orthosilicate (TEOS). Remarkably, the resultant QD@SiO2 had nearly the same high luminescent efficiency (50–65%) as that of initial oil-soluble QDs and exhibited excellent long-term photo and colloidal stability in harsh environments (pH range of 3–13, saturated NaCl solution and thermal treatment at 100 °C). It was demonstrated that the cytotoxicity of the resultant QD@SiO2 was significantly diminished. Moreover, the QD@SiO2 conjugated with folic acid exhibits high specific binding toward receptor-positive Hela cells over receptor-negative A549 cells, indicating the potential of our obtained QD@SiO2 as robust biomarkers in cells due to their chemical processibility and low cytotoxicity.
Co-reporter:Wenliang Feng, Yan Li, Jun Du, Wei Wang and Xinhua Zhong
Journal of Materials Chemistry A 2016 - vol. 4(Issue 4) pp:NaN1468-1468
Publication Date(Web):2015/12/23
DOI:10.1039/C5TA08209A
Limited by the volatilization and leakage of liquid electrolytes, the long-term stability of liquid-junction quantum dot sensitized solar cells (QDSCs) remains a main challenge for the application of QDSCs. Herein, a polyelectrolyte with superior water-absorbing and water-holding capacity, sodium polyacrylate (PAAS), was attempted to gelate conventional aqueous polysulfide electrolytes to construct quasi-solid-state QDSCs. PAAS gel electrolytes have a comparable conductivity with liquid polysulfide electrolytes. Meanwhile, the PAAS gel could penetrate readily into the framework of mesoporous TiO2 film electrodes due to the strong coordination ability of carboxylate groups on PAAS polymer chains with metal ions. Benefited from the high conductivity of the PAAS gel and its perfect contact with the TiO2 surface, an impressive photovoltaic performance with a power conversion efficiency of 8.54% in one full sunlight, which is among the best performance for QDSCs, was achieved for CdSeTe QDSCs. Furthermore, the light-soaking stability of the resulting cell devices is significantly improved in comparison with that of the conventional aqueous polysulfide electrolyte based ones.
Co-reporter:Guocan Jiang, Zhenxiao Pan, Zhenwei Ren, Jun Du, Cheng Yang, Wenran Wang and Xinhua Zhong
Journal of Materials Chemistry A 2016 - vol. 4(Issue 29) pp:NaN11421-11421
Publication Date(Web):2016/06/23
DOI:10.1039/C6TA04027F
Charge recombination losses are primarily responsible for the modest photovoltaic performance of quantum dot sensitized solar cells (QDSCs). Charge recombination occurring at the photoanode/electrolyte interface contributes significant energy loss in QDSC devices. Herein, a facile method to reduce the recombination loss by modifying the polysulfide electrolyte with the addition of poly(vinyl pyrrolidone) (PVP) as an efficient and general additive was introduced. It was found that the PVP modified polysulfide electrolyte could significantly improve the photovoltaic performance of QDSCs, especially the open-circuit voltage and fill factor. In addition, the PVP modified electrolyte is widely applicable to various QD sensitizer based systems. Impedance spectroscopy and open circuit voltage decay (OCVD) measurements reveal that the charge recombination processes occurring at the TiO2/QDs/electrolyte interfaces were remarkably inhibited using the PVP modified electrolyte. The average power conversion efficiency (PCE) was improved remarkably by 9% and a champion PCE of 9.77% was obtained with 20 wt% PVP in the polysulfide electrolyte for CdSexTe1−x based QDSCs. Moreover, the stability of the constructed QDSCs was also improved by employing the PVP modified polysulfide electrolyte.
Co-reporter:Zhonglin Du, Jing Tong, Wenxia Guo, Hua Zhang and Xinhua Zhong
Journal of Materials Chemistry A 2016 - vol. 4(Issue 30) pp:NaN11761-11761
Publication Date(Web):2016/06/28
DOI:10.1039/C6TA04934F
The development of a highly efficient stretchable counter electrode (CE) for quantum dot sensitized solar cells (QDSCs) is still challenging. In this work, a flexible Cu/Ni film has been pre-prepared via a novel redox reaction between Ni foam and Cu ions. Further, a flexible Cu2S/Ni CE was fabricated for the first time by sulfidation of the Cu/Ni film. A high photovoltaic conversion efficiency (PCE) of 8.94% for a model CdSeTe QDSC composed of the flexible Cu2S/Ni CE and a glass based photoanode was obtained, with the performance being strongly attributed to the excellent catalytic activity, high conductivity and good adhesion between Cu2S and Ni foam. Furthermore, flexible photovoltaic devices constructed using the as-prepared bendable Cu2S/Ni CE as well as a TiO2 based plastic photoanode have also been assembled with the highest PCE of 3.55%. Satisfactory mechanical properties and stability after repeated bending have also been achieved.
Co-reporter:Hua Zhang, Huili Bao and Xinhua Zhong
Journal of Materials Chemistry A 2015 - vol. 3(Issue 12) pp:NaN6564-6564
Publication Date(Web):2015/02/17
DOI:10.1039/C5TA00068H
A mixture composed of CuS and Cu1.8S has been easily fabricated via a solvothermal method followed by screen-printing to form a counter electrode. A highly reproducible record efficiency of 6.28% for the assembled CdSe-sensitized solar cells has been achieved, and the irradiation, as well as conservation stability, have also been greatly improved compared to the brass foil based solar cells. With different size and morphology, the phase of CuS shows a slightly superior performance than Cu1.8S through investigating the influence of S/Cu ratio on the efficiency. The sintering temperature of the counter electrode film has also been studied, and the results show that 400 °C is favorable for good conductivity, high electrochemical activity, low charge transfer resistance in a solid–solid interface and between the catalysts and electrolyte. Because of the low cost, convenient fabrication, easy of sealing, as well as the high efficiency, reproducibility and excellent stability of the devices, the as-prepared copper sulfide could be potentially and extensively utilized in semiconductor-sensitized solar cells.
