Jizheng Wang

Additive-Free Organic Solar Cells with Power Conversion Efficiency over 10%

Co-reporter:Hui Li;Dan He;Peng Mao;Yuanzhi Wei;Liming Ding

Advanced Energy Materials 2017 Volume 7(Issue 13) pp:

Publication Date(Web):2017/07/01

DOI:10.1002/aenm.201602663

Nowadays, solvent additives are widely used in organic solar cells (OSCs) to tune the nano-morphology of the active blend film and enhance the device performance. With their help, power conversion efficiencies (PCEs) of OSCs have recently stepped over 10%. However, residual additive in the device can induce undesirable morphological change and also accelerate photo-oxidation degradation of the active blend film. Thereby, their involvements are actually unfavorable for practical applications. Here, a donor material PThBDTP is employed, and PThBDTP:PC71BM based OSCs are fabricated. A PCE of over 10% is achieved without using any additives and film post-treatments. The device displays a high open-circuit voltage of 0.977 V, a large short-circuit current density of 13.49 mA cm-2, and a high fill factor of 76.3%. These results represent an important step towards developing high-efficiency additive-free OSCs.

Bilayer PbS Quantum Dots for High-Performance Photodetectors

Co-reporter:Zhenwei Ren;Jiankun Sun;Hui Li;Peng Mao;Yuanzhi Wei;Xinhua Zhong;Jinsong Hu;Shiyong Yang

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.

TiO2 Nanocrystal/Perovskite Bilayer for High-Performance Photodetectors

Co-reporter:Xiaohui Yi;Zhenwei Ren;Ningli Chen;Cheng Li;Xinhua Zhong;Shiyong Yang

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.

Solution-processed transparent coordination polymer electrode for photovoltaic solar cells

Co-reporter:Zhiwen Jin, Jie Yan, Xing Huang, Wei Xu, Shiyong Yang, Daoben Zhu, Jizheng Wang

Nano Energy 2017 Volume 40(Volume 40) pp:

Publication Date(Web):1 October 2017

DOI:10.1016/j.nanoen.2017.08.028

•A solution-processed transparent electrode was developed based on a two-dimensional metal-organic framework (2D-MOF) Cu-BHT.•The 2D-MOF Cu-BHT film displays high electrical conductivity over 2500 S cm-1 and optical transparency of 82%.•The 2D-MOF Cu-BHT transparent electrode on both glass and PI substrates is tested in peroverskite, quantum dot and organic solar cells, which indicates its performance is comparable to the widely used ITO.Currently, photovoltaic research area is short of solution-processed transparent electrodes, which can replace the widely used vacuum-deposited indium tin oxide (ITO). Here, by employing a two-dimensional metal-organic framework (2D-MOF) Cu-BHT (BHT = benzenehexathiol), a solution-processed transparent electrode with high conductivity over 2500 Scm−1 and high transmittance of 82% is developed. Three classic photovoltaic solar cells (perovskite solar cells, quantum dots solar cells and organic solar cells) are fabricated on both glass and flexible polyimide (PI) substrates with this Cu-BHT electrode, replacing conventionally used ITO. The performances of all the devices are comparable to their corresponding ones with ITO electrode, indicating the great potential of the Cu-BHT electrode in future low-cost and flexible optoelectronics.A solution-processed transparent electrode was developed based on Cu-BHT, which displays high electrical conductivity of 2500 S cm−1 and optical transparency of 82%. The Cu-BHT electrode on both glass and PI substrates is tested in peroverskite, quantum dot and organic solar cells, which indicates its performance is comparable to the widely used ITO.Download high-res image (285KB)Download full-size image

Junction diodes in organic solar cells

Co-reporter:Peng Mao, Yuanzhi Wei, Hui Li, Jizheng Wang

Nano Energy 2017 Volume 41(Volume 41) pp:

Publication Date(Web):1 November 2017

DOI:10.1016/j.nanoen.2017.10.027

•The fundamentals of semiconductor solar cells are carefully briefed.•The junction diodes in organic solar cells are fullydiscussed.•The factors dominating the junction diodes in OSCs are systematically analyzed.Organic solar cells (OSCs) have attracted great attention in the past 30 years due to their easy solution-processed preparation and material tunability, which could lead to light-weight, low-cost and large-area flexible solar products. Despite the shortcomings of their inferior device stabilities, their power conversion efficiencies (PCE) grow quickly with the development of new materials, and have surpassed 12% recently. However, the advance of physics in OSCs lags well-behind that of PCE. From a long-term perspective, an in-depth and systematic comprehension of internal physics in OSCs is essential for a lasting development of the field. Junction diodes are fundamental device units and of course cornerstones for understanding physics in OSCs. Although they have been investigated carefully in recent years, there are lots of confusions in understanding them. Therefore, it is of great importance to provide an in-depth discussion on such junction diodes. Here the research progress and status for understanding junction diodes in OSCs are systematically summarized and discussed. Firstly, the fundamentals of semiconductor solar cells are introduced and the particularities of OSCs are briefed. Secondly, the architecture evolution together with the nature of the junction diodes is described. Then key factors that dominate the junction diodes in OSCs are listed and discussed. In the end, a brief conclusion is presented and suggestions for optimizing the junction diodes are proposed.Download high-res image (260KB)Download full-size image

Graphdiyne for multilevel flexible organic resistive random access memory devices

Co-reporter:Zhiwen Jin;Yanhuan Chen;Qing Zhou;Peng Mao;Huibiao Liu;Yuliang Li

Materials Chemistry Frontiers 2017 vol. 1(Issue 7) pp:1338-1341

Publication Date(Web):2017/06/28

DOI:10.1039/C7QM00009J

Graphdiyne (GD), a new carbon allotrope with a 2D structure comprising benzene rings and carbon–carbon triple bonds, is employed in fabricating resistive random access memory (RRAM) devices. On inserting a GD nanoparticle (NP) discontinuous layer and thermally depositing an Al–Al2O3 core–shell (Al–Al2O3) NP discontinuous layer in insulating polyimide (PI) films on a PET substrate, the designed flexible three-state memory device is realized (PET/Ag/PI/GD/PI/Al–Al2O3/PI/Al). GD NPs and Al–Al2O3 NPs function as two types of strong electron traps with different energy levels, resulting in two ON states. The OFF state and the two ON states possess long retention times of more than 104 s. Our results here demonstrate that GD could have great potential applications in future information storage technologies.

Graphdiyne:ZnO Nanocomposites for High-Performance UV Photodetectors

Co-reporter:Zhiwen Jin;Qing Zhou;Yanhuan Chen;Peng Mao;Hui Li;Huibiao Liu;Yuliang Li

Advanced Materials 2016 Volume 28( Issue 19) pp:3697-3702

Publication Date(Web):

DOI:10.1002/adma.201600354

Graphdiyne: An Efficient Hole Transporter for Stable High-Performance Colloidal Quantum Dot Solar Cells

Co-reporter:Zhiwen Jin;Mingjian Yuan;Hui Li;Hui Yang;Qing Zhou;Huibiao Liu;Xinzheng Lan;Mengxia Liu;Edward H. Sargent;Yuliang Li

Advanced Functional Materials 2016 Volume 26( Issue 29) pp:5284-5289

Publication Date(Web):

DOI:10.1002/adfm.201601570

Graphdiyne, a novel large π-conjugated carbon hole transporting material, is employed as anode buffer layer in colloidal quantum dots solar cells. Power conversion efficiency is notably enhanced to 10.64% from 9.49% compared to relevant reference devices. Hole transfer from the quantum dot solid active layer to the anode can be appreciably enhanced only by using graphdiyne to lower the work function of the colloidal quantum dot solid. It is found that the all-carbon buffer layer prolongs the carrier lifetime, reducing surface recombination on the previously neglected back side of the photovoltaic device. Remarkably, the device also shows high long-term stability in ambient air. The results demonstrate that graphdiyne may have diverse applications in enhancing optoelectronic devices.

Efficiency-Enhanced Planar Perovskite Solar Cells via an Isopropanol/Ethanol Mixed Solvent Process

Co-reporter:Peng Mao, Qing Zhou, Zhiwen Jin, Hui Li, and Jizheng Wang

ACS Applied Materials & Interfaces 2016 Volume 8(Issue 36) pp:23837

Publication Date(Web):August 23, 2016

DOI:10.1021/acsami.6b08863

Solution processable perovskite solar cells traditionally employed isopropanol as the solvent of CH3NH3I in a two-step method. One of the largest issues of this technique is the uncontrollable morphology of the perovskite film. In this study, a homogeneous and dense PbI2 film was prepared by introducing DMSO as an additive into DMF and then reacting the mixture with CH3NH3I dissolved in an isopropanol/ethanol solvent to fabricate high-quality perovskite films. Results revealed that ethanol played a crucial role on morphology and components of perovskite films. When the ratio of isopropanol to ethanol was optimized, a power conversion efficiency of 15.76% was achieved, which was on average ∼50% higher than that of PSCs without DMSO and ethanol processing.Keywords: component; mixed solvent; morphology; perovskite; solar cell

All-solution-processed PIN architecture for ultra-sensitive and ultra-flexible organic thin film photodetectors

Co-reporter:Zhiwen Jin;Qing Zhou;Peng Mao;Hui Li

Science China Chemistry 2016 Volume 59( Issue 10) pp:1258-1263

Publication Date(Web):2016 October

DOI:10.1007/s11426-016-0080-6

An ideal organic thin film photodetectors (OTFPs) should adopt a hierarchical, multilayer p-type/blend-type/n-type (PIN) structure, with each layer having a specific purpose which could greatly improve the exciton dissociation while guarantee efficient charge transport. However, for the traditional layer-by-layer solution fabrication procedure, the solvent used can induce organic material mixing and molecular disordering between each layer. Hence, such architecture for OTFPs can now only be formed via thermal evaporation. In this paper, a contact-film-transfer method is demonstrated to all-solution processing organic PIN OTFPs on flexible substrates. The fabricated PIN OTFPs exhibit high photoresponse and high stability under continuous mechanical bending. Hence, the method we described here should represent an important step in the development of OTFPs in the future.

Bilayer Heterostructured PThTPTI/WS2 Photodetectors with High Thermal Stability in Ambient Environment

Co-reporter:Zhiwen Jin, Dan He, Qing Zhou, Peng Mao, Liming Ding, and Jizheng Wang

ACS Applied Materials & Interfaces 2016 Volume 8(Issue 48) pp:

Publication Date(Web):November 14, 2016

DOI:10.1021/acsami.6b12090

Organic-based photodetectors (PDs) have great potential applications in next-generation portable, low-cost, large-area displays and optical communications. However, for practical applications, they are facing big challenges due to their instabilities in ambient environments, especially under high temperatures. Robust materials and device architectures are highly demanded to overcome the problem. In this report, we employed a donor conjugated polymer PThTPTI and realized thin-film PDs which can stably operate in ambient air under temperatures as high as 300 °C. By adding a discontinuous thin layer of WS2 beneath the PThTPTI film, the device photosensitivity is significantly enhanced without loss of the high thermal stability. This work provides new insights in designing novel and stable organic-based devices for future optoelectronic applications.Keywords: heterojunction; organic; photodetector; thermal stability; WS2;

High-Performance Thermally Stable Organic Phototransistors Based on PSeTPTI/PC61BM for Visible and Ultraviolet Photodetection

Co-reporter:Zhe Qi;Jiamin Cao;Hui Li;Liming Ding

Advanced Functional Materials 2015 Volume 25( Issue 21) pp:3138-3146

Publication Date(Web):

DOI:10.1002/adfm.201500525

Phototransistors are three-terminal photodetectors which usually have higher photosensitivity than photodiodes due to the presence of gate electrode. In this report, organic phototransistors (OPTs) based on a donor material, namely, poly{2,5-selenophene-alt-2,8-(4,10-bis(2-hexyldecyl))thieno[2′,3′:5,6]pyrido[3,4-g]thieno[3,2-c]isoquinoline-5,11(4H,10H)-dione} (PSeTPTI), are fabricated and intensively studied. As unipolar p-type organic semiconductor usually has plenty of electron traps in the bulk to impede electron transporting, most of photogenerated electrons will fill the traps in PSeTPTI and this process can prolong the response time. By introducing [6,6]-phenyl C₆₁ butyric acid methyl ester on top, the p–n heterojunction can produce most of the photocurrent and eliminates the influence from the process of trapping electrons. This mechanism improves the photoresponsivity and response speed. Since ultraviolet (UV) detection is very important in some fields including military, aerospace, and biology, the OPTs are characterized under UV illumination besides the visible light and they present high sensitivity. Furthermore, organic semiconductors often have bad stability in harsh conditions and meanwhile some devices need to work in these environments. At high temperature even up to 200 °C, our OPTs can work normally and show very high stability, indicating the potential of the devices in applications of high-temperature environments.

Improving the photocurrent of a PBDTTT-CF and PCBM based organic thin film photoconductor by forming a bilayer structure

Co-reporter:Zhiwen Jin, Qing Zhou, Peng Mao, Aiji Wang, Boyang Shang, Yinshu Wang, Hui Li and Jizheng Wang

RSC Advances 2015 vol. 5(Issue 103) pp:84680-84684

Publication Date(Web):30 Sep 2015

DOI:10.1039/C5RA16998D

The performance of traditional organic thin film photoconductors (OTFPs) is limited by the low carrier mobility in the donor:acceptor (D:A) blend film. To overcome such a problem, a higher-mobility carrier transport layer should be included in the D:A blend based device. However doing so will certainly result in a bilayer or even multilayer structure, which is usually a challenge for all-solution processing methods. Here by carefully controlling and adjusting the fabrication process, an all-solution-processed PBDTTT-CF/PBDTTT-CF:PCBM bilayer OTFP is demonstrated. In such a bilayer device, the PBDTTT-CF:PCBM blend layer is responsible for light absorption and free photo carrier generation, and the underlying PBDTTT-CF layer is responsible for the photo carrier transport inside the device. The hole mobility in the PBDTTT-CF layer is measured to be 9.1 × 10−4 cm2 V−1 s−1, much higher than that in the PBDTTT-CF:PCBM blend film, which is only 4.3 × 10−5 cm2 V−1 s−1. As a result of the faster carrier transport, the bilayer device exhibits a greatly enhanced photocurrent, which is about 7 times higher than that of the single blend layer device. Meanwhile, the on/off response of the bilayer device is also improved, which is shorter than 0.1/0.1 s.

High-performance inverted PThTPTI:PC71BM solar cells

Co-reporter:Hui Li, Jiamin Cao, Qing Zhou, Liming Ding, Jizheng Wang

Nano Energy 2015 Volume 15() pp:125-134

Publication Date(Web):July 2015

DOI:10.1016/j.nanoen.2015.04.016

•TPTI as a promising polycyclic acceptor unit for developing high-performance D–A polymers is explored.•Inverted PThTPTI:PC71BM solar cells display an outstanding PCE as high as 9.20%.•DIO effects on device performance are systematically investigated.A highly efficient D–A conjugated polymer (PThTPTI) was applied in inverted organic solar cells. Optimized PThTPTI:PC71BM cells give an outstanding PCE as high as 9.20%, with Voc of 0.882 V, Jsc of 14.31 mA/cm2, FF of 72.9%, and over 72% EQE in the range of 420–640 nm. DIO (1,8-diiodooctane) effects on device performance are also systematically investigated. The result shows that the addition of DIO produces greatly improved nanoscale morphology of the blend film, which actually does not lead to significantly improved light absorption and build-in potential. Instead it leads to more efficient charge transfer, less carrier recombination, longer effective carrier lifetime and higher carrier mobility, which are the main contributors for the high efficiency.

Solution-Processed Ultrathin Organic Semiconductor Film: Toward All-Transparent Highly Stable Transistors

Co-reporter:Zhe Qi;Jiamin Cao;Hui Li;Liming Ding

Advanced Electronic Materials 2015 Volume 1( Issue 9) pp:

Publication Date(Web):

DOI:10.1002/aelm.201500173

Perylene diimides: a thickness-insensitive cathode interlayer for high performance polymer solar cells

Co-reporter:Zhi-Guo Zhang, Boyuan Qi, Zhiwen Jin, Dan Chi, Zhe Qi, Yongfang Li and Jizheng Wang

Energy & Environmental Science 2014 vol. 7(Issue 6) pp:1966-1973

Publication Date(Web):17 Mar 2014

DOI:10.1039/C4EE00022F

With the power conversion efficiency of polymer solar cells (PSCs) approaching the milestone value of 10%, their instability associated with a low work function metal cathode, particularly in the presence of oxygen and moisture, becomes a critical issue for real applications. To alleviate the air-sensitive problem, two easy-accessible solution-processed, environmentally friendly organic small-molecule cathode interlayers, with perylene diimides (PDI) as the core and amino (PDIN) or amino N-oxide (PDINO) as the terminal substituent, are explored. Benefitting from the extended planar structure of the PDI units, the two interlayer materials show high conductivities of ∼10−5 S cm−1, which make them capable of functioning efficiently in a wide thickness range of 6 to 25 nm. This is the first time that thickness-insensitive small-molecule-based cathode interlayers are reported. It is also found that the work function tuning effect of the two PDI-based interlayers allows high work function metals (such as Au and Ag) to act as the cathode. With the conventional device structure with PTB7 as a donor and PC70BM as an acceptor, the PDINO-based devices exhibit an efficiency of 8.24% with Al as the top electrode and 8.16% with Ag as the top electrode, much higher than that of the corresponding Ca/Al-based device (6.98%). The high efficiency of 8.35% is also achieved in the device with PTB7-Th as the donor. The success of the two PDI-interlayers indicates that π-delocalized planar structures with high electron affinities could be particularly useful in developing high-performance organic interlayer materials.

High efficiency P3HT:PCBM solar cells with an inserted PCBM layer

Co-reporter:Dan Chi, Shengchun Qu, Zhanguo Wang and Jizheng Wang

Journal of Materials Chemistry A 2014 vol. 2(Issue 22) pp:4383-4387

Publication Date(Web):10 Mar 2014

DOI:10.1039/C4TC00003J

By inserting a PCBM (phenyl-C61-butyric acid methyl ester) layer between a P3HT (poly(3-hexylthiophene)):PCBM blend and a Ca/Al cathode, the performance of P3HT:PCBM bulk-heterojunction polymer solar cells is greatly improved. The maximum power conversion efficiency reached 4.24%, which is much higher than that of the traditional standard P3HT:PCBM based device (3.57%). By exploring various experimental techniques including absorption spectroscopy, X-ray photoelectron spectroscopy and impedance spectroscopy, we have found that the enhancement of the device performance can mainly be attributed to two reasons: (1) the inserted-PCBM layer can enhance the overall light absorption of the whole device and hence improve the photocurrent. (2) The inserted-PCBM layer can increase the amount of PCBM at the interface between the active layer and the cathode electrode, and hence suppress carrier recombination and facilitate electron extraction.

Flexible high-performance ultraviolet photoconductor with zinc oxide nanorods and 8-hydroxyquinoline

Co-reporter:Zhiwen Jin and Jizheng Wang

Journal of Materials Chemistry A 2014 vol. 2(Issue 11) pp:1966-1970

Publication Date(Web):20 Dec 2013

DOI:10.1039/C3TC32426E

A flexible ultraviolet photoconductor based on ZnO and 8-hydroxyquinoline (8HQ) is fabricated. In such a device, the 8HQ film covers the ZnO layer and protects the ZnO from being affected by oxygen via slow adsorption and desorption processes, which would greatly deteriorate the response speed of the device. As a result, the photoconductor exhibits a shorter rise time (10 s) and decay time (27 s) than that of the bare ZnO film based device, in which the times are 133 s and 200 s, respectively. Meanwhile, the device displays a high responsivity of 484 A W−1 under a moderate electric field of 2 × 106 V m−1.

Improvement of organic solar cells with ammonium salt, tetrabutylammonium tetraphenylborate, as cathode buffer layer

Co-reporter:Xitian Wang, Boyuan Qi, Hui Li, Zhe Qi, Jizheng Wang

Synthetic Metals 2014 Volume 191() pp:36-40

Publication Date(Web):May 2014

DOI:10.1016/j.synthmet.2014.02.011

•A solution-processible ammonium salt is used as the cathode buffer layer for organic solar cells.•This buffer layer can be used in several common systems in organic solar cells.•The performance of solar cells with this buffer layer is better than that of devices with Ca as buffer layer.A solution-processible ammonium salt, tetrabutylammonium tetraphenylborate (TBATPB) was investigated as cathode buffer layer in organic solar cells (OSCs). Using this buffer layer the power conversion efficiencies of OSCs were improved greatly with Al as cathode, compared to those without buffer layer. These devices performed even better than those with Ca/Al as cathode. Explored by UPS, it was found that after TBATPB spin-coated onto the surface of Al, the work function of Al was pulled down. This suggested that there existed dipoles between TBATPB and Al. As a result the built-in potential was enhanced and it was beneficial to the extraction of charge carriers. Furthermore our results proved that TBATPB could be a very useful cathode buffer layer in three different donor:acceptor systems, namely P3HT:PC61BM, PBDTTT-C:PC71BM and PTB7:PC71BM, indicating its importance in fabricating high-performance OSCs.

Amine group functionalized fullerene derivatives as cathode buffer layers for high performance polymer solar cells

Co-reporter:Zhi-Guo Zhang, Hui Li, Boyuan Qi, Dan Chi, Zhiwen Jin, Zhe Qi, Jianhui Hou, Yongfang Li and Jizheng Wang

Journal of Materials Chemistry A 2013 vol. 1(Issue 34) pp:9624-9629

Publication Date(Web):05 Jul 2013

DOI:10.1039/C3TA12478A

An easy-accessible amine group functionalized fullerene derivative, DMAPA-C60, is explored as a cathode buffer layer (CBL) in polymer solar cells (PSCs) for our presently tested three different material systems, namely P3HT:PCBM, PBDTTT-C:PC70BM and PBDTTT-C-T:PC70BM. The power conversion efficiencies of the three systems with DMAPA-C60 as the CBL reach 3.88%, 6.29% and 7.42%, respectively, which are much higher than those of the corresponding PSCs with the Al-only cathode and even slightly higher than those of the corresponding Ca/Al devices of these systems. The DMAPA-C60 CBL also allows high work function metals (Ag, Cu, and Au) as cathodes.

Nonvolatile resistive memory devices based on Ag

Co-reporter:Zhiwen Jin, Guo Liu and Jizheng Wang

Journal of Materials Chemistry A 2013 vol. 1(Issue 20) pp:3282-3286

Publication Date(Web):04 Apr 2013

DOI:10.1039/C3TC30387J

Ag-based nonvolatile resistive memory devices are fabricated with the help of a simple soft-chemical process, which can transform Ag film into Ag2S/Ag nano-flake film. A very high ON/OFF ratio of 2.35 × 108 and satisfactory retention time of larger than 104 s are achieved. The redox reaction Ag+ (Ag2S) + e− → Ag at the Ag2S/Ag interface induced the filamentary conduction that is responsible for the observed memory effects.

High-responsivity solution-processed organic–inorganic hybrid bilayer thin film photoconductors

Co-reporter:Zhiwen Jin and Jizheng Wang

Journal of Materials Chemistry A 2013 vol. 1(Issue 48) pp:7996-8002

Publication Date(Web):11 Oct 2013

DOI:10.1039/C3TC31143K

We designed and fabricated an inorganic–organic hybrid bilayer thin film photoconductor. The advantages of the organic material's strong light absorption ability and the inorganic material's high carrier mobility are combined; a high responsivity (R) value of 11101 A W−1 is achieved, which is much higher than that of present pure inorganic and pure organic thin-film photoconductors.

All-brush-painted top-gate organic thin-film transistors

Co-reporter:Zhe Qi, Fengjiao Zhang, Chong-an Di, Jizheng Wang and Daoben Zhu

Journal of Materials Chemistry A 2013 vol. 1(Issue 18) pp:3072-3077

Publication Date(Web):25 Mar 2013

DOI:10.1039/C3TC30357H

Brush painting, a simple and fast solution processing technique, possesses promising multiple applications in ultra-low-cost organic electronics with large-area manufacture. Benefiting from effective brush painting of high quality conductive electrodes, semiconductive layers and dielectric layers, all-brush-painted top-gate transistors were successfully constructed with a maximum mobility of 0.14 cm2 V−1 s−1.

Fill factor in organic solar cells

Co-reporter:Boyuan Qi and Jizheng Wang

Physical Chemistry Chemical Physics 2013 vol. 15(Issue 23) pp:8972-8982

Publication Date(Web):03 Apr 2013

DOI:10.1039/C3CP51383A

The fill factor (FF) is an important parameter that determines the power conversion efficiency of an organic solar cell. There are several factors that can significantly influence FF, and these factors interact with each other very intricately. Due to this reason, a deep understanding of FF is quite difficult. Based on the three fundamental elements in the solar cell equivalent circuit, namely series resistance, shunt resistance and diode, we reviews the research progress in understanding on FF in organic solar cells. Physics lying behind the often-observed undesirable S-shaped J–V curves is also summarized. This paper aims to give a brief and comprehensive summary on FF from a fundamental point of view.

Open-circuit voltage in organic solar cells

Co-reporter:Boyuan Qi and Jizheng Wang

Journal of Materials Chemistry A 2012 vol. 22(Issue 46) pp:24315-24325

Publication Date(Web):05 Sep 2012

DOI:10.1039/C2JM33719C

Open-circuit voltage (VOC) is the maximum voltage a solar cell can provide to an external circuit, which is derived from the splitting of hole and electron quasi-Fermi levels. In crystalline Si solar cells, the effective density of states at the bottom (top) of the conduction (valence) band is constant, and the quasi-Fermi level can be directly calculated via the Fermi–Dirac distribution. However, in organic materials, similar to amorphous Si, disorder induces gap tail states. Relaxation of carriers into these tail states brings the electron quasi-Fermi level down and the hole quasi-Fermi level up, and hence reduces VOC. Furthermore, carrier recombination of various kinds can cause additional loss of VOC. This article reviews the research progress in understanding the origin of VOC in organic solar cells. In particular, the dependence of VOC on four important factors, namely temperature, light intensity, work function of the electrode and material microstructure are discussed based on the model of density of states. Techniques to enhance VOC are also briefly introduced and their mechanisms are analysed.

Structures and properties of conjugated Donor–Acceptor copolymers for solar cell applications

Co-reporter:Zhi–Guo Zhang and Jizheng Wang

Journal of Materials Chemistry A 2012 vol. 22(Issue 10) pp:4178-4187

Publication Date(Web):18 Jan 2012

DOI:10.1039/C2JM14951F

With the rapid evolution of photovoltaic polymer materials, power conversion efficiency of polymer solar cells has been markedly improved in recent years, and is now approaching a landmark value of 10 %. This review focuses on Donor–Acceptor (D–A) photovoltaic copolymers. Starting from briefly introducing the D–A concept, the fundamental donor and acceptor units for constructing polymer photovoltaic materials are introduced and classified. By summarizing the structure–property relationships of typical photovoltaic D–A copolymers, the important design rules for such materials are highlighted. Several crucial aspects, including proper combination of D–A units, high planarity of the backbone and proper incorporation of side chains are particularly emphasized. A new D–A architecture, namely main-chain donor and side-chain acceptor is introduced and reviewed. Moreover, the role of the electron-deficient group in fine-tuning energy levels of low-bandgap D–A photovoltaic polymers is discussed.

Graphdiyne for multilevel flexible organic resistive random access memory devices

Co-reporter:Zhiwen Jin;Yanhuan Chen;Qing Zhou;Peng Mao;Huibiao Liu;Yuliang Li

Inorganic Chemistry Frontiers 2017 - vol. 1(Issue 7) pp:

Publication Date(Web):2017/06/28

DOI:10.1039/C7QM00009J

Graphdiyne (GD), a new carbon allotrope with a 2D structure comprising benzene rings and carbon–carbon triple bonds, is employed in fabricating resistive random access memory (RRAM) devices. On inserting a GD nanoparticle (NP) discontinuous layer and thermally depositing an Al–Al2O3 core–shell (Al–Al2O3) NP discontinuous layer in insulating polyimide (PI) films on a PET substrate, the designed flexible three-state memory device is realized (PET/Ag/PI/GD/PI/Al–Al2O3/PI/Al). GD NPs and Al–Al2O3 NPs function as two types of strong electron traps with different energy levels, resulting in two ON states. The OFF state and the two ON states possess long retention times of more than 104 s. Our results here demonstrate that GD could have great potential applications in future information storage technologies.

Amine group functionalized fullerene derivatives as cathode buffer layers for high performance polymer solar cells

Co-reporter:Zhi-Guo Zhang, Hui Li, Boyuan Qi, Dan Chi, Zhiwen Jin, Zhe Qi, Jianhui Hou, Yongfang Li and Jizheng Wang

Journal of Materials Chemistry A 2013 - vol. 1(Issue 34) pp:NaN9629-9629

Publication Date(Web):2013/07/05

DOI:10.1039/C3TA12478A

An easy-accessible amine group functionalized fullerene derivative, DMAPA-C60, is explored as a cathode buffer layer (CBL) in polymer solar cells (PSCs) for our presently tested three different material systems, namely P3HT:PCBM, PBDTTT-C:PC70BM and PBDTTT-C-T:PC70BM. The power conversion efficiencies of the three systems with DMAPA-C60 as the CBL reach 3.88%, 6.29% and 7.42%, respectively, which are much higher than those of the corresponding PSCs with the Al-only cathode and even slightly higher than those of the corresponding Ca/Al devices of these systems. The DMAPA-C60 CBL also allows high work function metals (Ag, Cu, and Au) as cathodes.

Structures and properties of conjugated Donor–Acceptor copolymers for solar cell applications

Co-reporter:Zhi–Guo Zhang and Jizheng Wang

Journal of Materials Chemistry A 2012 - vol. 22(Issue 10) pp:

Publication Date(Web):

DOI:10.1039/C2JM14951F

All-brush-painted top-gate organic thin-film transistors

Co-reporter:Zhe Qi, Fengjiao Zhang, Chong-an Di, Jizheng Wang and Daoben Zhu

Journal of Materials Chemistry A 2013 - vol. 1(Issue 18) pp:NaN3077-3077

Publication Date(Web):2013/03/25

DOI:10.1039/C3TC30357H

Brush painting, a simple and fast solution processing technique, possesses promising multiple applications in ultra-low-cost organic electronics with large-area manufacture. Benefiting from effective brush painting of high quality conductive electrodes, semiconductive layers and dielectric layers, all-brush-painted top-gate transistors were successfully constructed with a maximum mobility of 0.14 cm2 V−1 s−1.

Fill factor in organic solar cells

Co-reporter:Boyuan Qi and Jizheng Wang

Physical Chemistry Chemical Physics 2013 - vol. 15(Issue 23) pp:NaN8982-8982

Publication Date(Web):2013/04/03

DOI:10.1039/C3CP51383A

The fill factor (FF) is an important parameter that determines the power conversion efficiency of an organic solar cell. There are several factors that can significantly influence FF, and these factors interact with each other very intricately. Due to this reason, a deep understanding of FF is quite difficult. Based on the three fundamental elements in the solar cell equivalent circuit, namely series resistance, shunt resistance and diode, we reviews the research progress in understanding on FF in organic solar cells. Physics lying behind the often-observed undesirable S-shaped J–V curves is also summarized. This paper aims to give a brief and comprehensive summary on FF from a fundamental point of view.

Open-circuit voltage in organic solar cells

Co-reporter:Boyuan Qi and Jizheng Wang

Journal of Materials Chemistry A 2012 - vol. 22(Issue 46) pp:NaN24325-24325

Publication Date(Web):2012/09/05

DOI:10.1039/C2JM33719C

Open-circuit voltage (VOC) is the maximum voltage a solar cell can provide to an external circuit, which is derived from the splitting of hole and electron quasi-Fermi levels. In crystalline Si solar cells, the effective density of states at the bottom (top) of the conduction (valence) band is constant, and the quasi-Fermi level can be directly calculated via the Fermi–Dirac distribution. However, in organic materials, similar to amorphous Si, disorder induces gap tail states. Relaxation of carriers into these tail states brings the electron quasi-Fermi level down and the hole quasi-Fermi level up, and hence reduces VOC. Furthermore, carrier recombination of various kinds can cause additional loss of VOC. This article reviews the research progress in understanding the origin of VOC in organic solar cells. In particular, the dependence of VOC on four important factors, namely temperature, light intensity, work function of the electrode and material microstructure are discussed based on the model of density of states. Techniques to enhance VOC are also briefly introduced and their mechanisms are analysed.

High-responsivity solution-processed organic–inorganic hybrid bilayer thin film photoconductors

Co-reporter:Zhiwen Jin and Jizheng Wang

Journal of Materials Chemistry A 2013 - vol. 1(Issue 48) pp:NaN8002-8002

Publication Date(Web):2013/10/11

DOI:10.1039/C3TC31143K

We designed and fabricated an inorganic–organic hybrid bilayer thin film photoconductor. The advantages of the organic material's strong light absorption ability and the inorganic material's high carrier mobility are combined; a high responsivity (R) value of 11101 A W−1 is achieved, which is much higher than that of present pure inorganic and pure organic thin-film photoconductors.

Nonvolatile resistive memory devices based on Ag

Co-reporter:Zhiwen Jin, Guo Liu and Jizheng Wang

Journal of Materials Chemistry A 2013 - vol. 1(Issue 20) pp:NaN3286-3286

Publication Date(Web):2013/04/04

DOI:10.1039/C3TC30387J

Ag-based nonvolatile resistive memory devices are fabricated with the help of a simple soft-chemical process, which can transform Ag film into Ag2S/Ag nano-flake film. A very high ON/OFF ratio of 2.35 × 108 and satisfactory retention time of larger than 104 s are achieved. The redox reaction Ag+ (Ag2S) + e− → Ag at the Ag2S/Ag interface induced the filamentary conduction that is responsible for the observed memory effects.

High efficiency P3HT:PCBM solar cells with an inserted PCBM layer

Co-reporter:Dan Chi, Shengchun Qu, Zhanguo Wang and Jizheng Wang

Journal of Materials Chemistry A 2014 - vol. 2(Issue 22) pp:NaN4387-4387

Publication Date(Web):2014/03/10

DOI:10.1039/C4TC00003J

By inserting a PCBM (phenyl-C61-butyric acid methyl ester) layer between a P3HT (poly(3-hexylthiophene)):PCBM blend and a Ca/Al cathode, the performance of P3HT:PCBM bulk-heterojunction polymer solar cells is greatly improved. The maximum power conversion efficiency reached 4.24%, which is much higher than that of the traditional standard P3HT:PCBM based device (3.57%). By exploring various experimental techniques including absorption spectroscopy, X-ray photoelectron spectroscopy and impedance spectroscopy, we have found that the enhancement of the device performance can mainly be attributed to two reasons: (1) the inserted-PCBM layer can enhance the overall light absorption of the whole device and hence improve the photocurrent. (2) The inserted-PCBM layer can increase the amount of PCBM at the interface between the active layer and the cathode electrode, and hence suppress carrier recombination and facilitate electron extraction.

Flexible high-performance ultraviolet photoconductor with zinc oxide nanorods and 8-hydroxyquinoline

Co-reporter:Zhiwen Jin and Jizheng Wang

Journal of Materials Chemistry A 2014 - vol. 2(Issue 11) pp:NaN1970-1970

Publication Date(Web):2013/12/20

DOI:10.1039/C3TC32426E

A flexible ultraviolet photoconductor based on ZnO and 8-hydroxyquinoline (8HQ) is fabricated. In such a device, the 8HQ film covers the ZnO layer and protects the ZnO from being affected by oxygen via slow adsorption and desorption processes, which would greatly deteriorate the response speed of the device. As a result, the photoconductor exhibits a shorter rise time (10 s) and decay time (27 s) than that of the bare ZnO film based device, in which the times are 133 s and 200 s, respectively. Meanwhile, the device displays a high responsivity of 484 A W−1 under a moderate electric field of 2 × 106 V m−1.

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