Here, the interfacial synergism of discontinuous spot shaped SnO2 and TiO2 mesoporous nanocomposite as electron transfer layer (ETL) underlayer is presented in highly efficient mesoscopic perovskite solar cells (M-PSCs). Based on this new strategy, strong charge recombination observed in previous SnO2-based ETLs is suppressed to a great extent as the pathways of charge recombination and energy loss are blocked effectively. Meanwhile, the internal series resistance of entire M-PSC is decreased remarkably. The new ETL is more kinetically favorable to electron transfer and thus results in significant photovoltaic improvement and alleviated hysteresis effect of M-PSCs.本文采用点分布SnO2和TiO2介孔层中的纳米粒子组成的“协同层”作为高效介孔钙钛矿太阳能电池的电子传输层衬层. 基于该新策略, 电荷复合和能量损失路径被有效阻隔, 使得之前报道的SnO2基电子传输层介孔钙钛矿太阳能电池中的强烈电荷复合被有效抑制. 同时, 整个介孔钙钛矿太阳能电池的串联电阻显著降低. 新型的电子传输层动力学上更有利的电子传输有效提升了介孔钙钛矿太阳能电池的光伏性能, 并明显抑制了电池的回滞.

•A blended-interfacial-layer was designed as efficiency ETL for perovskite solar cells.•New ETL could lower internal series resistance and regulate energy level.•New ETL has been proved to be more advantageous in avoiding interfacial degradation.•Inherent charge transfer mechanism of PSCs with the four components ETL was investigated.Based on a blended-interfacial-layer (BIL) with strongly coupled four components (FTO, SnO2, TiO2 and perovskite), we demonstrate in this work the design of a more advanced electron transfer layer (ETL) for mesoscopic PSCs. For the new ETL, SnO2 is a key component and is found to be essential to lower series resistance and enhance shunt resistance. Photovoltaic performance of PSCs using new ETL is much better than that of PSCs based on traditional ETL. In addition, the new ETL has been proved to be more advantageous in avoiding interfacial degradation and improving stability of the device.We put forward a new and rational ETL architecture for M-PSCs by creating a blended interface involving four components of FTO, SnO2, TiO2 and perovskite, which were strongly coupled and more advantageous for transfer of photoinduced electrons.Download high-res image (276KB)Download full-size image

•The role of Pt single-atom well illustrated both experimentally and theoretically.•A small amount of Pt raised the power conversion efficiency of DSCs immensely.•Single atom Pt could enhance the donating ability of catalysts.•Single atom Pt 5d orbital was accounted for the good catalytic activity.Although single-atom catalysts (SACs) that bridge homogeneous and heterogeneous catalysis exhibit excellent performance in various reactions, only a few examples have reported the use of SACs in electrocatalysis, especially in new types of photovoltaics. This work focused on the association between SAC Pt1/FeOx and the electrocatalysis in hybrid photovoltaics, with the role of single-Pt atom in facilitating triiodide (I3-) catalytic reduction and enhancing the conversion efficiency of dye-sensitized solar cells. Even with an extremely low dispersion density of one Pt atom per 100 nm2 (the atomic ratio between Pt and Fe is 1:12214), the conversion efficiency could be enhanced by 69.3% compared to bare FeOx. DFT calculation indicated that ionization potential (IP), which was responsible for the rate-determining step, decreased with the anchor of single-Pt atoms on an oxygen-terminated Fe2O3(001) slab, thereby the electron-donating ability of catalysts was enhanced. The interaction between I- and O3- terminated Pt1/Fe2O3(001) showed that charge transfer occurred mainly between I and Pt atoms. Single atom Pt played a powerful role in triiodide (I3-) catalytic reduction, since its 5d orbital interacted with the support Fe2O3, accompanied with much more concentrated electronic states and higher density of the occupied states of Pt1/Fe2O3(001) around the Fermi energy.The association between SACs Pt1/FeOx and electrocatalysis in hybrid photovoltaics, together with the powerful role of Pt single-atom in facilitating triiodide (I3-) catalytic reduction and enhancing the conversion efficiency are well illustrated both experimentally and theoretically.Download high-res image (338KB)Download full-size image

•The whole fabrication process of crystallized SnO2 ETLs below 80 °C is realized using sol–gel route for the first time.•Participation of atmosphere O2 and H2O by refluxing is crucial for SnO2 crystallization in solution at low temperature.•This SnO2 ETLs endow planar PSCs high PCEs of 19.20% and 16.11% on rigid and flexible substrates, respectively.•Due to a large band gap (4.13 eV), SnO2-ETLs-based PSCs show superior UV light stability.In fabrication of SnO2 electron transfer layer (ETL) via traditional solution routes, the strong dependence of film crystallization on high temperature annealing or robust thermal treatment makes it challengeable to prepare crystallized SnO2 ETLs at low temperature (< 150 °C). Here, we put forward a sol-gel route by which the whole fabrication process of crystallized SnO2 ETL below 80 °C is realized for the first time. In the new route, participation of atmosphere O2 and H2O by refluxing is crucial as it can greatly promote Sn2+ oxidation and controlled hydrolysis in SnCl2·2H2O alcohol solution, in turn opening up an energetically favorable pathway for SnO2 crystallization at low temperature. Systematical investigations reveal that SnO2 ETLs have high conductivity and transmittance and appropriate energy band level, by which PSCs obtain superior photovoltaic performance, with a champion power conversion efficiency (PCE) and steady-state PCE of 19.20% and 18.48% achieved, respectively, much higher than that of the devices using high temperature annealed TiO2 ETLs (16.61% and 15.03%). The SnO2-ETL-based flexible PSCs also attain a high PCE up to 16.11% and among the highest records of flexible PSCs. Due to a larger band gap, SnO2-ETLs-based PSCs show superior UV resistance against high intensity UV light irradiation.Low temperature fabrication of SnO2 electron transfer layer (ETL) below 80 °C is realized by synthesis of SnO2 nanocrystals through an energetically favorable wet chemical route. The SnO2-ETLs with high conductivity and transmittance, appropriate band edge and wide band gap endow planar PSCs with high efficiencies and superb UV resistance.Download high-res image (178KB)Download full-size image

Is it possible that one day flexible assembly, repeated detachment, facile repair and maintenance will all be realized for photovoltaic devices? Our work provides a feasible strategy. A flexibly assembled and readily detachable stacking perovskite solar cell (S-PSC) consisting of two individual half cells is reported for the first time. High adaptability to various electrode substrates is demonstrated, which endows S-PSCs with promising prospects in future manufacture and applications. Considering that a robust interface between two half cells is an essential precondition for repeated detachment, a series of interfacial modifications are conducted and eventually considerable power conversion efficiencies (PCEs) of up to 14.62% are attained. Meanwhile, the S-PSCs can withstand repeated assembly and disassembly tests more than 100 times without a decline in the PCE. This work charts a new path for future innovative design of solar cells featuring flexible and facile production, storage, and cost-effective repair and maintenance.

•Transport orientations consistency parallel to (010), (101) and (111) crystal planes.•Carrier mobility is the highest in (010) crystal plane.•Inconsistency was found that parallel to (100), (110), (011) and (001) crystal planes.All-solid-state organic-inorganic halide perovskite solar cells (PSCs) have attracted wide attention due to the rapid progress of power conversion efficiency in recent years. Hole transport material (HTM) in PSCs plays the role of extracting and transporting photo-excited holes. Anisotropy of carrier mobility is one important property for semiconductors, however, which still remains unclear for the dominant HTM spiro-OMeTAD used in PSCs. Based on Density Functional Theory (DFT) and Marcus theory, we for the first time conducted investigations on the anisotropy of carrier mobility along representative crystal planes of spiro-OMeTAD by recombination energy λ and electronic coupling integral V. Results indicate that the holes and electrons show transport orientations consistency parallel to the (010), (101) and (111) crystal planes while inconsistency was found parallel to (100), (110), (011) and (001) crystal planes (with an angle ranged from 40° to 70° between the hole and electron transport directions). Our work embodies the theoretical significance of controllable and oriented fabrication of HTM in PSCs.Download high-res image (235KB)Download full-size image

•Amorphous niobium-modified tungsten oxide W(Nb)Ox was prepared as ESL in flexible perovskite solar cells.•It was observed that modification using Nb5+ improved the electron transport in WOx-based ESL.•The photovoltaic performance of the simple planar flexible PSCs achieved a high PCEs of 15.65%.•A capacitance CE across the ESL was proposed to indicate the effect of ESL thickness on hysteresis behavior.Flexible perovskite solar cell (PSC) using plastic substrate is one of the most focal points in the studies of thin-film solar cells. Low-temperature preparation of suitable electron selective layer (ESL) is the key issue in the fabrication of flexible PSCs. In this work, amorphous niobium-modified tungsten oxide W(Nb)Ox was prepared as ESL for efficient flexible PSC. Modification using Nb5+ improved the electron transport of WOx-based ESL by enhancing donor density, reducing interfacial depletion width, and minimizing trap states in the ESL. Consequently, photovoltaic performance of the simple planar flexible PSCs was improved, and high PCEs of 15.65% and 13.14% were obtained when ESLs were fabricated at 120 °C and room temperature, respectively. In addition, the effect of ESL thickness on the hysteresis behavior of PSCs was carefully analyzed. A capacitance CE across the ESL in the ITO/ESL/perovskite structure was proposed. This capacitance could well indicate the effect of ESL thickness on hysteresis behavior. The proposed modification strategy and mechanism is expected to facilitate the development of novel and advanced functional materials.

2,2′,7,7′-Tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD), one of the classical organic photoelectric materials, has been widely used as a hole transport material (HTM) in perovskite solar cells (PSCs) due to its relatively higher conductivity, easier film formation, weak absorption in the visible region, etc. However, the complex synthesis process and the high synthesis cost of Spiro-OMeTAD severely limit the commercialization of this material. In this work, two economical methoxyaniline-substituted dibenzofuran derivatives, BF-002 and BF-003, are synthesized and successfully used as hole-transport materials in perovskite solar cells (PSCs). The important properties including light absorption, thermal stability, energy level, conductivity, as well as photovoltaic performance are systematically demonstrated. The highest power conversion efficiencies of the PSCs based on BF-002 and BF-003 are 14.20% and 14.07%, respectively, comparable to that of the PSCs based on Spiro-OMeTAD.

•Abundant structural defects on graphene enhance the ORR activity.•Balanced N distribution on graphene could also improve the ORR activity.•Structural defects and N distribution are adjusted by regulating temperature.•NG-1000 shows notable ORR activities in both alkaline and acid media.N-doped graphene (NG) is a promising candidate for oxygen reduction reaction (ORR) in the cathode of fuel cells. However, the catalytic activity of NG is lower than that of commercial Pt/C in alkaline and acidic media. In this study, NG samples were obtained using urea as N source. The structural defects and N distribution in the samples were adjusted by regulating the pyrolysis temperature. The new NG type exhibited remarkable catalytic activities for ORR in both alkaline and acidic media.

To obtain highly efficient perovskite solar cells (PSCs), effective controls on perovskite crystallinity, homogeneity, and surface morphology are crucial. Herein, we demonstrate the flexible and facile use of TBP to improve the crystallinity of perovskite in two-step or one-step routes. For the two-step route, addition of TBP into DMF when dissolving PbI2 for spin-coating resulted in a porous layer composed of randomly packed PbI2 nanocrystals. This approach subsequently offered a widely enlarged contact area facilitating interfacial reaction with CH3NH3I and greatly improved CH3NH3PbI3 crystallization. Based on this strategy, PCEs of CH3NH3PbI3-based PSCs were improved from 6.71% to 10.62% (i.e., 58% enhancement). For the one-step route, TBP as an additive resulted in orientational and better crystallinity, by which the PCEs of CH3NH3PbI3−xClx-based planar PSCs increased from 11.11% to 15.01%, showing a remarkable enhancement as high as 35%. Using TBP as one multifunctional additive, it is thought that our strategy in this work offers a new idea for the fabrication of highly efficient PSCs.

Exploiting an alternative of the Pt-based counter-electrode materials for the triiodide reduction reaction has become a major interest in the fundamental research of dye-sensitized solar cells. Transition-metal selenides have recently been demonstrated as promising non-precious metal electrocatalysts for the triiodide reduction reaction. Herein, we prepared a series of transition-metal selenides via a free-reductant solvothermal method and used them as counter-electrodes in high efficiency dye-sensitized solar cells. The electrochemical results showed that these selenides had excellent catalytic activity for the reduction of the triiodine/iodine couple, and except for MoSe2, the conversion efficiencies of the corresponding dye-sensitized solar cells were comparable to the sputtered Pt counter-electrode. Theoretical investigation clearly revealed that the unsatisfactory performance of MoSe2 mainly originated from the processes of adsorption and charge-transfer. These findings can help to better understand the electrocatalytic processes and thus offer some useful guidelines to develop more efficient electrochemical catalysts.

Carbon-based ZnO/CH3NH3PbI3/C planar heterojunction perovskite solar cells (PHJ-PSCs) were prepared at low-temperature without using organic hole conductor and metal electrode. When measured via reverse bias scan, rigid and flexible PHJ-PSCs achieved power conversion efficiencies (PCEs) up to 8% and 4% on fluorine-doped tin oxide (FTO)/glass substrates and flexible polymer substrates, respectively. The flexible devices were capable of maintaining 80% of their initial PCEs after 1000 times of bending.

Considering the remarkable progress in photovoltaic performance, scholars have focused on perovskite solar cells (PSCs) over the recent two years. TiO2 thin film is a semiconductor with a wide band gap and is usually used as an electron-selective layer (ESL) in PSCs. Although SnO2 exhibits conductivity higher than that of TiO2, its use as a compact ESL in PSCs has not been reported. In this study, nanocrystalline SnO2 thin film was prepared through a sol–gel method and then characterized. The prepared SnO2 thin film was composed of small tetragonal rutile nanocrystals. We applied the SnO2 compact ESL into PSCs and compared their performance with that of PSCs based on a TiO2 thin layer. SnO2-ESL-based PSCs (S-PSCs) showed higher short-circuit current density and lower open-circuit voltage, fill factor, and conversion efficiency than the conventional TiO2-ESL-based PSCs. Furthermore, the photovoltaic performance of S-PSCs was highly dependent on measurement means, and this relationship was investigated and is discussed in detail.

In perovskite solar cells (PSCs), issues of compatibility between the photoabsorber and the cell architecture arise. In this work, we systematically demonstrated the characteristics of PSCs with an organometal halide, CH3NH3PbI3 or CH3NH3PbI3–xClx, in a planar or mesoporous architecture, and the dependence of the cell photovoltaic performance on the architecture was illustrated in detail. In addition to the inherent photoelectric characteristics, CH3NH3PbI3 and CH3NH3PbI3–xClx also differ in other aspects, such as light absorption, crystallinity, surface coverage, and dissociation of the photogenerated electrons. For PSCs with CH3NH3PbI3, the mesoporous ones gave high power conversion efficiencies (PCE) of up to 14.05%, which is much higher than those of the planar ones (up to 6.76%). For PSCs with CH3NH3PbI3–xClx, the planar and mesoporous devices exhibited PCEs of up to 12.67% and 7.87%, respectively, quite in contrast with the case of CH3NH3PbI3.

The electron-selective layer (ESL) is an indispensable component of perovskite solar cells (PSCs) and is responsible for the collection of photogenerated electrons. Preparing ESL at a low temperature is significant for future fabrication of flexible PSCs. In this work, solution-processed amorphous WOx thin film was prepared facilely at low temperature and used as ESL in PSCs. Results indicated that a large quantity of nanocaves were observed in the WOx thin film. In comparison with the conventional TiO2 ESL, the WOx ESL exhibited comparable light transmittance but higher electrical conductivity. Compared with the TiO2-based PSCs, PSCs that use WOx ESL exhibited comparable photoelectric conversion efficiency, larger short-circuit current density, but lower open-circuit voltage. Electrochemical characterization indicated that the unsatisfied open-circuit voltage and fill factor were caused by the inherent charge recombination. This study demonstrated that this material is an excellent candidate for ESL.

We demonstrated that extracts from sea tangle can serve as a sensitizer, redox couple, as well as a counter electrode material, or even can be fabricated into an “all-natural solar cell”. Especially, the carbon counter electrode from sea tangle has achieved a comparable performance with Pt, favorable for the cost-reduction of DSCs.

Fe3O4 with hierarchical structures was successfully synthesized and introduced into dye-sensitized solar cells as the counter electrode. A power conversion efficiency of 7.65% based on Fe3O4 was achieved, which is superior to that of pyrolytic Pt (6.88%) and close to that for sputtered Pt (7.87%).

Sufficient contact, high catalytic activity, free electron transport and ionic diffusion are desired for liquid–solid heterogeneous electrocatalysis. However, preparing catalysts that simultaneously possess all of these four advantages has proven challenging. Nanostructures originating from anisotropic growth always exhibit specific structural advantages and unique physical, chemical or catalytic properties. Herein, via a facile and template-free solvothermal approach, we synthesized W18O49 nanofibers (NFs) and nanofiber bundles (NFBs), as well as hierarchical spheres (HSs). As catalyst for the counter electrode (CE) of dye-sensitized solar cells (DSCs), W18O49 NFs demonstrated remarkable electrocatalytic activity because: (i) abundant oxygen vacancies offered sufficient active sites for reduction of I3− into I−; (ii) the one dimensional NFs were more beneficial to electron transport; (iii) the two phases, the liquid electrolyte and the solid NFs, could fully contact each other, and meanwhile ions could diffuse freely among the networks constructed by the interlaced NFs. Notably, DSCs using the NF-based semitransparent CE achieved high photoelectric conversion efficiencies (PCEs) up to 8.58%, superior to those based on NFBs or HSs, and comparable to that of 8.78% using Pt as the CE. Furthermore, it was proven that both the electrolytic activity and the PCE deteriorated drastically when the NFs were destroyed. Our work here will be of great interest for both fundamental research and practical applications of W18O49 nanomaterials in other fields.

The ionic liquid N-butyl-N′-(4-pyridylheptyl)imidazolium bis(trifluoromethane)sulfonimide (BuPyIm-TFSI) was used as a dual-functional additive to improve the electrical properties of the hole-transporting material (HTM) for perovskite solar cells. BuPyIm-TFSI improved the conductivity of HTM and reduced the dark current of the solar cell simultaneously, thereby greatly increasing the power conversion efficiency.

A composite catalyst of rosin carbon/Fe3O4 with marvellous morphology was synthesized and applied as a counter electrode (CE) in dye-sensitized solar cells (DSCs), demonstrating notable electrocatalytic activity for the reduction of I3−. Based on this CE, a high power conversion efficiency of 8.11% was achieved, comparable to that of the traditional Pt CE.

Infrared dyes in dye-sensitized solar cells (DSCs) usually mismatch with the band structure of TiO2. This mismatch subsequently results in insufficient kinetics in charge separation. Researchers have started focusing on ternary oxide semiconductors because of their stability. Moreover, the chemical compositions and band structures of these semiconductors are easy to control. In this paper, a ternary semiconductor oxide, Zn2SnO4, was synthesized through a hydrothermal method and used as a photoanode for DSCs. Zn2SnO4 selectivity toward organic and ruthenium complex dyes was different from that of TiO2. Zn2SnO4–DSCs performance was improved at a greater degree with organic sensitizer 2-cyano-3-{4-[2-(4- diphenylamino-phenyl)-vinyl]-phenyl}-acrylic acid (TPC) than with cis-bis (isothiocyanato)-bis (2,2-bipyridyl- 4,4-dicarboxylato) ruthenium (II) bis-tetrabutyl-ammonium (N719). We further improved the power conversion efficiency of Zn2SnO4-DSCs to 5.72% through surface modification and structural optimization. Stepped light-induced measurement of photocurrent and photovoltage was used to systematically study electron behaviors in surface-modified and unmodified Zn2SnO4-based and TiO2-based DSCs. Zn2SnO4 exhibited higher electron diffusion coefficient than TiO2. The electron lifetime of Zn2SnO4-based DSCs increased after surface modification.

As an inorganic photoabsorber, selenium was used in a mesoscopic solar cell with a hybrid organic–inorganic structure of TiO2/Se/P3HT/PEDOT:PSS/Ag, in which the Se layer was prepared by vacuum thermal deposition and post thermal treatment. The microstructure, photoelectrical properties, as well as the rationality in structural design of the solar cell were illustrated in detail. Finally, the hybrid solar cell demonstrated a photoelectric conversion efficiency of 2.63%.

Low cost, high efficiency, and stability are straightforward research challenges in the development of organic–inorganic perovskite solar cells. Organolead halide is unstable at high temperatures or in some solvents. The direct preparation of a carbon layer on top becomes difficult. In this study, we successfully prepared full solution-processed low-cost TiO2/CH3NH3PbI3 heterojunction (HJ) solar cells based on a low-temperature carbon electrode. Power conversion efficiency of mesoporous (M-)TiO2/CH3NH3PbI3/C HJ solar cells based on a low-temperature-processed carbon electrode achieved 9%. The devices of M-TiO2/CH3NH3PbI3/C HJ solar cells without encapsulation exhibited advantageous stability (over 2000 h) in air in the dark. The ability to process low-cost carbon electrodes at low temperature on top of the CH3NH3PbI3 layer without destroying its structure reduces the cost and simplifies the fabrication process of perovskite HJ solar cells. This ability also provides higher flexibility to choose and optimize the device, as well as investigate the underlying active layers.Keywords: carbon electrode; low temperature; perovskite solar cells;

Developing Pt-free and highly efficient counter electrodes (CEs) is meaningful and necessary for the cost reduction of dye-sensitized solar cells (DSCs). In this work, via a facile and reductant-free solvothermal approach, we report the controllable synthesis of NbSe2 nanosheets (NSs), nanorods (NRs), as well as the composite NbSe2/C for use as CEs in high efficiency DSCs. The morphology and structure of the three samples were characterized by SEM, XRD and TEM. Meanwhile, by cyclic voltammetry measurements, electrochemical impedance spectroscopy and Tafel polarization, we found some key issues which explain the difference in their electrocatalytic activity in the reduction of triiodide (I3−). Compared with electrodes based on NbSe2 NRs, NbSe2 NS-based CEs demonstrated lower resistances in charge transfer and ionic diffusion. Subsequently, DSCs with NbSe2 NS-based CEs achieved a conversion efficiency of 7.34%. In addition, NbSe2/C composite-based CEs could further reduce the series resistance and finally a conversion efficiency of 7.80% was obtained, comparable to an efficiency of 7.90% for Pt-based CEs. The NbSe2 in our work provides a cost-effective CE alternative to the noble metal Pt in DSCs.

Low-cost bendable photoanodes and counter electrodes (CEs), as well as gel electrolytes, are potentially desired for the mass production of completely flexible dye-sensitized solar cells (DSSCs). In this work, via printing at low temperature, we fabricated titanium carbide (TiC)-functionalized conductive-carbon (CC) on flexible polyimide (PI) films to replace traditional and expensive Pt/ITO/PEN CEs. Morphology characterization revealed this composite CE was highly porous and homogeneous. Electrochemical investigations demonstrated that this Pt-and-ITO free flexible CE exhibited a high electro-catalytic activity. Finally, the conversion efficiencies of the all flexible quasi-solid DSSCs using this low-cost TiC-CC/PI CE achieved 86% of that based on a Pt/CC/PI CE. Thus, the facile fabrication process of this novel CE, along with its notable performance, are quite promising for the future roll-to-roll production of completely flexible DSSCs.

Two transition metal tellurides, CoTe and NiTe2, were synthesized and for the first time employed as the counter electrodes (CEs) with high catalytic activity for reduction of I3− in dye-sensitized solar cells (DSCs). Using CoTe and NiTe2-based CEs, photoelectric conversion efficiencies (PCEs) of 6.92% and 7.21% were achieved for DSCs, respectively, comparable to that of 7.04% achieved when using a Pt-based CE. The results indicated that, serving as a CE in DSCs, telluride could be a cost-effective and efficient alternative to the noble metal Pt.

Pyridyl iodides were synthesized to serve as effective, economical, green and dual function additives for high efficiency and stable DSCs. Using commercial P25 as the photoanode, a high PCE of 7.81% was achieved with a pyridyl iodide-containing electrolyte. Meanwhile, DSCs based on our novel electrolytes demonstrated better stability.

For the first time, nonstoichiometric WO2.72 was used as a counter electrode (CE) in dye-sensitized solar cells (DSSCs). Oxygen-vacancy-rich WO2.72 nanorod bundles with notable catalytic activity for triiodide and thiolate reduction were prepared in this study. The photovoltaic parameters of dye-sensitized solar cells (DSSCs) with WO2.72 nanorod bundles as CEs are superior compared with those of the WO3-based cells, and nearly the same as those of the precious metal Pt-based cells. In a non-corrosive organic redox couple, the performance of WO2.72 CEs is better than that of Pt and WO3 CEs in DSSCs.

For some specific catalytic reaction, how to construct active sites on two dimensional materials is of great scientific significance. Dye-sensitized solar cells (DSCs) can be viewed as one representative photovoltaics because in which liquid electrolyte with triiodide/iodide (I3−/I−) as redox couples are involved. In this study, amino-functionalized graphene (AFG) has been designed according to theoretically analyzing iodine reduction reaction (IRR) processes and rationally screening the volcanic plot. Then, such AFG has been successfully synthesized by a simple hydrothermal method and shows high electrocatalytic activity towards IRR when serving as counter electrode in DSCs. Finally, a high conversion efficiency of 7.39% by AFG-based DSCs was obtained, which is close to that using Pt as counter electrode.Amino-functionalized graphene (AFG) designed through rationally screening the volcanic plot demonstrates high electrocatalytic activity when serving as counter electrode in dye-sensitized solar cells.Download high-res image (157KB)Download full-size image

A composite catalyst of rosin carbon/Fe3O4 with marvellous morphology was synthesized and applied as a counter electrode (CE) in dye-sensitized solar cells (DSCs), demonstrating notable electrocatalytic activity for the reduction of I3−. Based on this CE, a high power conversion efficiency of 8.11% was achieved, comparable to that of the traditional Pt CE.

Two transition metal tellurides, CoTe and NiTe2, were synthesized and for the first time employed as the counter electrodes (CEs) with high catalytic activity for reduction of I3− in dye-sensitized solar cells (DSCs). Using CoTe and NiTe2-based CEs, photoelectric conversion efficiencies (PCEs) of 6.92% and 7.21% were achieved for DSCs, respectively, comparable to that of 7.04% achieved when using a Pt-based CE. The results indicated that, serving as a CE in DSCs, telluride could be a cost-effective and efficient alternative to the noble metal Pt.

For the first time, nonstoichiometric WO2.72 was used as a counter electrode (CE) in dye-sensitized solar cells (DSSCs). Oxygen-vacancy-rich WO2.72 nanorod bundles with notable catalytic activity for triiodide and thiolate reduction were prepared in this study. The photovoltaic parameters of dye-sensitized solar cells (DSSCs) with WO2.72 nanorod bundles as CEs are superior compared with those of the WO3-based cells, and nearly the same as those of the precious metal Pt-based cells. In a non-corrosive organic redox couple, the performance of WO2.72 CEs is better than that of Pt and WO3 CEs in DSSCs.

2,2′,7,7′-Tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD), one of the classical organic photoelectric materials, has been widely used as a hole transport material (HTM) in perovskite solar cells (PSCs) due to its relatively higher conductivity, easier film formation, weak absorption in the visible region, etc. However, the complex synthesis process and the high synthesis cost of Spiro-OMeTAD severely limit the commercialization of this material. In this work, two economical methoxyaniline-substituted dibenzofuran derivatives, BF-002 and BF-003, are synthesized and successfully used as hole-transport materials in perovskite solar cells (PSCs). The important properties including light absorption, thermal stability, energy level, conductivity, as well as photovoltaic performance are systematically demonstrated. The highest power conversion efficiencies of the PSCs based on BF-002 and BF-003 are 14.20% and 14.07%, respectively, comparable to that of the PSCs based on Spiro-OMeTAD.

Sufficient contact, high catalytic activity, free electron transport and ionic diffusion are desired for liquid–solid heterogeneous electrocatalysis. However, preparing catalysts that simultaneously possess all of these four advantages has proven challenging. Nanostructures originating from anisotropic growth always exhibit specific structural advantages and unique physical, chemical or catalytic properties. Herein, via a facile and template-free solvothermal approach, we synthesized W18O49 nanofibers (NFs) and nanofiber bundles (NFBs), as well as hierarchical spheres (HSs). As catalyst for the counter electrode (CE) of dye-sensitized solar cells (DSCs), W18O49 NFs demonstrated remarkable electrocatalytic activity because: (i) abundant oxygen vacancies offered sufficient active sites for reduction of I3− into I−; (ii) the one dimensional NFs were more beneficial to electron transport; (iii) the two phases, the liquid electrolyte and the solid NFs, could fully contact each other, and meanwhile ions could diffuse freely among the networks constructed by the interlaced NFs. Notably, DSCs using the NF-based semitransparent CE achieved high photoelectric conversion efficiencies (PCEs) up to 8.58%, superior to those based on NFBs or HSs, and comparable to that of 8.78% using Pt as the CE. Furthermore, it was proven that both the electrolytic activity and the PCE deteriorated drastically when the NFs were destroyed. Our work here will be of great interest for both fundamental research and practical applications of W18O49 nanomaterials in other fields.

To obtain highly efficient perovskite solar cells (PSCs), effective controls on perovskite crystallinity, homogeneity, and surface morphology are crucial. Herein, we demonstrate the flexible and facile use of TBP to improve the crystallinity of perovskite in two-step or one-step routes. For the two-step route, addition of TBP into DMF when dissolving PbI2 for spin-coating resulted in a porous layer composed of randomly packed PbI2 nanocrystals. This approach subsequently offered a widely enlarged contact area facilitating interfacial reaction with CH3NH3I and greatly improved CH3NH3PbI3 crystallization. Based on this strategy, PCEs of CH3NH3PbI3-based PSCs were improved from 6.71% to 10.62% (i.e., 58% enhancement). For the one-step route, TBP as an additive resulted in orientational and better crystallinity, by which the PCEs of CH3NH3PbI3−xClx-based planar PSCs increased from 11.11% to 15.01%, showing a remarkable enhancement as high as 35%. Using TBP as one multifunctional additive, it is thought that our strategy in this work offers a new idea for the fabrication of highly efficient PSCs.

Fe3O4 with hierarchical structures was successfully synthesized and introduced into dye-sensitized solar cells as the counter electrode. A power conversion efficiency of 7.65% based on Fe3O4 was achieved, which is superior to that of pyrolytic Pt (6.88%) and close to that for sputtered Pt (7.87%).

Low-cost bendable photoanodes and counter electrodes (CEs), as well as gel electrolytes, are potentially desired for the mass production of completely flexible dye-sensitized solar cells (DSSCs). In this work, via printing at low temperature, we fabricated titanium carbide (TiC)-functionalized conductive-carbon (CC) on flexible polyimide (PI) films to replace traditional and expensive Pt/ITO/PEN CEs. Morphology characterization revealed this composite CE was highly porous and homogeneous. Electrochemical investigations demonstrated that this Pt-and-ITO free flexible CE exhibited a high electro-catalytic activity. Finally, the conversion efficiencies of the all flexible quasi-solid DSSCs using this low-cost TiC-CC/PI CE achieved 86% of that based on a Pt/CC/PI CE. Thus, the facile fabrication process of this novel CE, along with its notable performance, are quite promising for the future roll-to-roll production of completely flexible DSSCs.

As an inorganic photoabsorber, selenium was used in a mesoscopic solar cell with a hybrid organic–inorganic structure of TiO2/Se/P3HT/PEDOT:PSS/Ag, in which the Se layer was prepared by vacuum thermal deposition and post thermal treatment. The microstructure, photoelectrical properties, as well as the rationality in structural design of the solar cell were illustrated in detail. Finally, the hybrid solar cell demonstrated a photoelectric conversion efficiency of 2.63%.

Exploiting an alternative of the Pt-based counter-electrode materials for the triiodide reduction reaction has become a major interest in the fundamental research of dye-sensitized solar cells. Transition-metal selenides have recently been demonstrated as promising non-precious metal electrocatalysts for the triiodide reduction reaction. Herein, we prepared a series of transition-metal selenides via a free-reductant solvothermal method and used them as counter-electrodes in high efficiency dye-sensitized solar cells. The electrochemical results showed that these selenides had excellent catalytic activity for the reduction of the triiodine/iodine couple, and except for MoSe2, the conversion efficiencies of the corresponding dye-sensitized solar cells were comparable to the sputtered Pt counter-electrode. Theoretical investigation clearly revealed that the unsatisfactory performance of MoSe2 mainly originated from the processes of adsorption and charge-transfer. These findings can help to better understand the electrocatalytic processes and thus offer some useful guidelines to develop more efficient electrochemical catalysts.

Developing Pt-free and highly efficient counter electrodes (CEs) is meaningful and necessary for the cost reduction of dye-sensitized solar cells (DSCs). In this work, via a facile and reductant-free solvothermal approach, we report the controllable synthesis of NbSe2 nanosheets (NSs), nanorods (NRs), as well as the composite NbSe2/C for use as CEs in high efficiency DSCs. The morphology and structure of the three samples were characterized by SEM, XRD and TEM. Meanwhile, by cyclic voltammetry measurements, electrochemical impedance spectroscopy and Tafel polarization, we found some key issues which explain the difference in their electrocatalytic activity in the reduction of triiodide (I3−). Compared with electrodes based on NbSe2 NRs, NbSe2 NS-based CEs demonstrated lower resistances in charge transfer and ionic diffusion. Subsequently, DSCs with NbSe2 NS-based CEs achieved a conversion efficiency of 7.34%. In addition, NbSe2/C composite-based CEs could further reduce the series resistance and finally a conversion efficiency of 7.80% was obtained, comparable to an efficiency of 7.90% for Pt-based CEs. The NbSe2 in our work provides a cost-effective CE alternative to the noble metal Pt in DSCs.

Pyridyl iodides were synthesized to serve as effective, economical, green and dual function additives for high efficiency and stable DSCs. Using commercial P25 as the photoanode, a high PCE of 7.81% was achieved with a pyridyl iodide-containing electrolyte. Meanwhile, DSCs based on our novel electrolytes demonstrated better stability.

The ionic liquid N-butyl-N′-(4-pyridylheptyl)imidazolium bis(trifluoromethane)sulfonimide (BuPyIm-TFSI) was used as a dual-functional additive to improve the electrical properties of the hole-transporting material (HTM) for perovskite solar cells. BuPyIm-TFSI improved the conductivity of HTM and reduced the dark current of the solar cell simultaneously, thereby greatly increasing the power conversion efficiency.