Simple hybrid dithiafulvenes-triphenylamine systems as dopant-free hole-transporting materials for efficient perovskite solar cells

Two extended hybrid conjugated systems based on a triphenylamine(TPA) core with two and three peripheral 1,4-dithiafulvenes(DTF) units coded WH-2 and WH-3 as hole-transporting materials(HTMs) applied in perovskite solar cells(PSCs) are synthesized by facile one-step reaction in good yield over 75%. DTF unit as electron donor can enhance the electron donating ability and the fusion of benzenic ring of TPA with DTF unit may lead to reinforced intermolecular interactions in the solid state. In addition,WH-2 and WH-3 exhibit a pyramid shape containing partial planarity and quasi three-dimensionality features, which is also conducive to enhancing the π-π stacking of molecules in the solid state. The above-mentioned structural characteristics make the two HTMs have good hole mobilities. As a result,WH-2 and WH-3 obtained the high intrinsic hole mobilities of 4.69 × 10^(-4)and 2.18 × 10^(-3)cm^(2)V^(-1)s^(-1)respectively. Finally, the power conversion efficiencies(PCEs) of PSCs with WH-2 and WH-3 as cost-effective dopant-free HTMs are 15.39% and 19.22% respectively and the PCE of PSC with WH-3 is on a par with that of PSC with Li-TFSI/t-BP doped Spiro-OMe TAD(19.67%).

Improvement on the performance of perovskite solar cells by doctor-blade coating under ambient condition with hole-transporting material optimization

Numerous fabrication methods have been developed for high-efficiency perovskite solar cells(PSCs). However, these are limited to spin-coating processes in a glove box and are yet to be commercialized. Therefore, there is a need to develop a controllable and scalable deposition technique that can be carried out under ambient conditions. Even though the doctor-blade coating technique has been widely used to prepare PSCs, it is yet to be applied to high-efficiency PSCs under ambient conditions(RH ~45%, RT ~25 °C). In this study, we conducted blade-coating fabrication of modified high-efficiency PSCs under such conditions. We controlled the substrate temperature to ensure phase transition of perovskite and added dimethyl sulfoxide(DMSO) to the perovskite precursor solution to delay crystallization, which can facilitate the formation of uniform perovskite films by doctor-blade coating. The as-prepared perovskite films had large crystal domains measuring up to 100 μm. Solar cells prepared from these films exhibited a current density that was enhanced from 17.22 to 19.98 m A/cm^2 and an efficiency that was increased from 10.98% to 13.83%. However, the open-circuit voltage was only 0.908 V, probably due to issues with the hole-transporting layer. Subsequently, we replaced poly(3,4-ethylenedioxythiophene) polystyrene sulfonate(PEDOT:PSS) with Ni O x as the hole-transporting material and then prepared higher-quality perovskite films by blade-coating under ambient conditions. The as-prepared perovskite films were preferably orientated and had large crystal domains measuring up to 200 μm;The open-circuit voltage of the resulting PSCs was enhanced from 0.908 to 1.123 V, while the efficiency increased from 13.83% to 15.34%.

Synthesis and Characteristics of Hole-transporting Materials Based on Biphenyl Diamine Derivatives with Carbazole Groups

Two hole-transporting materials containing carbazole moieties with TPD- and NPB-like structures, 4,4′-bis [ N- （4-carbazolylphenyl） -N-phenylamino ] biphenyl （ CPB ） and 4,4′-bis [ N- （ 4-carbazolylphenyl ） -N- （ 1-naphthyl ） amino] biphenyl（ CNB）, were synthesized via a modified Ullmann reaction. The resulting compounds were thermally stable with high glass transition temperatures ranging from 145 to 147 ℃ and possessed a good electrochemical reversibility and hole-transporting properties. Typical double-layer device evaluation with the structure ITO/CPB（40 nm）/ Alq3 （60 nm）/LiF/Al demonstrated that they were promising hole-transporting materials with a current efficiency of 5.25 cd/A and a power efficiency of 2.00 lm/W.

Phenylfluorenamine-functionalized poly(N-vinylcarbazole)s as dopant-free polymer hole-transporting materials for inverted quasi-2D perovskite solar cells

In order to improve the efficiency and stability of inverted three-dimensional(3D) or quasi-2D perovskite solar cells(PSCs) for future commercialization, exploring high efficient dopant-free polymer holetransporting materials(HTMs) is still desired and meaningful. One simple and efficient way to achieve high performance dopant-free HTMs is to synthesize novel non-conjugated side-chain polymers via rational molecular design. In this work, N-(4-methoxyphenyl)-9,9-dimethyl-9H-fluoren-2-amine(FMeNPh) groups are introduced into the poly(N-vinylcarbazole)(PVK) side chains to afford two nonconjugated polymers PVCz-DFMeNPh and PVCz-FMeNPh as dopant-free HTMs in inverted quasi-2D PSCs. Benefited from the flexible properties of polyethylene backbone and excellent optoelectronic natures of FMeNPh side-chain groups, PVCz-DFMeNPh with more FMeNPh units exhibited excellent thermal stability, well-matched energy levels and improved charge mobility as compared to PTAA and PVCzFMeNPh. Moreover, the morphologies investigation of quasi-2D perovskite on PVCz-DFMeNPh shows more compact and homogeneous perovskite films than those on PTAA and PVCz-FMeNPh. As a result,the dopant-free PVCz-DFMeNPh based inverted quasi-2D PSCs deliver power conversion efficiency(PCE) up to 18.44% as well as negligible hysteresis and favorable long-term stability, which represents as excellent performance reported to date for inverted quasi-2D PSCs. The results demonstrate the great potentials of constructing non-conjugated side-chain polymer HTMs based on phenylfluorenamine-func tionalized PVK for the development of high efficient and stable inverted 3D or quasi-2D PSCs.

Truxene-based Hole-transporting Materials for Perovskite Solar Cells

Three star-shaped truxene-based small molecules（namely TXH,TXM,TXO） were synthesized,characterized and used as hole-transporting materials（HTMs） for perovskite solar cells（Pv SCs）. The device based on TXO delivered a respectable power conversion efficiency（PCE） of 7.89% and a high open-circuit voltage（Voc） of 0.97 V,which far exceeded the values of the devices based on other two small molecules. The highest PCE for the device based on TXO is mainly contributed from its lowest series resistance（Rs） value and largest short-circuit current（Jsc） value under the same circumstances. All these results indicate that TXO is a promising HTM candidate for Pv SCs.

Application of phenonaphthazine derivatives as hole-transporting materials for perovskite solar cells

Two electron-rich, solution-processable phenonaphthazine derivatives, 5,12-bis(N-[4,4'-bis-(phenyl) aminophen-4 ''-yl]}-phenonaphthazine (BPZTPA) and 5,12-bis{N-[4,4'-bis(methoxy-phenyl)aminophen-4'-phenonaphthazine (MeO-BPZTPA) have been designed and employed in the fabrication of perovskite solar cells. BPZTPA and MeO-BPZTPA exhibit excellent thermal stabilities, hole mobilities (similar to 10(-4) cm(2)/(V.s)) and suitable HOMO levels (-5.34 and-5.29 eV, respectively) relative to the valence band of the CH3NH3PbI3 and Au work function, showing their potential as alternative hole-transporting materials (HTMs). Meanwhile, the corresponding mesoporous TiO2/CH3NH3PbI3/HTM/Au devices are investigated, and the best power conversion efficiency of 10.36% has been achieved for MeO-BPZTPA without using p-type dopant. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.

An asymmetrically substituted dithieno[3,2-b:2',3'-d]pyrrole organic small-molecule hole-transporting material for high-performance perovskite solar cells

Hole-transporting materials play a vital role in terms of the performance of perovskite solar cells(PSCs).The dithieno[3,2-b:2’,3’-d]pyrrole(DTP),an S,N-heterocyclic building block,has been proved to be desirable for molecular design of hole-transporting materials in PSCs.We developed an asymmetrically substituted DTP small-molecule(JW12)and a reference compound(JW11).The asymmetrical structure of JW12 leads to different absorption properties and electron distribution.The device in a planar n-i-p architecture using JW12 shows a much higher PCE(18.07%)than that based on JW11(15.46%),which is also better than the device based on spiro-OMe TAD(17.47%).We hope our research can provide a new perspective in molecular design of organic HTMs for perovskite solar cells.

Light-Emitting Diodes Based on All-Quantum-Dot Multilayer Films and the Influence of Various Hole-Transporting Layers on the Performance

We present a systematic analysis of the exciton-recombination zone within all-quantum-dot （QD） multilayer films using sensing QD layers in QD-based light-emitting diodes （QLEDs）, and demonstrate the a11-QD multilayer films with different sequences of layers prepared by inserting a sensing blue QD layer denoted as B at various positions within four red QD multilayers denoted as R. We also use different hole transporting layers （PVK, CBP as well as poly-TPD） to prevent the formation of leakage current and to improve the luminance. The results show that the total EL emission is mostly at the fourth （60%） and fifth （40%） QD monolayers, adjacent to ITO. This presents both decreasing current density and increasing brightness with different hole transporting layers, thus resulting in more efficient performance.

Anthradithiophene based hole-transport material for efficient and stable perovskite solar cells

A novel hole-transport material(HTM)based on an anthradithiophene central bridge named BTPA-7 is developed.In comparison to spiro-OMeTAD(2,2’,7,7’-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9’-spirobifluorene),the synthetic steps of BTPA-7 are greatly reduced from 6 to 3 and the synthetic cost of BTPA-7 is nearly a half that of spiro-OMeTAD.Moreover,BTPA-7 exhibits a relatively lower conductivity but higher hole mobility and higher glass transition temperature(Tg)than spiro-OMeTAD.Compared with the photovolatic performance for spiro-OMeTAD,FA0.85MA0.15PbI3 and MAPbI3 PSC devices based on BTPA-7 exhibit slightly lower PCEs with the values of 17.58%(18.88%for spiro-OMeTAD)and 11.90%(13.25%for spiro-OMeTAD),respectively.Nevertheless,a dramatically higher JSC of PSC based on BTPA-7is achieved,which arises from the higher hole mobility of BTPA-7.In addition,the relatively hydrophobic character of BTPA-7 eventually enhances the PSC device stability.Lower cost,higher hole mobility,higher Tg,satisfactory photovoltaic performance,and superior device stability of BTPA-7 can be utilized as a substitute for spiro-OMeTAD in PSCs.

The donor-dependent methoxy effects on the performance of hole-transporting materials for perovskite solar cells

In this work, a comprehensive study on the deliberate molecular design and modifications of electron donors is carried out to elucidate correlations between the methoxy effects and donor configuration of hole-transporting materials(HTMs). Our initial findings demonstrate the donor-dependent methoxy effects. Photovoltaic performance of the HTM with twisted donor highly depends on the methoxy substituent. In contrast, efficiency’s reliance on methoxy is insignificant for the HTM with planar donor. The HTM(M123) featuring the methoxy–substituted carbazole shows a decent power conversion efficiency of 19.33% due to synergistic effects from both planar structure and methoxy. This work gives a guideline to access HTMs reaching both high-performance and good stability.

A crosslinked polymer as dopant-free hole-transport material for efficient n-i-p type perovskite solar cells

A new crosslinked polymer,called P65,with appropriate photo-electrochemical,opto-electronic,and thermal properties,has been designed and synthesized as an efficient,dopant-free,hole-transport material(HTM)for n-i-p type planar perovskite solar cells(PSCs).P65 is obtained from a low-cost and easily synthesized spiro[fluorene-9,90-xanthene]-30,60-diol(SFX-OH)-based monomer X65 through a freeradical polymerization reaction.The combination of a three-dimensional(3 D)SFX core unit,holetransport methoxydiphenylamine group,and crosslinked polyvinyl network provides P65 with good solubility and excellent film-forming properties.By employing P65 as a dopant-free hole-transport layer in conventional n-i-p type PSCs,a power conversion efficiency(PCE)of up to 17.7%is achieved.To the best of our knowledge,this is the first time a 3 D,crosslinked,polymeric dopant-free HTM has been reported for use in conventional n-i-p type PSCs.This study provides a new strategy for the future development of a 3 D crosslinked polymeric dopant-free HTM with a simple synthetic route and low-cost for commercial,large-scale applications in future PSCs.

Effect of hole-transporting materials on the photovoltaic performance and stability of all-ambient-processed perovskite solar cells

High-efficiency perovskite solar cells（PSCs） reported hitherto have been mostly prepared in a moisture and oxygen-free glove-box atmosphere, which hampers upscaling and real-time performance assessment of this exciting photovoltaic technology. In this work, we have systematically studied the feasibility of allambient-processing of PSCs and evaluated their photovoltaic performance. It has been shown that phasepure crystalline tetragonal MAPbI;perovskite films are instantly formed in ambient air at room temperature by a two-step spin coating process, undermining the need for dry atmosphere and post-annealing.All-ambient-processed PSCs with a configuration of FTO/TiO;/MAPbI;/Spiro-OMeTAD/Au achieve opencircuit voltage（990 mV） and short-circuit current density（20.31 mA/cm;） comparable to those of best reported glove-box processed devices. Nevertheless, device power conversion efficiency is still constrained at 5% by the unusually low fill-factor of 0.25. Dark current–voltage characteristics reveal poor conductivity of hole-transporting layer caused by lack of oxidized spiro-OMe TAD species, resulting in high seriesresistance and decreased fill-factor. The study also establishes that the above limitations can be readily overcome by employing an inorganic p-type semiconductor, copper thiocyanate, as ambient-processable hole-transporting layer to yield a fill-factor of 0.54 and a power conversion efficiency of 7.19%. The present findings can have important implications in industrially viable fabrication of large-area PSCs.

Progress in hole-transporting materials for perovskite solar cells

In recent years the photovoltaic community has witnessed the unprecedented development of perovskite solar cells（PSCs） as they have taken the lead in emergent photovoltaic technologies. The power conversion efficiency of this new class of solar cells has been increased to a point where they are beginning to compete with more established technologies. Although PSCs have evolved a variety of structures, the use of hole-transporting materials（HTMs） remains indispensable. Here, an overview of the various types of available HTMs is presented. This includes organic and inorganic HTMs and is presented alongside recent progress in associated aspects of PSCs, including device architectures and fabrication techniques to produce high-quality perovskite films. The structure, electrochemistry, and physical properties of a variety of HTMs are discussed, highlighting considerations for those designing new HTMs. Finally, an outlook is presented to provide more concrete direction for the development and optimization of HTMs for highefficiency PSCs.

Optical and NH₃Gas Sensing Properties of Hole-Transport Layers Based on PEDOT: PSS Incorporated with Nano-TiO₂

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) incorporated with nanocrystalline TiO2 powder (PEDOT:PSS+nc-TiO2) films were prepared by spin-coating technique. SEM surface morphology, UV-Vis spectra and NH3 gas sensing of were studied. Results showed that the PEDOT:PSS+nc-TiO2 film with a content of 9.0 wt% of TiO2 is most suitable for both the hole transport layer and the NH3 sensing. The responding time of the sensor made from this composite film reached a value as fast as 20 s. The rapid responsiveness to NH3 gas was attributed to the efficient movement of holes as the major charge carriers in PEDOT:PSS+nc-TiO2 composite films. Useful applications in organic electronic devices like light emitting diodes and gas thin film sensors can be envisaged.

Carbon-based perovskite solar cells with electron and hole-transporting/-blocking layers

Towards commercialization of perovskite solar cells(PSCs),further reducing the cost and increasing the stability of PSCs have been the most important tasks of researchers,as the efficiency of single-junction PSCs has reached a competitive level among all kinds of single-junction solar cells.Carbon-electrode-based PSCs(CPSCs),as one of the most promising constructions for achieving stable economical PSCs,now attract enormous attention for their cost-effectiveness and stability.Here,we briefly review the development of CPSCs and reveal the importance of n-i-p architecture for state-of-the-art CPSCs.However,despite their promising potential,challenges still exist in CPSCs in the n-i-p architecture,which mainly stem from the incompact contact of the hole-transporting layer(HTL)/carbon electrode.Thus,new carbon materials and/or novel manufacturing methods should be proposed.In addition,HTL is yet to be appropriate for state-of-the-art CPSCs because the fabrication of carbon electrode could result in the destruction of the underlayer.To further enhance the performance of CPSCs,both the HTL and electron transport layer as well as their interfaces with perovskite active layer need to be improved.We recommend that the perovskite active layer,with its long carrier lifetime,strong carrier transport capability,and long-term stability,is necessary as well for improved performance of CPSCs.We also highlight current researches on CPSCs and provide a systematic review of various types of regulation tools.

钙钛矿太阳能电池中无掺杂聚合物空穴传输材料研究进展

基于传统空穴传输材料(HTM)的钙钛矿太阳能电池(PSC)已经实现了超过25%的能量转换效率,然而这些HTM通常需要添加吸湿性掺杂剂来实现高迁移率和可加工性,从而降低了器件稳定性。为解决该问题,无掺杂HTM受到广泛关注。总结了近年来用于高效PSC的无掺杂聚合物HTM的结构和性能,并分析了其中的构效关系,提出了高效无掺杂聚合物HTM的结构设计原理,并展望了未来的发展趋势。

Increasing open circuit voltage by adjusting work function of hole-transporting materials in perovskite solar cells

A series of conductive polymers, i.e., poly（3-methylthiophene） （PMT）, poly（thiophene） （PT）, poly（3-bromothiophene） （PBT） and poly（3-chlorothiophene） （PCT）, were prepared via the electrochemical polymerization process. Subse- quently, their application as hole-transporting materials （HTMs） in CHBNI-I3Pb｜3 perovskite solar cells was explored. It was found that rationally increasing the work function of HTMs proves beneficial in improving the open circuit voltage （Voc） of the devices with an ITO/conductive-polymer/CHBNHBPbIg/C60/BCP/Ag structure. In addition, the higher-Voc devices with a higher-work-function HTM exhibited higher recombination resistances. The highest open circuit voltage of 1.04 V was obtained from devices with PCT, with a work function of -5.4 eV, as the hole-transporting layer. Its power conversion efficiency attained a value of approximately 16.5%, with a high fill factor of 0.764, an appreciable open voltage of 1.01 V and a short circuit current density of 21.4 mA.cm-2. This simple, controllable and low-cost manner of preparing HTMs will be beneficial to the production of large-area perovskite solar cells with a hole-transportin~ laver.

利用溶液加工的界面阻挡层实现高效三维和准二维金属卤化物钙钛矿发光二极管

为了保护金属卤化物钙钛矿发光层免受强酸性聚合物(poly-(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid),PEDOT:PSS)的腐蚀,一种具有空穴传输能力的有机小分子材料(N,N-dicarbazolyl-3,5-benzene, mCP)被当作界面阻挡层引入三维钙钛矿发光层(CsPbBr_(3))和PEDOT:PSS之间。研究表明,mCP不仅可以从空间上隔离CsPbBr_(3)和PEDOT:PSS,抑制PEDOT:PSS对CsPbBr_(3)发光层的降解,还可以使钙钛矿薄膜的覆盖率更高,颗粒更小,提高薄膜质量,减少薄膜缺陷对激子的淬灭。同时,mCP的引入可以提高空穴注入和传输能力,使得相同电压下形成的激子更多;由于mCP具有比PEDOT:PSS更高的最低电子不占有态和更大的能隙,能更好地将激子限制在发光层中,进一步提高激子的发光辐射复合和器件的电致发光效率。与原始不加mCP的器件相比,基于mCP的3D CsPbBr_(3)钙钛矿发光二极管(Perovskite light-emitting diode, PeLED)的电致发光性能得到了显著提升,获得了4.86 cd/A最大电流效率。接着,这种方法在基于PEA_(2)Cs_(n-1)Pb_(n)Br_(3n+1)的准二维PeLED中也被证实是可行的,器件的最大电流效率被提升到24.79 cd/A。

基于金刚线切片的钙钛矿/硅叠层太阳电池

提出一种免空穴传输层的策略,将自组装单分子层材料作为钙钛矿活性层的添加剂,通过一步旋涂法直接将钙钛矿薄膜制备在导电基底表面,其中薄膜的质量与均一性都得到改善。进一步地,将该方法应用在低成本的商用金刚线切片上,可在高粗糙度的硅表面制备出覆盖度高、形貌致密、无空洞的钙钛矿薄膜。在光电性能方面,用该方法得到的单结钙钛矿太阳电池的光电转换效率为21%,填充因子高达83%,两端钙钛矿/硅叠层太阳电池的光电转换效率为28%。

A Cost-Effective D-A-D Type Hole-Transport Material Enabling 20% Efficiency Inverted Perovskite Solar Celis

High-performance,cost-effective hole-transport materials(HTMs)are greatly desired for the commercialization of perovskite solar cells(PVSCs).Herein,two new HTMs,TPA-FO and TPA-PDO,are devised and synthesized,which have a donor-acceptor-donor(D-A-D)type molecule design featuring carbonyl group-functionalized arenes as the acceptor(A)units.The carbonyl group at the central core of HTMs can not only tune frontier molecular orbital(FMO)energy levels and surface wettability,but also can enable efficient surface passivation effects,resulting in reduced recombination loss.When employed as HTMs in inverted PVSCs without using dopant,TPA-FO with one carbonyl group yields a high power conversion efficiency(PCE)of 20.24%,which is among the highest values reported in the inverted PVSCs with dopant-free HTMs.More importantly,the facile one-step synthetic process enables a low cost of 30 USD g^(-1) for TPA-FO,much cheaper than the most studied HTMs used for high-efficiency dopant-free PVSCs.These results demonstrate the potential of D-A-D type molecules with carbonyl group-functionalized arene core in developing the low-cost dopant-free HTMs toward highly efficient PVSCs.