钙钛矿太阳能电池中小分子空穴传输材料的研究进展

Recent Progress in Hybrid Perovskite Solar Cells Based on p-Type Small Molecules as Hole Transporting Materials

有机-无机钙钛矿太阳能电池(PSCs)从2009年低于5%的能量转换效率到现在经过认证的超过22%的效率,成为科研热点和最有希望商业化的新型太阳能电池。在高性能的PSCs中,空穴传输材料是关键的一环,起到从钙钛矿活性层材料到对电极有效抽取和传输空穴的作用。本文在现有研究成果的基础上,对有机分子空穴传输材料在PSC中的应用进行总结,并强调分子材料结构对PSC器件性能(效率和稳定性)的影响。

Organic-inorganic perovskite solar cells(PSCs)have become one of the most promising solar cells,as the power conversion efficiency(PCE)has increased from less than 5%in 2009 to certified values of over 22%.In the typical PSC device architecture,hole transport materials that can effectively extract and transmit holes from the active layer to the counter electrode(HTMs)are indispensable.The wellknown small molecule 2,2',7,7'-tetrakis-(N,N-di-4-methoxyphenyl amino)-9,9'-spirobifluorene(spiro-OMeTAD)is the best choice for optimal perovskite device performance.Nevertheless,there is a consensus that spiro-OMeTAD by itself is not stable enough for long-term use in devices due to the sophisticated oxidation process associated with undesired ion migration/interactions.It has been found that spiro-OMeTAD can significantly contribute to the overall cost of materials required for the PSC manufacturing,thus its market price makes its use in large-scale production costly.Besides,another main drawback of spiro-OMeTAD is its poor reproducibility.To engineer HTMs that are considerably cheaper and more reproducible than spiro-OMeTAD,shorter reaction schemes with simple purification procedures are required.Furthermore,HTMs must possess a number of other qualities,including excellent charge transporting properties,good energy matching with the perovskite,transparency to solar radiation,a large Stokes shift,good solubility in organic solvents,morphologically stable film formation,and others.To date,hundreds of new organic semiconductor molecules have been synthesized for use as HTMs in perovskite solar cells.Successful examples include azomethine derivatives,branched methoxydiphenylamine-substituted fluorine derivatives,enamine derivatives,and many others.Some of these have been incorporated as HTMs in complete,functional PSCs capable of matching the performance of the best-performing PSCs prepared using spiro-OMeTAD while showing even better stability.In light of these results,we describe the advances made in the synthesis of HTMs that have been tested in perovskite solar cells,and give an overview of the molecular engineering of HTMs.Meanwhile,we highlight the effects of molecular structure on PCE and device stability of PSCs.This review is organized as follows.In the first part,we give a general introduction to the development of PSCs.In the second part,we focus on the introduction of the perovskite structure,device architecture,and relevant work principles in detail.In the third part,we discuss all kinds of molecular HTMs applied in PSCs.Special emphasis is placed on the relationship between HTM molecular structure and device function.Last but not least,we point out some existing challenges,suggest possible routes for further HTM design,and provide some conclusions.