D-π-A-π-D型非掺杂小分子空穴传输材料的合成及其在反向钙钛矿太阳能电池中的应用

Perovskite solar cells (PVSCs) have recently gained much attention for the advantages of low cost and high efficiency. Based on the different device structures, PVSCs can be simply classified into conventional and inverted categories. Compared with the inverted devices, conventional PVSCs generally exhibited higher PCE. Especially, a milestone PCE value of 24.3% was obtained in conventional PVSCs. However, the complexity and high-temperature process in device fabrication further limit their application in flexible and large-scale devices, while the inverted PVSCs can make up the shortcomings of the conventional PVSCs. Commonly, PVSCs devices contain electrodes, electron/hole transporting layers and the perovskite layer. Among the function layers, hole transporting layers (HTLs) play a crucial role in improving the photovoltaic performance of inverted PVSCs. From the materials point of view, the efficient hole transporting materials (HTMs) are mostly inorganic compounds and polymers. On the other side, taking advantages of easy modification, low price, easy preparation and homogeneity in batches, small molecular HTMs afford superior promising in fabricating efficient and stable PVSCs. However, up to date, small molecular HTMs are relatively less explored. To enrich the material species of small molecular HTMs and illustrate their superiorities in constructing stable PVSCs, in this paper, we designed and synthesized three D-π-A-π-D type small molecular HTMs based on triphenylamine (TPA) unit, namely 1-T, 1-OT and 1-OTCN. The optoelectronic properties of these molecules were modified by introducing different electron acceptor/donor groups. Afterwards, employing as dopant-free HTMs in inverted PVSCs, the three small molecules demonstrated distinguished performance. We found that introduction of electron-donating methoxy into 1-T, 1-OT exhibited increased energy levels and hole mobility. On the other hand, the energy levels of 1-OTCN were down-shifted compared to 1-OT, which was attributed from the stronger electron-withdrawing ability of dicyanovinylene group than carbonyl group. Among the devices with new HTMs, 1-OTCN based PVSCs achieved the best PCE of 16.8%, with open-circuit voltage (V_OC) of 1.09 V, short-circuit current density (J_SC) of 20.13 mA•cm^-2 and fill factor (FF) of 78%. Compared with other HTMs, the higher J_SC of 1-OTCN based PVSCs was ascribed from more efficient charge transfer and extraction in the interface of HTL/perovskite. Moreover, in contrast with the hydrophilicity of PEDOT:PSS, the hydrophobicity of 1-OTCN contributed to the satisfactory stability of PVSCs.