Low-cost and efficient hole transport materials based on 9-phenyl-9H-carbazole branch for perovskite solar cells

Hole transport materials (HTMs) play a pivotal role in the hole extraction and transportation processes in perovskite solar cells (PSCs). Although a great number of HTMs based on various planar conjugated cores have been explored, the development of branches is rather limited. In this work, branches of 9-phenyl-9H-carbazole derivatives have been incorporated in different N-alkylated dithieno[3,2-b:2′,3′-d]pyrrol (DTP) core to construct HTMs (TM-9 to TM-14). Among them, TM-13 with 9-(4-methoxyphenyl)-9H-carbazole branch exhibites excellent performance in hole extraction and transportation ability. Consequently, the PSCs based on TM-13 have achieved the power conversion efficiency (PCE) of 20.44%, which is comparable to the PCE of 20.62% with the widely used Spiro-OMeTAD HTM. More importantly, the synthetic cost of TM-13 (62 $/g) is much lower than that of Spiro-OMeTAD (400 $/g), suggesting its promising commercialization for low-cost and efficient HTMs for PSCs.