The dopant-free hole transport material based on benzo[1,2-b:4,5-b']dithiophene with high efficiency in inverted perovskite solar cells

In the commercialization process of organic-inorganic hybrid perovskite solar cells (OIH–PSCs), the research of dopant-free hole transport materials (HTMs) with high efficiency is still an urgent problem. In this work, we synthesize two organic small molecule HTMs with well-known benzodithiophene (BDT) as the central unit, abbreviated as BDTO-MTP and BDTT-PMTP. Compared with BDTO-MTP (with oxygen-substituted alkyl chain and diphenylamine derivatives as the terminal group), BDTT-PMTP introduces thiophene to replace oxygen beside the central group, triphenylamine to replace diphenylamine derivatives as the terminal group. Both BDTO-MTP and BDTT-PMTP exhibit high hole mobility without doping. It is worth noting that two new materials are introduced into inverted OIH-PSCs as a doped-free hole transport layer, the champion efficiency of MAPbI3-based devices based on BDTT-PMTP reaches 21.08%, and the highest efficiency of BDTO-MTP-based devices can also reach 19.54%. The results show that the planar building blocks with the similarity of BDT will be an excellent and universal choice for the future design of dopant-free small molecule HTMs with high efficiency.