Efficient and Stable Mesoscopic Perovskite Solar Cells Using a Dopant-Free D-A Copolymer Hole-Transporting Layer

Addressing the stability issue in perovskite solar cells (PSCs) is a crucial step for commercialization purposes. Finding a novel and stable hole-transporting layer (HTL) is one of the most effective strategies to solve this problem. Herein, a new polymeric HTL, namely poly{2,7-[(5,5-bis(3 ',7 '-dimethyloctyl)-5 H-1,8-dithia-as-indacenone]-alt-5,5-[5 ',6 '-bis(octyloxy)-4 ',7 '-di-2-thienyl-2 ',1 ',3 '-benzothiadiazole]} (PDTIDTBT) is synthesized, indicating a great hole-transporting property as compared with the commonly used 2,2 ',7,7 '-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9 '-spirobifluorene (spiro-OMeTAD) HTL. This polymer shows good mobility with suitable band alignment with respect to the triple A-cation perovskite film, which is comparable with the state-of-art polymeric HTLs. Therefore, mesoscopic PSCs are fabricated by PDTIDTBT HTL and considered interface engineering technique using a thin layer of poly(methyl methacrylate) (PMMA) at the perovskite/HTL interface. Based on these modifications, a PSC with a maximum power conversion efficiency (PCE) of 19.89% is achieved, higher than the PCE of the spiro-based PSC (19.28%). In addition, the PDTIDTBT-based PSCs show excellent operational and ambient stability better than the spiro ones.