Star-like, dopant-free, corannulene-cored hole transporting materials for efficient inverted perovskite solar cells

Hole transporting materials (HTMs), owing to their unique bottom position in inverted perovskite solar cells (PSCs), exert a considerable influence on the hole-transporting process and the morphology/performance of the perovskite layers. Considering the well-known interfacial problems associated with commonly-used NiOx and poly(triarylamine) HTMs in traditional inverted PSCs, there is an urgent need for exploring efficient HTMs exhibiting good film formability/processability and interfacial contact to meet the specific requirements of high-performance and stable inverted PSCs. Herein, we fabricated inverted PSCs involving two star-like, dopant-free, corannulene-cored HTMs with O-terminals (sym-penta(N, N-bis(4-methoxyphenyl)aniline)corannulene, namely Cor-OMePTPA) and S-terminals (sym-penta(N, N-bis(4-(methylthio)phenyl)aniline)corannulene, namely Cor-SMePTPA) for the first time. The Cor-SMePTPA HTM exhibited a stronger hole-transporting ability and a better interfacial chemical linkage when compared to the Cor-OMePTPA HTM. The device containing Cor-SMePTPA HTM delivered a power conversion efficiency of 21.70%, which was the highest among inverted PSCs based on methylthio (SMe)-terminated HTMs. Furthermore, comprehensive experimental and theoretical characterizations clearly showed that the core and outer terminals (O or S) affected the optoelectric and chemical properties of the HTMs as well as the photovoltaic performance and stability of the corresponding PSCs, highlighting the superiority of the design involving a corannulene core and SMe groups in HTMs for inverted PSCs. We believe that such dopant-free corannulene-cored HTMs can have considerable potential for realizing highly efficient and stable PSCs in the future.