Indoloindole‐Based Hole Transporting Material for Efficient and Stable Perovskite Solar Cells Exceeding 24% Power Conversion Efficiency

Abstract The new concept of hole transporting materials (HTMs) has inspired researchers to develop high‐performing and stable perovskite solar cells (PSCs). In particular, small molecular organic semiconductors have been extensively studied for HTM due to their high reproducibility and easy synthesis. In this work, a novel linear‐type series of indoloindole (IDID)‐based hole transporting materials comprising a fluorinated IDID core(IDIDF) and multiple thiophene rings is developed. The structure‐property relationship in the IDIDF derivatives is investigated systematically by changing the alkyl position and length of the backbone. The intrinsic properties of the material are significantly different depending on the alkyl position of inner thiophene ring. The optimized material exhibits improved solubility, favorable molecular packing patterns, and superior hole mobility. The champion PSCs using the optimum molecule, IDIDF2, yield a power conversion efficiency of 23.16% in non‐doped and 24.24% in doped conditions, which represent one of the highest performances in n‐i‐p planar device configuration. For the first time, the IDIDF2‐based PSCs achieve outstanding thermal and moisture stabilities under thermal aging (85 °C) and relative humidity of 85%, respectively, for 1500 h.