Molecular Regulation of Perylenediimide and Fluorene‐Based Cathode Interfacial Materials for Efficient Inverted Perovskite Solar Cells

Abstract In inverted perovskite solar cells (PSCs), n‐doping fullerene electron transport layers (ETLs) have been found to prepare high efficiency devices due to their excellent performance in electrochemistry, film formability, and surface passivation. Herein, two cathode interface layers (CILs) 2PDI‐FN and 2PDIT‐FN are prepared with dimethylamino functional groups and PDI units. The addition of thiophene makes the 2PDIT‐FN conjugated framework coplanar and enhances the effect of dimethylamino functional groups, which give 2PDIT‐FN with higher electrical conductivity, electron mobility, self‐doping property, and film formability. Moreover, dopant N‐DMBI can further enhance these advantages of 2PDIT‐FN. Consequently, a peak power conversion efficiency (PCE) of 20.44% is achieved with 2PDIT‐FN(+) as CIL, much higher than 18.77% of 2PDI‐FN(+) one, which is only 17.71% and 19.06% for 2PDI‐FN and 2PDIT‐FN‐based one, respectively. The significant improvement in device efficiency is due to reduced defect density, lower dark current, larger recombination resistance, and better surface morphology, which improves charge transport and collection at the PC 61 BM/Ag interface. In a word, this molecular design approach with molecular configuration regulation and functional groups provides a direction for the preparation of cathode interface materials to achieve high performance of PSCs.