Simple‐Synthesis Isomer‐Free Multi‐Adduct Fullerenes as Electron Transport Materials Enable 26.66% Efficiency of Perovskite Solar Cells

ABSTRACT The laggard advancement in electron transport layer materials is one of the bottleneck problems, impeding the further improvement of photovoltaic performance of perovskite solar cells (PSCs). Fullerene derivatives are widely used as electron transport layer materials for PSCs, but significant imperfections remain unresolved. Herein, an efficient and facile method was developed to prepare isomer‐free multi‐adduct fullerene derivatives, C 60 (NHR) 4 O, with high yield and meet the multifunctional requirements of electron transport layer materials of PSCs. Among the multi‐adduct fullerene derivatives, tetra[methyl 2‐amino‐3‐(thiophen‐2‐yl)propanoate]C 60 epoxide (TATPC) was selected to incorporate into PCBM as an electron transport material for PSCs. Benefiting from multi‐adduct groups, TATPC presents a higher LUMO energy level, superior passivation capability, and stronger interaction with perovskite than the classical PCBM. It enables PCBM:TATPC to afford improved coverage and a smoother surface, increased contact potential difference, reduced trap density, higher electron mobility, and inhibited self‐aggregation, thus facilitating electron extraction, suppressing charge carrier recombination, and enhancing durability for PSCs. Therefore, PCBM:TATPC‐based PSCs achieve an impressive efficiency of 26.66% (25.81% for devices with an area of 1.04 cm 2 ) with enhanced operational stability. This work highlights an efficient molecular design strategy to develop isomer‐free multi‐adduct fullerenes and thus regulate the electron transport layer for high‐efficiency and stable PSCs.