Terminal Effects of Fulleropyrrolidine Electron Transport Materials for Efficient Perovskite Solar Cells

Abstract Fullerene (C 60 ) and its derivatives are the most prevalent and efficient electron transport materials (ETMs) for state‐of‐the‐art perovskite solar cells (PSCs). Benefiting from the high performance, simple synthesis, and easy availability of raw materials, fulleropyrrolidine derivatives (FDs) are potential next‐generation ETM alternatives to currently used fullerene materials. However, the power conversion efficiency (PCE) of FDs still lags far behind that of methanofullerene derivatives such as [6,6]‐phenyl‐C 61 ‐butyric acid methyl ester (PCBM). Moreover, the underlying mechanism remains unclear. In this work, six FD ETMs are designed and synthesized, i.e., CN‐TPAX (X = H, Me, OMe, Cl, Br, I), for p‐i‐n PSCs, and obtained a champion PCE of over 25% for the CN‐TPACl ETM, outperforming all reported FDs until now. Subsequently, their performance is systematically characterized in terms of molecular characteristics, including single‐crystal structure, electronic properties, film formability/morphology, and electron dynamics, which helped reveal the terminal effects of FD ETMs on the molecular characteristics and photovoltaic performance of PSCs. This approach clarified the structure–performance relationships between the FDs and the resulting devices, highlighting the importance of the terminal design of fullerene ETMs for high‐performance PSCs.