Compacting Molecular Stacking and Inhibiting Self‐Aggregation in Fullerene Transporting Layer for Efficient and Stable Perovskite Solar Cells

The underdevelopment of electron transport layer (ETL) materials remains a critical bottleneck limiting the overall photovoltaic performance of inverted perovskite solar cells (PSCs). Fullerene derivatives, such as PCBM, are widely employed ETL materials in PSCs due to their excellent electron affinity and energy level alignment with the perovskite layer. However, PCBM suffers from high energy disorder, self-aggregation predilection, and insufficient defect passivation ability, leading to significant charge carrier recombination and accumulation at interfaces. Herein, a phosphate-substituted fullerene derivative, FuPE, is developed to enhance the performance of PCBM-based ETLs for PSCs. Incorporating FuPE efficiently compacts molecular stacking, enforces crystallinity and intermolecular interaction, suppresses self-aggregation, and improves interfacial compatibility of the FuPE:PCBM blend. Such endows the FuPE:PCBM blend film with enhanced electron mobility (0.183 cm² V^-1 s^-1), lower trap density, more uniform film morphology, and superior defect-passivation ability, compared to the PCBM pristine one. Consequently, PSCs employing FuPE:PCBM as the ETL achieve reduced trap-assisted recombination, enhanced charge carrier extraction, and thus a remarkable power conversion efficiency exceeding 26% alongside improved operational stability. This work highlights an effective strategy for optimizing fullerene-based ETLs, advancing the development of highly efficient and durable PSCs.