Modifying 6,6‐Phenyl‐C61‐Butyric Acid Methyl Ester With a Multifunctional Organic Molecule Improves Performance of Electron Transport Layer and Passivates Defects in Inverted Perovskite Solar Cell

Inverted perovskite solar cells (PSCs) attract wide attention for their strong performance. Recent advances have improved both stability and power conversion efficiency (PCE). However, the common fullerene electron transport layer (ETL) material in p‐i‐n(inverted) PSCs, 6,6‐Phenyl‐C61‐butyric acid methyl ester (PCBM), agglomerates easily, blocks water and oxygen poorly, and provides weak perovskite passivation. We address these issues by adding 1,3,5‐Tri(1‐phenyl‐1H‐benzimidazol‐2‐yl)benzene(TPBi) to PCBM, leveraging TPBi’s strong hole‐blocking capability. This combination creates a uniform, highly hydrophobic ETL. The composite ETL passivates surface defects, improves energy level alignment, and boosts device performance. Experimentally, the TPBi‐blended ETL increases PCE, short‐circuit current density ( J SC ), and fill factor (FF). PCE rises from 17.86% to 21.04% and hysteresis decreases. The new composite ETL strengthens PSC stability and offers a simple, effective way toward commercializing efficient inverted PSCs.