Non-fullerene electron-transporting materials for high-performance and stable perovskite solar cells

The electron-transporting material (ETM) is a key component of perovskite solar cells (PSCs) optimizing electron extraction from perovskite to cathode. Fullerenes, specifically C₆₀ and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM), have been used as the benchmark ETMs for inverted PSCs. However, C₆₀ is restricted to thermal evaporation, and PCBM suffers from poor photothermal stability and suboptimal electron transport, limiting their PSC applications. Here a solution-processable non-fullerene ETM, cyano-functionalized bithiophene imide dimer (CNI2)-based polymer (PCNI2-BTI), holds multiple advantages, including excellent photothermal stability, efficient electron transport and improved interaction with the perovskite layer. Consequently, inverted PSCs incorporating PCNI2-BTI deliver an outstanding power conversion efficiency (PCE) of 26.0% (certified 25.4%) and remarkable operational stability, with a T₈₀ approaching 1,300 h under ISOS-L-3. Moreover, we synthesize three additional CNI2-based polymer ETMs, yielding an average PCE of >25% in PSCs. These findings demonstrate unprecedented potential of non-fullerene ETMs enabling high-performance and stable PSCs.