Solubilizing and stabilizing C₆₀ with n-type polymer enables efficient inverted perovskite solar cells

Pristine fullerene C₆₀ is currently the best-performing electron transport layer (ETL) for perovskite solar cells (PSCs) but suffers from significant aggregation in solution. Consequently, the high-cost and complex thermal evaporation method is typically used to deposit high-quality C₆₀ ETLs. To address this challenge, we introduce an n-type polymeric additive that can solubilize and stabilize C₆₀ molecules for solution processing, leading to efficient and stable solution-processed-C₆₀ (SP-C₆₀) ETLs. The achievement is attributed to the well-matched properties of the n-type polymer and the precisely controlled intermolecular interactions between the polymer and C₆₀. As a result, the SP-C₆₀ ETL with 5-wt % polymer addition afforded a champion power conversion efficiency of 25.60% (certified 25.09%). This is not only the highest performance among the current SP-C₆₀ devices but also highly competitive to the state-of-the-art thermally evaporated C₆₀ devices. Importantly, the champion device showed significantly enhanced stability (T_{95, light} > 1,800 h; T_{80, heat} = 700 h).