Solubilizing and stabilizing C<inf>60</inf> 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 (T95, light > 1,800 h; T80, heat = 700 h).