This study investigates the impact of repeated thermal evaporation processes on the performance of perovskite-based solar cells, specifically focusing on the role of C60 as the electron transport layer (ETL). The researchers found that commercial C60 source materials can coalesce during repeated evaporation, leading to the formation of deep states within the perovskite bandgap and a systematic decrease in solar cell performance. To address this issue, they purified the C60 through sublimation to 99.95% purity before evaporation, which significantly reduced coalescence and improved device reproducibility. The sublimed C60 maintained consistent device performance over multiple deposition cycles, even in perovskite/silicon tandem solar cells, achieving a certified power conversion efficiency of 30.9%. The findings highlight the importance of material purification in achieving high yield and reproducibility in the industrial production of perovskite-based solar cells.This study investigates the impact of repeated thermal evaporation processes on the performance of perovskite-based solar cells, specifically focusing on the role of C60 as the electron transport layer (ETL). The researchers found that commercial C60 source materials can coalesce during repeated evaporation, leading to the formation of deep states within the perovskite bandgap and a systematic decrease in solar cell performance. To address this issue, they purified the C60 through sublimation to 99.95% purity before evaporation, which significantly reduced coalescence and improved device reproducibility. The sublimed C60 maintained consistent device performance over multiple deposition cycles, even in perovskite/silicon tandem solar cells, achieving a certified power conversion efficiency of 30.9%. The findings highlight the importance of material purification in achieving high yield and reproducibility in the industrial production of perovskite-based solar cells.