Bowl-Assisted Ball Assembly for Solvent-Processing the C₆₀ Electron Transport Layer of High-Performance Inverted...

Pristine fullerene C₆₀ is an excellent electron transport material for state-of-the-art inverted structure perovskite solar cells (PSCs), but its low solubility leaves thermal evaporation as the only method for depositing it into a high-quality electron transport layer (ETL). To address this problem, we herein introduce a highly soluble bowl-shaped additive, corannulene, to assist in C₆₀ -assembly into a smooth and compact film through the favorable bowl-ball interaction. Our results show that not only corannulene can dramatically enhance the film formability of C₆₀ , it also plays a critical role in forming C₆₀ -corannulene (CC) supramolecular species and in boosting intermolecular electron transport dynamics in the ETL. This strategy has allowed CC devices to deliver high power conversion efficiencies up to 21.69 %, which is the highest value among the PSCs based on the solution-processed-C₆₀ (SP-C₆₀ ) ETL. Moreover, the stability of the CC device is far superior to that of the C₆₀ -only device because corannulene can retard and curb the spontaneous aggregation of C₆₀ . This work establishes the bowl-assisted ball assembly strategy for developing low-cost and efficient SP-C₆₀ ETLs with high promise for fully-SP PSCs.