Design of fullerene-based interface passivation coatings for n-i-p perovskite solar cells: Addend size matters!

Perovskite solar cells (PSCs) have gained much attention because of their impressive power conversion efficiency (PCE) of up to 25.5%. Currently, low-temperature-processed SnO2 thin films are widely used as the ETLs to achieve efficient and stable planar PSCs. Surface passivation of SnO2 as electron transport layer (ETL) by fullerene derivatives is known as one of the ways to enhance the performance of n–i–p devices. Herein, we report a synthesis of new fullerene derivatives with hydroxyl and carboxyl functional groups, which are expected to contribute to more efficient modification of SnO2 surface. A comparative study of five fullerene derivatives as passivation layers allowed to establish the correlation between the molecular formula and performance of PSCs. Moreover, optimized passivation interlayers of monocyclopropanated fullerene derivative with carboxylic group improved the efficiency of perovskite solar cells in compare with conventional PCBA from 17.0% to 19.5%. This study highlights the key role of molecular design in passivation of SnO2 for pursuing high performance PSCs with n-i-p configuration.