Enhancing electron transport via graphene quantum dot/SnO2 composites for efficient and durable flexible perovskite photovoltaics

Recent advances in flexible perovskite solar cells (PSCs) have attracted considerable attention owing to their great potential for bendable and wearable electronic devices. In particular, developing high-quality low-temperature processed electron transport layers (ETLs) plays a pivotal role in realizing highly efficient flexible PSCs. Herein, we develop a facile strategy to fabricate graphene quantum dot/SnO2 composites (G@SnO2) as effective ETLs. Systematic optimization and investigation reveal that SnO2 blended with graphene quantum dots with ca. 5 nm diameter (G5@SnO2) has higher electron mobility, better film coverage and better energy level alignment compared to pristine SnO2, leading to promoted charge transfer and suppressed charge recombination. PSCs based on G5@SnO2 demonstrate superior photovoltaic performance with a champion power conversion efficiency (PCE) of 19.6% and average PCE of 19.0%. Amazingly, the G5@SnO2 based flexible PSCs obtain a best PCE and stabilized PCE of 17.7% and 17.2%, respectively, comparable to the highest PCEs recorded for flexible devices. Moreover, our flexible PSCs demonstrate outstanding mechanical durability, retaining over 91% of the initial PCE value after 500 bending cycles with a bending radius of 7 mm.