Semi-Planar Non-Fullerene Molecules Enhance the Durability of Flexible Perovskite Solar Cells.

Flexible perovskite solar cells (FPSCs) represent a promising technology in the development of next-generation photovoltaic and optoelectronic devices. SnO 2 electron transport layers (ETL) typically undergo significant cracking during the bending process of FPSCs, which can significantly compromise their charge transport properties. Herein, the semi-planar non-fullerene acceptor molecule Y6 (BT-core-based fused-unit dithienothiophen [3,2-b]-pyrrolobenzothiadiazole derivative) is introduced as the buffer layer for SnO 2 -based FPSCs. It is found that the Y6 buffer layer can enhance the ability of charge extraction and bending stability for SnO 2 ETL. Moreover, the internal stress of perovskite films is also reduced. As a result, SnO 2 /Y6-based FPSCs achieved a power conversion efficiency (PCE) of 20.09% and retained over 80% of their initial efficiency after 1000 bending cycles at a curvature radius of 8 mm, while SnO 2 -based devices only retain 60% of their initial PCE (18.60%) upon the same bending cycles. In addition, the interfacial charge extraction is also effectively improved in conjunction with reduced defect density upon incorporation of Y6 on the SnO 2 ETL, as revealed by femtosecond transient absorption (Fs-TA) measurements.