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 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 -based FPSCs. It is found that the Y6 buffer layer can enhance the ability of charge extraction and bending stability for SnO ETL. Moreover, the internal stress of perovskite films is also reduced. As a result, SnO /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 -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 ETL, as revealed by femtosecond transient absorption (Fs-TA) measurements.