Ameliorating the Interfacial Mismatch of SnO₂ and Perovskite Enabling High Mechanical Stability for Flexible Perovskite Solar Cells

SnO2 has been a widely used electron transport layer, due to its high electron mobility and stable chemical properties in n-i-p type perovskite solar cells (PSCs). However, the interfacial mismatch, especially on the residual strain and the different mechanical properties between SnO2 and perovskite films, leads to an obvious decrease in power conversion efficiency (PCE) and flexibility in the SnO2-based PSCs. This limitation has severely hindered the large-scale implementation of flexible PSCs. Herein, polydopamine is introduced in SnO2 as "depletion intermediary", which significantly improves the interfacial contact and mitigates the inherent brittleness of SnO2 film. The obtained PSCs have achieved a PCE of 22.70% and 21.04% based on the rigid and flexible devices, respectively. Most importantly, the flexibility has been largely improved, that after 3000 bending cycles with a 5 mm bending radius, approximately 87% of its original efficiency has been retained.