A Self-Adaptive Buffer Layer with Photoswitchable Responses for Durable Perovskite Photovoltaics

The long-term operational stability of perovskite solar cells (PSCs) remains a major barrier to commercialization due to interfacial ion migration and electrode-induced degradation under illumination and electrical bias. Here, we report a self-adaptive, photoswitchable inorganic buffer layer based on zinc sulfide (ZnS) that dynamically regulates interfacial charge transport while suppressing ion diffusion. Under illumination, light activation enhances the conductivity of ZnS and induces the formation of a ZnS/Cu_2-xS heterointerface, enabling adaptive interfacial reconstruction and efficient carrier extraction. When illumination ceases, ZnS returns to a relatively inert state, maintaining a physical and electric-field barrier against metal-halide interdiffusion. As a result, PSCs exhibit markedly improved durability, retaining over 97% of their initial power conversion efficiency after 7128 h of dark storage and 84.8% after 1632 h of continuous light soaking. The devices also show an enhanced tolerance to reverse-bias stress, establishing a self-regulated interfacial strategy for stable perovskite photovoltaics.