Lamination-Compatible SnO₂/Reactive-Sputtered ITO/Ag Rear Contacts for Stable Perovskite Solar Cells

Lamination is a key encapsulation process for the practical deployment of perovskite solar cells, but the accompanying thermal and mechanical stress can damage fragile interfacial layers and rear metal contacts. In this work, conventional C60/BCP/Ag devices showed performance degradation after lamination, which was attributed to the thermal and mechanical vulnerability of the organic BCP interlayer. Replacing BCP with an inorganic SnO₂ buffer layer effectively suppressed lamination-induced performance loss and even improved the open-circuit voltage after lamination. However, SnO₂-based devices still suffered from poor long-term stability under harsh aging conditions, accompanied by rear-side discoloration following the metal electrode pattern. This behavior suggests electrode-associated metal–halide interdiffusion rather than uniform bulk perovskite degradation. To address this issue, a reactive-sputtered ITO interlayer was inserted between SnO₂ and the Ag electrode. Unlike conventional transparent electrodes, this buried ITO layer is designed to function as an electronic and ionic interlayer, where oxygen-vacancy control plays a critical role in Fermi-level tuning, electron-selective contact formation, and dense diffusion-barrier formation. Reactive sputtering in an oxygen-containing atmosphere is expected to reduce oxygen-vacancy concentration in ITO, modulating its carrier density and Fermi level while forming a denser layer that suppresses Ag diffusion. As a result, the SnO₂/reactive-sputtered ITO/Ag rear contact suppresses both lamination-induced initial degradation and long-term metal-electrode-related instability, providing a promising process strategy for high-performance and highly stable perovskite solar cells compatible with lamination-based encapsulation.