Suppressing Thermal Evaporation-Induced Iodine Outgassing and Interfacial Degradation in Perovskite Solar Cells

Abstract

Vacuum thermal evaporation is widely used to deposit buffer layers and metal electrodes in perovskite solar cells, but the associated thermal radiation can damage the perovskite surface before the device stack is completed. Here we show that, under practical evaporation conditions, this hidden process stress drives near-surface degradation at the perovskite interface, leading to grain-boundary-localized morphological weakening and a shift in surface energetics toward a higher-work-function, more electron-deficient near-surface state. By integrating an Ag-mesh trapping experiment with X-ray photoelectron spectroscopy, we directly verify iodine outgassing from irradiated films. An L-ascorbic acid (LAA) surface treatment suppresses iodine volatilization, largely preserves the surface energetic landscape, and mitigates the associated solar cell degradation. These results move beyond simply recognizing evaporation-induced damage by identifying a chemically addressable interface-degradation mechanism and a practical strategy for protecting scalable perovskite solar cell fabrication.