Thermal Evaporation of Overlayers Induces Degradation of Metal Halide Perovskites

Metal halide perovskites offer significant potential for optoelectronics but face stability challenges. This study demonstrates that vacuum thermal evaporation, a standard technique for depositing overlayers like charge transport layers (CTLs) and metal electrodes during device fabrication, induces a detrimental degradation mechanism in the underlying perovskite film. Photoluminescence (PL) lifetime measurements show consistent degradation for various perovskite compositions subjected to thermal evaporation. X-ray photoelectron spectroscopy (XPS) analysis identifies irreversible chemical changes at the perovskite surface, including iodide loss and altered bonding environments. We show that incidental thermal radiation and the high-vacuum conditions inherent to thermal evaporation are the major factors inducing the degradation. This process-induced damage negatively impacts device-relevant properties, demonstrated by a higher amplified spontaneous emission (ASE) threshold in full diode structures with thermally evaporated CTLs compared to those with a solution-processed CTL. These findings highlight the critical impact of manufacturing process selection on perovskite stability and performance, necessitating careful evaluation of process compatibility for developing robust devices.