Thermal Evaporation of Overlayers Induces Degradation of Metal Halide Perovskites
Kanak Kanti Bhowmik, Danqing Ma, Brian Topper, Kelliann Koehler, Stephen H. Foulger, Hai Xiao, Lin Zhu, Lianfeng Zhao
Abstract
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.