Mechanisms of Ultraviolet-Induced Degradation in Perovskite Solar Cells: Insights from Microscopic Analysis

In recent years, tandem devices combining low-bandgap (LBG) and wide-bandgap (WBG) perovskite solar cells (PSCs) have emerged as a promising approach in photovoltaic research. However, the issue of stability remains a significant hurdle for perovskite commercialization, with ultraviolet (UV)-induced degradation being one of the important branches. It is well established that UV light causes degradation in PSCs, but the microscopic mechanisms behind this degradation remain unclear. This gap in understanding poses a major challenge to the commercial viability of perovskite-based tandem solar cells. This work illustrates the mechanisms of UV-induced degradation in WBG PSCs and LBG PSCs by correlating cell performance with microscopic electrical and mechanical properties. UV light compromises the conductive pathways and the rise in leakage current especially in the grain boundaries of WBG perovskite films. UV light leads to the formation of halide ion defects in WBG films, resulting in uneven potential distribution, and the breakage of Br-Pb bonds causes a significant decrease in Young's modulus at grain boundaries. In contrast, LBG films do not exhibit the above changes. However, degradation is particularly evident when UV light is incident from the Indium Tin Oxide (ITO) side, primarily affecting the open-circuit voltage (VOC) and Young's modulus. These results indicated stabilizing the light-facing interface or reinforcing the near-surface region of PSCs is a key aspect in suppressing UV degradation.