Studying the Effects of Voltage on Degradation Pathways in Perovskite Solar Cells

Silicon solar cells currently dominate the photovoltaic market; however, they are already approaching their thermodynamic performance limit. By pairing halide perovskites with silicon in a tandem solar cell, or using halide perovskite tandems, the thermodynamic limit can be raised from 33% up to 45%. The key technological hurdle to realize these higher performance solar cells is material stability in real-world solar cell operation. Halide perovskites consist of an ABX₃ crystal structure, where the A (1⁺ cation), B (2⁺ metal cation), and X-site (halide) components are manipulated to obtain desired properties. In this work, CsPbI₃ was used as a model halide perovskite for a variety of experiments to better understand the phase change that are common across many halide perovskite compositions. Material stability is challenging, as there are many degradation pathways, including pathways involving multiple stressors. Due to the ionic nature of the constituent species, voltage was used to promote ion migration and observe the phase change from CsPbI₃ perovskite to the nonperovskite phase. These experiments were run in a controlled environment to isolate the materials from external stressors, such as humidity, and the phase transition was imaged in real-time using optical microscopy. Additional factors, such as heat and voltage were added to the system to track how their presence influenced the rate at which the samples changed from the dark perovskite phase to the light non-perovskite phase. This work provides a step toward a better understanding of voltage-driven and mixed degradation modes in halide perovskites that are critical to real-world stability.