Correlating Halide Segregation with Iodide Oxidation via In-Situ Opto-Gravimetric Analysis

Halide oxidation plays an important role in halide segregation and degradation of metal halide perovskites. However, a direct and quantitative measurement of halide oxidation in solid-state perovskite samples is still required to fully understand and evaluate the effect of halide oxidation. In this work, we employed a quartz crystal microbalance to achieve an <i>in-situ</i> opto-gravimetric measurement of solid-state perovskite films and quantify the iodine loss rate under light excitation. Combining photoluminescence, X-ray photoelectron spectroscopy, X-ray diffraction, and <i>in-situ</i> opto-gravimetric measurements on a series of mixed-halide perovskite with different halide ratios, we are able to explain the degradation mechanism of mixed-halide perovskite under prolonged light illumination (photolysis of iodine), and demonstrate an identical compositional threshold for both light-induced halide segregation and iodide oxidation. These results not only reveal the correlation between light-indued halide segregation and iodide oxidation, which experimentally proves the photoelectrochemical origin of light-induced halide segregation, but also provide a powerful tool to quantitatively study halogen loss and degradation kinetics of metal halide perovskites.