Multi‐Stage Phase‐Segregation of Mixed Halide Perovskites under Illumination: A Quantitative Comparison of Experimental Observations and Thermodynamic Models

Photo- and charge-carrier-induced ion migration is a major challenge when utilizing metal halide perovskite semiconductors for optoelectronic applications. For mixed iodide/bromide perovskites, the compositional instability due to light- or electrical bias induced phase-segregation restricts exploitation of entire bandgap range. Previous experimental theoretical work suggests that excited states charge carriers trigger process, but exact mechanism still under debate. To identify cause light-induced phenomena, full range methylammonium lead bromide/iodide samples are investigated, MAPb(BrxI1-x)3 with x = 0…1, by simultaneous in situ X-ray diffraction (XRD) photoluminescence (PL) spectroscopy during illumination. The quantitative comparison composition-dependent XRD PL shows at excitation densities 1 sun, only initial stage photo-segregation rationalized previously established thermodynamic models. However, progression phase segregation observed considering long-lived accumulative photo-induced material alterations. It suggested (additional) defects, possibly vacancies interstitials, need be considered fully rationalize anticipate findings provide crucial insight development more sophisticated