Mixed halide perovskites are materials with great potential in photovoltaics. In this work, we aim to describe halide segregation in perovskites under illumination. Using in-situ measurements of  X-ray diffraction and reciprocal space mapping we investigate the distribution of halide concentrations within perovskite single crystals and thin layers. We observe fast segregation under illumination and subsequent slower and only partial relaxation in darkness.

In this talk I will introduce our methodology, show results measured on several samples, and discuss our results in context of different studies of the same effects.