Journal Article photovoltaics perovskites X‐ray diffraction blue emissions buried interfaces crystal size density functional theory diffraction electron microscopy electrostriction halide perovskites heterojunction high efficiencies hysteresis imperfections ion migrations ionic movements low-dimensional luminescence microstructural reconstruction optical properties passivation perovskite perovskite light-emitting diodes perovskite photovoltaics perovskite solar cell photoinduced ion migration photoluminescence photosegregation