Free Exciton and Defect-Related States in CH₃NH₃PbCl₃ Perovskite Single Crystal

Chloride perovskites are promising semiconductor materials for creating optoelectronic devices in the near-ultraviolet range. The study of defect-related states is essential for future improvements in device performance. This article presents an investigation of the photoluminescence, photoluminescence excitation, and reflectivity of MAPbCl(3) (MA(+) = CH3NH (+)(3)) halide perovskite single crystals at the low-temperature orthorhombic phase in the T = 4-174 K temperature range. The position of the free exciton was determined, and defect-related states, which appeared as equally polarized narrow emission lines up to 100 K, were analyzed in detail. The assumption that these states were phonon replicas was ruled out using photoluminescence excitation spectroscopy, and it was concluded that these narrow lines correspond to the emission of actual defect-related states that absorb light. This study provides new insights into the nature of defect-related states in perovskite single crystals, which could have important implications for the development of more efficient optoelectronic devices.