Observation of photoreflectance spectra of MAPbBr\(_{3}\) single crystal

Abstract

We report the first observation of photoreflectance (PR) spectra in MAPbBr\(_{3}\) single crystals and systematically investigate their optical properties using photoluminescence (PL) and PR spectroscopies. High-quality MAPbBr\(_{3}\) single crystals were grown by the seed-induced inverse temperature crystallization method. Low-temperature PL measurements reveal four emission peaks at 2.09, 2.14, 2.17, and 2.20 eV. The 2.20 eV emission is attributed to free-exciton (FE) recombination, while the 2.14 and 2.17 eV peaks originate from bound-exciton (BE) recombination. The lowest-energy emission at 2.09 eV is associated with defect-related states in the orthorhombic phase. With increasing temperature, all PL emissions exhibit a blueshift, which is attributed to a thermally induced structural phase transition from the orthorhombic to the tetragonal phase occurring near 140 K. Consistent with the PL results, low-temperature PR measurements show a transition at 2.20 eV, corresponding to the FE-related band-to-band transition. The PR transition energy exhibits a blueshift with increasing temperature from 24 to 140 K, followed by a redshift between 140 and 180 K, reflecting the orthorhombic-to-tetragonal phase transition. Electron–phonon interactions primarily govern the temperature-dependent energy shifts observed in both PL and PR spectra. Notably, the transition energies obtained from PR are higher than those from PL, which is attributed to the surface-sensitive band-to-band transitions probed by PR. The excellent agreement between PL and PR results confirms the reliability of the PR measurements and provides a comprehensive understanding of the excitonic and band-edge properties of MAPbBr\(_{3}\) single crystals.