Observation of photoreflectance spectra of MAPbBr3 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 MAPbBr3 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.