Electron–Phonon-Mediated Temperature-Dependent Optical Bandgap of MAPbClxBr3–x Single Crystals

Methylammonium-lead-halide compounds have emerged as promising bandgap engineering materials due to their ability to fine-tune the energy gap through halogen element mixing. We present a comprehensive investigation of the temperature-dependent photoluminescence (PL) transition characteristics exhibited by single crystals of chlorine- and bromine-based methylammonium lead halides. MAPbCl3 and MAPbBr3 crystals exhibit a distinct, sharp, free exciton transition with an abrupt transition behavior associated with the structural phase transition as the temperature varies. However, when the two halogen elements are mixed within the crystals, no structural phase transition is observed. This study explores the temperature-dependent variations in integrated PL intensity, full width at half-maximum, and peak transition energy of the crystals. The obtained results discuss the intricate interplay between temperature, crystal structure, and composition, providing valuable insights into the optical properties and potential applications of organic–inorganic hybrid methylammonium lead halide single crystals as tunable energy gap semiconductor materials.