Elucidating the phase transitions and temperature-dependent photoluminescence of MAPbBr3 single crystal

We investigated the fundamental properties of MAPbBr3 single crystal by applying temperature-dependent x-ray diffraction and photoluminescence (PL) measurements from 10 K to 270 K. The structural and spectral analyses illustrate the phase transitions of MAPbBr3 single crystal from cubic phase (-MAPbBr3) to tetragonal phases (-MAPbBr3 and -MAPbBr3), and then to orthorhombic phase (-MAPbBr3) at ~230 K, ~160 K and ~150 K, respectively. The Time-resolved PL results show that both free excitons (FE) and bound excitons (BE) have contributions to the PL emissions. The PL at high temperature mainly originates from the BE transitions, while the PL at low temperature (-MAPbBr3 phase) comes from both BE and FE transitions, and the FE related PL becomes more and more dominant at lower temperatures. The first-principle calculation at zero temperature reveals that the BE-related PL was caused by defects from the anti-site substitution of MA and Br ions.