The thermal stability of FAPbBr nanocrystals from temperature-dependent photoluminescence and first-principles calculations.

The temperature dependence of FAPbBr perovskite nanocrystals (PNCs) is investigated experimentally by steady-state and time-resolved photoluminescence (PL) spectroscopies. With the temperature increase, photon energies of line width and emission peak become larger due to stronger exciton-phonon coupling. Furthermore, theoretical calculations of first-principles simulations are used to estimate comparatively the thermal stability of typical FAPbBr PNCs. It is found that the PL peaks of PNCs slightly change with increasing temperature below 175 K and then blueshift steeply decreases rapidly till 400 K, which is related to phase transition from orthorhombic to tetragonal and cubic phase. The simulated results show the PL and the crystal structure of FAPbBr are largely dependent on the temperature. With higher temperature, the photon energy of the PL peak becomes larger, and the calculated band gap of FAPbBr is about 2.15 eV at 80 K, which is in good agreement with the experimental results. It is confirmed that temperature-dependent PL is composed of a band-edge exciton state and trapping state emission. The results obtained will be of certain significance to further expand other hybrid organometal perovskite materials.