Fig. 1: Comparison between before and after annealing.

a The atomic structures before and after annealing at 100 °C for 10 min. The as-received MAPbBr3 thin film showed MAPbBr and PbBr2 structures. However, the residual elements disappeared after annealing, b UV-visible absorption spectra before and after annealing. The optical bandgap is 2.23 eV in the annealed sample, and c, d Top-view SEM images before and after annealing. After annealing, the partially unfilled surface also disappeared.