We utilized time-resolved photoluminescence (PL) spectroscopy to investigate the photocarrier recombination dynamics in CH3NH3PbI3 thin films as a function of the time elapsed from the film's fabrication. We found that the PL lifetime gradually increased and began to level out once the age of the film reached ∼30 h. Even under weak excitation, the PL dynamics depended on the excitation intensity in the fresh sample, while the mature sample displayed no excitation-intensity dependence associated with the PL dynamics. We submit that this can be explained by the fact that a significant number of defects are initially formed in CH3NH3PbI3 thin films fabricated by the sequential method and are spontaneously reduced by room-temperature annealing. Our results provide important insights for reducing the nonradiative recombination centers, which improves the power conversion efficiency of perovskite solar cells.
Keywords: carrier trapping; nonradiative recombination; optical characterization; photocarrier lifetime; photovoltaics.