Charge relaxation associated with photon-induced deactivation of various traps in MAPbI3 films

Abstract

Photon-induced deactivation of traps in MAPbI3 can strongly affect charge relaxation behavior. Charge relaxation associated with photo-induced deactivation of various traps in MAPbI3 films was investigated through steady-state and time-resolved photoluminescence (PL) spectroscopy under laser excitation at 635 and 430 nm to investigate the properties of the traps. Three types of traps that could be deactivated by photons were observed in the MAPbI3 films, namely TL, TH, and TGB. TL and TH, which were related to MAPbI3 bulk, had low and high photon energy thresholds (red and blue photons) for deactivation, respectively. TGB was related to the traps at grain boundaries in MAPbI3 and had a low photon energy threshold (red photons) for deactivation. The energy level of TGB was higher than that of the conduction band of MAPbI3. Under blue excitation, TGB mediated a fast nonradiative recombination at few nanoseconds, and TL and TH mediated a slow nonradiative recombination at few 100 ns. The fast nonradiative recombination led to a significantly low initial normalized photoluminescence quantum yield (PLQY) (1/22) under blue excitation, compared with that obtained under red excitation (1/4). The deactivation of TL and TH resulted in increases in both the amplitude of PL and recombination time. The deactivation of TGB resulted only in a significant increase in PLQY of blue excitation.