Inter-band and mid-gap luminescence in CH3NH3PbBr3 single crystal

Abstract

Photoluminescence is informative to other optoelectronic processes that are less directly accessible in metal halide perovskites. In this study, we conducted optical studies on CH3NH3PbBr3 single crystals with robust cubic lattices and atomically flat surfaces. Inter-band luminescence peaking aside from the absorption cutoff was observed, and its shifts toward shorter wavelength upon cooling. Cooling the crystal below 150 K leads to the occurrence of mid-gap luminescence partly at the expense of the inter-band luminescence, which indicates bulk photoluminescence quenching by trap-mediated electronic trapping and subsequent mid-gap radiation following electronic de-trapping. Time-resolved photoluminescence probed at the mid-gap luminescence maxima shows two-stage mono-exponential traces, directly corroborating the trapping and de-trapping processes. In the presence of mid-gap luminescence at low temperatures, time-resolved inter-band luminescence demonstrates triplet decaying pathways, in sharp contrast to the doublet decaying pathways at higher temperatures in the absence of mid-gap luminescence. Time- and temperature-resolved inter-band photoluminescence gave rise to a characteristic photocarrier lifetimes evolution against temperature in a close analogy to the material's dielectric constant.