Influence of Atmospheric Constituents on Spectral Instability and Defect-Mediated Carrier Recombination in Hybrid Perovskite Nanoplatelets

Excellent optoelectronic properties make organometallic halide perovskites (OHPs) promising materials for solar photovoltaics and light-emitting devices, however, degradation under various atmospheric conditions severely restricts their potential. To realize stable OHP nanocrystals (NCs) and films resistant to adverse environmental effects, it is imperative to characterize defects created by interactions with surrounding gases and their influence on carrier recombination. Here, we investigate temporal instability of photoluminescence (PL) spectra of individual methylammonium lead bromide (MAPbBr3) nanoplatelets (NPs) under sequential changes of the ambience. In contrast to studies on PL intermittency (blinking) of OHP NCs, spectral trajectories allow us to monitor fluctuations in both PL intensity and transition energy of each NPs in different atmospheres, as well as obtain diversity in nature of active traps under each environmental condition. Analyses of single-NP spectral trajectories in air, Ar, and O2 under varied moisture contents reveal that exposure to light in dry inert conditions induce deep nonradiative traps in OHP crystals. In contrast, O2 and moisture mediates efficient radiative recombination via relatively deep and shallow defects, respectively. While the PL features of NPs do switch reversibly between Ar and O2 (or moist Ar), interaction with moist oxygen under illumination leads to rapid irreversible spectral changes culminating in permanent material degradation. Interestingly, however, removal of moisture from inert (Ar) environments often restores PL spectral features to those observed under dry conditions. This demonstrates that neither oxygen nor moisture individually affects the optical properties of OHP materials as adversely as a combination of the two, which should therefore be avoided to enhance the stability of OHP-based devices.