Role of excitons in light emission properties of thermally evaporated $CH_{3}NH_{3}PbBr_{3}$ perovskite.

Metal halide perovskite semiconductors have attracted great attention for their outstanding properties, enabling their application as active materials in optoelectronic devices. For perovskites, the spontaneous emission is ruled by competitive mechanisms that affect the spectral features of the optical emission, namely free-carrier recombination, excitons (EXs) and trap states. This contribution investigates the role of light-emitting species in the spontaneous and stimulated emission of thermally evaporated thin layers of $CH_{3}NH_{3}PbBr_{3}$ perovskite after wet air UV light trap passivation. The EXs are identified as the main actors in the spontaneous emission process. The sample morphology strongly affects their emission properties and gives rise to a spatially inhomogeneous photoluminescence (PL), both in terms of intensity and wavelength of emission, with free and localized EXs involved to a different extent depending on the local morphological features. Amplified spontaneous emission (ASE) measurements confirm the excitonic nature of emitting species. The constant PL background is attributed to the localized EXs, while the ASE signal is due to stimulated emission from the free EXs.