Amplified spontaneous emission dependence on temperature-induced crystalline phase transition in a solution processed MAPbBr3 thin film

Abstract

Hybrid metal–halide perovskites are attracting huge research interest for possible applications in optoelectronic and photonic devices. In particular, the demonstration of optical gain and amplified spontaneous emission (ASE) at room temperature stimulates their development as active materials in light amplifiers and lasers. However, understanding of the basic photophysics of the processes affecting the ASE properties to date is still limited. In this work, we report a systematic investigation of the temperature dependence of the ASE and the photoluminescence (PL) of an MAPbBr₃ thin film in the 20–300 K range. We confirm that the ASE threshold is strongly temperature dependent, due to the thermal activation of non-radiative processes. In addition, the ASE temperature dependence shows clear discontinuities at around 90 K and 190 K, related to the orthorhombic–tetragonal and tetragonal–cubic phase transitions, respectively. The film spontaneous emission under nanosecond and continuous wave pumping shows the interplay of emission of Free Excitons (FEs), Bound Excitons (BEs), and trap states, with relative contributions depending on the temperature and the excitation regime. Our findings result in a detailed description of the energy states generating the ASE and the ASE properties of the different crystalline phases.