Systematic approach to the study of the photoluminescence of MAPbI3

In this work, we perform steady-state, continuous wave (cw), photoluminescence (PL) measurements on $\mathrm{MAPb}{\mathrm{I}}_{3}$ thin films in the temperature range of 10--160 K, using excitation densities spanning over almost seven orders of magnitude, in particular investigating very low densities that are rarely used in the published literature. The temperature range used in this study is below or at the edge of the orthorhombic-tetragonal phase transition in $\mathrm{MAPb}{\mathrm{I}}_{3}$. In particular, we show that even in high-quality $\mathrm{MAPb}{\mathrm{I}}_{3}$, capable of providing high photovoltaic efficiency, the defect density is high enough to give rise to an energy level band. Furthermore, we show that the intensity ratio between the two PL components related to the two crystalline phases is a function of temperature and excitation density. At high excitation intensities, we show that amplified spontaneous emission is attainable even in cw conditions. Time-resolved PL is also performed to justify the assignments of the PL features. Finally, our systematic approach, typical for the characterization of semiconductors, suggests that it should also be applied to hybrid halide perovskites and that, under suitable conditions, the PL characteristics of $\mathrm{MAPb}{\mathrm{I}}_{3}$ can be reconciled with those of conventional inorganic semiconductors.