  Lead halide perovskites are a remarkable class of materials that have emerged
over the past decade as being suitable for application in a broad range of
devices, such as solar cells, light-emitting diodes, lasers, transistors, and
memory devices, among others. While they are often solution-processed
semiconductors deposited at low temperatures, perovskites exhibit properties
one would only expect from highly pure inorganic crystals that are grown at
high temperatures. This unique phenomenon has resulted in fast-paced progress
toward record device performance; unfortunately, the basic science behind the
remarkable nature of these materials is still not well understood. This review
assesses the current understanding of the photoluminescence (PL) properties of
metal halide perovskite materials and highlights key areas that require further
research. Furthermore, the need to standardize the methods for characterization
of PL in order to improve comparability, reliability and reproducibility of
results is emphasized.
