Metal halide perovskites are exotic hybrid crystalline materials developed out of curiosity. Unexpectedly, solar cells and light-emitting diodes (LEDs) incorporating these perovskites are rapidly emerging as serious contenders to rival the leading technologies. Photovoltaic power conversion efficiencies have jumped from 3% to over 22% in just seven years of academic research, and we are witnessing a similarly astonishing pace in LEDs. Here, I will give an overview of some of our key photophysical findings to advance understanding of the optoelectronic behaviour of the perovskite materials and operation of the state-of-the-art devices. I will cover topics including charge carrier diffusion and recombination, as well as ion migration and its potential impact on device performance. I will identify avenues towards eliminating losses by focusing on the relationships between micro- and nano-scale optoelectronic, chemical and structural properties of these materials as neat films and in operating devices. Understanding these properties is key to further development of the field and to bringing the perovskite technology to commercialisation.