Metal halide perovskites have emerged as next-generation semiconductors for light emission, owing to their bright luminescence, excellent charge-transport properties, ease of processing and tunable bandgap. In less than a decade, the external quantum efficiency of perovskite light-emitting diodes (PeLEDs) has increased rapidly to over 25%, which is comparable with that of organic LEDs. The behaviour of PeLEDs is determined by the device processes including charge injection and transport, recombination and light extraction. Understanding the physics governing these processes is significant for controlling the performance of PeLEDs.

This thesis focuses on the photonic and electronic device physics that controls the performance of PeLEDs. In the first study, we identify that non-radiative losses in bulk perovskites and interfaces reduce the performance of PeLEDs. To address this, we design a novel multifunctional molecular additive to control the optoelectronic, structural and morphological properties of perovskite films. This approach efficiently suppresses non-radiative loss pathways in bulk perovskite films and interfaces in the devices, thus achieving improved device performance. However, the efficiency of PeLEDs is severely limited by light extraction. We then discuss light extraction losses in different models by considering the photon recycling effect. Based on this understanding, we develop a strategy to improve light outcoupling in PeLEDs by enhancing the photon recycling in perovskites. In the last study, we identify that the unique device characteristics of PeLEDs necessitates a more profound understanding of their device physics. We then develop an archetypical device structure and employ drift-diffusion modelling to explore the working principles and unique device physics of PeLEDs.