Elemental segregation and dimensional separation in halide perovskite light-emitting diodes

Compositional engineering is a promising avenue for enhancing external quantum efficiency and adjusting emission wavelengths in halide perovskite light-emitting diodes (PeLEDs). However, the occurrence of ion migration within these materials poses a notable challenge as it can lead to elemental segregation during crystallization or under external stimuli such as heat, light, and bias, especially when simple mixing and alloying are employed. Such non-uniform distribution of elements detrimentally impacts color purity and long-term device stability in PeLEDs, highlighting the need to address elemental segregation issues. Additionally, quasi-2D perovskites have garnered attention for their potential to mitigate ion migration while maintaining superior optoelectronic properties attributable to the quantum confinement effect. Nevertheless, precise control over dimensionality remains challenging due to the thermodynamically favored 2D/3D phase separation, hindering efficient energy transfer. This review aims to provide an in-depth analysis of these phenomena. It explores the underlying mechanisms of elemental segregation and dimensionality separation, while summarizing recent efforts to overcome these challenges. Furthermore, the review discusses ongoing obstacles and suggests potential directions for future research in this evolving field.