The role of the organic cation in developing efficient green perovskite LEDs based on quasi‐2D perovskite heterostructures

Two dimensional/three-dimensional (2D/3D) metal halide perovskite heterostructures have attracted great interest in photovoltaic and light-emitting diode (LEDs) applications. In both, their implementation results in an improvement in device efficiency yet the understanding of these heterostructures remains incomplete. In this work the role of organic cations, essential for the formation of 2D perovskite structures is unraveled, in a range of metal halide perovskite heterostructures. These heterostructures are used to fabricate efficient green perovskite LEDs and a strong dependence between cation content and device performance is shown. The crystal structure, charge-carrier transport and dynamics, and the electronic structure of these heterostructures are studied and it is shown that the presence of crystalline 2D perovskite inhibits electron injection and ultimately lowers device performance. This work highlights the importance of optimizing the composition of these heterostructures in ensuring optimal device performance across all parameters and suggests that developing routes to inject charge-carriers directly into 2D perovskite structures will be important in ensuring the continued development of perovskite LEDs based on these heterostructures.