Red Perovskite Light‐Emitting Diodes with Efficiency Exceeding 25% Realized by Co‐Spacer Cations

Abstract Perovskite light-emitting diodes (PeLEDs) own great attention in recent years, due to their narrow emission bandwidth and tunable emission spectrum. Efficient red emission is one of most important part for lighting and display. Quasi-two-dimensional (quasi-2D) perovskite could deliver high emission efficiency due to the strong carrier confinement, while the external quantum efficiencies (EQE) of red quasi-2D PeLEDs are inefficient at present, which is due to the complex distribution of different n-value phases in quasi-2D perovskite films. Here, we finely control the phase distribution of the quasi-2D perovskite by mixing two different large organic cations, which effectively reduce the amount of smaller n index phases, meanwhile the passivation of lead and halide defects in perovskite films is realized. Accordingly, the PeLEDs showed 25.8% EQE and 1300 cd∙m-2 maximum brightness at 680 nm, which exhibit the highest performance for red PeLEDs up to now.