Blue light-emitting diodes based on quasi-two-dimensional perovskite with efficient charge injection and optimized phase distribution via an alkali metal salt

Perovskite light-emitting diodes are of potential use in the development of colour displays and solid-state lighting. This requires high-performance blue perovskite emission. However, quasi-two-dimensional blue perovskite light-emitting diodes exhibit lower performance than green- and red-emitting devices due to poor charge injection between the hole injection layers and perovskite film, high amounts of non-radiative recombination and random phase distribution. Here we show that the addition of an alkali metal salt (caesium chloride) to a hole injection layer (poly(3,4-ethylenedioxythiophene) polystyrene sulfonate) can improve carrier transport in the injection layer and create better band alignment for increased charge injection efficiency. The growth of perovskite layers on the caesium-chloride-incorporated substrates also causes a rearrangement of their phase distribution, which leads to lower non-radiative recombinations and enhanced charge transport. With this approach, we create sky-blue quasi-two-dimensional perovskite light-emitting diodes with an emission peak located at 486 nm, a peak external quantum efficiency of 16.07% and encouraging operational stability.