Enhanced Charge Balance for Efficient Electroluminescence from Cesium Copper Halides

Cesiumcopper halides have the advantages of high photoluminescencequantum efficiency and good stability, making them attractive forreplacing toxic lead halides in the field of perovskite light-emittingdiodes (LEDs). However, due to their shallow conduction band and thelack of electron transport layers compatible with it, it remains agreat challenge to achieve charge balance in LED devices. This drawbackmanifests as the accumulation of holes at the interface between theemitting layer and electron transport layer, resulting in nonradiativerecombination. Here, we demonstrate an effective approach to addressthis issue by suppressing hole injection, which is realized throughmodification of the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)layer with polyethylenimine. This leads to cesium-copper-halideLEDs with a high external quantum efficiency of 5.6%, representingan advance in device architecture for efficient electroluminescencefrom cesium copper halides.