Halide perovskite light emitting diodes (LEDs) have gained great progress in recent years. However, mixed-halide perovskites for blue LEDs usually suffer from electroluminescence (EL) spectra shift at a high applied voltage or current density, limiting their efficiency. In this work, we report a strategy of using single-layer perovskite quantum dots (QDs) film to tackle the electroluminescence spectra shift in pure-blue perovskite LEDs and improve the LED efficiency by co-doping copper and potassium in the mixed-halide perovskite QDs. As a result, we obtained pure-blue halide perovskite QD-LEDs with stable EL spectra centred at 469 nm even at a current density of 1,617 mA·cm⁻². The optimal device presents a maximum external quantum efficiency (EQE) of 2.0%. The average maximum EQE and luminance of the LEDs are 1.49% and 393 cd·m⁻², increasing 62% and 66% compared with the control LEDs. Our study provides an effective strategy for achieving spectra-stable and highly efficient pure-blue perovskite LEDs.

We report the formation of high-quality Cs_0.4MA_0.6PbBr₃ thin films with nearly full surface coverage and good emission properties upon the introduction of Cs⁺ into perovskite crystals. The Cs_0.4MA_0.6PbBr₃ thin films were applied as emissive layers in light-emitting diodes. A maximum external quantum efficiency of ~2.0% was achieved for these green-emitting devices.