30-Fold efficiency enhancement achieved in the perovskite light-emitting diodes

Abstract

Efficient cesium lead halide perovskite light-emitting diodes (PeLEDs) are demonstrated using nearly 100% coverage of CsPbBr₃ film as the emitter. The PeLEDs with only a pumping away process deposited from equimolar PbBr₂–CsBr exhibit more than 30 fold electroluminescent (EL) performance improvement compared to the ones with both pumping away and annealing processes. And to further improve the EL performance, the molar ratio of PbBr₂ to CsBr is optimized. CsBr-rich PeLEDs (PbBr₂ : CsBr = 1 : 1.2) show longer stability and better EL performance with maximum luminance of 5046 cd m⁻², maximum current efficiency of 3.25 cd A⁻¹, maximum external quantum efficiency (EQE) of 0.85%. The physical mechanism to the enhanced EL performance in the PeLEDs with only pumping away can be attributed to three factors: better coverage rate and smoother surface which reduce current leakage, smaller grain size which can spatially limit the diffusion length of excitons or charge carriers and decrease the possibility of exciton dissociation into carriers, and increased CsBr content of the perovskite precursor solution which may reduce the nonradiative defect densities.