A method towards 100% internal quantum efficiency for all-inorganic cesium halide perovskite light-emitting diodes

An efficient all-inorganic cesium halide perovskite light-emitting diode (PeLED) was demonstrated by utilizing a mixed perovskite film of CsPbBr3:4,5-di (9H-carbazol-9-yl) phthalonitrile (2CzPN) as the light-emitting layer, where 2CzPN was a thermally activated delayed fluorescence (TADF) material with very high internal quantum efficiency approaching to 100%. This PeLED exhibited improved EL performance with the maximum luminance of 22,063 cd/m(2), highest current efficiency of 8.74 cd/A and best EQE of 2.26%, which were 3.42, 4.33 and 4.35 times to that of neat CsPbBr3 film based PeLED, respectively. The enhanced EL performance was enabled by utilization of TADF molecule as the assistant dopant that permitted efficient Forster energy transfer of all electrically generated excitons from the assistant dopant to the excited state of the perovskite emitter.