| Summary: | High efficiency perovskite light-emitting diodes (PeLEDs) using PEDOT:PSS/MoO<sub>3</sub>-ammonia composite hole transport layers (HTLs) with different MoO<sub>3</sub>-ammonia ratios were prepared and characterized. For PeLEDs with one-step spin-coated CH<sub>3</sub>NH<sub>3</sub>PbBr<sub>3</sub> emitter, an optimal MoO<sub>3</sub>-ammonia volume ratio (0.02) in PEDOT:PSS/MoO<sub>3</sub>-ammonia composite HTL presented a maximum luminance of 1082 cd/m<sup>2</sup> and maximum current efficiency of 0.7 cd/A, which are 82% and 94% higher than those of the control device using pure PEDOT:PSS HTL respectively. It can be explained by that the optimized amount of MoO<sub>3</sub>-ammonia in the composite HTLs cannot only facilitate hole injection into CH<sub>3</sub>NH<sub>3</sub>PbBr<sub>3</sub> through reducing the contact barrier, but also suppress the exciton quenching at the HTL/CH<sub>3</sub>NH<sub>3</sub>PbBr<sub>3</sub> interface. Three-step spin coating method was further used to obtain uniform and dense CH<sub>3</sub>NH<sub>3</sub>PbBr<sub>3</sub> films, which lead to a maximum luminance of 5044 cd/m<sup>2</sup> and maximum current efficiency of 3.12 cd/A, showing enhancement of 750% and 767% compared with the control device respectively. The significantly improved efficiency of PeLEDs using three-step spin-coated CH<sub>3</sub>NH<sub>3</sub>PbBr<sub>3</sub> film and an optimum PEDOT:PSS/MoO<sub>3</sub>-ammonia composite HTL can be explained by the enhanced carrier recombination through better hole injection and film morphology optimization, as well as the reduced exciton quenching at HTL/CH<sub>3</sub>NH<sub>3</sub>PbBr<sub>3</sub> interface. These results present a promising strategy for the device engineering of high efficiency PeLEDs.
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