Improved Efficiency of Perovskite Light-Emitting Diodes Using a Three-Step Spin-Coated CHNHPbBr Emitter and a PEDOT:PSS/MoO-Ammonia Composite Hole Transport Layer.

High efficiency perovskite light-emitting diodes (PeLEDs) using PEDOT:PSS/MoO-ammonia composite hole transport layers (HTLs) with different MoO-ammonia ratios were prepared and characterized. For PeLEDs with one-step spin-coated CHNHPbBr emitter, an optimal MoO-ammonia volume ratio (0.02) in PEDOT:PSS/MoO-ammonia composite HTL presented a maximum luminance of 1082 cd/m 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-ammonia in the composite HTLs cannot only facilitate hole injection into CHNHPbBr through reducing the contact barrier, but also suppress the exciton quenching at the HTL/CHNHPbBr interface. Three-step spin coating method was further used to obtain uniform and dense CHNHPbBr films, which lead to a maximum luminance of 5044 cd/m 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 CHNHPbBr film and an optimum PEDOT:PSS/MoO-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/CHNHPbBr interface. These results present a promising strategy for the device engineering of high efficiency PeLEDs.