Light Manipulation And Interface Engineering For Efficient Perovskite Light-Emitting Diodes

Metal halide perovskite materials have been widely used for producing perovskite light-emitting diodes(PeLEDs)for their various excellent properties,such as tunable bandgap,solution processibility,high photoluminescent quantum yield and color purity Compared with methylamine(MA)and formamidine(FA)-based organic-inorganic hybrid perovskite materilas,inorganic perovskites using cesium(Cs)hold great application potential due to their higher chemical and thermal stability.However,dense pinholes and defects are inevitable during the crystallization and film formation of inorganic peorvskites,which results in inferior efficiencies of PeLEDs.During recent years,Cs-based PeLEDs have been rapidly developed benefitting from effective film control and defect passivation.Though the Cs-based perovskite films have been sufficiently improved,their relevant PeLEDs still lag behind organic light-emitting diodes(OLEDs)in device performance.One main factor is the severe light-loss effect induced by refractive-index difference inside a PeLED device.What's more,the under interfaces of perovskite films play an important role in improving the performance of PeLEDs,since they have great influence on the crystalline quality of perovskite grainsIn order to weaken the light-loss effect,CsPbBr3 perovskite films were patterned by the quasi-perodic "moth-eye" nanostructures via nano-imprinting method.By this way,the waveguide-mode light loss could be effectively reduced,which improved the EQE of rigid PeLEDs from 13.4%to 20.3%.Meanwhile,the EL spectra stayed identical.A half-ball lens was also applied to release the light trapped inside glass substrate,hence further increased the EQE to 28.2%.As for the interface engineering,we doped the PEDOT:PSS hole transport layer with organic small molecule ethanolamine(ETA),which not only passivated the interface defects of perovskite,but also enhanced the crystallinity of perovskite thin films and optimized the crystal orientation.Based on this interface control method,the EQE of the rigid plane PeLED device was increased to 17.2%.Further combining flexible silver nanowire transparent electrode(TCE)and light-outcoupling method,we successfully produced a flexible PeLED device with EQE up to 24.5%,which provides a possible reference for the application of PeLEDs.