Research Of Efficient Mixed Halide Blue Perovskite On Light Emitting Diodes

Metal halide perovskites are widely used in the light-emitting diodes（LED）benefitting from their outstanding advantages,like low cost,excellent photoluminescence performance and tunable band gap.So far,the red and green perovskites possess prominent photoelectric properties,and the efficiencies of related devices have achieved great breakthrough.However,blue perovskite has a lagging development with technical difficulties,like poor photoelectric performance,serious phase separation and poor stability,which may be the technical bottleneck in the development of perovskite light emitting diodes（PeLEDs）in full-color display.Therefore,the preparation of blue perovskite with high stablility and excellent optical properties is very critical for the all-round development of PeLEDs in display field.Firstly,aiming at the serious technical problems of low photoluminescence quantum yield（PLQY）and phase separation of blue perovskite CsPb（Br/Cl）₃,this paper put forward a coordinated regulation strategy of metal Cu²⁺ions doping and Br^-anion exchange post-treatment,and successfully prepared mixed halide blue nanosheets with ultra-high PLQY.The experiment results show that Cu²⁺ions replaced Pb²⁺ions inside perovskite lattice,which effectively passivates the chlorine defects in the lattice,reduces the degree of lattice disorder and improves the photoluminescence performance of CsPb Cl₃.In addition,the strong force between Cu²⁺ions and halide ions contributed to the formation of two-dimensional CsPb Cl₃nanosheets with higher exciton binding energy.Subsequently,Br^-anion exchange post-treatment was used to prepare mixed haldie blue CsPb（Br/Cl）₃ nanosheets with ultra-high PLQY and great stability,and these nanosheets showed more radiation recombination and less ion migration.Based on the doped CsPb（Br/Cl）₃ nanosheets,this paper successfully developed a deep blue PeLEDs with an EL peak of 462 nm,a maximum brightness of 761 cd m^-2 and a current density of 205 m A cm^-2.Secondly,this paper proposed a simple and efficient di-ammonium-salts passivation strategy to effectively inhibit the dual intrinsic halide defects in the mixed halide blue perovskite CsPb（Br/Cl）₃quantum dots,which significantly enhances their photoelectric properties and stability.The di-ammonium-salts passivation strategy effectively reduced the dual halide defects in CsPb（Br/Cl）₃ lattice,and improved their effective radiation recombination ratio,PLQY and exciton binding energy.At the same time,the effective combination between ammonium ions and surface halide ions promoted the formation of organic ligand protective layer on the perovskite lattice surface,which enhance the stability of CsPb（Br/Cl）₃quantum dots against external field.Finally,deep blue PeLEDs were prepared by using CsPb（Br/Cl）₃quantum dots passivated by di-ammonium-salts,and showed an EL peak of 461 nm,a maximum brightness of 733 cd m^-2 and an EQE was 1.11%.Finally,this paper explored the influence of di-ammonium-salts passivation strategy on the carrier behavior of blue PeLEDs,deeply analyzed the promotion mechanism and working principle of blue PeLEDs from the aspects of device energy level,film morphology,hysteresis and carrier behavior,and revealed the electroluminescent mechanism of different blue PeLEDs.The results show that the di-ammonium-salts passivation strategy improved the film morphology of CsPb（Br/Cl）₃ quantum dots,reduced the hole injection barrier and energy loss,enhanced the carrier injection balance of blue PeLEDs,and improved the hysteresis behavior of blue PeLEDs.Finally,the carrier behavior of blue PeLEDs before and after di-ammonium-salts passivation strategy was summarized,and the influence of defects on carrier behavior of PeLEDs was expounded.