Organic-inorganic Hybrid Perovskite Electroluminescent Materials And Devices

Recently,perovskite light-emitting diodes?Pe LEDs?have received significant attention due to their advantages of low-cost,high color purity,tunable bandgaps over the visible and infrared region,and ease of solution processing.Although green,red and near-infrared Pe LEDs showed external quantum efficiency?EQE?more than 20%,realizing efficient blue perovskite electroluminescent devices at room temperature still faces severe challenges,which are essential for full-colour display applications.In addition,anti-solvent engineering was widely used in achieving high efficiency Pe LEDs,however,the preparation technology of anti-solvent method is difficult to control and not suitable for future massive production.Therefore,this paper is dedicated to improve the Pe LEDs performance by developing new perovskite materials,optimizing the device structures and processing technology.In chapter 2,efficient solution-processed Pe LEDs were fabricated by controlling the morphology of thin perovskite films and developing suitable hole-transport layers?HTLs?.On the one hand,CH₃NH₃Pb Br₃ precursor solution was blended with a traditional polymeric host PVK[poly?vinylcarbazole?]to obtain perovskite films with high surface coverage.On the other hand,the perovskite films could be further improved through crystal modification to obtain a more uniform morphology and smaller grain size.In combination with the good solution processability of the polymer hole-transport materials and small molecular hole-transport materials with high hole-mobility,suitable HTLs with appropriate energy level,film-forming property and solvent resistance were fabricated.Overall,efficient green Pe LEDs were achieved via a solution process,giving a maximum EQE of 1.88%.The Commission Internationale de l'Eclairage?CIE?coordinates of these Pe LEDs are?0.066,0.809?,which are excellent for display application.Our study demonstrates an effective method to control the morphology of perovskite films and develop suitable co-mixed small molecular and polymer HTLs,which is beneficial for further optimization and development of high-performance solution processed Pe LEDs.In chapter 3,we demonstrate both the efficient photoluminescence and electroluminescence of the blue perovskite quantum dots?QDs?via a simple FABr-modified multication hot-injection?FMMHI?method.The FMMHI method is unique in both the addition of FABr into the Pb Br₂ precursor solution and the incorporation of small rubidium?Rb⁺?into the blue perovskite QDs light-emitting diodes?QLEDs?.The addition of FABr into the precursor solution can realize strong quantum confinement effect,large exciton binding energy and high-quality perovskite QD films.Besides,the bandgap can be enlarged by the Rb⁺-induced perovskite octahedral distortion and strong quantum confinement effect.Excellent photoluminescence quantum yields?PLQYs?of 64.5%and 49.8%were achieved for the developed greenish-blue QDs(Rb_0.33Cs_0.67)_0.42FA_0.58Pb Br₃ and deep-blue QDs(Rb_0.33Cs_0.67)_0.42FA_0.58Pb Cl_1.25Br_1.75 in solid film state.Moreover,maximum EQEs of 3.6%and0.61%were also achieved with electroluminescence peak wavelengths at 502 and 466 nm,respectively,indicating that the perovskite QDs incorporated with Rb⁺have great potential for the development of high-performance blue perovskite electroluminescence diodes.In chapter 4,we report a simple and effective co-interlayer strategy to develop efficient quasi-two-dimensional?quasi-2D?perovskites with a chemical formula of L₁L₂An-1Pb_nX_3n+1,where L₁ and L₂ are denoted as the co-interlayer ligands.Phenylbutylammonium bromide?PBABr?and propylammonium bromide?PABr?were selected as the representative co-interlayer ligands materials.Preparation of these co-interlayer quasi-2D perovskite films is simple and highly controllable without using anti-solvent treatment.The co-interlayer engineering provides a much more flexibility in the tuning of dielectric property,defect passivation and morphology modulation in contrast to the single-interlayer counterparts.PLQY of the perovskite film is dramatically improved to 89%due to the combined optimization of exciton binding energy and suppression of trap state formation.Accordingly,a high current efficiency of 66.1 cd A^-1corresponding to an EQE of 15.1%was achieved for green co-interlayer quasi-2D perovskite LEDs without using any light out-coupling techniques,indicating that co-interlayer engineering is a simple and effective approach to develop high-performance perovskite electroluminescence devices.