Study On Interface Control Of Zinc Oxide-Based Inverted QLED Device Structure

The all-inorganic perovskite CsPbBr₃QD prepared by solution method has many excellent properties:adjustable luminescence spectrum,high luminous efficiency,high carrier mobility,high fluorescence quantum yield,simple synthesis process,etc.Industry research hotspots.Although the photoluminescence quantum efficiency?PLQY?of perovskite quantum dots?QDs?solutions is high,the high luminous efficiency and stability are maintained in solid films and corresponding quantum dot light emitting diodes?QLEDs?Sexual problems are still a challenge,especially the problems of excitonic quenching and unbalanced charge transport caused by the unstable transport interface and energy level mismatch caused by the transport layer/light emitting layer interface.In order to discuss the above issues in depth,this paper uses zinc oxide as the electron transport layer and all-inorganic perovskite quantum dots as the light-emitting layer to prepare an inverted structure QLED device,focusing on reducing the fluorescence quenching of the light-emitting layer film and affecting the transport layer/light-emitting layer The factors of non-radiative recombination between the interfaces and the unbalanced transmission of carriers at the cathode and anode,through the use of interface adjustment methods such as host-guest compound passivation of the luminescent layer,functional layer doping and surface modification,improve the fluorescence of the luminescent layer film Efficiency,balanced carrier injection of the device and electroluminescence efficiency.The specific research content is divided into the following three parts:First,for the purpose of improving the PLQY of the CsPbBr₃QD luminescent layer solution and the corresponding spin-on film,the optimal conditions of the quantum dot solution in cleaning times and different dispersion solvents were experimentally studied,and the surface ligand and solvent dielectric constant,The influence of factors such as polarity on PLQY,it is preferable to clean the quantum dot material with heptane as the dispersing solvent twice for subsequent device and interface state research.Next,in order to solve the perovskite quantum dot surface ligands and enhance the current carrying For the problem of sub-injection,a high-mobility semiconductor 2,7-dioctyl[1]benzothieno[3,2-b]benzothiophene?C8-BTBT?and CsPbBr₃quantum dots are used to form a host-guest composite light-emitting layer,The wide-bandgap host material can effectively confine carriers injected into the light-emitting layer,improve the injection efficiency of electron holes,and reduce carrier losses.Then,the hole transport material of the inverted QLED device is selected to reduce the energy level barrier with the luminescent layer.The inverted QLED device prepared by the ITO/ZnO/EML/CBP/Mo O₃/Al device structure,the experiment shows that based on the composite material system The prepared device EQE is 7 times that of pure CsPbBr₃QLED.By reducing the leakage current,the current efficiency is improved,and the effectiveness of the carrier-injection compound to improve the carrier injection is verified.Next,based on the composite light-emitting layer composed of C8-BTBT and all-inorganic perovskite CsPbBr₃quantum dots,the effect and mechanism of the magnesium ion doping process of the zinc oxide electron transport layer on the fluorescence quantum efficiency and interface stability of the light-emitting layer were studied.Magnesium ion doping can linearly regulate the optical band gap of the electron transport layer within a certain range,and at the same time effectively improve the surface morphology of the film,thereby improving the quality of the interface with the light-emitting layer.The experiment found that,compared with the undoped ZnO film,the surface roughness and surface energy of the Mg_0.09Zn_0.91O film decreased significantly,the optical band gap increased by 0.2e V,and the corresponding conductivity mainly due to electron drift also decreased significantly.By further adjusting the ratio of host and guest in the composite light-emitting layer,the hole injection ratio can be adjusted to improve the balance of carrier transport.Compared with the pure quantum dot light-emitting layer film,the light-emitting layer composed of host and guest has higher fluorescence quantum efficiency and fluorescence lifetime on the ITO/Mg_0.09Zn_0.91O substrate.Finally,in order to solve the quenching effect of the polar hydroxyl groups on the surface of the ZnO film on the photoluminescence fluorescence of the QD luminescent layer and reduce the influence of the interface environment on the photoluminescence of the QD film.The surface polarity of the ZnO film is adjusted by chemical modification of phenylethyl trichlorosilane?PETS?self-assembled monolayer?SAM?.The experiment found that by reducing the density of hydroxyl groups on the oxide layer,a hydrophobic surface can be produced after surface treatment,thereby reducing the subsequent optical quenching of the CsPbBr₃ quantum dot film.In addition,by changing the PETS concentration to design the surface polarity,it helps to increase the photoluminescence quantum yield?PLQY?by 50%.At the same time,the thermal stability of the photoluminescence is improved,showing a temperature tolerance of up to 140?.