Study On Quantum Dot Light-Emitting Diode Based On Tin Dioxide Electron Transport Layer

In the QLED structure,the electron transport layer is an important part of it and is critical to enhancing device performance.Currently,zinc oxide（ZnO）nanoparticles are widely used as the electron transport layer for QLED,and external quantum efficiency（EQE）of over 20%have been obtained.However,the commercialization of QLED is significantly hindered by the positive aging phenomenon of ZnO nanoparticles.SnO₂ nanoparticles have similar optoelectronic properties to ZnO nanoparticles but superior stability for an ideal electron transport layer material in preparation of efficient and stable QLED.In the orthotropic QLED structure,the orthogonalization of the SnO₂ solvent needs to be taken into account,and at the same time,the SnO₂ nanoparticles need to be well dispersed to form smooth and dense films,thus reducing the QLED leakage current.Based on the above considerations,this thesis investigates the preparation of welldispersed SnO₂ in ethanol using various methods,and the preparation of orthotropic structured QLED using SnO₂ nanoparticles as an electron transport layer,studying transition metal ion doping of SnO₂ nanoparticles to improve device performance and solve the positive aging phenomenon.Details are as follows:（1）Well-crystalline SnO₂ nanoparticles were synthesized by hydrothermal method,and the introduction of tetraethylammonium hydroxide ligand followed by treatment of SnO₂ nanoparticles provided greater spatial site resistance through quaternary ammonium groups,which effectively prevented nanoparticle agglomeration.QLED devices based on post-processed SnO₂ electron transport layers have significantly improved performance,with turn-on voltage reduced from 2.3 V to 2 V,maximum EQE increased from 4.6%to 7.9%,and maximum current efficiency increased from 4.4 cd/A to 7.3 cd/A.In addition,SnO₂-based QLED exhibited excellent storage stability and avoided the aging phenomenon prevalent in ZnO-based devices.（2）Stably dispersed SnO₂ nanoparticles（o-SnO₂）in ethanol were synthesized in one step by sol-gel method under low temperature conditions.This method employed organotin compounds as Sn precursors to provide organic ligands to stabilize SnO₂ nanoparticles during the crystal formation process and to obtain stably dispersed oSnO₂ ethanol solutions.The o-SnO₂ films were smooth and dense,and a maximum EQE of 2.2%and a maximum current efficiency of 2.1 cd/A were achieved in the orthotropic QLEDs prepared with them as the electron transport layer.And the device was placed in the air for a week,the EQE of the device did not change significantly,the storage stability was better.（3）Based on the preparation of SnO₂ nanoparticles by sol-gel method,Mn-SnO₂ nanoparticles with excellent optoelectronic properties were furher prepared by doping with transition metal Mn ions.After doping,the conduction band position of Mn-SnO₂ nanoparticles was shifted downward,which reduced the electron injection barrier between the Mn-SnO₂ films and the QD layer and facilitated charge transport.In addition,the doping of Mn enhanced the electron mobility.Applying both electron transport layers to ortho-red QLEDs,the turn-on power of Mn-SnO₂-based QLED was significantly reduced;the maximum EQE was increased from 8.2%to 11.4%,a 40%improvement;and the maximum current efficiency was increased from 8.3 cd/A to 12.4 cd/A,a 50%improvement.And the device storage stability was excellent,solving the positive aging phenomenon.