Highly Efficient QLED Construction Based On High Hole Conductivity Copper-Tin-Sulfur-Gallium-Oxygen Hole Injection Layer

Quantum Dot Light Emitting Diodes（QLEDs）have the advantages of high color purity,wide color gamut,and good color reproduction,and are expected to become a new generation of display and lighting technology with wide application prospects in areas such as high-definition display and high-end lighting.Up to now,the hole injection layer material commonly used in QLED devices is poly（3,4-ethylenedioxythiophene）:polystyrene sulfonate（PEDOT:PSS）,which has high transmittance,good electrical conductivity and thermal stability,but the PSS in PEDOT:PSS shows acidity,which can cause corrosion of ITO electrodes and thus lead to degradation of device performance.Therefore,finding new hole injection materials without acid additives is an effective way to solve the above problems.Transition metal oxide（TMO）is expected to be a replacement material for PEDOT:PSS due to its suitable work function and high transmittance.A series of TMO materials,including Ni O,Mo O₃,V₂O₅,WO₃,Cu O,etc.,have been used to construct QLEDs,but unfortunately,the anisotropic and localized characteristics of the oxygen wave function in the lattice in the above TMO materials lead to strong localization effect of oxygen on electrons in all directions,which eventually leads to low hole mobility and conductivity of the films.Compared with QLED devices based on PEDOT:PSS hole injection layer,although the stability of the device constructed using TMO is effectively improved,the device efficiency is low due to the lower hole injection efficiency.Therefore,how to break the local effect of oxygen ions on hole isotropy in TMO will be an effective means to improve the electrical conductivity of the film,and then it is expected to obtain high efficiency QLED devices.Different from the above TMO materials,it is shown that the 5s orbitals of Sn O can be used for oxygen-to-hole delocalization in the valence band.In addition,in some layered TMO materials,such as Cu Ga O₂,high hole conductivity within the layer can be obtained through the anisotropy of the crystal structure.On this basis,the introduction of a less electronegative element S is expected to further reduce the hole ground localization effect and further enhance the hole conductivity of the film to promote carrier injection equilibrium.On this basis,we propose to prepare copper-tin-sulfur-gallium-oxygen（CTSGO）multi-alloys with disordered structure（amorphous or heterogeneous structure of amorphous/layered crystals）for in situ growth of high hole conductivity CTSGO films;furthermore,CTSGO is used as the hole injection layer to construct red QLED devices,and the specific research work includes:（1）Preparation and characterization of CTSGO thin films by sol-gel methodThe CTSGO films were prepared by sol-gel method using copper acetate monohydrate,thiourea,tin chloride and gallium nitrate hydrate as reactants and ethylene glycol methyl ether as solvent.By optimizing the experimental parameters,the CTSGO films were able to form continuous dense films with smaller contact angle,better wettability and better permeability in ITO compared with the PEDOT:PSS films.Under 200°C annealing conditions,the CTSGO films have no obvious crystallization peaks,indicating that the samples have low crystallinity and amorphous amorphous phase,resulting in smoother surface roughness and better permeability.the CTSGO films have a work function of 4.5 e V,VBM of 5.38 e V,and CBM of 1.78 e V,and their valence band positions are different from the highest electron orbital occupied by PEDOT:PSS（HOMO）by 0.28 e V,which reduces the energy level barrier between the hole injection and hole transport layers,improves the hole injection efficiency,and promotes carrier injection equilibrium.It is assumed that CTSGO films are suitable for constructing QLED devices as a hole injection layer.（2）CTSGO as a hole injection layer for QLED devicesThe conductivity of CTSGO films was investigated in different molar ratios of Sn and Ga elements and different ozone time conditions,and the results showed that the Hall mobility increased after the addition of Ga elements,and the resistivity gradually increased as the molar ratio of Ga elements continued to increase.The CTSGO films prepared by the sol-gel method were applied to red QLED devices,and the thickness,molar ratio of Sn and Ga elements,UV ozone treatment time,and annealing temperature of the CTSGO films were optimized.The experimental parameters such as thickness,molar ratio of Sn and Ga,UV ozone treatment time,and annealing temperature were optimized to improve the device performance,and the results showed that the device performance was best when the spin-coating speed was 3000 rpm,the ratio of Sn to Ga was 1:1,the UV ozone time was 2 min,and the annealing temperature was 200℃.The CE_maxand PE_maxof the final device were 31.92 cd/A and 29.49 lm/W,respectively,and the L_maxand EQE_maxwere 217400 cd/m²and 21.32%,respectively.