Electrode Interface Modification And Carrier Injection Regulation Of Ultraviolet Organic Light-emitting Devices

Organic Light-Emitting Diode?OLED?has become a research hotspot at home and abroad as a solid-state lighting and flexible display technology due to excellent mechanical flexibility,thin portability,energy conservation and environmental protection.Visible and ultraviolet OLED with shorter wavelength emission show attractive application prospects in the fields of new generation flat panel display,excitation light source and high density information storage.Indium tin oxide?ITO?is a transparent conducting electrode widely used at present,which has high transmittance,good conductivity,good stability and moderate work function?4.7 e V?.However,the band gap of UV organic light-emitting molecules is wide and it is difficult to match the ITO electrode,which results in limited carrier injection.Compared to the traditional vacuum thermal evaporation process,the solution processing technology meets the current needs for low-cost,large-scale mass production,precise and controllable characteristics.In this paper,a series of anode buffer layers?hole injection layers?and cathode buffer layers?electron injection layers?are prepared based on solution-processable technology to overcome the limitation of carrier injection,thereby regulating the carrier balance in the light-emitting layer and improving the device performance.The main research work is summarized as follows:In view of the high hole injection barrier between ITO and organic light-emitting molecules,we used solution method to prepare different concentrations of germanium dioxide?Ge O₂?aqueous solution and modified ITO electrode.Atomic force microscope,X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy tests show that solution-treated Ge O₂ exhibits excellent film morphology and enhanced surface work function.Using 0.6%Ge O₂ as the anode buffer layer of OLED,the maximum luminous efficiency of visible light devices with Alq₃ as the light-emitting layer is 6.5 cd/A,and the power efficiency is 3.5 lm/W.The UV OLED with TAZ as the light-emitting layer has excellent short wavelength emission,with an electroluminescence peak of 376 nm,a half-peak width of 42 nm,a maximum irradiance is 3.36 m W/cm² and an external quantum efficiency of 1.5%.By preparing the corresponding single hole device and analyzing the voltammetric characteristic curve and impedance spectrum,it is clarified that the anode buffer layer formed by an appropriate concentration of Ge O₂ aqueous solution is conducive to enhancing hole injection and improving device performance.For inverted OLED devices,the electron injection barrier between ITO as the cathode and the UV organic light-emitting molecule TAZ is as high as 2.1 e V.The solution method was used to prepare a zinc oxide?Zn O?methanol solution and a cesium carbonate?Cs₂CO₃?ethanol solution,and a mixed solution of Cs₂CO₃ doped Zn O?s-Zn O+Cs₂CO₃?and a corresponding composite electron injection layer were prepared.X-ray photoelectron spectroscopy analysis showed that s-Cs₂CO₃,s-Zn O and s-Zn O+Cs₂CO₃ have excellent electrical properties.The inverted structure of the inverted OLED with TAZ as the light-emitting layer and s-Zn O+Cs₂CO₃?1:1?as the composite electron injection layer is380 nm,the half-width is 37 nm,and the maximum irradiance is 2.42 m W/cm²,external quantum efficiency is 0.85%,its performance is better than that of using s-Cs₂CO₃,s-Zn O,e-Li F and e-Cs₂CO₃ as reference devices of single electron injection layer,and also better than that of using s-Zn O/s-Cs₂CO₃ as reference devices of double electron injection layer.By constructing a single electronic device and conducting current-voltage characteristic tests and impedance spectroscopy analysis,it was confirmed that the optimal doping ratio of s-Zn O+Cs₂CO₃?1:1?has strong electron injection ability,thereby improving the device performance.