PEDOT:PSS And Its Doping As Anode Interfacial Layers For Tailoring Electroluminescent Device Performance

The solid-state lighting and flat-panel display technologies of organic electroluminescent devices(OLEDs)and quantum dot electroluminescent devices(QLEDs)have been attracted wide attentions due to its flexibility,low-cost,scalable manufacturing,self-luminous,high color purity and low power consumption.However,the deep HOMO level of organic layer counteracts hole injection from the mostly widely used indium-tin-oxide(ITO)anode,and thus serious carrier imbalance in the emissive layer as well as unsatisfactory power conversion efficiency.Meanwhile,operation causes aging of the functional layers,which greatly affects device performance.Solution-processed technology caters to demande of industry in the background of current low-cost,large-area,precise and controllable production.In this paper,a series of OLED and QLED which focused on the adjustment of anode interface to enhance the hole injection ability were prepared.In addition,the hole injection mechanism of the solution-processed anode interface materials and the device aging mechanism were systematically investigated,tunning carrier balance in the emissive layer as well as improving the device performance.The main contents are summarized as follows:1)Two types of PEDOT:PSS(AI4083,PH1000)are demonstrated for hole injection tuning and accordingly optimizing electro-optic performance in quantum dots light-emitting diode(QLED).The results show that PEDOT:PSS-PH1000 deteriorates QLED performance owing to its higher hole mobility and herein serious carrier imbalance.The effect of PEDOT:PSS-AI4083 concentration is investigated in details.With Cd Se/Zn S quantum dots as emitter and optimal concentration of PEDOT:PSS-AI4083 as hole injection layer,the QLED produces typical green emission with electroluminescent peak of527 nm and full width at half maximum of 24 nm.It gives maximum luminous efficiency of 18.4 cd/A,power efficiency of 5.8 lm/W and external quantum efficiency of 5.9%with overwhelming superiority over the corresponding references.The current-voltage and impedance spectroscopy analysis of hole-only cells indicate that the hole injection can be facilely tuned by using different types of PEDOT:PSS and/or altering PEDOT:PSS concentration,which accounts for regulation of carrier balance and optimization of device performance.2)Solution-processed ethanol tungsten disulfide and its doping in PEDOT:PSS for tailoring hole injection in near ultraviolet organic light-emitting diodes(NUV OLEDs)are investigated in details.With PBD as organic emitter and WS₂-doped PEDOT:PSS as HIL,the NUV OLED gives attractive EQE of 2.1%and radiance of 4.7 m W/cm²,together with short-wavelength emission peaking at 404 nm.Raman spectrum,scanning electron microscopy,atomic force microscopy(AFM)and X-ray/ultraviolet photoelectron spectroscopy(XPS/UPS)show that WS₂and its composites behave superior film morphology and exceptional electronic properties.Impedance spectroscopy measurements indicate that the hole injection ability is enhanced by using WS₂,UV-Ozone-treated WS₂,PEDOT:PSS and PEDOT:PSS+WS₂in this order.The robust hole injection contributes to carrier balance and accounts for high device performance of the fabricated NUV OLEDs.3)The effects of aging time on current density and radiance of near UV OLEDs are investigated.Devices are fabricated with PCZTZ as the fluorescent molecule,PEDOT:PSS as the hole injection layer.It is found that the current density is decayed much faster than radiance,and accordingly promoting device external quantum efficiency from 2.5%initially to giant value of 8.2%after a certain period of aging.The impedance,phase,and capacitance as a function of voltage transition curves indicate that carrier injection/transport gradually decreases during aging,which accounts for the reduced current density and radiance.Our results provide a new approach for analyzing durability and advancing applications of UV OLEDs.