Study On Carrier Regulation And Luminance Efficiency Improvement Of OLED

At present,the organic light-emitting diode has gradually entered the practical stage.But there still have been many challenges to realize the large-scale industrialization of OLED.Because there are many unresolved problems,such as carrier transport capacity,energy level matching degree,film uniformity,which will affect the injection and transmission performance of carriers and hinder the improvement of luminescence efficiency and working stability of OLED.Focusing on above problems,the carriers are regulated by developing new electrode,introducting inorganic oxide,doping modification material,improving device structure,etc.Then the luminescence properties of OLED can be improved.The main work includes:?1?The effect of different thicknesses V₂O₅ as hole buffer layer on green phosphorescent OLED is studied.It shows that V₂O₅ can effectively improve the contact between ITO and organic layer.The higher HOMO level of V₂O₅ also can increase the hole injection barrier and reduce the hole migration rate.Meanwhile,the continuous accumulation of the holes at the ITO/V₂O₅ interface will promote the electron migration,which will make the carrier quantitis become more balanced and improve the luminescence efficiency.When the V₂O₅ thickness is 30 nm,the device can obtain a maximum brightness of 28990 cd/m² and a maximum current efficiency of 54.36 cd/A.Furthermore,the brightness and current efficiency are 32% and 34% higher than those of the device without V₂O₅ respectively.?2?The effect of graphene oxide/MoO₃ with different MoO₃ thicknesses as hole injection layer on green fluorescent OLED is studied.It shows that the introduction of graphene oxide/MoO₃ can not only make barrier present a step change,but also can form the p type doping effect.Morover,the conductivity and transmittance of graphene oxide film are improved after the modification of MoO₃.So both the hole transmission rate and the effective light emission are increased.When the thickness of MoO₃ is 5 nm,the transmittance of graphene oxide/MoO₃ composite film is the highest and reaches 88% at 550 nm.The device also has the best performance and the maximum current efficiency reachs 5.87 cd/A,which is increased by 50% compared with that of the device with graphene oxide as hole injection layer.?3?The effect of Ca:Mg:Al alloy with different Mg doping mass ratios as cathode on red phosphorescence OLED is studied.It shows that the doping of Mg can reduce the work function of alloy and decrease the interfacial barrier between cathode and adjacent functional layer,which can make it easier for electrons to overcome the interface barrier and inject into the light emitting layer.When the doping mass ratio of Mg is 20%,the performance of the device can be improved greatly.The device can obtain a maximum luminance of 10250 cd/m²,which is 3.7 times as much as that of the device with Ca:Al alloy as cathode.With the current density increasing from 14.08 mA/cm² to 130.57 mA/cm²,the current efficiency rolls off smaller and can be stabilized at 23.72 cd/A.?4?The effect of Bphen:BCP:Cs₂CO₃ with different BCP doping concentrations as electron transport layer on green fluorescent OLED device is studied.It shows that the doping of BCP with high LUMO and HOMO levels can reduce the electron injection barrier and accelerate electron transfer rate.Meanwhile,the holes can be effectively blocked in the light emitting layer,and the carriers can be fully compounded.In addition,BCP also can obstruct the Cs of Cs₂CO₃ diffusing to emitting layer,and luminescence quenching caused by chemical reaction of Cs and Alq3 is declined.When the BCP doping concentration is 10%,the device can obtain a maximum current efficiency of 3.89 cd/A,which is 46% higher than that of the device without BCP.?5?The blue OLED is prepared,in which both blue fluorescent material TBPe and blue-green material DPAVBi are incorporated into host material ADN to form a double emitting layer.It shows that the double emitting layer structure can widen the carrier composite region,which can make the composite region away from the electrode to reduce the luminescence quenching and carrier accumulation at the interface.At the same time,there is no barrier difference between two emitting layers for using the same host ADN,which is benefit to the energy transfer and improves the luminance efficiency.Compared with the single emitting layer devices,the double emitting layer device has a higher luminance efficiency and a better chroma stability.The maximum current efficiency and the maximum luminance the device can obtain are 11.96 cd/A and 13050 cd/m² respectively.The color coordinate also can be basically stable at?0.16,0.25?during the device operation.?6?The phosphorescent and fluorescent hybrid white OLED with ADN:TBPe as blue fluorescence emitting layer,ADN:DPAVBi as blue-green emitting layer and CBP:R-4B as red phosphorescent emitting layer is prepared.It shows that by changing the thickness of red emitting layer can modulate the carrier recombination region and reduce the probability of light annihilation.Meanwhile,the doping of blue-green light material DPAVBi can not only provide green light,but also can increase the blue light emission.With the appropriate light intensity of red,green and blue,the device finally can present a better white light emission.When the thickness of red phosphorescent emitting layer is 20 nm,the color of the device is relatively the purest and the color coordinate is?0.33,0.34?.The maximum current efficiency of 6.35 cd/A can be obtained at the current density of 47.59 mA/cm².