| Organic Light-emitting devices(OLED)have been seen as one of the most promising technologies for solid-state lighting and flat panel display due to their attractive advantages such as high brightness,wide viewing angle,fast response speed,thin and flexible,etc.With the development of science and technology,virtual reality(VR)and augmented reality(AR)technology have attracted extensive attention.Therefore,multi-light color-tunable OLED based on bidirectional charge transmission has become a hot topic in scientific research and industry.At present,color-adjustable OLED devices with multiple optical colors have been reported.One of them is an Alternating Current Driven/Direct Current Driven OLED(AC/DC OLED)stacked OLED device with an intermediate connection layer,which can not only realize the color tunable function of multilight colors.In addition,there is no need for fine mask plate alignment technology in preparation,which reduces the cost of preparation.Compared with voltagedependent OLED devices and OLED devices with an external intermediate electrode using fine mask technology,the research on this device is relatively scarce and still has a certain research value.Therefore,this thesis studies the bidirectional charge transfer organic electroluminescence devices driven by AC/DC,from the aspects of the intermediate connection layer,electron transport layer,hole transport layer,buffer layer and color adjustment.The main work content is as follows:(1)The influence of Ag on the performance of stacked OLED devices was studied from the electrical and optical character-istics,and the organic electroluminescent devices with multi-optical color and bi-directional charge transfer were prepared by using Ag connection layer.Then,the thickness of Ag film is optimized and its influence on the device performance is compared.It is found that Ag films of 10 nm have suitable transmittance and reflectance.Meanwhile,the current density-voltage characteristic curve of the device with Ag as the intermediate connection layer reflects that the device has good carrier generation and injection ability under forward and reverse voltage,which meets the standard of being the intermediate connection layer.Under forward bias,the positive unit of the device emits green light,while under reverse bias,the inverted unit of the device emits red light.There is no mutual influence between the positive unit and the inverted unit in the luminescence of the organic light-emitting device prepared by using Ag as the intermediate connecting layer.In addition,the experimental results of Ag thickness optimization show that 12 nm and 10 nm Ag as the intermediate connecting layer have the best efficiency under forward and reverse bias respectively.Under forward voltage,the maximum brightness,current efficiency and power efficiency of 12 nm Ag devices are 1012.5 cd/m2,20.9 cd/A and 11.6 lm/W respectively.At reverse voltage,the maximum brightness,current efficiency and power efficiency of the device prepared with 10 nm Ag are 56.8 cd/m2,1.1 cd/A and 0.24 lm/W respectively.It can be seen from AFM and SEM images that the increase of Ag film thickness can improve the density of the film.(2)The effects of different thicknesses and different kinds of electron transport layers,hole transport layers and buffer layers on the performance of multi-color bi-directional charge transfer organic luminescence devices were analyzed and studied.It is found that NPB/TAPC as the hole transport layer can improve the device performance under forward and reverse bias.The forward voltage of the device is 4.5 V,the maximum brightness is increased to 1593.6 cd/m2,the maximum current efficiency and the maximum power efficiency are increased to 35.1 cd/A and 24.7 lm/W.At the same time,10 nm thick TmPyPB and 25 nm thick ET20 as electron transport layer,the device performance is the best,the initial voltage is 11.8 V,the maximum brightness is 95.9 cd/m2,the maximum current efficiency and the maximum power efficiency are improved to 2.08 cd/A and 0.56 lm/W under reverse bias.This was a effective optimization of the performance of bi-directional charge transfer devices.In addition,the device with buffer layer ET20:Yb has better performance in all aspects,and the maximum brightness under reverse bias is increased to 125.7 cd/m2,and the maximum current efficiency and power efficiency are increased to 2.6 cd/A and 0.7 lm/W,which is the highest device performance under reverse bias in this thesis.(3)The effect of Ag:Mg interlayer on the performance of multi-color organic light-emitting devices is studied.Under reverse bias,the device performance of Ag:Mg is better,with a maximum brightness of 261.6 cd/m2,maximum current efficiency and maximum power efficiency of 5.3 cd/A and 1.6 lm/W.In addition,the color modulation of multi-color bi-directional charge transfer devices is studied.Experiments show that Ag:Mg has better performance than Ag as the intermediate connection layer under reverse bias,which may be related to the surface roughness of the film.It can be seen from AFM and SEM images that the surface of Ag:Mg was smoother than that of Ag film.Finally,the different polarity of the positive and negative half periods of the AC drive signal was used to independently address the vertically stacked green and red emission units,so as to achieve the color tunable function,in which the emitted color can be adjusted from green to yellow to red. |
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