Study On Efficiency Roll-off Of Top-emitting Organic Light-emitting Devices

There are many advantages of top-emitting organic light-emitting devices as high aperture ratio,high color purity and high luminous efficiency.More and more researchers are interested in TOLED and gradually develop commercial applications of the photoelectric display.However,there are a series of problems of the top-emission OLED device,such as the efficiency roll-off and angular dependence,which affect its light emission characteristics,severely restrict its further development and application.In order to obtain a TOLED device with excellent luminescence properties,accelerate the research process of the top emission device and allow the OLED to be better developed in the display market,three aspects have been studied in the present paper.Firstly,the TCTA:TPBi:Ir(ppy)3(3:1,8wt%)double-host co-doped light-emitting layer was used to study its effect on the efficiency roll-off of the TOLED device.The results show that the device with double-host light-emitting layer expands the recombination zone of carriers and uniforms the distribution of excitons.The device has a current efficiency of 62 cd/A at a luminance of 1000 cd/m2 and a current efficiency of 58 cd/A at 10000 cd/m2.It is not only 50%more efficient than the single-host luminescent layer device,but also has a significant reduction in the efficiency roll-off,which drops from 16.7%to 6.5%.Secondly,the top emission device structure with low power consumption and high stability is obtained through the selection of electrode materials.We have found that when Ag/LiF is used as the cathode of the top-emission device,the device is prone to short-circuiting,and it is necessary to add an appropriate thickness of A1 between them to ensure normal light emission of the device.The device we obtained had a driving voltage of 5.4 V at 10 mA/cm2.In addition,we also found that the efficiency of the top-emitting device with Al/Ag as its anode is higher than that with A1 alone.Finally,the paper studies the effect of the microcavity effect on the angular dependence of the TOLED device.By adjusting the thickness of the organic layer of the device,the microcavity effect is applied to the part of the wavelength band with weak intensity,which does not affect the main emission wavelength of the device.Therefore,the luminescence spectrum of the top emission device is similar to that of the original device.When the viewing angle changes from 0° to 60°,the color coordinate changes only(0.014,0.004),with almost no angular dependence.In addition,by adding a capping layer on top of the cathode of the TOLED device,the luminous efficiency of the device increased 1.6 times.The research on the efficiency roll-off and angle dependence of the TOLED device can improve the instability of the device in a certain extent,which can provide some help for further research.