Study On The Influence Of Ultrathin Interlayer On The Performance Of Phosphorescent OLED

Organic light-emitting device(OLED) has been widely used, for its advantages in the flat-panel display and solid-state lighting, such as eco-friendly, ultrathin, large-area, full-color, and so on. However, the competition of OLED with liquid crystal display(LCD) still subjects to many restrictions, since the efficiency, lifetime and cost of OLED have many technique bottlenecks. Compared with fluorescent OELD, the phosphorescent device has a much higher efficiency. Therefore, numerous researchers carry on research to obtain higher performance of phosphorescent OLED. However, there are still many problems to be solved for phosphorescent device, such as its spectral stability, efficiency, et al.To solve the above problems in phosphorescent OLED, in this work, the emissive layer/emissive layer and emissive layer/hole blocking layer interfaces were modified by an interlayer, which could improve charge carriers balance, reduce exciton quenching and modify energy level of the device. The specific contents contain the following three aspects:(1) The yellow light material PO-01 on the device performance was investigated. The experimental results showed that the OLED yielded a high luminance, external quantum efficiency, current efficiency, power efficiency of 17671 cd/m2, 11.1 %, 32.3 cd/A, 23 lm/W with 1 nm thick interlayer PO-01. The reason to cause this phenomenon is that the proper thickness of PO-01 would lead to the improvement of charge carrier transmission capacity and reductions in exciton quenching.(2) The device performance was investigated by adding the n-type material TPBi to the middle of the blue emissive layer and yellow emissive layer. The experiments showed that the OLED yielded a slight CIE coordinates variation of(0.031, 0.006) in 8 V to 12 V. OLED exhibited a high external quantum efficiency, a current efficiency of 8.2 %, 25 cd/A. Additionally, the turn-on bias voltage decreased to the lowest bias of 2.95 V with 2.5 nm thick interlayer TPBi. This was primarily due to the appropriate thickness of interlayer TPBi could change the distribution of charge carriers in the emissive layer and improve the balance of charge carriers.(3) The device performance was investigated by adding the p-type interlayer CBP to the middle of the hole-blocking layer and the emissive layer. The results showed that the luminance of 17671 cd/m2 raised to a maximum of 23652 cd/m2, an external quantum efficiency from 11.1 % to a maximum of 18.1 % and a current efficiency of 32.3 cd/A raised to a maximum of 50.4 cd/A of the OLED with 5 nm thick interlayer CBP. This was mainly due to the double exciton-blocking layer with appropriate thickness of interlayer CBP and TPBi could effectively confine the exciton diffusion and modify the energy level.In summary, we utilized TPBi/CBP as an interlayer in this master thesis to study spectral stability and efficiency of organic electroluminescent device, which could extend the application of OLED in the near future.