利用缓变结提高蓝色有机发光二极管的寿命

Lifetime Prolongation by Graded Junction for Blue Organic Light Emitting Diodes

在空穴传输层(HTL)和发光层(EML)界面加入缓变结的蓝色有机电致发光器件(Cell-GJ)。与传统的异质结结构的有机电致发光器件(Cell-HJ)相比,寿命有了明显的提高:半寿命在初始亮度为100 cd/m2的条件下达到了8460 h,比Cell-HJ的半寿命长6倍。寿命的延长归功于穿过非突变界面的局部电场的消除,减少了焦耳热的产生从而提高了器件的寿命。但是实验证实Cell-GJ的效率比Cell-HJ的效率低。为了提高Cell-GJ的效率在其TBADN/AlQ交界处蒸镀GaQ薄层制得一种新型器件Cell-GJGaQ。由于GaQ的最低未占有轨道能级介于AlQ和TBADN之间,从AlQ到GaQ再到TBADN形成的多阶势垒可以极大地提高电子(少子)注入,从而使发光效率也有了明显改善。研究结果表明Cell-GJGaQ的效率比Cell-GJ的效率高20%,半寿命同时也达到了6998 h,比Cell-HJ长5倍,整体性能有了较大提高。

Blue organic light emitting diode （OLED） with a graded junction at hole transporting layer （HTL） and emitted layer （EML） interface was constructed （Cell-GJ）. Compared with conventional heterojunction OLED （Cell- HJ）, it exhibited significantly improved lifetime, and the half lifetime achieved 8460 h at initial luminance 100 cd/ m^2 , more than 6 times longer than that of Cell-HJ. This improvement is attributed to the elimination of local electric field across the non-abrupt heterojunction, which thereby decreases the production of Joule heat and enhances the lifetime of device. However, the efficiency of Cell-GJ is lower than that of Cell-HJ. In order to redeem the decrease in efficiency of Cell-GJ, another device with a GaQ thin layer inserted in the TBADN/AIQ interface was made （Cell- GJGaQ）. For the LUMO energy level of GaQ is between the energy level of A1Q and TBADN, the multi-step energy barrier between AlQ-GaQ-TBADN improves the electron （minority） injection greatly, so the luminescence efficiency is greatly improved. This Cell-GaQ shows efficiency 20% higher than that of Cell-GJ and also 5 times longer half lifetime than that of Cell-HJ. The whole performance is greatly improved.