紫外有机发光器件的激子形成区域优化与掺杂调控

采用空穴传输兼发光层CBP和电子传输兼发光层TAZ构建了紫外有机电致发光器件(UVOLED),通过调控功能层厚度可以优化激子形成区域,进而改善器件性能。实验结果表明:CBP厚度的变化对器件性能影响甚微,而TAZ厚度变化则有显著影响。当CBP和TAZ厚度分别为50 nm和30 nm时,获得了最大辐照度为4.4 m W/cm2@270 m A/cm2、外量子效率(EQE)为0.94%@12.5 m A/cm2,发光来自于CBP主发光峰~410nm以及TAZ肩峰~380 nm的UVOLED器件。在此基础上,通过在CBP/TAZ界面引入超薄CBP∶TAZ]掺杂层可以加速激子复合,降低器件驱动电压,同时还有利于改善载流子平衡性,提高发光效率(最大EQE达到了0.97%@20 m A/cm2)而不影响光谱特性。

Optimization of Excimer Forming Zone and Doping Engineering in Ultraviolet Organic Light-emitting Device

Ultraviolet organic light-emitting devices (UVOLEDs) were constructed by using hole-transport-emitting layer of 4,4'-bis(carbazol-9-yl)biphenyl (CBP) and electron-transport-emitting layer of 3-(4-biphenyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole (TAZ). The excimer forming zone was optimized by adjusting the functional layer thickness, which contriuted to device performance improvement. Our results indicate that the thickness variation of CBP has negligible effect on device performance while that of TAZ shows considerable effect. The maximum radiance of 4.4 mW/cm²@270 mA/cm² and external quantum efficiency (EQE) of 0.94%@12.5 mA/cm² are achieved in UVOLED with optimal thickness of 50 nm CBP and 30 nm TAZ. The electroluminescence peak of ~410 nm and shoulder of ~380 nm, resulted from CBP and TAZ, respectively, are observed. Moreover, an ultrathin layer ofCBP:TAZ] inserted between CBP and TAZ accelerates excimer recombination rate and reduces driving voltage. Meanwhile, the carrier balance is improved and thus device efficiency is slightly promoted (the maximum EQE reaches 0.97%@20 mA/cm²) without altering spectrum characteristics.