利用发光层梯度掺杂改善顶发射白光有机发光二极管光谱的稳定性

Improvement of the color-stability in top-emitting white organic light-emitting diodes by utilizing step-doping in emission layers

在具有顶发射结构的白光有机发光二极管(TWOLED)中,稳定的纯白光比较难以实现.本文在蓝光/红光/蓝光三发光层基础上,进一步采用了红光层梯度掺杂的方式提高TWOLED的性能.制备了一系列的梯度掺杂器件,通过与均匀掺杂器件的对比,详细分析了梯度掺杂对发光层中载流子漂移以及激子扩散的影响,解释了白光稳定性提高的物理机理.此外,顶发射器件中的微腔效应也是影响白光光谱的一个重要因素,本文利用微腔理论计算分析了微腔共振对器件光谱的影响.

Chromatic stability and purity cannot be acquired easily in the top-emitting white organic light-emitting diode （TWOLED） due to its special device structure with metal film as both anode and cathode. Blue/ red/ blue emission layers are utilized to optimize the chromaticity and to improve the stability. Then step-doping is introduced into the red emission layer to further improve the device stability. In order to explain the mechanism of the improvement in chromaticity stability, effects of step-doping on the device performances are analyzed in detail. Experimental results reveal that the built-in electric field induced by the step-doping changes the carrier drifting and exciton recombination in emission layers. When the doping concentration gradually increases from the anode side to the cathode side （increasing step-doping）, the built-in electric field is facilitated to suppress the electron drafting and the exciton diffusing, which helps control the exciton recombination zone. Color stability can be improved in the TWOLED with increasing step- doping. Additionally, as an important factor influencing the emission spectra of TWOLEDs, microcavity resonance is calculated and used to explain the variation of spectra induced by device structural changes.