College of Science and Engineering, James Cook University, Townsville QLD 4811, Australia.
Centre for Organic Photonics and Electronics, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane QLD 4072, Australia.
J Chem Phys. 2023 Jul 21;159(3). doi: 10.1063/5.0152922.
Phosphorescent organic light emitting diodes (OLEDs) suffer from efficiency roll off, where device efficiency rapidly decays at higher luminance. One strategy to minimize this loss of efficiency at higher luminance is the use of non-uniform or graded guest:host blend ratios within the emissive layer. This work applies a multi-scale modeling framework to elucidate the mechanisms by which a non-uniform blend ratio can change the performance of an OLED. Mobility and exciton data are extracted from a kinetic Monte-Carlo model, which is then coupled to a drift diffusion model for fast sampling of the parameter space. The model is applied to OLEDs with uniform, linear, and stepwise graduations in the blend ratio in the emissive layer. The distribution of the guests in the film was found to affect the mobility of the charge carriers, and it was determined that having a graduated guest profile broadened the recombination zone, leading to a reduction in second order annihilation rates. That is, there was a reduction in triplet-triplet and triplet-polaron annihilation. Reducing triplet-triplet and triplet-polaron annihilation would lead to an improvement in device efficiency.
磷光有机发光二极管 (OLED) 存在效率滚降问题，即在更高亮度下器件效率迅速下降。在更高亮度下最小化这种效率损失的一种策略是在发射层中使用不均匀或分级的客体：主体混合比。这项工作应用了多尺度建模框架来阐明非均匀混合比如何改变 OLED 的性能。迁移率和激子数据从动力学蒙特卡罗模型中提取，然后将其与漂移扩散模型耦合，以便快速对参数空间进行采样。该模型应用于发射层中具有均匀、线性和阶跃混合比梯度的 OLED。发现薄膜中客体的分布会影响电荷载流子的迁移率，并且确定具有分级客体分布会拓宽复合区，从而降低二级复合率。也就是说，三重态-三重态和三重态-极化子复合的概率降低了。降低三重态-三重态和三重态-极化子复合的概率将导致器件效率的提高。
