School of Physical Science and Technology, MOE Key Laboratory on Luminescence and Real-Time Analysis, Southwest University , Chongqing 400715, People's Republic of China.
ACS Appl Mater Interfaces. 2018 Jan 17;10(2):1948-1956. doi: 10.1021/acsami.7b17695. Epub 2018 Jan 4.
Singlet fission is usually the only reaction channel for excited states in rubrene-based organic light-emitting diodes (OLEDs) at ambient temperature. Intriguingly, we discover that triplet fusion (TF) and intersystem crossing (ISC) within rubrene-based devices begin at moderate and high current densities (j), respectively. Both processes enhance with decreasing temperature. This behavior is discovered by analyzing the magneto-electroluminescence curves of the devices. The j-dependent magneto-conductance, measured at ambient temperature indicates that spin mixing within polaron pairs that are generated by triplet-charge annihilation (TQA) causes the occurrence of ISC, while the high concentrations of triplets are responsible for generating TF. Additionally, the reduction in exciton formation and the elevated TQA with decreasing temperature may contribute to the enhanced ISC at low temperatures. This work provides considerable insight into the different mechanisms that occur when a high density of excited states exist in rubrene and reasonable reasons for the absence of EL efficiency roll-off in rubrene-based OLEDs.
单线态裂变通常是室温下基于苝的有机发光二极管（OLED）中激发态的唯一反应通道。有趣的是，我们发现基于苝的器件中的三重态融合（TF）和系间窜越（ISC）分别在中等和高电流密度（j）下开始。这两个过程都随着温度的降低而增强。这一行为是通过分析器件的磁电致发光曲线发现的。在室温下测量的 j 依赖性磁导率表明，由三重态-电荷湮灭（TQA）产生的极化子对内部的自旋混合导致 ISC 的发生，而高浓度的三重态则负责产生 TF。此外，随着温度的降低，激子形成减少和 TQA 升高可能导致低温下 ISC 的增强。这项工作为理解在苝中存在高密度激发态时发生的不同机制以及解释基于苝的 OLED 中不存在电致发光效率滚降提供了重要的见解。
