Modeling and Analysis of Exciton Dynamics on “Hot Exciton” Process in Blue Fluorescent Organic Light‐Emitting Diodes

A comprehensive understanding on exciton dynamics in organic light‐emitting diodes (OLEDs) is of great significance for evaluating their electroluminescence (EL) performance. “Hot exciton” organic emissive materials have attracted widespread interest due to their highly efficient reverse intersystem crossing (hRISC), but their underlying exciton dynamics remain elusive. Herein, an exciton dynamic model on “hot exciton” process in blue fluorescent OLEDs is proposed. The model perfectly reproduces the external quantum efficiency (EQE) versus current density (EQE‐J) characteristics in blue fluorescent OLEDs based on four hot exciton materials, and the fundamental kinetic rates are well obtained. This model reveals that S1‐Tn (n ≥ 2) annihilation (S1TnA) is the primary quenching process, accompanied by certain T1‐T1 annihilation (T1T1A) and S1‐polaron (P) annihilation (S1PA), and T1T1A is mainly attributed to the loss caused by internal conversion (IC). The transient electroluminescence (TrEL) measurements further demonstrate that the decline in singlets is due to the aforementioned quenching. Importantly, the device lifetime exhibits a perfect positive linear relationship with the obtained kinetic rates, thereby simply enabling to predict the lifetime of OLEDs. This work contributes to improving the physical understanding on “hot exciton” behaviors, greatly aiding the development of high performance blue fluorescent OLEDs based on hot exciton materials.