Unusual stepwise increases of efficiency in fluorescent organic light-emitting diodes (OLEDs) was reported, which has not been observed in phosphorescent devices. However, the root cause of this phenomenon is unclear. Herein, we investigate the correlation between non-linear efficiency characteristics and the leakage current in conjunction with exciton formation in the electron blocking layer (EBL) as a function of voltage. Hole and electron transporting layers with different injection characteristics were selected to control the leakage current into the EBL. It was revealed that a significant amount of excitons were formed in the EBL. It was discovered that the degree of variation in the efficiency curve was directly related to the amount of leakage electrons from the emitting layer (EML) and the number of excitons in the EBL. Moreover, the exciton formation zone (EFZ) gradually shifted from the EBL into the EML as the voltage increased. After device degradation, the stepwise shape of the efficiency curves was significantly deformed, strongly implying that contributions to efficiency by excitons in the EBL vanished. Thus, the unusual stepwise increase in efficiency can be fully attributed to exciton formation in the EBL and shifting of the EFZ from the EBL to the EML.

据报道，荧光有机发光二极管 (OLED) 的效率出现了不寻常的逐步提高，而这在磷光器件中尚未观察到。然而，这种现象的根本原因尚不清楚。在此，我们研究了非线性效率特性与泄漏电流之间的相关性，以及电子阻挡层 (EBL) 中激子形成与电压的关系。选择具有不同注入特性的空穴和电子传输层来控制进入 EBL 的漏电流。结果表明，在 EBL 中形成了大量的激子。发现效率曲线的变化程度与从发射层（EML）的漏电子量和EBL中的激子数量直接相关。而且，随着电压的增加，激子形成区（EFZ）逐渐从EBL转移到EML。在器件退化后，效率曲线的逐步形状显着变形，强烈暗示 EBL 中激子对效率的贡献消失了。因此，效率的异常逐步提高可以完全归因于 EBL 中的激子形成和 EFZ 从 EBL 转移到 EML。