An efficient organic light-emitting diode based on the BCzPh:CN-T2T exciplex as an emitting layer (EML) has been fabricated by exploiting charge balance and favorable molecular orientations. To further understand the details of the exciplex-forming mechanism, time-resolved photoluminescence (TRPL), capacitance-voltage (CV), impedance spectroscopy (IS), and transient electroluminescence (EL) measurements were used to probe the photophysical and electrical characteristics of EL devices by incorporating interfacial (BCzPh/CN-T2T) and bulk (BCzPh:CN-T2T) exciplexes as the emitting layer. Interfacial- and bulk-exciplex devices exhibit a maximum external quantum efficiency (EQE) of 7.7 and 26.4%, respectively. The reason for different device performances was rationalized by comparing the accumulated amount of charge density at the EML’s interface responsible for exciplex emission. In addition, the TRPL measurement monitored from short to long wavelengths was used to explore the harvest of nonradiative triplets back to singlets via reverse intersystem crossing and to examine the efficiency of delayed fluorescence. The bulk-exciplex system showed a distinct delayed fluorescence as compared to the interfacial one, which was also corroborated by the observation in the transient EL. The result indicates that the bulk exciplex can reduce the accumulated charge in the EML rapidly, resulting in improvement of EL efficiency. This assumption was further verified by CV and IS measurements. Our results reveal that the accumulated charge density and the bulk resistance of the bulk-exciplex device are much lower as compared to those of the interfacial counterpart device.

中文翻译：

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通过光物理和电学特性对高效有机发光二极管的界面和本体激基形成系统的比较研究。

通过利用电荷平衡和良好的分子取向，制造了一种基于BCzPh：CN-T2T激基复合物作为发光层（EML）的高效有机发光二极管。为了进一步了解激基复合物形成机理的细节，使用了时间分辨光致发光（TRPL），电容电压（CV），阻抗谱（IS）和瞬态电致发光（EL）测量来探测光致发光的光物理和电特性。通过结合界面（BCzPh / CN-T2T）和体（BCzPh：CN-T2T）激基复合物作为发光层的EL器件。界面和本体激基复合物器件的最大外部量子效率（EQE）分别为7.7％和26.4％。通过比较负责激基复合物发射的EML接口处电荷密度的累积量，可以合理地解释不同器件性能的原因。另外，从短波长到长波长监测的TRPL测量用于探索非辐射三重体通过反向系统间穿越而返回单峰的收获，并检查延迟荧光的效率。与界面体系相比，本体-复杂体系显示出明显的延迟荧光，这在瞬态EL中也得到了证实。结果表明，本体激基复合物可以迅速减少EML中的累积电荷，从而提高EL效率。通过CV和IS测量进一步验证了这一假设。