Manipulating the energy transfer path to achieve a high-efficiency red fluorescent OLED by using a novel interface sensitization layer and multiple reverse intersystem crossing (RISC) channels

Abstract

In co-host sensitized fluorescent devices, the triplet energy loss caused by a conventional fluorescent dopant (CFD) in the emitting layer (EML) prevents further improvement in device efficiency performance. In this article, we fabricate a thermally activated delayed fluorescence-sensitized fluorescent (TSF) organic light-emitting diode (OLED) with a dual-layer EML, which consists of an interface sensitized layer (ISL) and a red fluorescent EML. This device achieves a separation effect between the exciton generation region and the energy utilization region, which can effectively reduce the triplet energy lost through a CFD (DCJTB). Energy is mainly transferred from the sensitizer to the CFD through Förster energy transfer (FET). Furthermore, we introduce a TADF material (DMAC-MPM) into the ISL to form three RISC channels, corresponding to DMAC-MPM, DMAC-MPM:PO-T2T and TCTA:PO-T2T. The multiple reverse intersystem crossing (RISC) channels can effectively improve the up-conversion rate of triplet excitons, while also reducing exciton quenching in the ISL. After optimizing the relative position and thickness of the sensitizer (DMAC-MPM:PO-T2T) and the CFD, we achieve the maximum EQE of 14.33% in TSF-OLED device C1, which is the highest efficiency achieved among those of the reported fluorescent devices using DCJTB. The efficiency roll-off performance has also been improved, reaching 12.20% at a luminance of 1000 cd m⁻².