Single‐Layer Organic Light‐Emitting Diode with Trap‐Free Host Beats Power Efficiency and Lifetime of Multilayer Devices

Organic light‐emitting diodes (OLEDs) employing a single active layer potentially offer a number of benefits compared to multilayer devices; reduced number of materials and deposition steps, potential for solution processing, and reduced operating voltage due to the absence of heterojunctions. However, for single‐layer OLEDs to achieve efficiencies approaching those of multilayer devices, balanced charge transport is a prerequisite. This requirement excludes many efficient emitters based on thermally activated delayed fluorescence (TADF) that exhibit electron trapping, such as the green‐emitting bis(4‐(9,9‐dimethylacridin‐10(9H)‐yl)phenyl)methanone (DMAC‐BP). By employing a recently developed trap‐free large band gap material as a host for DMAC‐BP, nearly balanced charge transport is achieved. The single‐layer OLED reaches an external quantum efficiency (EQE) of 19.6%, which is comparable to the reported EQEs of 18.9–21% for multilayer devices, but achieves a record power efficiency for DMAC‐BP OLEDs of 82 lm W−1, clearly surpassing the reported multilayer power efficiencies of 52.9–59 lm W−1. In addition, the operational stability is greatly improved compared to multilayer devices and the use of conventional host materials in combination with DMAC‐BP as an emitter. Next to the obvious reduction in production costs, single‐layer OLEDs therefore also offer the advantage of reduced energy consumption and enhanced stability. Single‐layer organic light‐emitting diodes offer many benefits compared to multilayer devices. However, in such single‐layer devices, balanced charge transport is a prerequisite, which is uncommon in organic emitters. Here, a trap‐free host is employed to achieve balanced charge transport in the emissive layer, resulting in lower operating voltage, higher power efficiency, and greatly extended lifetime compared to multilayer devices.