Optimizing energy transfer for highly efficient single-emissive-layer white thermally activated delayed fluorescence organic light-emitting diodes

Thermally activated delayed fluorescence (TADF) white organic light-emitting diodes (WOLEDs) with simplified structures have great potential for daily lighting applications. However, the complicated energy and charge transfer processes between TADF emitters impede the development of single-layer white TADF systems. Here we demonstrate high-efficiency WOLEDs with single-emissive layers composed of blue and yellow TADF emitters with appropriate steric hindrances and energy gaps, which optimize the energy transfer from blue to yellow dopants for rational exciton allocation. As a consequence, the single-emissive-layer WOLEDs achieve the maximum external quantum efficiency beyond 20% and small roll-offs, which are among the best results of full-TADF WOLEDs.