Fig. 1. Proposed energy-relaying mechanism.

Exciton allocation in single-emissive-layer, TADF WOLEDs comprising a D–A exciplex host, a blue emitter, and a yellow emitter. Inefficient energy transfer occurs from the exciplex host to the blue emitter and subsequently to the yellow emitter, due to a large energy gap between the blue and yellow emitters (~0.6 eV). The proposed exciplex, based on a high triplet donor and a low triplet acceptor, generates a large triplet gap between a high-lying T₂ and a low-lying T₁. This design enables efficient ladder-like (~0.3 eV ladder spacing) triplet energy transfer from T₂ → blue emitter → T₁ → yellow emitter. ET, IC, ISC, and RISC refer to energy transfer, internal conversion, intersystem crossing, and reverse ISC, respectively.