Efficient Solution‐Processed Red Fluorescent OLEDs Using Diluted Exciplex Host to Reduce Non‐Radiative Loss of Triplet Excitons

Abstract High‐performance red fluorescent organic light‐emitting diodes (OLEDs) are fabricated via a diluted exciplex host strategy to suppress non‐radiative triplet exciton loss in the exciplex sensitized fluorescent emitter system. The solution‐processed red fluorescent OLEDs based on the diluted TCTA:PO‐T2T exciplex host demonstrate higher external quantum efficiency (EQE) than the theoretical 5% limit for traditional fluorescent OLEDs. In the TCTA:PO‐T2T exciplex sensitized fluorescent emitter system, the excess content of TCTA is employed relative to PO‐T2T to manipulate the decay process of triplet excitons. A part of TCTA adjacent to PO‐T2T involves forming the exciplex pair that efficiently converts triplet excitons to singlet excitons via reverse intersystem crossing (RISC), while the other TCTA donors act as the host for the exciplex sensitizer and fluorescent emitter, which inhibits both concentration quenching of the exciplex sensitizer and short‐range dexter energy transfer from the exciplex sensitizer to the fluorescent emitter DCJTB without affecting ISC, RISC, and long‐range Föster energy transfer rate significantly. With this strategy, the formed triplet excitons can be converted to singlet excitons with reduced loss contributing to efficient fluorescent emission under electric excitation. The solution‐processed red fluorescent OLEDs achieve an EQE of 8.1%, much higher than 3.5% of the conventional exciplex sensitized OLEDs.