A Simple Non-Doped Donor/Acceptor Quaternary Exciplex System for Enhanced Triplet Exciton Utilization

The interface exciplex does not require precise doping process and exhibits higher efficiency than conventional fluorescent emitter. The utilization of triplet excitons has been identified as a critical factor in achieving high-efficiency luminescence in such systems. Here, a simple interface structure with conventional transport materials for facilitate utilization of exciton and energy transfer can be constructed by inserting ultrathin layers between the interface exciplex. This strategy dispenses with precise doping process and fluorescent guest to form a quaternary exciplex at interface to constructing energy trasnfer between the exciplexes. The optimized quaternary exciplex device achieves an external quantum efficiency (EQE) of 13.4% and a current efficiency (CE) of 34.3 cd/A, exceeding the performance of individual exciplex devices. The photoluminescence quantum yields (PLQYs) rising from 28.7% to 52.7% and the reverse intersystem crossing (RISC) rate is enhanced from ${1}.{5}\times {10}^{{5}}$ to ${2}.{2}\times {10}^{{5}~}$ ${\mathrm {s}}^{-{1}}$ after inserting ultrathin layers. These improvements are attributed to the presence of multiple energy transfer and RISC channels, which accelerate the consumption of singlet exciton and facilitate triplet exciton upconversion to singlet for rising the utilization of triplet exciton. This study presents a new method to efficiently utilize triplet excitons for high-efficiency interface exciplex organic light-emitting diodes (OLEDs).