Exciplex OLED
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 quaternary exciplex with conventional transport materials can be construct by inserting ultrathin layers between the interface exciplex layer by non-doped process. A gradient energy level with three exciplexes are established between interface layer to facilitate multi-channels energy transfer and utilization of triplet exciton. The pronounced redshift in the photoluminescence spectra signify efficient energy transfer within the quaternary exciplex. The photoluminescence quantum yields (PLQYs) rising from 28.7% to 52.7% and the reverse intersystem crossing (RISC) rate is enhanced from 1.5×105 to 2.2×105 s−1 after inserting ultrathin layers. 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. 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).
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