Multiple-Resonance-Type TADF Emitter as Sensitizer Improving the Performance of Blue Fluorescent Organic Light-Emitting Diodes

Due to the limitation of donor and acceptor group selection, the efficient thermally activated delayed fluorescence (TADF) type sensitizer used for blue organic light-emitting diodes (OLEDs) is rare. Multiple resonance (MR) type TADF emitters can easily achieve efficient blue emission. And the compounds exhibit small Stokes shift and lower absorption energy under the same emission color compared with traditional TADF, mitigating the damage of high-energy absorption of sensitizer on material stability. However, their characteristics as sensitizers have not been explored. In this work, a deep-blue MR-TADF compound (3tPAB) is selected as a sensitizer for both blue traditional fluorescence and MR-TADF OLED. Given the improved photoluminescence quantum yield and the utilization of triplet excitons, the TADF-sensitized fluorescent device using 3tPAB as sensitizer presents a maximum external quantum efficiency (EQE(max)) of 14.4%, showing approximate to 2.4 times increase compared with the device without sensitizer. More impressively, TADF-sensitized TADF (TST) device using 3tPAB as sensitizer and MR-TADF compound PhDMAC-BN as emitter exhibits EQE(max) of 33.9%. And in TST device, efficient Forster energy transfer is demonstrated, thus, the device can maintain high color purity. The work first demonstrates the feasibility of MR-TADF as a sensitizer and provides a new strategy for developing high-performance blue OLED with high color purity.

Automated summary

Due to the limitation of donor and acceptor group selection, efficient thermally activated delayed fluorescence (TADF) type sensitizers for blue organic light-emitting diodes (OLEDs) are rare. This study demonstrates the feasibility of using multiple resonance (MR) type TADF emitters as sensitizers, achieving efficient blue emission and significantly improving the external quantum efficiency by improving the photoluminescence quantum yield and utilizing triplet excitons.