Bridged triazatruxene-based host materials for solution-processed thermally activated delayed fluorescence organic light emitting diodes with high power efficiency

A series of host materials (1FTAT-2Ph, 2FTAT-1Ph, 3FTAT) containing a hole-transport triphenyl-substituted triazatruxene conjugated skeleton and different numbers of diphenyl methylene-bridging groups were developed for solution-processed yellow thermally activated delayed fluorescence (TADF) organic light emitting diodes (OLEDs). These host materials possessed relatively high triplet energy (≈2.8 eV), which ensured effective energy transfer from host to TADF emitter. Meanwhile, the peripheral diphenyl methylene bridging groups effectively separated the TADF emitters to suppress intermolecular aggregation and exciton quenching. They also showed high thermal stability and good solubility in organic solvents. Benefited from the elevated highest occupied molecular orbital level matched well with the Fermi level of ITO/PEDOT:PSS anode and significantly suppressed excited state non-radiative transition of TADF emitter, solution-processed OLED using 2FTAT-1Ph as host exhibited a low turn on voltage of 2.8 V and high external quantum efficiency of 20.9% with a remarkable high power efficiency of 72.7 lm W−1, which was far superior to those of the control device with 4,4′-N,N′-Dicarbazole-biphenyl (CBP) as host. This work demonstrated the great potential of diphenyl methylene bridged triazatruxene derivatives as host materials to achieve high-performance solution-processed TADF OLED.