Solution-processed multiple exciplexes via spirofluorene and S-triazine moieties for red thermally activated delayed fluorescence emissive layer OLEDs

A series of novel binary and ternary components of the exciplexes as the cohosts for a red thermally activated delayed fluorescence (TADF) dopant were investigated in the solution-processed OLEDs, where 1,3-bis[(4-tert-butylphenyl)-1,3,4-oxadiazolyl] phenylene (OXD-7) as a conventional acceptor, and 1,3-bis(carbazol-9-yl)benzene (mCP) as a conventional donor were respectively mixed with two molecules containing spirofluorene and s-triazine moieties (TDP-TRZ or DTDP-TRZ) with excellent thermal stability and high electron mobility as the second acceptors. Particularly, the power efficiencies of the devices with the exciplexes are generally enhanced via this strategy of host engineering. The designed devices could achieve a percentage increase of 179% in the power efficiency, compared with the reference device with single-component host, mainly owing to the synergistic effects of electron block, balanced injection of charge carriers and efficient exciton harvesting. The working mechanism of energy transfer in binary and ternary components of the exciplexes hosted red TADF OLEDs is studied. This work provides a novel device design philosophy with the multiple exciplexes cohosts for solution-processed TADF OLEDs, which would help to simplify the fabrication processing, lower the cost, and popularize OLED technology.