Effects of acceptor on the performance of exciplex-based OLED

•Exciplex-based OLEDs are fabricated with TAPC as the donor and a series triazine derivatives as the acceptors.•Electrical and optical properties of the devices are systematically investigated.•The efficiency of the devices is primarily determined by the photoluminance quantum yield of the emitting layers.•An efficiency roll-off less than 20% is observed for all the devices. In this work, exciplex-based OLEDs (ExOLEDs) are fabricated with 1,1-bis((di-4-tolylamino)phenyl)cyclohexane (TAPC) as the donor and a series triazine derivatives, e.g., 2,4,6-tris(biphenyl-3-yl)-1,3,5-triazine (T2T), 2,4,6-tris(3-(1H-pyrazol-1-yl)phenyl)-1,3,5-triazine (3P-T2T), and 2,4,6-tris(m-(diphenylphosphinoyl)phenyl)-1,3,5-triazine (PO-T2T), as the acceptors. With different acceptors and mole ratios of donor:acceptor, the effects of the photoluminescence quantum yield (PLQY), charge carrier balance, and exciton lifetime on the EQE and efficiency roll-off are systematically investigated. It is found that the external quantum efficiency (EQE) of the ExOLEDs is primary determined by the PLQY of the mixed donor:acceptor film and tuned in a certain extent by the charge carrier balance. Furthermore, the efficiency roll-offs of different ExOLEDs are all less than 20%, which are simultaneously determined by the photoluminescence (PL) lifetime and the charge carrier balance.