An efficient solution-processable hybridized local and charge-transfer (HLCT)-based deep-red fluorescent emitter for simple structured non-doped OLED

The development of highly efficient deep-red fluorescent emitters is still a challenging task due to their intrinsic low bandgap characteristics resulting in low fluorescence emission in solid-state. Moreover, most of efficient deep-red organic light-emitting diodes (OLEDs) have complex device structures and are fabricated by high-cost vacuum deposition techniques. Herein, a novel solution-processable hybridized local and charge-transfer (HLCT) deep-red fluorescent molecule, TPA-NZF, is designed and synthesized as an emitter for low-cost and simple-structured OLEDs. TPA-NZF comprises a strong electron-deficient naphthothiadiazole (NZ) functionalized with triphenylamine (TPA) as a donor and dioctylfluorene as a solubilizing moiety. The photophysical results and theoretical calculations reveal a strong donor-acceptor feature and deep-red fluorescent emission with a solid-state photoluminescence quantum yield as high as 44%, decent hole-transporting mobility, good film morphology, and thermal and electrochemical stabilities. TPA-NZF is successfully fabricated as a solution-processed non-doped emitter in simple structured OLEDs. The device shows excellent electroluminescence (EL) performance (maximum external quantum efficiency (EQEmax) of 3.59%) and a deep-red emission with CIE coordinates of (0.66, 0.33).