The rational design of host materials with intrinsic bipolar characteristics is critical for achieving high-performance phosphorescent organic light-emitting diodes (PhOLEDs). In this work, three diphenylquinoxaline (DPQ) derivatives functionalized with cyano (−CN), phenylcarbazole, and dibenzofuran groups were developed as versatile acceptors and paired with tris(4-carbazoyl-9-ylphenyl)amine (TCTA) as an electron donor. All acceptors exhibited well-balanced carrier-transport properties and optimized energy-level alignment. Among them, the TCTA:DPQCN-PhDBF exciplex host system achieved outstanding performance, delivering an ultralow turn-on voltage (Von) of 1.8 V, the lowest reported to date, along with a maximum luminance (Lmax) of 42,457 cd m–2 and a peak external quantum efficiency (EQEmax) of 16.8%. The superior performance is attributed to extended π-conjugation, increased molecular torsion, and the rigid dibenzofuran unit, which collectively enhance charge-transfer (CT) state formation, hole-transport efficiency, film morphology stability, and energy-level modulation. In comparison, DPQCN-DBF exhibited limited performance due to crystallization tendencies during film formation, whereas the TCTA:DPQCN-CzPh system achieved a high EQEmax of 17.8% with a low Von of 2.0 V, benefiting from improved hole-transport properties imparted by the carbazole unit. This study establishes a systematic molecular design strategy that integrates energy-level tuning, charge-transport balancing, and CT-state optimization, offering valuable insights for the development of high-efficiency, high-luminance, and energy-saving OLED technologies.
Yang et al. (Wed,) studied this question.