An exciplex forming cohost system is employed to achieve a highly efficient organic light-emitting diode (OLED) with good electroluminescent lifetime. The exciplex is formed at the interfacial contact of a conventional star-shaped carbazole hole-transporting material, 4,4',4″-tris(N-carbazolyl)-triphenylamine (TCTA), and a triazine electron-transporting material, 2,4,6-tris[3-(1H-pyrazol-1-yl)phenyl]-1,3,5-triazine (3P-T2T). The excellent combination of TCTA and 3P-T2T is applied as the cohost of a common green phosphorescent emitter with almost zero energy loss. When Ir(ppy)(acac) is dispersed in such exciplex cohost system, OLED device with maximum external quantum efficiency of 29.6%, the ultrahigh power efficiency of 147.3 lm/W, and current efficiency of 107 cd/A were successfully achieved. More importantly, the OLED device showed a low-efficiency roll-off and an operational lifetime (τ) of ∼1020 min with the initial brightness of 2000 cd/m, which is 56 times longer than the reference device. The significant difference of device stability was attributed to the degradation of exciplex system for energy transfer process, which was investigated by the photoluminescence aging measurement at room temperature and 100 K, respectively.

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We report a new efficient exciplex-forming system consisting of a biscarbazole donor and a triazine-based acceptor. The new exciplex was characterized with a high photoluminescence quantum yield up to 68% and effective thermally activated delayed fluorescence behavior. The BCzPh:3P-T2T (2:1, 30 nm) blend was examined not only as an emitting layer (device D1) but also a reliable co-host of fluorescent and phosphorescent emitters for giving highly efficient exciplex-based organic light-emitting diodes (OLEDs) with a high maximum external quantum efficiency of 15.5 and 29.7% for devices doped with 1 wt % C545T (device D2) and 8 wt % Ir(ppy)(acac) (device D4), respectively. More strikingly, a strongly enhanced lifetime ( T = 16 927 min.) of the C545T-doped device was obtained. The transient electroluminescence measurement as well as capacitance-voltage and impedance-voltage correlations were utilized to explore the factors governing the high efficiency and stability. The obtained results clearly show that the energy transfer and charge transport is highly efficient; they also show the photoelectric semiconducting characteristics of exciplex-based OLEDs, which are significantly different from those of unipolar host-based reference devices D3 (Alq: 1 wt % C545T) and D5 (CBP: 8 wt % Ir(ppy)(acac)). Our works have established a systematic protocol to shed light on the mechanisms behind exciplex-based devices. The combined results also confirm the bright prospect of the exciplex-forming system as the co-host for highly efficient and stable OLEDs.

With the remarkable progress in solution‐processed optoelectronics, high performance is required of the carrier transport/injection layer. Ternary oxides containing a variety of crystal structures, and adjustable composition that results in tunable optical and electrical properties, are one of the promising class of candidates to fulfill the requirements of carrier transport/injection layers for high‐performance and stable optoelectronic devices. Solution‐processed ternary oxides have seen considerable progress in recent decades, due to their advantages in the quest to design low‐cost, high‐performance, large‐scale, and stable optoelectronic devices. Herein, the recent advances of solution‐processed ternary oxides are reviewed. The first section consists of a brief introduction to the topic. In the following section, the fundamentals of the effect of tuning ternary oxide composition are summarized. Section three briefly reviews the synthesis approaches for preparing ternary oxides. Section four discusses the recent progress of solution‐processed ternary oxide as carrier transport/injection layer in optoelectronic devices (such as organic solar cells, perovskite solar cells, organic light emitting diodes, etc.). In this section, the impact of controlling ternary oxide composition on device performance and stability is highlighted. Finally, a brief summary and an outlook are given.