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Solution-processed Organic light-emitting diodes (OLEDs) have aroused serious attention because of its lower cost and easier fabrication. Herein, a novel triazine-based molecular emitter is reported for solution-processed OLEDs for the first time. The emitter, 4,4′,4′'-(1,3,5-triazine-2,4,6-triyl)tris(N,N-bis(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)aniline) denoted as Tri-2tCzPA-TRZ, shows excellent solubility in common organic solvents, facilitating solution-processed OLEDs. The resultant OLEDs doped with 1,3-di(9H-carbazol-9-yl)benzene (mCP) achieved a maximum current efficiency of 18.8 cd A−1 and maximum luminance of 12,580 cd m−2, which is higher than the maximum current efficiency of the most solution-processed OLEDs in simple structures. [ABSTRACT FROM AUTHOR]

Hole-transporting materials (HTMs) capable of forming thermally stable amorphous film and possessing high electrochemical stability play an important role in organic light-emitting diodes (OLEDs), which can enhance the device performance. Herein, spirobifluorene-based HTM N-([1,1′-biphenyl]-2-yl)-N-(9,9-dimethyl-9H-fluoren-2-yl)-9,9′-spirobifluoren-2-amine (SFAF), employing fluorene-contained arylamine as the hole transporting unit, was synthesized, and the comprehensive properties of material were systematically investigated. Owing to the highly twisted spiro conformation, the SFAF exhibited a high glass transition temperature of 140 °C and a high thermal decomposition temperature of 402 °C. Moreover, a stably and homogeneously amorphous SFAF film was formed by increasing the treatment temperature up to 140 °C for 12 h and a smooth surface film was characterized by the atomic force microscope. In addition, the compound presented excellent electrochemical stability with nearly identical cyclic voltammetry curves during the 100 cycles. Green fluorescent OLED based on SFAF as the hole-transporting layer showed a satisfactory device performance. The SFAF with high stability was also applied as HTM in phosphorescence device, which exhibited a turn-on voltage of 2.2 V, a maximum brightness of 191127 cd m−2 and the maximum current efficiency of 63.80 cd A−1. This results indicate that SFAF is a great promising and potential hole-transporting material for highly efficient optoelectronic devices. [ABSTRACT FROM AUTHOR]

Three s-triazine/carbazole based bipolar molecules: 9,9′,9″-(1,3,5-triazine-2,4,6-triyl)tris(3,6-di- tert-butyl-carbazole) (TazTCz), 9,9′-(6-phenyl-1,3,5-triazine-2,4-diyl)bis(3,6-di- tert-butyl-carbazole) (PhTazDCz) and 9-(4,6-diphenyl-1,3,5-triazine-2-yl)-3,6-di- tert-butyl-carbazole (DPhTazCz) were synthesized and applied as host materials for blue phosphorescent organic light-emitting diodes (PHOLEDs). The triplet state energy levels are ~2.86 eV for these compounds, ensured their application in blue PHOLEDs. X-ray single crystal structural analysis revealed a non-planar structure of TazTCz, which prevented the intermolecular close-packing in the solid state. X-ray diffraction spectra also confirmed that TazTCz and PhTazDCz could form amorphous films with spin-coating method. The bipolar characteristics of as-synthesized compounds were confirmed by carrier mobility measurement. The device parameters of blue PHOLEDs based on these compounds as host materials exhibit that the balance of electron and hole mobilities is benefit for reducing turn-on voltage and efficiency roll-off at high current density. [ABSTRACT FROM AUTHOR]

[Display omitted] • Indium tin oxide was hybrid modified with MoO 3 and self-assembled monolayer. • Self-assembled monolayer was used to adjust oxygen vacancies in MoO 3. • Solution-processed hole transport layer-free OLED achieved EQE max of 18.18% Compared with current vacuum-deposited multilayer organic light-emitting diodes (OLEDs), solution-processed simplified-structured OLEDs are more appealing by merits of low costs and promising potentials in large-area OLEDs. Nevertheless, it remains challenging due to intermixing between adjacent organic layers. Herein, indium tin oxide (ITO) surface was deposited with molybdenum trioxide (MoO 3) and then modified with self-assembled monolayer (SAM) of pentafluorobenzyl phosphonic acid. The SAM modification process made the MoO x film rich in oxygen vacancies, which ensured effective hole injection from the hybrid modified ITO directly to the emitting layer. This strategy facilitates HTL-free OLEDs and then completely avoids interlayer intermixing. Using the hybrid modified ITO as anode, HTL-free solution-processed green phosphorescent OLED was prepared and achieved a maximum current efficiency of 63.24 cd A−1 and a maximum external quantum efficiency of 18.18%. Meanwhile, preferable operational stability than standard multilayer OLEDs was obtained. For red phosphorescent OLED, a maximum external quantum efficiency of 17.49% was achieved. This work proposed a new way of adjusting cation valence to improve hole injection, contributing to solution-processed OLED fabrication. [ABSTRACT FROM AUTHOR]

• Two vinyl-based cross-linkable hole transporting materials are synthesized. • Cross-linking temperature is markedly lowered by doping photoinitiator. • Hole mobility is also enhanced by doping photoinitiator. • The highest external quantum efficiencies are 15.5% (green) and 15.0% (red). Recently, developing insoluble cross-linkable functional layers plays a vital role for solution-processed organic light emitting diodes (OLEDs). Here, two vinyl-based cross-linkable hole transporting materials V-TPAVTPD and V-TPAVCBP are designed and synthesized. Additionally, cationic photoinitiator 4-octyloxydiphenyliodonium hexafluoroantimonate (OPPI) is first introduced to chemically induce vinyl-based photo cross-linking process, aiming at lowering cross-linking temperature and enhancing hole mobility. As a result, cross-linking can occur at expressly low temperature of 120 °C with >95% solvent resistance. Moreover, hole mobility is markedly enhanced with the value higher than 10−3 cm2 V−1 s−1. When applying hole transporting layers (HTLs) to solution-processed green and red phosphorescent OLEDs, devices exhibit excellent properties. Particularly, the maximum current efficiency of 54.0 cd A−1 (green), 9.8 cd A−1 (red) and external quantum efficiency of 15.5% (green), 15.0% (red) are obtained when OPPI doped V-TPAVCBP serves as HTL. This low temperature feasible cross-linking process to prepare HTLs with preferable hole mobility promotes the development of OLEDs. [ABSTRACT FROM AUTHOR]