Enabling high-efficiency organic light-emitting diodes with a cross-linkable electron confining hole transporting material

• Design, synthesis, and characterization of a thermally cross-linkable hole transporting material VPEC.
• The resulting VPEC material shows a hole mobility of 1 × 10−4 cm2 V−1 s−1 and a triplet energy of 2.88 eV.
• Hole transporting material also shows effective electron confining function with LUMO energy level of –2.0 eV.
• The resulting solution process red, green and blue (RGB) OLED devices show high efficiency at higher luminance.

Wet-process enables flexible, large area-size organic devices to be fabricated cost-effectively via roll-to-roll manufacturing. However, wet-processed devices often show comparatively poor performance due to the lack of solution-process feasible functional materials that exhibit robust mechanical properties. We demonstrate here a cross-linkable material, 3,6-bis(4-vinylphenyl)-9-ethylcarbazole (VPEC), to facilitate the injection of hole and meanwhile effectively confine electron to realize, for examples, high efficiency organic light-emitting diodes, especially at high luminance. The VPEC shows a hole mobility of 1 × 10−4 cm2 V−1 s−1 and a triplet energy of 2.88 eV. Most importantly, the VPEC not only works for devices containing low band-gap red or green emitters, but also for the counterpart with high band-gap blue emitter. With the electron confining hole transporting material, the power efficiency of a studied red device, at 1,000 cd m−2 for example, is increased from 8.5 to 13.5 lm W−1, an increment of 59%, and the maximum luminance enhanced from 13,000 to 19,000 cd m−2, an increment of 46%. For a high triplet energy blue emitter containing device, it is increased from 6.9 to 8.9 lm W−1, an increment of 29%, and the maximum luminance enhanced from 9,000 to 11,000 cd m−2, an increment of 22%.

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