Low-Temperature Cross-Linkable Hole Transport Material Based on Carbazole Derivatives Design and Applications in Solution-Processed OLEDs

Cross-linking is demonstrated to be an effective strategy to resolve the interface erosion problem facing solution process technique for large area commercial applications of organic electronics. However, most of the reported cross-linkable materials require a high temperature of over 150 degrees C, which is detrimental to device performance. In this study, an in situ cross-linking protocol is proposed based on a triphenylamine/carbazole core linked with a hexyl chain and styryl moiety, and a low cross-linking temperature down to 120 degrees C is achieved for the first time. The resultant thermally cross-linkable hole transportation molecules of TPA-VBCz and HTPA-VBCz possess high triplet energy levels of around 3.0 eV and high decomposition temperatures over 410 degrees C. The solution-processed hole transportation layer (HTL) is cured at 120 degrees C in 30 min to finish the cross-linking net structure. Applications of this HTL in solution-processed multilayer thermally delayed fluorescent green OLEDs are explored with significantly improved current efficiency up to 78.3 cd A(-1) and external quantum efficiency of 24.6%.