Low-temperature cross-linkable hole transporting materials through chemical doping for solution-processed green PHOLEDs

Since the inter-layer mutual solubility is an obstacle to the development of solution-processed OLED, crosslinking is considered to be the best method to obtain solvent resistance. Vinyl is the most widely reported crosslinking group, but a problem raised that crosslinking usually need a high temperature. Here, two vinyl-crosslinked hole transporting materials, 3,3'-(1,3,4-oxadiazole-2,5-diyl)bis (N-phenyl-N-(4-vinylphenyl)aniline) (OXZ-VPAN), 3,3'-(4-phenyl-4H-1,2,4-triazole-3,5-diyl)bis (N-phenyl-N-(4-vinylphenyl)aniline) (TRZ-VPAN) were designed and synthesized. The introduction of pentaerythritol tetra(3-mercaptopropionate) (PETMP) and vinyl groups by thiol-ene reaction to reduce the crosslinking temperature. As a result, crosslinking can be achieved at 120 degrees C with the solvent resistance higher than 99%. The surface morphology of the films before and after crosslinking were characterized by atomic force microscope, and it was found that the roughness of the film was improved after dopped with PETMP. The solution-processed green phosphorescent OLEDs devices based on the obtained HTM exhibit excellent performance. Maximum current efficiency of 57.1 cd A(-1) and external quantum efficiency of 16.0% (Ir (mppy)(3)) are obtained when OXZ-VPAN served as HTL. This low temperature feasible cross-linking process to prepare HTLs promotes the development solution-processed OLEDs.

Automated summary

This study successfully achieved crosslinking of hole transporting materials by lowering the crosslinking temperature, resulting in materials with high solvent resistance, which promotes the development of solution-processed OLEDs.