Liquid-Formed Glassy Film of N,N‘-Diphenyl-N,N‘-bis(3-methylphenyl)benzidine:  Formation, Carrier Transporting Ability, Photoluminescence, and Stability

A detailed study of the hole transporting property and stability of the liquid-formed glassy film of a traditional hole transporting material N,N‘-diphenyl-N,N‘-bis(3-methylphenyl)benzidine (TPD) prepared by rapid cooling of the melt was carried out. The film obtained via supercooled liquid by a rapid-cooling method has been demonstrated to be amorphous and have a hole mobility of 1.0−1.2 × 10^-3 cm²/Vs, which is higher than that of conventional vacuum-deposited film (6−8 × 10^-4 cm²/Vs). The low dependence of the hole mobility on the electric field for the TPD film prepared by the rapid-cooling method is attributed to the high relative dielectric constant. Our study also revealed that when it was transferred into glass via supercooled liquid, the thermal and morphological stabilities of TPD film were remarkably improved.