The Hole Transport Characteristics of 1, 4, 5, 8, 9 and 11-Hexaazatriphenylene-Hexacarbonitrile by Blending*

The hole transport characteristics of molecule blends of 1, 4, 5, 8, 9 and 11-hexaazatriphenylene-hexacarbonitrile (HAT-CN): N,N'-di(naphthalene-1-yl)-N,N'-diphenyl-benzidine (NPB) and HAT-CN: 4,4'-cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine] (TAPC) with various NPB and TAPC mixing concentrations (5–90 wt%) are studied. When the concentration is in the range of 5–80 wt%, it is found that the hole conductions in the two blends are space-charge-limited current (SCLC) with free trap distributions. The current–voltage characteristics of the two blends show SCLC with exponential trap distributions at the concentration of 90 wt%. The hole mobilities of the two blends are very close (10−4–10−3 cm2V−1s−1), the dependence of electric field and temperature can be described by the modified Poole–Frenkel model. The hole mobility and activation energy of the two blends depending on concentration are similar.