Hole and Electron Transport in Triarylamine-Based Charge-Transport Materials Investigated by the Time-of-Flight Method

For the organic charge-transport molecule N – N ′-diphenyl- N, N ′-bis(3-methlyphenyl)-[1,1′-biphenyl]-4,4′-diamine (TPD), theoretical predictions indicate that the mobility of holes should be significantly greater than that of electrons. In this report, a time-of-flight study of the hole and electron transport properties of TPD is presented. It is revealed that TPD has similar mobility for both holes and electrons, for example, a mobility of 1 × 10 –3 cm 2 V –1 s –1 for holes and 9 × 10 –4 cm 2 V –1 s –1 for electrons at 10 V μm –1 . The ability for the material to transport electrons is additionally demonstrated by the photoinduced discharge of a TPD-based photoreceptor with a positive electrostatically charged surface. The hole and electron charge transporting properties of TPD are of particular importance due to the widespread use of this material in a variety of organic electronic devices.