Drift mobility of holes in vacuum-deposited films of zinc tetraphenylporphyrin

Abstract

Drift mobilities (μ) of holes in zinc tetraphenylporphyrin (ZnTPP) films were measured using the time-of-flight method. The plot of log μ vs. a square root of electric field ( E 1 2 ) fit a straight line and its extrapolation to E = 0 yielded an extremely small μ value of the order 10 −10 cm 2 V −1 s −1 at 20°C. The field dependencies of the hole mobilities at different temperatures were analyzed on the basis of the disorder formalism developed by Bässler and co-workers. As a result, the slow hole transport in the ZnTPP films was ascribed to a greater disorder parameter ( σ = 0.15 eV) resulting from a nearly amorphous structure of the ZnTPP films.