Effect of polar additives on charge transport in a molecularly doped polymer: Survey of various additives

Abstract

We have investigated the mobility of holes in a molecularly doped polymer, polystyrene doped with tri‐p‐tolylamine and small amounts of polar additives. The additives come from several chemical families (including cyano, nitro, and sulfonyl compounds) and range in dipole moment from 0 to 6.6 D. The mobility is dramatically reduced and its dependence on electric field strength is greatly increased by some of them. The size of both effects depends mainly on the concentration and net dipole moment of the additive; structure‐specific variations are secondary. The results are compared with two current models. A model in which the additive acts as a ‘‘dipole trap’’ predicts the wrong dependence on the concentration of the additive. Attempts to interpret the effects with the Gaussian disorder model of Bässler and co‐workers [H. Bässler, Phys. Status Solidi B 175, 15 (1993)] are only partially successful. Possible reasons are described.