PHOTOCONDUCTIVE POLYMERS - STRUCTURE, MECHANISMS AND PROPERTIES

Charge carrier transport properties of organic polymers can vary over a wide range. The paper shows that the electron- and hole mobilities of polymers with pendant photoconductive groups (i.e. carbazole) are on the order of 10(-6) cm2/Vs. In these materials the flow of electronic charge is maintained by the overlap of the pi-orbitals of the pendant molecular groups. The large variation of this short-range interaction, depending on the local configurations encountered in polymer glasses, leads to a large variation of hopping probabilities and, hence, to wide rate-distributions. These distributions are reflected in the slow algebraic decay characteristics of the observed photocurrents. The typical time exponents alpha (alpha less-than-or-equal-to 1) are shown to carry a great deal of physical information, if the dynamical range of the experiments is sufficiently large. The paper also refers to quasi-conjugated polymers (polysilanes) whose dynamic transport parameters are about 10(3) times better (faster) as compared to polymers with pendant groups. These new materials open interesting aspects for the development of new polymeric materials with better transport parameters and, hence, shorter 'switching times'.