Spin resonance, hall effect, and transport properties of poly(N‐vinyl carbazole)—iodine complex

The results and interpretations of Hall effect, resistivity, electron spin resonance, Dember effect, and thermoelectric measurements on the poly(N‐vinyl carbazole)—iodine complex are presented. The existence of a charge‐transfer state in this system is demonstrated by three independent techniques: (1) the variation of resistivity with iodine content; (2) study of unpaired spin concentration; (3) optical absorption measurements. Many complexes have high impedances that have prohibited heretofore measurement of fundamental characteristics such as Hall mobility. The development of an AC technique9 for the measurement of the Hall effect in materials of high resistivity and low mobility has permitted the measurement of the Hall mobility in compressed pellets of poly(N‐vinyl carbazole) complexed with iodine (impedance ∼1 megohm). It is believed that the Hall mobilities are the first to be reported for a charge‐transfer complex. A discrepancy in the sign of the majority carriers is observed: the Hall coefficient is negative, the Seebeck coefficient is positive. The Dember voltage supports n‐type conduction as found in the Hall effect. It is suggested that this sign discrepancy can be resolved by consideration of surface states. The concentration of carriers deduced from Hall measurements is four orders of magnitude smaller than the unpaired spin concentration. The mechanism of conduction proposed invokes a hopping process in which a localized electron in an unpaired spin state makes phonon‐assisted jumps from site to site.