THE ROLE OF IMPURITIES ON THE ELECTRON-PARAMAGNETIC-RESONANCE RESPONSE OF POLARONS IN CONJUGATED POLYMERS

Poly(3-hexylthiophene) prepared by oxidative coupling using ferric chl oride and with varying residual impurity levels of Fe, was used to stu dy the temperature dependence of charge carriers in conjugated polymer s. The temperature was ramped from room temperature to 110 K and Elect ron Paramagnetic Resonance (EPR) data for the iron impurity as well as the polymer were obtained. The doubly integrated area of the dispersi on curves due to the polymer and the Fe impurity were calculated and s how that the former exhibits a Curie Law behavior while the latter exh ibits an exponential behavior on a background of immobile charge carri ers. The exponential behavior is characteristic of a charge transfer c omplex (CTC) with a thermally activated excited state whose activation energy was calculated to be: E-CTC = (3.3 +/- 0.5) x 10(-2) eV and th e background component which is independent of temperature was: S-0 = (7.5 +/- 0.5) x 10(16) spins/g.