Spin relaxation mechanism in a highly doped organic polymer film

We report systematic studies on the spin current transport and relaxation mechanism in thin films of the highly doped organic polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), in which hopping charge transport is dominant. In this study, we determined the spin diffusion length, spin lifetime, and spin diffusion constant using different experimental techniques. The experimentally obtained spin lifetime is much shorter than that of nondoped organic semiconductors. This clearly shows considerable enhancement of spin relaxation in highly doped PEDOT molecules, which form the trapping centers of hopping transport. Also, we obtained a longer spin diffusion length than the average hopping length, indicating that spins are almost conserved during the hopping process. These facts suggest that spin relaxation of this material mainly occurs in the nanograins of the PEDOT molecules.