Low-Temperature Transport Properties of Photogenerated Charges in Organic Materials

We report a new experimental method to measure the localization length of photogenerated carriers in an organic donor-acceptor photovoltaic blend by comparing their dielectric and electron spin-resonance susceptibilities, which are simultaneously measured by monitoring the resonance frequency of a superconducting resonator. We show that at cryogenic temperatures excitons are dissociated into long lived states, but that these are confined within a separation of around 4 nm. We determine the Debye and recombination times, showing the coexistence of a fast electrical response corresponding to delocalized motion, with glasslike recombination kinetics.