Polaron Photoconductivity in the Weak and Strong Light-Matter Coupling Regime.

Abstract

We investigate the potential for cavity-modified electron transfer in a doped organic semiconductor through the photocurrent that arises from exciting charged molecules (polarons). When the polaron optical transition is strongly coupled to a Fabry-Perot microcavity mode, we observe polaron polaritons in the photoconductivity action spectrum and find that their magnitude depends differently on applied electric field than photocurrent originating from the excitation of uncoupled polarons in the same cavity. Crucially, moving from positive to negative detuning causes the upper and lower polariton photocurrents to swap their field dependence, with the more polaronlike branch resembling that of an uncoupled excitation. These observations are understood on the basis of a phenomenological model in which strong coupling alters the Onsager dissociation of polarons from their dopant counterions by effectively increasing the thermalization length of the photoexcited charge carrier.