We investigate the impact of strong coupling on photoinduced electron transfer by studying the photocurrent in p-doped organic semiconductor (TAPC) microcavities at low temperature (100K). When we resonantly excite polariton modes derived from the transition of charged TAPC molecules (holes), we observe a systematic difference in the bias dependence of the photocurrent originating from the lower and upper polariton branches. The more matter-like branch shows a stronger bias dependence across cavities with different detunings and incident angles (see graphic) . Moreover, we observe that photocurrent originating from uncoupled excitations exhibits the strongest bias dependence near zero detuning. Our findings can be phenomenologically explained on the basis of Onsager theory, which predicts the dissociation probability of the charge transfer complex consisting of a hole and its dopant counterion based the field, temperature, and thermalization length of the photoexcited hole. From this perspective, the unusual bias dependence that we observe suggests that the thermalization radius is smallest for uncoupled excitations, and increases as a given polariton mode becomes more photon-like. We discuss possible mechanisms to explain this increase in charge transfer efficiency, focusing in particular on the inhomogeneous distribution of intermolecular electronic couplings in the thin film, which highlights an important role of disorder in polariton photochemistry.

Evidence of cavity-modified electron transfer from charged polariton photoconductivity

ACS Spring 2022

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