Cavity-mediated charge transfer in a donor-acceptor photovoltaic: experiments and modeling insights

Light-induced charge and energy transfer is the basis of many natural and engineered light-harvesting systems such as photosynthetic complexes and photovoltaics. While much work has focused on synthetic design strategies to optimize and control this process, a new field of research has emerged in which strong coupling between quantized light and matter enables drastic changes in a material's potential energy landscape and eigenstate structure. By embedding a material in an optical microcavity, its polarization strongly interacts with a confined electromagnetic field mode to form hybridized light-matter states known as polaritons. How polaritons can be leveraged to access unseen and useful charge and energy transfer pathways has stimulated a lot of interest. In this talk, I will discuss recent spectroscopic experiments in our group on a cavity-embedded donor-acceptor photovoltaic (P3HT/PCBM) demonstrating that charge transfer can proceed by means of polariton states despite the photon's relatively short lifetime (~100 fs). I will also present a model Hamiltonian of the combined electron-hole-photon system together with open quantum dynamics simulations that provide insights into the underlying relationships between system properties and the production of free charge carriers including the strength of light-matter coupling and energetic disorder, the latter of which notably localizes the exciton and inhibits efficient formation of charge-transfer states. By studying this model, we capture energetic and coupling regimes in which polaritons can potentially outperform the energy conversion efficiency in bare organic photovoltaics.