The performance of organic donor-acceptor heterojunctions in solar cell devices is fundamentally determined by factors such as charge separation efficiency, charge carrier mobility, exciton diffusion lengths, and energy losses due to exciton recombination. Despite advancements in organic photovoltaic materials, exciton transport is frequently hindered by structural disorder, which limits overall device efficiency. Exciton-polaritons, formed through the strong coupling of cavity-coupled organic materials, exhibit delocalized states that enhance exciton transport and reduce the effects of disorder. Thus, it is of interest to elucidate the influence of strong coupling on charge transfer dynamics in organic photovoltaic materials. Using transient absorption spectroscopy, we explore the effect of cavity-strong-coupling in DBPC70 donor-acceptor blends integrated with a distributed Bragg reflector cavity. We find that the presence of the cavity slows the charge transfer process in such heterojunction systems.
The concept of modifying molecular dynamics in strongly coupled exciton-polariton systems is an emerging topic in photonics. However, there is no consensus on the types of molecular systems whose dynamics can be modified using strong coupling. These open questions stem from persistent uncertainties concerning the lifetime and conversion dynamics of exciton-polaritons and localized excited states as well as the proper way to measure such interactions in the time-domain. Here, we provide a framework for measuring dynamical interactions between exciton-polaritons and a diverse manifold of singlet, triplet, and multiexciton states, using a model molecular spin conversion (singlet fission) system that is strongly coupled to an optical microcavity. In addition to the usual population dynamics, transient optical measurements on microcavities are sensitive to transient modifications of the exciton-polariton transition energies, exciton-photon coupling conditions, and thermal excitations of the cavity mirrors.
Coupling between excitons belonging to organic dyes and photons in a microcavities forming cavity polaritons have been receiving attention for their fundamental interest as well as potential applications in coherent light sources. Organic materials are of particular interest as the coupling is particularly strong due to the large oscillator strength of conjugated organic molecules. The resulting coupling in organic materials is routinely in the strong regime. Ultrastrong coupling between photons and excitons in microcavities containing organic dyes and semiconductors has been recently observed in room temperature. We have studied the coupling between cavity pairs in the ultrastrong regime and found that the high order terms in the modified Jaynes-Cummings model result in broken degeneracy between the symmetric and antisymmetric modes.
The unusually strong coupling between cavity photons and organic excitons dovetail with the robust nonlinear optical responses of the same materials. This provides a new and promising hybrid material for photonics. We report on measurements of photorefraction in organic cavities containing a derivative of the photorefractive organic glass based on 2-dicyanomethylene-3-cyano-2,5-dihydrofuran (DCDHF).
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