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  1. In order for a photovoltaic cell to function, charge carriers produced by photoexcitation must fully dissociate and overcome their mutual Coulomb attraction to form free polarons. This becomes problematic in organic systems in which the low dielectric constant of the material portends a long separation distance between independent polaron pairs. In this paper, we discuss our recent efforts to correlate the role of density of states, entropy, and configurational and energetic disorder to the open-circuit voltage, V OC , of model type-II organic polymer photovoltaics. By comparing the results of a fully interacting lattice model to those predicted by a Wigner–Weisskopf type model we find that energetic disorder does play a significant role in determining the V OC ; however, mobility perpendicular to the interface plays the deciding role in the eventual fate of a charge-separated pair.
  2. Recent theories and experiments have explored the use of entangled photons as a spectroscopic probe of physical systems. We describe here a theoretical description for entropy production in the scattering of an entangled biphoton Fock state within an optical cavity. We develop this using perturbation theory by expanding the biphoton scattering matrix in terms of single-photon terms in which we introduce the photon-photon interaction via a complex coupling constant, ξ. We show that the von Neumann entropy provides a concise measure of this interaction. We then develop a microscopic model and show that in the limit of fast fluctuations, the entanglement entropy vanishes, whereas in the limit of slow fluctuations, the entanglement entropy depends on the magnitude of the fluctuations and reaches a maximum. Our result suggests that experiments measuring biphoton entanglement give microscopic information pertaining to exciton-exciton correlations.
  3. Recent theories and experiments have explored the use of entangled photons as a spectroscopic probe of physical systems. We describe here a theoretical description for entropy production in the scattering of an entangled biphoton Fock state within an optical cavity. We develop this using perturbation theory by expanding the biphoton scattering matrix in terms of single-photon terms in which we introduce the photon-photon interaction via a complex coupling constant, . We show that the von Neumann entropy provides a concise measure of this interaction. We then develop a microscopic model and show that in the limit of fast fluctuations, the entanglement entropy vanishes, whereas in the limit of slow fluctuations, the entanglement entropy depends on the magnitude of the fluctuations and reaches a maximum. Our result suggests that experiments measuring biphoton entanglement give microscopic information pertaining to exciton-exciton correlations.