Theoretical description of a novel dye-sensitized solar cell

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A better understanding of the processes in organic/hybrid optoelectronic devices may enable the utilization of novel technologies. This understanding requires the development of new methods in theoretical chemistry and theoretical physics that allow for the description of supramolecular systems in solution and on surfaces in atomic detail. As planned for the original project this continuation project is to treat the model of a dye sensitized solar cell. The system consists of a molecular aggregate built of porphyrin derivatives and fullerenes deposited on tin (IV) oxide. The processes that are to be investigated are excitation energy transfer, electron transfer as well as electron injection into the semiconductor. First experimental results on this system have been published. A detailed theoretical investigation of the system is to answer open questions that may finally result in the construction of more efficient dye sensitized solar cells. In order to model the whole system in atomic resolution a mixed quantum-classical methodology is to be utilized. The method bases on the reduction of the system Hamiltonian to the relevant electronic states. The wavefunction is expanded with respect to these relevant electronic states. This allows for the numerical solution of the time-dependent Schrödinger equation. The respective Hamiltonmatrix depends parametrically on the nuclear coordinates which are to be derived from classical molecular dynamics simulations. The crucial criterion regarding the quality of the results is the accurate parameterization of the effective Hamiltonmatrix. During the last three years I demonstrated that the treatment of dispersive (London van-der-Waals) interaction has a huge impact on the energies of molecular states and on optical spectra of molecular aggregates. It is planned to apply the respective method to the model of a dye sensitized solar cell. Additionally, the methodology is to be improved and, particulary, extended to allow for the calculation of environmentally induced screening of excitonic coupling. The excitonic couplings are the non-diagonal elements of the excitonic Hamiltonmatrix and have a huge impact on the overall results. The respective model system for the further development of this methodology will be crystalline structures of the perylene derivative PTCDI. Optical spectra and transfer processes are to be modeled. In the case of the porphyrin-derivate/fullerene aggregate the injection efficiency in dependence of the aggregate configuration are to be understood and optimized. Thereby, the complete model of a dye-sensitized solar cell will be described in atomic resolution.