Theoretical Study Of Photoinduced Charge Transfer In Organic Solar Cell

The solar cell is a kind of photoelectric device that can convert the light energy into the electrical energy. The most common salar cell on the market is silicon solar cell whose basic structure is silicon, such as the monocrystalline silicon solar cell, polycrystal silicon solar cell and so on. Although their photoelectric conversion efficiency can be as high as 24%, they have many shortages: consuming more resources, high-cost, complex process and so on. The organic solar cells have lower photoelectric conversion efficiency than silicon solar cells. However, the advantages of much more sources of raw material ease of processing and eco-friendly make the organic solar cells become an important hot area of scientific research. For both silicon solar cells and origanic solar cells, improving the photoelectric conversion efficiency of solar cells is the constant goal of scientists.In this thesis, the chlorophyll a, carotenoid, BT molecule as well as PC61 BM molecule were chosen as the active materials of organic solar cells. Quantum mechanical calculations were performed to study the photoinduced charge and energy transfer mechanisms, the coherence of electrons and holes, and the excited state properties in such organic molecules system. We used three-dimensional(3D) visualization technology to visualize the process of photoinduced charge transfer, and further to reveal the charge and energy transfer mechanisms of optical function materials in the excited state. Utilizing the 3D visualization technology, the orientation of charge transfer can be determined. We used Gauss View 5.0 to construct the molecular model, and optimized the geometries of donor and acceptor using density funetional theory(DFT). All calculations were performed by Gaussian 09. We used time dependent density functional theory(TD-DFT) with CAM-B3 LYP function and 6-31G(d) basis set, to calculate the excited states of molecules, and further to calculate the oscillator strength and the vertical excitation energy of the molecules. Bsed on Marcus theory and Marcus-Levich-Jortner’s theory, we studied the reorganization energy and free energy of molecular electric charge transfer. We used DFT to optimize the positive ion balance structure of donor and the negative ion balance structure of acceptor, where B3 LYP function and 6-31G(d) basis set were used. Bases on the optimal negative/neutral, the energy of neutral/charged acceptor were calculated using single point energy. The lowest excited state and cationic state of acceptor were optimized using TD-DFT method, where CAM-B3 LYP function and 6-31G(d) basid set were used.