Theoretical Study On The New D-π-A Polymer Dye Molecule Photoinduced Charge Transfer Mechanism

With the development of economy, the demand for energy is increasing, while coal、petroleum、natural gas and other energies are not renewable, and the burning will emit a lot of harmful gases, causing pollution to the environment and therefore people are working to find new sources of energy. Due to solar energy has outstanding advantages, such as rich、no pollution and so on, the scientists hope the conversion of solar energy can be used by people, such as chemical and electrical energy and so on. Solar cells can convert solar energy into electrical energy, so it is widely concerned by people. Dye-sensitized Solar Cells(DSSCs) has caused many scientific workers because of its simple preparation, high photoelectric conversion efficiency. Dye sensitizer is the core of DSSCs, its performance has a significant impact on the DSSCs photoelectric conversion efficiency, this paper will take the dye sensitizer as the research key content.In this paper we research three kinds of D-π-A type of dye sensitizer phenyl-indoline-quinoxaline derivatives IQ4、YA421、YA422 moleculars as the research object. The ground-state geometry of three kinds of molecular is optimized and the excited state properties by use density functional theory (DFT) and Time-dependent density functional theory(TD-DFT) with the B3LYP function and 6-31G(d) basis set. The energy difference between the HOMO and LUMO is 2.639eV、2.612eV and 2.503eV respectively. Drawing absorption spectrum, according to the information of the moleculars excited states, there are mainly appeared two peaks from the spectrum, the first absorption peak wavelength range is 300nm to 400nm, the second absorption peak at 500nm to 600nm. YA4421、 YA422 compared with IQ4 molecule the highest energy absorption peak occurs red shift, the reason is that the growth of the donor group chain, lead to molecular inter-atomic forces enhancing.On the basis of optimization of IQ4、YA421、YA422 ground state, we calculated the density of states (DOS) by using GaussSum. It can be seen that the charge transfer ability is increasing from the electron donor to acceptor, as to the conjugated chainlength growth, the photoinduced charge separated state is easy forming. In order to further study the intramolecular lectron transfer, we use the three-dimensional real space analysis method(transition density(TD), charge difference densities(CDD)) for their visualization. Then, we use the two-dimensional(2D) real space analysis method to analyze coherence of the electron hole. Finally, the results of the calculation are compared with experimental values, consistent. We can provide a theoretical reference for future research dye sensitizer by studying the three molecular of poperties.