Theoretical Design And Characterization Of High Performance Arylamine-based Or Ganic D-π-A Dyes For Dye-Sensitized Solar Cells

As the energy crisis and environmental pollution is serious, the desire for clean energy is more and more intense. After the breakthrough of dye sensitized solar cell from Gr?tzel in 1991, the DSSC has attracted the attention of all over the world due to its lots of advantages as compared to the traditional silicon based solar cells, such as the low cost, easy fabrication, flexibility, et al. The record efficiency of DSSC has reached to 13.0%, however it is still lower than that of the silicon-based solar cells. Thus, it is still necessary to further improve the efficiency of the cell for the large scale commercial production. As the key component of DSSC, the properties of the sensitizers play an important role in determining the performace of the cell. Thus, it is important to reveal the relationship between molecular structure and its perperties. Through the quantum calculations, key parameters affecting the performance of the cell including short circuit current density(Jsc) and open circuit photovoltage(Voc) were discussed in this thesis to construct the structure-property relationship. We hope this work could show some theoretical guidance for the experiment to design more efficient sensitizers in order to improve the efficiency of the cell.This paper mainly includes two parts of work:1. Factors associated with Jsc and Voc of dye sensitized solar cells(DSSCs) have been analyzed through DFT and TDDFT calculations to explore the origin of the significant performance differences with only tiny structure difference(1.24% for 1 and 8.21% for 2)(Advanced Functional Materials 2012, 22, 1291-1302). Our results reveal that the insertion of phenyl ring in 2 enlarges the distance between the dye cation hole and the semiconductor surface and makes the benzothiadiazole(BTDA) unit, which has strong interaction with the electrolyte, far away from the semiconductor, resulting in a decreased charge recombination rate compared with that of 1. However, the insertion of phenyl ring also results in a distortion of the molecular structure, leading to a decreased light harvesting ability. Hence, two dyes(6 and 7) derived from 2 with better conjugation degree, farther position of BTDA unit and longer molecular length have been designed to keep the advantages and overcome the disadvantages of 2 simultaneously. The results demonstrate that we have got the desired properties of dyes through reasonable molecular design, and these two dyes could be promising candidates in DSSC field and further improve the performance of the cell.2. The geometries, electronic structures, absorption spectra, electron injections, conduction band energy shift and charge recombination process of six organic sensitizers used for dye sensitized solar cells were investigated in this part through density functional theory and time-dependent density functional theory calculations. The results demonstrated that all the molecules show comparable light harvesting ability as compared to TPA-T-CA except for TPA-P-BTBA. And the electron injection life of all the dyes were on femtosecond(fs) scale, showing ultrafast electron injection rate. Moreover, as for the charge recombination process, TPA-T-CA is about 44 times larger than that of TPA-T-EBTBA and TPA-P-EBTBA, and 11 times larger than that of TPA-T-BTBA. Thus, we predict that TPA-P-EBTBA, TPA-T-EBTBA and TPA-T-BTBA could show larger Jsc, Voc and therefore the overall efficiency, which could make them as the promising candidates of DSSC.