Theoretical Design Of Dye Molecules And Investigations On The Photoelectric Properties Of Dyes In Dye-sensitized Solar Cells

The vital role in light harvesting and electron injection at dye/semiconductor interface has led to an explosion in dye sensitizer research. In this thesis, to identify potential good dyes for dye-sensitized solar cells(DSSCs), the electronic and optical properties of isolated and adsorbed dyes were investigated with the aid of density functional theory(DFT) and time-dependent DFT(TDDFT) approaches. We hope that our theoretical results can be useful for experimental design of more efficient dyes for DSSCs.Based on a Zn(II)-coordinated phthalocyanine dye(TT7), a series of phthalocyanine(Pc) dyes with different metal ions and peripheral/axial groups have been designed. DFT and TDDFT calculated results show that Al(III)-based Pc dyes are potential good dyes for their appropriate energy-level arrangements of frontier orbitals and good optical properties. In particular, the iodinated Al-based Pc dye with dimethylamino as the periphery group exhibits the largest red-shift in the maximum absorbance(λmax). It has further been found that there is weaker intermolecular π-π staking interaction in Al-I-Pc molecules, which may effectively reduce the dye aggregation on semi-conductor surface. Therefore, Al-I-Pc dyes are potential phthalocyanine sensitizers for DSSCs.The carboxylic acid group in two organic dyes(CN11 and CN12) were replaced by diverse anchoring groups in the present study. The theoretical investigations on dye performance including electronic and optical properties demonstrate that the designed-CSSH-based dyes(CN11-CSSH and CN12-CSSH) show the biggest maximum absorbances(λmax), the broadest spectral response, and the longest lifetime of the first excited state. Therefore, the biscarbodithiolic acid group is a promising acceptor for high-efficiency dye sensitizer.By replacing the 3,4-ethylenedioxythiophene(EDOT) unit in unsymmetrical squaraine(SQ) dye of WCH-SQ11 by electron-rich and electron-deficient groups, four novel SQ dyes were designed. Systematic investigations based on DFT and TDDFT calculations show that the novel dye with dithienopyrrole(DTP) as a π-linker(WCH-SQ11-1) is a promising sensitizer for DSSC due to its good performance in light absorption, electron injection, charge transfer(CT), and a larger μnormal. Further investigations of the WCH-SQ11-1/(TiO2)38 complex reveal a red-shifted absorption spectrum compared to the free dye. Furthermore, the analysis of the molecular orbitals responsible for the maximum absorption indicate a direct electron injection mechanism for the WCH-SQ11-1/(TiO2)38 system. All these results suggest WCH-SQ11-1 to be a competitive alternative to WCH-SQ11.Three novel silicon-core JD analogues were designed using the nitrogen-containing heterocycle(ullazine group) based dye(JD21) as the prototype. A detailed theoretical investigation shows that the dithienosilole(DTS) containing Y2 dye displays remarkable light-harvesting capability, favorable thermodynamic property, good kinetic parameters, and high stability for the adsorbed system of Y2/(TiO2)38. It is thus proposed to be a potential dye toward more efficient DSSCs. The results also highlight the significant influence of silicon atom on the performance of a JD21-based dye.