Theoretical investigation of novel phenothiazine-based D-π-A conjugated organic dyes as dye-sensitizer in dye-sensitized solar cells

摘要

The structural and electronic properties of four phenothiazine-based sensitizers (TMH-CN_(cis), TMH- CN_(trans), TMH-COOH, and TMH-2COOH) have been examined by means of density functional theory (DFT) and time-dependent DFT calculations. And the periodic DFT method is used to investigate the adsorption of dyes on the TiO_2 anatase (101) surface within the DMol~3 code. The results promise that anchor dyes with strong withdrawing CN group can effectively injected electrons to the conduction band of semiconductor TiO_2 surface implying that TMH-CN_(cis) and TMH-CN_(trans) will show better performance among four dyes. Particularly, the adsorption energies and charge density difference maps are calculated to investigate the possible adsorption modes of the dye on the TiO_2 surface. After establishing the preferred anchoring configurations, we performed a detailed analysis on the electronic structures of the dye-TiO_2 complexes to explore the absorption spectra, charge distribution and the composition of the density of states (DOS), providing a quantitative description of the variation in electronic coupling induced by the different anchoring group. The results show that after binding to the semiconductor, the absorption spectra of four dyes-TiO_2 complexes are all red-shifted significantly as compared to that of the isolated dyes, and the TMH-CN_(trans)-TiO_2 will transfer more electrons during the photoexcitation, showing an obvious charge transfer characteristic.