Computational simulations are performed to understand the structure and the electronic properties of dye@TiO₂ interfaces and thus complement experimental work. A common computational approach is to perform calculations of adsorbate-nanocrystalline TiO₂ surface systems using periodic boundary conditions. With a relatively small periodic TiO₂ slab model, the electronic structure of TiO₂ can be described and a density of states (DOS) with a bandgap close to the bulk value can be obtained. As the interaction between dye and TiO₂ can strongly influence the electronic coupling between dye and TiO₂, we have focused our research on the adsorption of dyes on TiO₂ by employing periodic-DFT methods. We have studied different possible adsorption configurations of organic d-π-A dyes on extended anatase TiO₂ (101) surface and evaluated their adsorption strengths with the TiO₂. The calculated adsorption energies are in proportion to the experimental short-circuit photocurrent densities (J_sc).¹ The electronic structure of the dye sensitized TiO₂ is explained from the calculated DOS which shows an overlap of the unoccupied molecular orbitals of the dye and the TiO₂ conduction band.² We also used alternative cluster models, which enable studies of the interaction of large adsorbates with nanostructured TiO₂ substrates.³ We have studied the adsorption geometry and optical absorption spectra of thiocyanate free cyclometalated ruthenium dyes on (TiO₂)₃₈ cluster which allowed us to understand the electron injection (direct/indirect) mechanism and the electronic structure of the dye@TiO₂ assemblies.⁴

References

1. Srinivas, K.; Kumar, C. R.; Reddy, M. A.; Bhanuprakash, K.; Rao, V. J.; Giribabu, L., D-π-A organic dyes with carbazole as donor for dye-sensitized solar cells. Met. 2011, 161, 96-105.
2. Srinivas, K.; Sivakumar, G.; Ramesh Kumar, C.; Ananth Reddy, M.; Bhanuprakash, K.; Rao, V. J.; Chen, C.-W.; Hsu, Y.-C.; Lin, J. T., Novel 1,3,4-oxadiazole derivatives as efficient sensitizers for dye-sensitized solar cells: A combined experimental and computational study. Met. 2011, 161, 1671-1681.
3. Chitumalla, R. K.; Gupta, K. S. V.; Malapaka, C.; Fallahpour, R.; Islam, A.; Han, L.; Kotamarthi, B.; Singh, S. P., Thiocyanate-free cyclometalated ruthenium(ii) sensitizers for DSSC: A combined experimental and theoretical investigation. Chem. Chem. Phys. 2014, 16, 2630-2640.
4. Chitumalla, R. K.; Jang, J., Density functional theory study on ruthenium dyes and dye@TiO2 assemblies for dye sensitized solar cell applications. Sol. Energy. 2018, 159, 283-290.