Influence of a local electric field on the light harvesting efficiency of a cyclopentadithiophene-bridged D-A-π-A indoline dye on pure and N-doped TiO2 surfaces

Abstract

The primary objective of this paper is to study the influence of the local electric field at the dye/semiconductor (pure and nitrogen doped TiO2) interface on the performance of dye sensitized solar cells (DSSCs). In this regard, as a first step, we explored the influence of electric field on the performance of the WS-51 dye by computing its properties in an electric field up to 15 × 10−4 a.u. The electronic and optical properties of an established, efficient, donor-acceptor-π-acceptor dye in different electric field strengths were probed with density functional theory (DFT) and time-dependent DFT. The calculated results indicate that, under an electric field, the dye shows significant changes in absorption spectrum due to considerable changes in molecular structure. The TD-DFT results indicate that the absorption spectrum of the dye in acetonitrile solution have shown a blue shift with decreasing molecular extinction coefficient by rising electric field strength. Secondly, we investigated the dye adsorbed on Ti48O96 and Ti48O95N clusters. In the applied field off state, the absorption spectrum of the dye/Ti48O95N system is red shifted with an improved molecular extinction coefficient as compared to the dye/Ti48O96 system, indicating that the nitrogen doped TiO2 surface is more favourable for enhancing the efficiency of the DSSCs. Finally, the calculated results suggested that the light harvesting efficiency (LHE) of the dye/Ti48O95N system is higher than that of the dye/Ti48O96 system. But, under an electric field the LHE of the dye on Ti48O96 and Ti48O95N clusters is likely to decrease with increasing electric field strength. The photon to current response of the DSSCs is limited by the local electric field generated at the dye – semiconductor interface. Finally, results indicate that the doping of a nitrogen atom in TiO2 moderates the electric field intensity at the dye – semiconductor interface. Therefore, the results obtained in this study will provide a valuable reference for understanding the role of local electric field for the further optimization of DSSCs.