Molecular Design of Organic Dyes with Double Electron Acceptor for Dye-Sensitized Solar Cell

We designed and synthesized novel organic dyes of double electron acceptor type based on phenothiazine framework, as photosensitizers for the dye-sensitized solar cell (DSC). The density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were used to estimate the photovoltaic properties of the dyes in the design stage. The molecular structure having two electron acceptors on both sides of phenothiazine moiety provided the efficient electron extraction paths from electron donor part, which was demonstrated by the analysis of the electronic structures on donor and acceptor, and the excitations between HOMOs and LUMOs. In accordance, the measurements of photovoltaic properties of the DSCs prepared in the laboratory scale showed that the organic dyes Of double electron acceptor type gave about 20% higher performance than their counterparts of single electron acceptor type. The effect of the kind of electron acceptor (C, cyanocrylic acid and R, rhodanine-acetic acid) on the performance of DSC was studied as well. We found that (tie organic dyes with R as acceptor gave much lower efficiencies, compared to those with C. for both single and double electron acceptor type. It was attributed to (lie electronic decoupling between anchoring and TiO2 conduction band accompanying the lack of pi-conjugation of carboxylic group as anchoring on R, despite that the dyes with R had relatively broad and intense absorption spectra in the visible region.