Expanding π-bridge and introducing auxiliary acceptor for realizing panchromatic absorption of the phenothiazine dyes in dye-sensitized solar cells

Dyes with panchromatic absorption of the solar radiation is crucial for the photovoltaic performances of dye sensitized solar cells (DSSCs). In this paper we have constructed four phenothiazine dyes (PS1, PS2, PID1 and PID2), and applied to fabricate the DSSCs. Some important results have been found: (I) PID1 and PID2 with isoindigo as auxiliary acceptor successfully achieve nearly panchromatic absorption. (II) thieno[3,2-b]thiophene is a better pi-bridge than 2,2'-bithiophene in terms of facilitating the intramolecular transport of photoexcited electrons, reducing the dye aggregation and improving the photovoltaic properties of DSSCs; (III) it is surprised that PID1 and PID2 exhibit broader absorption spectra, but achieve lower conversion efficiencies than PS2 with thieno[3,2-b]thiophene as pi-bridge; (IV) The low device efficiencies of the isoindigo-based dyes might be due to the strong electron-withdrawing ability of isoindigo moiety, affecting the electron transport. These findings suggest that it might be an effective way to realize panchromatic absorption of the organic dyes by introducing isoindigo as an auxiliary acceptor, and a balanced perspective on the molecular design of dye is necessary to improve the performance of DSSCs.