Incorporating a stable fluorenone unit into D-A-π-A organic dyes for dye-sensitized solar cells

Two new organic dyes based on a donor-acceptor-pi-bridge-acceptor/anchor (D-A-pi-A) configuration, HIQF1 and HIQF2, were synthesized, characterized, and successfully employed in dye-sensitized solar cells. The incorporation of the weakly electron-withdrawing fluorenone group as an additional acceptor enhanced the dyes' properties for solar energy conversion in several ways. First, the absorption spectra of the dyes were broadened, covering a large range of sunlight. Second, the absorption spectra observed upon dye adsorption on TiO2 were only slightly blue-shifted as compared to the spectra of the dyes in solution. Third, the orbital energy levels and electron distributions of the D-A-pi-A backbone were ideal for highly efficient electron transport and injection. The incorporation of long electron-donating alkoxy groups in the donor unit of HIQF1 further increased the dye's short-circuit photocurrent density (J(sc)), open-circuit voltage (V-oc), and overall conversion efficiency (eta), but had little negative effect on the fill factor (FF). Solar cells sensitized with HIQF1 showed excellent current-voltage characteristics; the J(sc), V-oc, and FF values were 12.26 mA cm(-2), 0.70 V, and 0.73, corresponding to a eta value of 6.26%.