Benzo[1,2-b:4,5-b′]dithiophene and benzo[1,2-b:4,5-b′]difuran based organic dipolar compounds for sensitized solar cells

• Organic dyes for sensitized solar cells.
• Organic dyes consisting a benzo[1,2-b:4,5-b′]dithiophene group.
• Organic dyes consisting a benzo[1,2-b:4,5-b′]difuran group.
• Solar cell with highest conversion efficiency 6.12%.
• Deoxycholic acid as a co-absorbent.

Novel organic dyes that consist of either a benzo[1,2-b:4,5-b′]dithiophene or a benzo[1,2-b:4,5-b′]difuran core exhibited remarkable solar-to-energy conversion efficiency in dye-sensitized solar cells. The planar geometry of bridge moiety and its bulky substituents helped the dyes to form a high quality monolayer on the surface of titanium oxide. A typical device displayed photon-to-current conversion efficiency 60% in the region of 380–575 nm, a short-circuit photocurrent density 13.45 mA cm−2, an open-circuit photovoltage 0.72 V, and a fill factor 0.63, corresponding to an overall conversion efficiency 6.12%. In a test of using deoxycholic acid as a co-absorbent, an improvement of quantum efficiencies 8.37% was observed for certain compounds. However, for others the quantum efficiency decreased in 6.60–7.91%. The latter result indicated that the quality of some films cannot be further improved by the addition of deoxycholic acid. The photophysical properties were analyzed with the aid of TDDFT.

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