Dye-sensitized solar cells using retinoic acid and carotenoic acids: Dependence of performance on the conjugation length and the dye concentration

Titanium oxide-based dye-sensitized solar cells (DSSC) were fabricated by the use of retinoic acid and carotenoic acids having the number of conjugated double bonds, n = 5–13. The incident photon-to-current conversion efficiency, the photocurrent density and the solar energy-to-electricity conversion efficiency exhibited the highest values at n = 7, and then decreased toward both sides. The effects of dilution of CA7 with deoxycholic acid were also examined. The above parameters per unit CA7 concentration progressively increased toward the lowest concentration, which is ascribed to the isolated excitation free from singlet–triplet annihilation in the dye molecules on the TiO2 layer.