A model for recombination in Type II dye-sensitized solar cells: Catechol-thiophene dyes

► Direct injection band for catechol-thiophene dyes on TiO2 modeled with dye-Ti(OH)2. ► Energy, intensity of the new band vs number of thiophene units agree with experiment. ► Recombination in dye/TiO2 is modeled as internal conversion in dye-Ti(OH)2. ► Trend in recombination vs extent of conjugation connected to vibrational spectrum. ► Simple formula for vibrational factors of the internal conversion rate is derived.