Bistriphenylamine-based organic sensitizers with high molar extinction coefficients for dye-sensitized solar cells

A series of novel bistriphenylamine-based organic sensitizers (coded as RC-dyes) with high molar extinction coefficients (>5.0 × 10⁴ M^-1 cm^-1) have been synthesized for dye-sensitized solar cells (DSSCs). By changing the length of the π-conjugation bridge thiophene from zero to two between the donor and the acceptor part, the range of absorption and its corresponding photon-to-current conversion was modulated gradually to the low energy region in the visible spectrum. Based on the electrochemical and theoretical investigations on the electronic and geometrical structure, RC dyes were shown to be a promising candidate for efficient metal-free organic sensitizers with strong light absorption. Among RC dyes (11∼13) tested, the highest power conversion efficiency of 5.67% was obtained from RC-13 with a short circuit current of 10.78 mA cm^-2, an open circuit voltage of 0.71 V, and a fill factor of 0.74 under standard AM 1.5 measurement conditions.