Tetraarylthienothiophene: An efficient charge recombination-suppressed center for wide-gap dyes in dye-sensitized solar cells

Abstract

To take on the challenge of maintaining high open-circuit voltage (V_OC) while boosting short-circuit current density (J_SC) of auxiliary dyes with restricted spectral response for efficient co-sensitization in dye-sensitized solar cells, three wide-gap organic dyes YYQ11-13 featuring diverse decorations on triphenylamine (TPA) electron donors and thieno[3,2-b]thiophene (TT) π-spacers have been designed and synthesized. Compared with non-modified D1π6A1, tethering general hexyloxy chains to the peripheral of TPA donors (YYQ11) could raise the power conversion efficiency (PCE) by 10 % while transforming the TT core to tetraarylthienothiophene (TATT) center (YYQ12) could even enhance the PCE by 30 %. By joining both embellishments together (YYQ13), the PCE could be cumulatively increased by 40 % in comparison to reference D1π6A1. Finally, the megamerger YYQ13 achieved the PCE of 7.54 % under the standard AM 1.5 G irradiation using iodine electrolytes. Studying on the optical property, theoretical calculation and electrochemical impedance spectroscopy revealed that the three-dimensional TATT-based center could effectively elevate both V_OC and J_SC through suppressing charge recombination while the twisted TATT is beneficial for confining the absorption band at ideal wavelength, all that makes it a promising candidate for co-sensitization.