Supramolecular Co-adsorption on TiO2 to enhance the efficiency of dye-sensitized solar cells

Abstract

Three novel push–pull dyes, with carbazole donors, coded AJ502, TZ101 and TZ102 are synthesized and applied as co-sensitizers in dye-sensitized solar cells (DSSCs). TZ101 and TZ102 have similar structures except for two fluorine atoms introduced on the benzotriazole (BTZ) unit. AJ502 shows a near-IR absorption spectrum that is suitable for co-sensitization with TZ101 and TZ102. The co-sensitized DSSC device based on CO-1 (AJ502 : TZ101 = 3 : 4 (0.075 mM : 0.1 mM)) achieves a power conversion efficiency (PCE) of 10.3% under AM 1.5G irradiation, with 1.06 V open-circuit voltage (V_oc), 13.75 mA cm⁻² short-circuit photocurrent density (J_sc), and 70.8% fill factor (FF), a significant improvement compared to the single dye, 6.0% for AJ502 and 5.1% for TZ101 with a copper(I/II)-based redox electrolyte. A PCE of 8.9% is also obtained by devices based on CO-2 (AJ502 : TZ102 = 3 : 4). For CO-1, the fluorine atoms in TZ101 play a critical role by widening the active light capturing bands of both TZ101 and AJ502 on the TiO₂ film while TZ102 and AJ502 show weaker interaction under the same conditions. The UV-vis spectrum and Raman spectrum revealed that AJ502 can form supramolecules with TZ101 and TZ102 formed on the TiO₂ film.