Indoline and benzothiazole-based squaraine dye-sensitized solar cells containing bis-pendent sulfonate groups: Synthesis, characterization and solar cell performance

Abstract

Two new symmetric squaraine sensitizers (SQTHZ and SQIND) carrying benzothiazole and indoline moieties as strong electron donating groups to inject the electron into the TiO2 nanoparticles were tested as DSSC. The theoretical calculations and absorption results show that the electron density of LUMO of SQTHZ is delocalized in the whole chromophore, leading to strong electronic coupling between SQTHZ sensitizer and the conduction band of TiO2. Furthermore, the presence of long alkyl chain with pendent bis-SO3- groups would inhibit recombination and decrease the dye aggregation. Interestingly, SQTHZ displayed UV–Vis and NIR absorption at a longer wavelength compared to SQIND. This structure feature, as well as optical properties, would lead to improved efficiency of dye-sensitized solar cell with overall better photovoltaic performance (η of 3.31%, Jsc of 7.65 mA/cm2, Voc of 0.59, ff of 0.71 and IPCE of 47% at 674 nm) compared to SQIND.