Far-red active squaraine dye-sensitized photoanode for dye-sensitized solar cells with a copper (II/I) electrolyte

In dye-sensitized solar cells (DSSC), controlling the dye-aggregation on TiO₂ and charge recombination between electrons present in TiO₂ and electrolyte can be achieved by wrapping the long alkyl groups around the dye structure and further introducing bulky donor on the dye is a potential approach to enhance both the open-circuit potential and short-circuit current parameters. Additionally, bulky donor containing dye structures modulates the photophysical and electrochemical properties of the sensitizer which helps reducing the over potentials required for the dye regeneration process by utilizing a multidentate ligand containing [Cu(tme)]^2+/+ and I⁻/I₃⁻ redox electrolytes. Hagfeldt donor appended far-red NIR active unsymmetrical squaraine dye (SQ-HF) has been designed, synthesized, and characterized. SQ-HF dye showed an intense absorption at 676 nm (ε 1.7 × 10⁵ M⁻¹cm⁻¹). Photophysical and electrochemical studies indicated that the LUMO and HOMO energy levels of the SQ-HF dye were suited for charge injection (from the LUMO of the dye to the conduction band of TiO₂) and dye-regeneration processes, respectively. The DSSC device efficiency of 5.15 % (J_SC of 10.83 mA/cm² and V_OC of 0.690 V) has been achieved for SQ-HF dye by utilizing a literature reported [Cu(tme)]^2+/+ and 4.11 % (J_SC of 8.74 mA/cm² and V_OC of 0.702 V) in I⁻/I₃⁻ redox shuttles, respectively.