Near-infrared absorbing porphyrin dyes with perpendicularly extended π-conjugation for dye-sensitized solar cells

Abstract

Two new porphyrin dyes, coded as ZZX-N6 and ZZX-N6C12, with photon-to-electron response up to 800 nm in the solar spectrum were synthesized for dye-sensitized solar cells (DSCs). Four alkynyl groups were conjugated perpendicularly to the donor–π–acceptor axis of the porphyrins through triple bonds, resulting in 40–56 nm red-shift of absorption onset compared to porphyrin dye YD2-o-C8, leading to higher short-circuit current density. Post treatment of dye-coated TiO₂ films by chenodeoxycholic acid (CDCA) with a concurrent increase of iodide concentration in an electrolyte improved the cell performance. Both impedance spectroscopic and photovoltage decay measurements showed that charge resistance at the TiO₂–electrolyte interface increased after the CDCA treatment. Increasing iodide concentration in the electrolyte enhanced the reduction of I₃⁻ at the Pt counter electrode, leading to a higher short-circuit current density (J_SC) and fill factor (FF). Under the optimized conditions, the ZZX-N6 based device exhibited an energy conversion efficiency of 7.21%, which is comparable to the YD2-o-C8 based device. The results demonstrate an alternative to broaden the light absorption capability of porphyrin dyes for high efficiency solar cells.