Humic Acid as a Sensitizer in Highly Stable Dye Solar Cells: Energy from an Abundant Natural Polymer Soil Component

Humic acid (HA), a natural polymer and soil component, was explored as a photosensitizer in dye-sensitized solar cells (DSSCs). Photophysical and electrochemical properties show that HA covers a broad visible range of the electromagnetic spectrum and exhibits a quasi-reversible nature in cyclic voltammetry (CV). Because of its abundant functionalities, HA was able to bind onto the nano-titania surface and possessed good thermal stability. HA was employed as a sensitizer in DSSCs and characterized by various photovoltaic techniques such as <i>I</i>–<i>V</i>, incident-photo-to-current conversion efficiency (IPCE), electrochemical impedance spectroscopy (EIS), and Tafel polarization. The HA-based device shows a power conversion efficiency (PCE) of 1.4% under 1 sun illumination. The device performance was enhanced when a coadsorbent, chenodeoxycholic acid (CDCA), along with HA was used and displayed 2.4% PCE under 0.5 sun illumination. The DSSCs employing HA with CDCA showed excellent stability up to 1000 h. The reported efficiency of devices with HA is better than that of devices with all natural sensitizers reported so far

Anisotropic One-Dimensional Aqueous Polymer Gel Electrolyte for Photoelectrochemical Devices: Improvement in Hydrophobic TiO₂–Dye/Electrolyte Interface

Aqueous photoelectrochemical devices have emerged recently as promising area because of their economic and ecological friendliness. In the present work, we have expedited surface active amphiphilic quasi-solid aqueous polymer gel electrolyte (PGE) with hydrophobic sensitizer SK3 in water-based dye sensitized solar cell (DSSC). PGE was prepared from amphiphilic block copolymer (PEO)–(PPO)–(PEO) with iodide–triiodide couple in pure aqueous media without any organic solvent. This block copolymer, with iodide-triiodide salt exhibits 1D-lamellar microcrystalline phase which shows stability in the temperature range of 25–50 °C. Parallel (||^al) and perpendicular (⊥^ar) alignment of anisotropic lamellar microcrystalline phase pertaining by PGE were characterized and applied in quasi-solid DSSC. Temperature dependency of ionic conductivity, triiodide diffusion, differential scanning calorimetry, viscosity, and 1-D lamellar anisotropic behavior were studied. Surface active effect of PGE at the hydrophobic dye sensitized photoanode was investigated and compared with liquid water based electrolyte. Because of the amphiphilic nature and thermoreversible sol–gel transition of PGE at a lower temperature (0 to −2 °C) allowing PGE to penetrate efficiently inside the hydrophobic surface of dye–TiO₂ and resulted in a fused contact between dye–TiO₂/PGE interface. This aqueous PGE successfully enhances the performance of DSSCs over liquid water based devices by improving their <i>V</i>_oc and stability. Under 0.5 sun illumination, DSSC with 1-D lamellar perpendicularly align PGE shows an efficiency of 2.8% and stability up to 1000 h at 50 °C