Concentrated-Polymer-Brush-Modified Silica Nanoparticles Self-Assembled in Ionic Liquid Containing Iodide/Triiodide (I^–/I₃^–)‑Redox System as Quasi-Solid Electrolytes for Dye-Sensitized Solar Cells

By combining concentrated-polymer-brush-modified silica nanoparticles (PSiPs) with an ionic liquid (IL) electrolyte of the iodide/triiodide (I^–/I₃^–) redox system in a specific ratio, a colloidal crystal membrane was fabricated and applied as a quasi-solid electrolyte of a dye-sensitized solar cell. Improved affinity between the polymer-brush component and the IL electrolyte allowed for the formation of a face-centered-cubic (fcc) structure of PSiPs, wherein the electrolyte filled the spaces between the PSiPs and formed a continuous ion-conducting channel. This study clearly demonstrated that the highly repulsive and non-interpenetrating interaction of swollen concentrated polymer brushes was responsible for the self-assembly of PSiP in suspension. The PSiP-type I^–/I₃^– redox electrolyte had a high conductivity of 0.35 ± 0.05 mS cm^–1. Despite being a quasi-solid system, the dye-sensitized solar cell using this PSiP-type electrolyte exhibited photovoltaic characteristics similar to those of a cell using the PSiP-free liquid electrolyte. The good performance of the former was attributed to the successful thinning of the electrolyte membrane without short-circuiting and its good contact with an uneven TiO₂ electrode due to the synergistic effects of enhanced mechanical property and plastic deformability.