Bragg stack-functionalized counter electrode for solid-state dye-sensitized solar cells

A highly reflective counter electrode is prepared through the deposition of alternating layers of organized mesoporous TiO₂ (om-TiO₂) and colloidal SiO₂ (col-SiO₂) nanoparticles. We present the effects of introducing this counter electrode into dyesensitized solar cells (DSSCs) for maximizing light harvesting properties. The om-TiO₂ layers with a high refractive index are prepared by using an atomic transfer radical polymerization and a sol-gel process, in which a polyvinyl chloride-g-poly(oxyethylene) methacrylate graft copolymer is used as a structuredirecting agent. The col-SiO₂ layers with a low refractive index are prepared by spin-coating commercially available silica nanoparticles. The properties of the Bragg stack (BS)-functionalized counter electrode in DSSCs are analyzed by using a variety of techniques, including spectroscopic ellipsometry, SEM, UV/Vis spectroscopy, incident photon-to-electron conversion efficiency, electrochemical impedance spectroscopy, and intensity modulated photocurrent/voltage spectroscopy measurements, to understand the critical factors contributing to the cell performance. When incorporated into DSSCs that are used in conjunction with a polymerized ionic liquid as the solid electrolyte, the energy conversion efficiency of this solid-state DSSC (ssDSSC) approaches 6.6 %, which is one of the highest of the reported N719 dye-based ssDSSCs. Detailed optical and electrochemical analyses of the device performance show that this assembly yields enhanced light harvesting without the negative effects of charge recombination or electrolyte penetration, which thus, presents new possibilities for effective light management.