Easwaramoorthi Ramasamy

Ordered mesoporous Zn-doped SnO2 synthesized by exotemplating for efficient dye-sensitized solar cells

Ordered mesoporous zinc-doped SnO2 (Zn-doped meso-SnO2) particles with a high surface area and a 2D hexagonal-type pore structure are synthesized by a double-replication procedure using SBA-15 silica and CMK-3 carbon as successive hard templates. The double-replication procedure provides large mesopores (diameter ∼10 nm), which are essential in dye-sensitized solar cells (DSCs) for the facile diffusion of redox electrolytes. It is shown that Zn doping into an ordered mesoporous SnO2 framework induces a negative shift in the flat-band potential (VFB) and also increases the isoelectric point. Consequently, DSCs employing Zn-doped meso-SnO2 photoanodes demonstrate longer electron lifetimes and increased dye loading than their undoped meso-SnO2 counterparts. A maximum energy-conversion efficiency (η) of 3.73% is achieved from solar cells fabricated with 3 mol% Zn-doped meso-SnO2 photoanodes, a nearly five-fold improvement compared to undoped meso-SnO2 photoanode DSCs (η = 0.81%).

Ordered mesoporous tungsten suboxide counter electrode for highly efficient iodine-free electrolyte-based dye-sensitized solar cells.

A disulfide/thiolate (T(2)/T(-)) redox-couple electrolyte, which is a promising iodine-free electrolyte owing to its transparent and noncorrosive properties, requires alternative counter-electrode materials because conventional Pt shows poor catalytic activity in such an electrolyte. Herein, ordered mesoporous tungsten suboxide (m-WO(3-x)), synthesized by using KIT-6 silica as a hard template followed by a partial reduction, is used as a catalyst for a counter electrode in T(2)/T(-)-electrolyte-based dye-sensitized solar cells (DSCs). The mesoporous tungsten suboxide, which possesses interconnected pores of 4 and 20 nm, provides a large surface area and efficient electrolyte penetration into the m-WO(3-x) pores. In addition to the advantages conferred by the mesoporous structure, partial reduction of tungsten oxide creates oxygen vacancies that can function as active catalytic sites, which causes a high electrical conductivity because of intervalence charge transfer between the W(5+) and W(6+) ions. m-WO(3-x) shows a superior photovoltaic performance (79 % improvement in the power conversion efficiency) over Pt in the T(2)/T(-) electrolyte. The superior catalytic activity of m-WO(3-x) is investigated by using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel polarization curve analysis.