Efficient dye-sensitized photoelectrochemical cells made from nanocrystalline tin(IV) oxide zinc oxide composite films

Abstract

Dye-sensitized photoelectrochemical cells based on nanocrystalline films of TiO₂ yield energy conversion efficiencies ~10%. The efficiencies of similar cells with films of other oxide materials (SnO₂, ZnO) are well below the above value. However, the cells made from SnO₂–ZnO composite films give efficiencies comparable to TiO₂ cells. Two types of composite systems with SnO₂ and ZnO are possible. In the first type, SnO₂ crystallites are covered with an ultra-thin (2 and in the second type, the film comprises SnO₂ crystallites (~10 nm) with a thin ZnO outer shell and larger ZnO particles (~100 nm). The short-circuit photocurrent and efficiency of these cells are ~17 mA cm⁻², 19 mA cm⁻² and 7%, 8% respectively. This paper explains in detail how a thin shell of ZnO on SnO₂ could effectively counteract recombinations of electrons with acceptors in the electrolyte (e.g., I₃⁻) and increase the efficiency although SnO₂ and ZnO are individually not good materials for dye-sensitized photoelectrochemical cells. In the second type, larger ZnO crystallites reduce the rate of geminate recombinations, in addition to the effect of the outer shell.