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

Dye-sensitized photoelectrochemical cells based on nanocrystalline films of TiO 2 yield energy conversion efficiencies ∼10%. The efficiencies of similar cells with films of other oxide materials (SnO 2 , ZnO) are well below the above value. However, the cells made from SnO 2 –ZnO composite films give efficiencies comparable to TiO 2 cells. Two types of composite systems with SnO 2 and ZnO are possible. In the first type, SnO 2 crystallites are covered with an ultra-thin (<1 nm) outer shell of ZnO 2 and in the second type, the film comprises SnO 2 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 SnO 2 could effectively counteract recombinations of electrons with acceptors in the electrolyte (e.g., I 3 − ) and increase the efficiency although SnO 2 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.