Enhanced Efficiency of a Dye-Sensitized Solar Cell Made from MgO-Coated Nanocrystalline SnO2

Abstract

Nanocrystalline SnO₂-based dye-sensitized photoelectrochemical solar cells have very low open-circuit voltages of 325–375 mV and efficiencies of ∼ 1%. However, on coating the SnO₂ crystallites with a thin film of MgO, the voltage and efficiency are increased to 650–700 mV and ∼ 6.5%, respectively. Evidence is presented to show that the photoexcited dye on the outer MgO shell could tunnel electrons to SnO₂ and that the low probability of reverse tunneling suppresses recombinations, thus increasing the efficiency. An explanation is also given as to understand why dye-sensitized TiO₂ cells are more efficient than those made from SnO₂ alone.