Enhanced efficiency of a dye-sensitized solar cell made from MgO-coated nanocrystalline SnO2

Nanocrystalline SnO2-based dye-sensitized photoelectrochemical solar cells have very low open-circuit voltages of 325-375 mV and efficiencies of simil ar to 1%. However, on coating the SnO2 crystallites with a thin film of MgO , the voltage and efficiency are increased to 650-700 mV and similar to 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 probab ility of reverse tunneling suppresses recombinations, thus increasing the e fficiency. An explanation is also given as to understand why dye-sensitized TiO2 cells are more efficient than those made from SnO2 alone.