Effect of Insulating Oxide Overlayers on Electron Injection Dynamics in Dye-Sensitized Nanocrystalline Thin Films

Abstract

Insulating metal oxide coatings has been investigated as a potential approach for improving the efficiency of dye-sensitized solar cells. Thin insulating overlayers were thought to improve the cell efficiency by retardation of the recombination kinetics of injected electrons in semiconductor thin films with the oxidized sensitizer molecules and the electrolytes. However, how they affect the electron injection dynamics is still unclear. In this work, we examined the effects of Al2O3 overlayers on the electron injection dynamics in Ru and Re bipyridyl complexes sensitized nanocrystalline TiO2 and SnO2 films. Electron injection dynamics was measured as a function of the number of overlayers by ultrafast infrared transient absorption spectroscopy. The uniformity of the coating was also probed using interfacial charge-transfer complexes. The injection rate was found to decrease when the number of Al2O3 overlayers increases, and the mechanisms by which the overlayers affect the injection dynamics were discussed.