The role of ZnO-coating-layer thickness on the recombination in CdS quantum-dot-sensitized solar cells

To prevent recombination at the interface of TiO2/polysulfide-electrolyte, a ZnO layer was deposited on a TiO2 electrode. The optimized ZnO-coated solar cell exhibited a 32% increase in the power-conversion efficiency compared to the bare cell. The coating layer acts as an energy barrier, which plays an important role in reducing the charge recombination from the TiO2 electrode to the electrolyte. Moreover, CdS quantum-dot adsorption was enhanced by employing the ZnO-coated layer. The thicker ZnO layer (more than 8-cycle deposition), however, led to a less porous electrode, as confirmed by electrolyte diffusivity, and also deteriorated the cell efficiency by introducing defect states verified by electron lifetime and chronoamperometric reduction current. (C) 2013 Elsevier Ltd. All rights reserved.