We report herein one of our recent studies on nanostructured ZnO electrodes for application in dye-sensitized solar cells, focusing on achieving a higher open-circuit voltage (VOC). ZnO films were obtained through solution-processed routes including pyrolytic conversion of layered hydroxide zinc acetate (LHZA) films deposited on a fluorine-doped tin oxide-coated conducting glass substrate by a chemical bath deposition method. The morphology of the initial LHZA and the converted ZnO films was tuned from a thick (approximately 12 μm) flower bed-/lawn-like bilayer structure to a thin (1.2 μm) lawn-like quasi-monolayer structure by decreasing the Zn source concentration in the chemical bath. VOC was found to be enhanced with this morphological change from 0.692 (the bilayer structure) to 0.735 V (the quasi-monolayer structure). Fine tuning of the quasi-monolayer structure by introducing the grain growth effect led to VOC of the cell as high as 0.807 V, although a short-circuit photocurrent density (JSC) remained low. Further attempts were then made to increase JSC while maintaining the high VOC. When the thickness of the lawn-like monolayer film was increased up to approximately 5 μm, the resultant cell showed VOC = 0.750 V, JSC = 6.20 mA cm−2 and a conversion efficiency (η) of 2.83%. The film with a modified flower bed-/lawn-like bilayer structure approximately 11 μm in thickness finally yielded VOC = 0.741 V, JSC = 13.6 mA cm−2, and η = 5.44%.
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