Electrochemical synthesis of one-dimensional ZnO nanostructures on ZnO seed layer for DSSC applications

Publication date: 15 January 2018
Source:Applied Surface Science, Volume 428
Author(s): T. Marimuthu, N. Anandhan, R. Thangamuthu
Electrochemical deposition of vertically aligned zinc oxide (ZnO) nanorods were prepared on ZnO seeded fluorine doped tin oxide (FTO) substrate in the solutions consisting of different concentrations of hexamethylenetetramine (HMTA). The electrochemical, structural, morphological, vibrational and optical properties were characterized by cyclic voltammetry (CV), X-ray diffraction (XRD), scanning electron microscope (SEM), Raman spectroscopy and photoluminescence (PL) spectroscopy, respectively. CV curves confirm that metallic zinc phase is not deposited as the HMTA concentration is about 9mM in a deposition solution. XRD patterns of the as-prepared films show that the increasing HMTA concentrations from 0mM to 9mM not only increase the formation of zinc hydrate chloride (Zn5(OH)8Cl2·H2O) but also decrease and finally disappear the metallic Zn deposition. After the as-prepared films annealed at 450 °C, the crystalline phases of Zn and Zn5(OH)8Cl2·H2O are completely converted to ZnO hexagonal wurtzite phase with high intense growth (002) plane orientation. SEM images support that the vertical growth of ZnO nanostructures (nanorods and petals) with a few flowers is found to be in the cordillera structure as the films are deposited in the solutions consisting of 3mM, 6mM and 9mM HMTA respectively. Raman and PL spectra confirm that the ZnO film deposited in the solution consisting of 9mM HMTA has a higher crystalline nature with lesser atomic defects and is also higher c-axis growth than that of other films deposited in the solutions consisting of 0mM, 3mM and 6mM, respectively. UV–vis absorbance spectra corroborate that the ZnO film deposited in the solution consisting of 9mM HMTA shows a high dye absorbance as compared with other films. The efficiency of DSSCs based on ZnO photoanodes deposited in the solutions consisting of 0mM and 9mM HMTA was 1.79 and 3.75%, respectively. Electrochemical impedance spectra revealed that DSSC based on ZnO photoanode deposited in the solution consisting of 9mM HMTA has a higher charge recombination resistance (Rrec) than that of another DSSC.

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