Synthesis of High Density ZnO Nanowire Arrays for Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) have been extensively studied for the past few years because of their low-cost and high-efficiency. The surface area of the photoanode, which determines the amount of photons absorbed, is one of the most critical factors to improve the efficiency of DSSCs. Although conventional TiO₂ nanoparticle-based DSSCs have shown promising results, their performance has been limited to ~11% because of diffusion and back reaction problems.  Due to its excellent band gap (3.37 eV) and high exciton binding energy (60 meV) properties, one-dimensional ZnO nanowire arrays are capable of overcoming the limitation of nanoparticle-based DSSCs by improving electron injection and axial electron diffusion. Based on models proposed by our group, the efficiency of DSSCs based on TiO₂ core-shell ZnO nanowire arrays (40 µm in lengths, 40 nm in diameter and ~10¹¹ /cm² of density) can significantly surpass current efficiencies. To reach our objective, we focused on pH value control and using two-step anodized aluminum oxide (AAO) as a template to control the dimension of ZnO nanowire arrays. The synthesis was carried out using both hydrothermal and CVD methods. After that, SEM, TEM, and XRD were applied to characterize these ZnO nanowire arrays. By using this technique, it provides a new approach to obtain vertically-aligned ZnO nanowire arrays with both high density and aspect-ratio through a large-scale process.

Keywords: Dye sensitized solar cell (DSSC), ZnO Nanowire Arrays, AAO Template, Hydrothermal, CVD