Hydrothermal Synthesis of Branched ZnO Nanowire Array as an Effective Photoanode for Quantum-Dot-Sensitized Solar Cells

Abstract

I have focused on the synthesis of branched ZnO nanowires and the understanding of the growth kinetics during my thesis. Furthermore, the branched ZnO nanowire array was introduced as a photoelectrode of a quantum-dot-sensitized solar cell, and the correlation between the nanostructures and solar cell performance was investigated in terms of both optical (light trapping) and electrical (charge recombination) characteristics. Three-dimensional branched ZnO nanowires were synthesized by a seed-mediated hydrothermal growth. The fast growth-rate of (001) direction was possible due to the anisotropic nature of ZnO and the capping agents blocking a lateral growth of nanowire. About two-fold enhancement of power conversion efficiency (PCE) was obtained by growing secondary branches, and both short-circuit current and open-circuit voltage were enhanced. Highly increased surface area of photoelectrode, resulting in higher light harvesting from increased quantum-dot loading amount, and the higher diffused reflectance was observed due to enhanced light-scattering of 3D structure. In addition, electrochemical impedance spectroscopy and open-circuit voltage decay revealed the reduced recombination and higher lifetime of branched ZnO nanowires.