Electrochemically Grown ZnO Nanorod Arrays Decorated with CdS Quantum Dots by Using a Spin-Coating Assisted Successive-Ionic-Layer-Adsorption and Reaction Method for Solar Cell Applications

CdS quantum dots (QDs) decorated ZnO nanorod (NR) arrays were fabricated by a two-step method. The first step consisted in electrochemical growth of single-crystalline ZnO NR arrays, followed by the novel spin-coating assisted SILAR method for decorating the ZnO NRs with CdS QDs. Structural, morphological and optical characterization of CdS QDs/ZnO NR arrays were done. ZnO NRs had a single crystal wurtzite structure growing along the c-axis. The decorated CdS QDs had a quasi-spherical shape with a mean diameter of about 5 nm. The increase of CdS content produces an increase in the visible part of the absorption spectrum. Bandgap energy values for ZnO between 3.26-3.29 eV were obtained. For CdS the measured absorption edge values are between 2.35-2.65 eV (decreasing with the number of coating cycles). Numerical simulations based on effective medium approximation were done to verify these features. The Urbach tail parameter in CdS absorption edge is between 44-52 meV. The photovoltaic performance of ZnO and CdS QDs/ZnO NRs have been evaluated in a photoelectrochemical solar cell configuration with a polysulfide electrolyte under white illumination. The decoration of ZnO NRs with CdS QDs leads to a cell performance of J(SC) = 2.67 mA/cm(2), V-OC = 0.74 V, FF = 0.30 and eta = 1.48%. (C) 2013 The Electrochemical Society. All rights reserved.