Comparative investigation of structural, optical properties and dye-sensitized solar cell applications of ZnO nanostructures.

Dye-sensitized solar cells (DSSCs) based on ZnO nanostructures with two different morphologies, such as nanowires (ZNWs) and nanoparticles (ZNPs), were synthesized by microwave combustion (MCM) and conventional combustion (CCM) method. The obtained ZnO nanostructures were characterized by X-ray diffraction (XRD), high resolution scanning electron microscopy (HR-SEM), high resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray analysis (EDX), diffuse reflectance (DRS) and photoluminescence (PL) spectroscopy. The XRD results confirmed the formation of hexagonal wurtzite ZnO. The crystallite size of the ZnO nanostructures was calculated using Sherrer's formula. The formation of ZNWs and ZNPs was confirmed by HR-SEM and HR-TEM. The optical absorption and PL emissions were determined by DRS and PL spectra respectively. ZnO nanostructures with band gap energies of 3.36 eV (MCM) and 3.25 eV (CCM) were obtained. The dye-sensitized ZnO nanowire arrays exhibit much stronger optical absorption as compared with ZnO nanoparticle arrays, suggesting that the larger surface area improves light harvesting. The dye-sensitized solar cell based on the optimized ZnO nanowires array reaches a conversion efficiency of 1.73%, which is higher than that obtained from ZnO nanoparticles (0.69%) under the light radiation of 1000 W/m2. As-prepared ZNWs have potential applications in fabricating next generation nanodevices.