Light-trapping effects and dye adsorption of ZnO hemisphere-array surface containing growth-hindered nanorods

Textured ZnO hemisphere-array films which consist of growth-hindered ZnO nanorods with different length are fabricated on ITO glass substrates and used for solar cell applications. The fabrication process includes formation of ZnO seed, self-assembled polymeric hollow particles as nanosphere mask, growth of ZnO nanorods, and removal of nanosphere mask. Fixing the nanosphere mask on the substrate and controlling the interstices size between adjacent spheres are very important to the fabrication of ZnO nanorods at selective sites. The surface roughness, feature size and shape of the hemisphere pore can be tuned by changing the ZnO rod-growth time and the nanosphere size. Compared with smooth ZnO films made by the electrochemical deposition process, the light-trapping effect of ZnO hemisphere-array film is proven by the decrease in the transmittance and reflectance. The energy-dispersive X-ray (EDX) spectrometry and scanning electron microscopy (SEM) images reveal that the amount of adsorbed N719 dye increased after the O2 plasma treatment. The hemisphere-array surface texture enhances the light-trapping effects and increases the interface area. The performance of dye-sensitized solar cells is improved by introducing the ZnO hemisphere-array surface and the O2 plasma treatment.