Structural and antireflective properties of ZnO nanorods synthesized using the sputtered ZnO seed layer for solar cell applications

We report the structural and antireflective properties of ZnO nanorod arrays (NRAs) on silicon (Si) substrate by wet chemical growth using the sputtered ZnO seed layer for solar cell applications. The size, height, shape, and number of ZnO nanorods depend strongly on the ZnO seed layer thickness as well as the molar zinc nitrate concentration. Clearly, the ZnO nanorods are of wurzite crystal structure from the X-ray diffraction analysis. To achieve the low reflectance over a wide wavelength range, the ZnO seed layer thickness, molar concentration, and growth time are optimized. It is found that the specular reflection spectrum of ZnO NRAs is closely related to the ZnO seed layer thickness. The solar weighted reflectance, Rw, of ZnO NRAs as antireflection coatings for Si solar cells is estimated under AM1.5 g illumination. For ZnO NRAs with 50 nm ZnO seed layer in 10 mM aqueous solution for 12 hours, the low specular reflectance (i.e., <7%) is obtained at wavelengths of 300-1200 nm, indicating a low Rw of 3.86%.