Texture optimization process of ZnO:Al thin films using NH4Cl aqueous solution for applications as antireflective coating in thin film solar cells

ZnO:Al thin films varying the thickness from 80 to 110 nm were deposited on polished float zone < 100 > Si wafers by radio frequency magnetron sputtering at 100 °C. To texturize these surfaces with the aim of being used as antireflective coating, a wet etching process based on NH4Cl was applied. Taking into account that the layer thickness was small, the control of the etch parameters such as etchant concentration and etching time was evaluated as a function of the textured film properties. An appropriate control of the etching rate to adjust the final thickness to the 80 nm required for the application was realized. Using NH4Cl concentrations of 10 wt.% and short times of up to 25 s, an increase of the film roughness up to a factor of 5.6 of the as-deposited films was achieved. These optimized textured films showed weighted reflectance values below 15% and considerable better electrical properties than the as-deposited 80 nm-thick ZnO:Al films.