A processing method described herein provides a method of patterning a MoSe.sub.2 and/or Mo material, for example a layer of such material(s) in a thin-film structure. According to one aspect, the invention relates to etch solutions that can effectively etch through Mo and/or MoSe.sub.2. According to another aspect, the invention relates to etching such materials when such materials are processed with other materials in a thin film photovoltaic device. According to other aspects, the invention includes a process of etching Mo and/or MoSe.sub.2 with selectivity to a layer of CIGS material in an overall process flow. According to still further aspects, the invention relates to Mo and/or MoSe.sub.2 etch solutions that are useful in an overall photolithographic process for forming a photovoltaic cell and/or interconnects and test structures in a photovoltaic device.