Highly transparent low resistance Ga doped ZnO/Cu grid double layers prepared at room temperature*Project supported by the Key Project of the National Natural Science Foundation of China (No. 91333203), the Program for Innovative Research Team in University of Ministry of Education of China (No. IRT13037), the National Natural Science Foundation of China (No. 51172204), and the Zhejiang Provincial Department of Science and Technology of China (No. 2010R50020). (December 2015)