Towards Lower Deposition Temperatures of Spray Deposited ZnO Films

Highly transparent, conductive ZnO:Al doped films have been deposited by a non-vacuum spray deposition method. At substrate temperatures above 400C we attain resistivites of 5x10-3Ohmcm and free charge carrier concentrations of 10-20cm -3 . ZnO film growth and quality are sensitive to the precursor solution. For a non-vacuum process the properties of the films are excellent. The challenge is to lower the deposition temperature to a maximum of 250C to be useful for Cu(In, Ga)(S, Se) 2 solar cells and yet maintain the ZnO film quality and conductivity. As the deposition temperature decreases the resistivity of the ZnO drastically increases yet is conducting enough to be used undoped as the intrinsic ZnO layer. This is particularly relevant as the deposition technique is readily up-scalable to roll to roll coating processes.