Reactively sputtered ZrN for application as reflecting back contact in Cu(In,Ga)Se2 solar cells

We investigate reactively sputtered films of zirconium nitride, ZrN, for use as highly reflecting back contacts in Cu(In,Ga)Se2 (CIGS) devices with sub-micrometer absorbers. We identify the nitrogen flow and the sputter current as the decisive parameters for the composition, and demonstrate a method for determining the nitrogen flow at which the transition from metallic to compound sputtering mode occurs for a given current. Films prepared at this working point consist of stoichiometric ZrN with a low resistivity, a high reflectance for red and infrared light, and have a fairly high sputter rate. Calculations show that the reflectance at the ZrN/CIGS interface is significantly superior to that at the standard Mo/CIGS interface.