Characterization of Na-doped CuInS2 thin film absorber layer formed by a non-vacuum ink process

Na-doped CuInS₂ (Na-CIS₂) thin films were fabricated by a non-vacuum ink process. The copper (Cu), indium (In) and sulfur (S) precursors were first synthesized by a sonochemical colloidal route, which is simpler and cheaper than the other preparation methods. The CuInS₂ (CIS₂) thin film absorber layers were then formed via spray-coating method using ink precursors consisting of Cu, In and S components. Finally, sodium (Na) was doped onto the CIS₂ thin film by wet solution methods. The Na doping condition and the Cu to In ratio were found to play important roles in controlling the structural and optoelectronic properties of the absorber layer.