Cd2+/NH3 treatment of Cu(In,Ga)(S,Se)2 thin-film solar cell absorbers: a model for the performance-enhancing processes in the partial electrolyte

To obtain highly efficient chalcopyrite-based thin-film solar cells where the conventionally used CdS buffer is replaced by a ZnO layer prepared by the ILGAR (ion layer gas reaction) process, the Cu(In,Ga)(S,Se)2 absorber has to be pretreated in a Cd2+/NH3 solution. Based on the measured characteristics of the pH-value in the Cd2+/NH3 solution during the treatment, a model of the processes in the bath can be established. The conclusions are correlated with results from X-ray-photoelectron and X-ray-excited Auger electron spectroscopy of the Cd2+/NH3-treated Cu(In,Ga)(S,Se)2 surface, giving an explanation for the observed formation of Cd-compounds on the surface of the absorber.