Na Incorporation in Cu(In,Ga)(Se,S)2 Films Grown on Insulator-Coated Stainless Steel Foil Using a Metal Precursor Reaction

Cu(In,Ga)(Se,S)
₂
(CIGSS) films are formed on flexible 430 stainless steel foils through reacting Cu-In-Ga metal precursors in H
₂
Se and H
₂
S. The foils are coated using an electrically insulating silicone-based resin that can sustain temperatures as high as 600 °C. NaF films with various thicknesses are deposited between the metal precursor and Mo back contact in order to incorporate Na into the CIGSS films. The metal precursor reaction with the extrinsic Na incorporation results in greater Ga homogenization and S incorporation. The higher Na incorporation enhances V
_OC
and lowers J
_SC
. The temperature-dependent V
_OC
and drive-level capacitance profiling measurements reveal that the Na incorporation results in higher activation energy of the recombination and increased carrier density.