The Zn(S,O,OH)/ZnMgO buffer in thin-film Cu(In,Ga)(Se,S)₂-based solar cells part II: Magnetron sputtering of the ZnMgO buffer layer for in-line co-evaporated Cu(In,Ga)Se₂ solar cells

A ZnS/Zn_1-xMg_xO buffer combination was developed to replace the CdS/i-ZnO layers in in-line co-evaporated Cu(In,Ga)Se ₂(CIGS)-based solar cells. The ZnS was deposited by the chemical bath deposition (CBD) technique and the Zn_1-xMg_xO layer by RF magnetron sputtering from ceramic targets. The [Mg]/([Mg] + [Zn]) ratio in the target was varied between x = 0.0 and 0.4. The composition, the crystal structure, and the optical properties of the resulting layers were analyzed. Small laboratory cells and 10×10 cm² modules were realized with high reproducibility and enhanced stability. The transmission is improved in the wavelength region between 330 and 550 nm for the ZnS/Zn_1-xMg _xO layers. Therefore, a large gain in the short-circuit current density up to 12% was obtained, which resulted in higher conversion efficiencies up to 9% relative as compared to cells with the CdS/i-ZnO buffer system. Peak efficiencies of 18% with small laboratory cells and 15-2% with 10 × 10 cm² mini-modules were demonstrated.