Influence of Cadmium Sources on Properties of Chemically Deposited Cadmium Sulfide Thin Films for Highly Efficient Cu(In,Ga)(Se,S)2 Solar Cells

Thin films of CdS were prepared by chemical bath deposition (CBD) for use as a buffer layer in high efficiency Cu(In,Ga)(Se,S)(2) (CIGS) thin film solar cells. Cadmium sulfate (CdSO4) and cadmium acetate (Cd(CH3CO2)(2), CdAc2) were used as cadmium sources; we investigated the influence of the particular cadmium source on the properties of the films. Crystalline structure was analyzed using X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM), and optical transmittance and reflectance were measured by ultravioletvisible-near infrared (UV-VIS-NIR) spectrophotometry. The CdS films deposited from CdSO4 are more uniform, exhibit better crystallinity, and have higher optical transmittance. Thin film CIGS solar cells having a CdS buffer layer from CdSO4 show higher efficiency: 14.26% compared to 11.83% for CdS from CdAc2. This is mainly a result of higher short-circuit current density (J(sc)) and increased fill-factor.