Structure and Optical Properties of Cu (In0.7, Ga0.3) Se2 Absorbers on Copper Substrate for Photovoltaic Solar Cells Application

Abstract

Polycrystalline thin films Cu (In0.7, Ga0.3) Se2 (CIGSe) were grown on copper foils at various cathodic potentials by using electrodeposition technique. Scanning electron microscopy (SEM) displays that average diameter of CIGSe grain increases from 0.1μm to 1μm when cathodic potential decreases. The structure and surface morphology were investigated by x-ray diffraction (XRD) and atomic force microscopy (AFM) techniques. This structure study shows that the thin films were well crystallized in chalcopyrite structure without unwanted secondary phase with preferred orientation along (112) plane. Energy-dispersive x-ray analysis (EDAX) confirms the existence of CIGSe single phase on copper substrate. AFM analysis indicated that the root mean square (RMS) roughness decreases from 64.2 to 27.4 when the potential deposition increases from −0.95V to −0.77V. Using Raman scattering spectroscopy, the A1 optical phonon mode was observed in 173cm−1 and two other weak peaks detected at 214cm−1 and 225cm−1 associated to the B2 and E modes of the CIGSe phase. Through spectroscopy ellipsometry (SE) analysis, three layer optical model was exploited to derive the optical properties and layer thickness of the CIGSe film by least-squares fitting the measured variation in polarization light versus the obtained microstructure.