Characteristics of RF Magnetron Sputtered Cu(In,Ga)Se2 Thin Films Prepared by CIGS Single Target

Abstract

Thin film solar cells have been extensively investigated due to their small consumption of raw materials. Among them, Cu(In,Ga)Se2 (CIGS) solar cell has attracted great attention due to its merits such as direct band gap, high absorption coefficient, high conversion efficiency, and high radiation resistance, etc. CIGS thin films have been fabricated by using various deposition methods and the highest conversion efficiency of ~20% could be obtained by using CIGS thin films deposited by three-stage co-evaporation method[1]. However, this method may be inappropriate for a mass production of large area CIGS solar cells. As an alternative, we tried to utilize the sputtering method because it has been widely used for fabricating large area thin films. In this work, CIGS thin films were deposited on Mo/glass substrates at various substrate temperatures by using rf magnetron sputtering. Employing a single CIGS target, CIGS films could be successfully produced. Composition and structural, optical properties of the CIGS thin films were investigated by using EPMA, XRD, SEM, spectrophotometer, and photoluminescence, etc. Al/AZO/i-ZnO/CdS/CIGS/Mo/glass structure was fabricated to measure the conversion efficiency. CdS buffer layer was coated by chemical bath deposition (CBD) method and i-ZnO and Al-doped ZnO(AZO) layers were deposited by sputtering method, sequentially. Al metal electrode was deposited by using thermal evaporation. GIGS grain size was increased with increasing deposition temperatures as shown in Fig. 1.(a). X-ray diffraction patterns revealed that CIGS films consist of chalcopyrite structure CIGS including secondary-phase (In0.62Ga0.38)2Se3 as shown in Fig. 1.(b). Details will be presented for a discussion.