1. Introduction
The field of renewable energy and today takes a very important interest in scientific researchers. Thin-films photovoltaic cells continue to grow through the production of new materials to improved solar cell efficiency, the most well-known cells are those that have based on absorbent materials CdTe and CIGS, the latter will reach maximum efficiency of 19.6% and 20.4% respectively [1].These results encourage the use of this type of materials and the development of new polycrystalline materials. But, the toxicity of Cd causes an environmental stress for CdTe-based cells and the rarity of In and Ga makes the use of CGIS as active material in the more expensive solar cells, this motivated the search for absorbent layers with new materials available and which respect the environment. For this purpose, two materials have emerged and can be considered as a promising alternative to CGIS and CdTe, in this case Cu2ZnSnS4 (CZTS) and tin sulphide (SnS). The SnS tin sulphide is a semiconductor belonging to the IV-VI family; it is of type p [2] with a large absorption coefficient (> 104 cm-1) [3] and a direct gap of the order of 1.3 eV[4] which coincides perfectly with the solar spectrum and makes it a serious candidate for cell realization solar cheap. Theoretical predictions predict a return of around 24%.
Impedance spectroscopy (IS ) analytic theory is increasingly being applied as an analytical tool in chemical material research [32–34] and has been shown to be invaluable for studies of polycrystalline semiconductor materials and devices such as CIGS-[35–39], CdTe- [40,41] and Cu2ZnSnS4 [42] related solar cells. We have previously investigated the defects at the CdS/CIGS p-n-interface by examining the constant phase element (CPE) index through IS . The CPE reflects the depletion layer thickness and the uniformity and quality of the p-n-interface [43]. In particular, the CPE-p value, which is an index of the impedance of the CPE, expresses the quality around the CdS/CIGS interface in terms of defect existence and in homogeneity of the hetero junction. Our previous result showed that IS is a simple method for characterizing the heterogeneity around a p-n-interface, and therefore, IS may be a promising tool for directly observing and examining the doping damage with the Si. In this paper, the doping damage around the p-n-interface in a solar cell is investigated by IS. We first investigate the relationship between the impedance properties and the equivalent circuit of the CIGS solar cells through observation of impedance variations under dark conditions. We then critically discuss the application of IS as a simple method for characterizing the heterogeneity around the p-n-interface in CIGS solar cells with different materials and deposition techniques of the p-type layer.
This study, utilization of Impedance spectroscopy (IS) is investigated to characterize the impedance properties of CIGS solar cells. First, the equivalent circuit of CIGS solar cells is proposed for IS analysis. Then, the correlation between the impedance properties and equivalent circuit of CIGS solar cells is investigated through observation of impedance variations under dark conditions. Finally, we critically discuss the application of impedance spectroscopy as a simple method for characterizing the heterogeneity around the p-n interface in CIGS and CIGS-Si solar cells with different thicknesses of the CIGS and CIGS-Si absorber layer.