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.