• *Modification of the structure*

Modification of the buffer layer by the Cadmium Selenide (CdS) layer and the introduction of the ZnO: Al window layer enhanced absorption of the solar spectrum at short wavelengths. As of today, many materials have already been used as a buffer layer in particular (In2S3, ZnS, ZnSe, Zn (S, OH)) and as a window layer we will see for example zinc oxide doped with Boron (ZnO: B).

#### • *Introduction of Gallium*

Beginning in 1987, Chen et al. [9] attempted to incorporate Gallium atoms into the CISe structure. The partial substitution of indium by gallium has improved the electrical performance of the solar cell.

#### • **Influence of sodium**

In the 1990s, Hedson et al., working on the substitution of the initial substrate to soda glass in order to reduce costs, found that the performance of solar cells was

<sup>1</sup> It was in 1991 that Gräetzel's cell was discovered by Michael GRÄETZEL, a Swiss chemist and professor at the Swiss Federal Institute of Technology in Lausanne.

greatly improved. They attributed this observed beneficial effect to the influence of sodium from the glass on the doping of the CIGSe layer.

which it is built. Consequently, the support has a very strong influence on the

*Thin-Film Solar Cells Performances Optimization: Case of Cu (In, Ga) Se2-ZnS*

Much work already exists in the context of optimizing the performance of CIGSe cells with various materials as a buffer layer. It is in this tertiary perspective that this work is also part of, that is to say to seek the optimized properties of the material used as a buffer layer and to control the micro-activities behind perfor-

Zinc Sulfide (ZnS) is a semiconductor formed by the association of an element atom from column II with another element atom from column VI of the periodic table of chemical elements. It has intrinsic properties which make it a material of choice in the search for good performance in the CIGSe-based thin film chain. It is recognized as having the following properties: It is non-toxic to the environment

The crystallography of compounds II-VI6 to which Zinc Sulfide belongs poses some problems because of the polymorphism of these compounds. They can have crystallographic structures of two main types: the cubic structure of the sphalerite type (Zinc Blende), and the hexagonal structure of the Wurtzite type. The cubic structure (Zinc Blende) is stable at room temperature (27°C), while the hexagonal structure is more stable at very high-top temperatures of around 1020°C [10]. Indeed, with a lattice parameter *aCIGS* ¼ 0*:*58 *nm* for the CIGSe chalcopyrite structure and *a*0\_*ZnS* ¼ 0*:*541 *nm* respectively*a*0\_*ZnS* ¼ *b*0\_*ZnS* ¼ 0*:*3811*nm* for ZnS in its cubic and hexagonal structure respectively, CIGSe forms a better lattice agreement with ZnS in its sphalerite structure which is furthermore its stable structure [11]. A deposition technique by ALD [12] or by laser sputtering [11] would make it possible to obtain a layer of ZnS having a crystallographic orientation preferentially

> **Column IV B**

Li3 Be4 B5 C6 N7 O8 F9 Na11 Mg12 Al13 Si14 P15 [S16] Cl17 Cu29 [Zn30] Ga31 Ge32 As33 Se34 Br35 Ag47 Cd48 In49 Sn50 Sb51 Te52 I53 Au79 Hg80 Ti81 Pb82 Bi83 Po84 At85

**Column V B**

**Column VI B**

**Column VII B**

and its constituents are abundant in nature (Zinc and Sulfur) (**Table 1**).

structural properties of the layer deposited thereon.

*DOI: http://dx.doi.org/10.5772/intechopen.93817*

**3. Material choosing, methods and general principle**

**3.1 Material choosing and structure of our solar cell**

mance losses.

sphalerite.

**Column I A-B**

**Table 1.**

**89**

*3.1.1 Reason for choosing ZnS*

*3.1.2 ZnS material global properties*

*3.1.2.1 ZnS crystallographic properties*

**Column II A-B**

**Column III B**

*Chemical elements of the Mendeleev table of columns II and VI [13].*
