• **First window layer: ZnO: B**

Most CIGSe-based solar cells use Aluminum-doped Zinc oxide (ZnO: Al) as the Transparent Conductive Oxide (TCO). Within the framework of this work we opt for ZnO doped with boron (ZnO: B) as OCT. Boron doping would be more beneficial for solar cells. Its standard thickness varies between 450 and 1400 nm [18].

#### • **The buffer layer: ZnS**

Its standard thickness varies between 40 and 60 nm. It has an N-type conductivity and its gap is greater than that of the absorber layer. Three roles are mainly attributed to it:


• **A role of protective layer**: it protects the surface of the absorber during the deposition of the ZnO layer, which can cause defects on the surface of the CIGSe.

From Won Song et al. work [19], only the values of properties recorded for the cubic structure will be taken into account during this study, since that structure is more stable at room temperature, and forms a better lattice matching with the chalcopyrite structure of CIGSe. That allows us to record as dielectric constant value *ε<sup>r</sup>* ¼ 8*:*3.
