Nanostructured surfaces
The morphology investigation of the cadmium sulphide thin films for solar cell applications
Vakaliuk I.V.1, Nykyruy L.I.1, Ilnitsky R.V.1, Naidych B.P.1, Yavorskyi R.S.1 Matkivskyi O.M.1, Katanova L.O.1
1Vasyl Stefanyk Precarpathian National University, T. Shevchenko, 57, 76-018, Ivano-Frankivsk, Ukraine 
E-mail: ivanna.maliarska@pnu.edu.ua 

The solar cells on the basis of cadmium telluride (CdTe) have recommended themselves as a perspective thin film technology of the future market of renewable energy. In spite of that the Silica solar cells are still dominant, CdTe occupies about 7% of the this market and is the first of technologies of the second generation which has effectively carried out a jump to the mass introduction.
In the solar cells based on cadmium telluride the n-type of conductivity CdS layer (2.4 eV bandgap) directly contacts with p-CdTe and form p-n heterojunction. The CdS layer is not a photoelectricity active layer but has a «window» function. The solar irradiation penetrates under CdS into the photoelecticly active CdTe layer (absorber). As a rule, the CdS layer must be as thin as possible in order to permit to the best part of photons with energy, higher than its bandgap, to reach the CdTe and, therefore, to provide the higher values of photoelectric current. But too thin CdS layer increases the possibility of a local by-passing.
The CdS thin films were deposited onto glass substrates by the method of the open evaporation in vacuum. The SEM analysis used for morphology investigation of the obtained polycrystal CdS thin films. It has been determined that scales type of the surface structure characteristic for smaller widths of films. The presence and the size of these plates are directly depended on the time of deposition. Specifically, it has been concluded that the increasing of the deposition time results in the decreasing of the lateral size of scales: from about 30 mm during the deposition time 60 sec to about 20 mm during the deposition time 90 sec. Due to the reduction of the surface plates in size, we can assume that with increasing of deposition time, the process of their fusion begins. A further increase of the deposition time leads to blurred outlines of such plates, and for the thickest films they are absent. 

1.	Philipps, S. Warmuth, W. photovoltaics report – Fraunhofer ISE; 2016, web-source: https://www.ise.fraunhofer.de/en/publications/studies/photovoltaics-.