ELECTRODEPOSITION OF P & N SEMICONDUCTOR LAYERS FOR PHOTOVOLTAIC APPLICATIONS

Thin film solar cells appear today as a feasible alternative to the silicon waferbased cells. The main drawbacks in their production are the need of rare and expensive elements (the common thin film cells use CdTe or Cu(In,Ga)Se2), as well as the employment of difficult and energy expensive processes for their fabrication. Therefore research in the photovoltaic field needs to focus on alternatives to minimize the exploitation of these rare elements and on more sustainable production processes. Compounds such as Kesterites (CZTS, ternary and quaternary copper and zinc sulfides) could be used in virtue of their semiconductor behavior; also, to simplify the productive process, electrodeposition from acqueous media was proposed; in particular E-ALD (Electrochemical Atomic Layer Deposition) method seems a legit alternative to the high pressure and temperature methods used since today. My work focused on the preparation of two layers of semiconductors, one above the other, to assess the possible usage of the obtained film in the photovoltaic field; first a CuZnS (Kesterite precursor with p electronic proprieties) layer was obtained on an Ag(111) substrate, then the other binary CdS (with n electronic proprieties) layer was grown over. These single compounds and their deposition by means of EALD method were largely studied by my research group, but their union to form a junction wasn't tested already. Therefore the first step of my work was the study of the deposition conditions of the CdS on the CuZnS. Using cyclic voltammetry i was able to detect at first the electrochemical inactivity window of the ternary compound, and then the deposition potentials of the Cd and S on the ternary. To determine if the binary compound shows the underpotential deposition phenomenon above the ternary compound, two deposition methods were tested. The first uses the E-ALD methodology, the second was a simple charge-controlled deposition method. The obtained samples were characterized morphologically, qualitatively and optically. Scanning electron mycroscopy (SEM) was used to evaluate both the morphological and the compositional aspects. Composition was also evaluated by x-ray photoelectronic spectroscopy (XPS). In the end diffused reflectance UV-vis spectrometry (DRS) was used to determine the photoadsorbance of the samples.