Electrochemical atomic layer deposition of CuZnS and CdS films for photovoltaic applicationsWednesday (28.09.2016) 12:00 - 12:15 Part of:
In the search of a viable alternative to silicon wafer-based cells, thin film solar cells are the ones that show better performances, such as higher durability and conversion efficiency. Their main drawback resides in the production process, which is today limited by the need of rare and expensive elements (the common thin film cells use CdTe or Cu(In,Ga)Se2), as well by 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. This 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 E-ALD method were largely studied by our 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 to obtain CdS on the CuZnS. Cyclic voltammetry tests were first used to detect the electrochemical inactivity window of the ternary compound, then the deposition potential of the Cd and S on the ternary was investigated.
To determine if the binary compound shows the underpotential deposition phenomenon above the ternary compound, two deposition methods were tested. The first used the E-ALD methodology, the second was a simple charge-controlled deposition method.
The obtained samples were characterized morphologically, qualitatively and optically. Scanning electron microscopy (SEM) was used to evaluate both the morphological and the compositional aspects (using an EDX microanalysis). Composition was then evaluated by X-ray photoelectron spectroscopy (XPS).