Sustainable photovoltaics – Cu2ZnSnS4 thin films produced by the conversion of mechano-chemical synthesised precursors

Mokhtarimehr, Mehrnoush (2018) Sustainable photovoltaics – Cu2ZnSnS4 thin films produced by the conversion of mechano-chemical synthesised precursors. Doctoral thesis, Northumbria University.

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Abstract

To develop sustainable photovoltaic materials in a competitive power-generation market, several parameters such as cost, resource availability, environmental constrains in both material selection, and processing should be taken into account. In this context, Cu2ZnSnS4 (CZTS) compound can be a promising candidate for Photovoltaic (PV) applications since apart from its material properties, which make it a suitable choice for PV applications; all its constituent elements are abundant in the crust. This leaves us to focus on synthesising such a compound in order to improve the quality and consequently enhance the performance of devices fabricated from CZTS thin films.

The purpose of the work proposed for this PhD project is to develop a low cost and energy efficient non-vacuum deposition processing and to gain an in-depth understanding of the key parameters required to synthesise the CZTS thin film absorber layers for PV solar cells. The research includes the processing technique to (i) prepare a precursor solution with the use of metal oxide/sulphide compounds, (ii) establish a scalable deposition technique, and (iii) study the sulphurisation process by varying the conversion condition. To achieve this, a preliminary study has been done on the established technology of fabricating the Cu2ZnSnSe4 (CZTSe) thin films via vacuum deposition technique in order to provide a key insight into critical process parameters in developing Kesterite formation and the CZTS thin films. Finally, the life cycle assessment of fabricating CZTS thin films using vacuum and non-vacuum deposition methods has been studied. The four main damage categories of climate change, human health, eco-toxicity, and resources have been estimated using SimaPro Software with regard to the consideration of CuInxGa(1-x)Se2 (CIGS) (as a reference) processed via vacuum deposition technique.

The present study suggests an optimising route to prepare CZTS compound from metal oxide/sulphide compounds using a non-vacuum deposition technique. The study offers promising results using two techniques of spraying and slot-die for producing the deposition at lab-scale, which has a potential for large-scale processing. The results illustrated the impacts of conversion conditions on the micro and crystal structures of the CZTS thin films. In terms of environmental impacts, both vacuum and non-vacuum deposition techniques exhibited a significant potential benefit over CIGS thin films. However, the environmental impacts were found to depend critically on the compounds selected for the precursor and the processing.

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