In recent years, the use of solar energy has been rising globally. This is a good trend because solar cells are not only sustainable energy source but also has the flexibility of not needing to be connected to a grid. This means that building solar cells can be highly beneficial especially for people living in rural areas without existing supply of electricity where it is too costly and would take too much time to build a conventional grid system. However, most of the growth of solar cell we have seen this far comes mostly from developed countries (e.g. Japan, USA, and Germany) or quickly developing countries with strong economies (e.g. China and India). It is important that rural areas without existing supply of electricity be electrified by solar energy as well. To achieve electrification of rural areas, it is important that the cost of the solar cell is brought further down to make it more accessible. In this study, we will approach the production of CZTS (copper zinc tin sulfide) solar cells with a new method that can make it more efficient and cheap. CZTS solar cells are very cheap solar cells that uses only abundant and non-toxic materials. Currently, CZTS is deposited on top of a molybdenum film sputtered on glass. This step has the issue of the need of sputtering, which requires a high amount of energy. Here we propose the replacement of glass and molybdenum by copper substrate. The copper substrate could function as the structural support (replacing glass), the conductor (replacing molybdenum), and copper source for CZTS formation.

To understand CZTS formation on a copper substrate, first, tin and zinc were deposited on top of a copper substrate by electroplating. After the deposition, the substrate was then heated in an oven with some sulfur source in nitrogen atmosphere at various temperatures and time (this process is called sulfurization). The sulfur would evaporate and react with the copper substrate deposited with tin and zinc. The phase change of the samples were studied to understand the reaction that happened during the sulfurization process to help understand how to grow CZTS by this method. An issue is that the excessive amount of sulfur available during the high temperature reactions reacts with the whole copper substrate turning it into copper sulfide. To prevent the formation of copper sulfide, some modification to the standard sulfurization process are necessary. CZTS can be obtained by reaction of copper sulfide (CuS), zinc sulfide (ZnS), and (SnS). Since SnS can evaporate at lower temperature, a copper substrate with zinc plating on it, that has been sulfurized at lower temperature could be reacted at higher temperature with an SnS source that will provide the tin for CZTS formation. This method has the advantage not having excessive amount of sulfur at high temperature that can convert the whole copper substrate.