Cu6Sn5 binary phase as a precursor material of the CZTSe compound: Optimization of the synthesis process, physical properties and its performance as an absorbing material in a solar cell

Nowadays there is a wide range of alternative materials to silicon that are used for the processing of photovoltaic (PV) devices, including Perovskites, GaAs, CdTe, Cu(In,Ga)(S,Se)2, Cu2ZnSn(S,Se)4 (the so-called kesterites) and the recently emerged Sb2(S,Se)3, among others. In particular, kesterites are a very interesting family of materials because they are based on earth abundant elements, ensuring the possibility of large scale PV production in the future. However, the efficiencies that have been reported for kesterites in recent years have not had significant increases. Consequently, the search for alternatives that allow reducing problems such as the appearance of undesirable secondary phases, have a better control of stoichiometry, as well as making the synthesis process of this family of materials efficient, has become essential to enhance their implementation as absorbents in commercial devices. In this work, the synthesis of the kesterite compound CZTSe from the binary phase of bronze (Cu6Sn5) is presented, as a proposal to accelerate the process of its formation and with good properties to be implemented in second generation solar cells. Likewise, the adaptation of the thermal processes commonly used during the manufacture of the material that allows the incorporation of bronze is also presented. The first results show that the implementation of bronze suggests a better control of the exchange of elements with the atmosphere (which could represent a decrease in the formation of undeceivable secondary phases and elemental residues) and a good crystallization of the material in periods of short time (up to a reduction of 33.33% of the time used for the synthesis of the compound from pure metallic stacks according to previous reports). Furthermore, photovoltaic devices with a conversion efficiency close to 7% reproducible were obtained.