NAFTA

With the growing demand for energy due to the population increase, there is a crucial need for sustainable energy resources. This is driving demand for renewable energy sources such as solar energy and is the key factor in the development of photovoltaic (PV) energy. However, PV panels are often made from materials whose elements are considered scarce on the planet, such as indium, or toxic, such as lead. The Nafta project proposes to develop a top cell based on indium-free, earth-abundant and non-toxic nitride, namely the (Zn1 – xMgx)3N2 alloy compatible with the c-Si technology used in tandem solar cells, one of the most promising technologies for high-efficiency PV panels. We have optimized the growth conditions of the (Zn1 – xMgx)3N2 layer to obtain a material with an optimum band gap of 1.7 eV on the MgO(100) substrate using the molecular beam epitaxy growth method. In the case of the II-nitride system, this non-equilibrium technique has the advantage of allowing the growth of alloys with a wide range of compositions without significant degradation of crystalline quality. This technique was used to produce a series of samples covering the entire composition range from Zn3N2 to Mg3N2 compounds. The quality of the material was studied by X-ray diffraction, which showed a monocrystalline epitaxy of the (Zn1 – xMgx)3N2 layers with satisfactory quality. The term “monocrystalline epitaxial” means that all the crystalline grains in the layer adopt a single orientation and their atomic arrangement is linked to that of the substrate. Using a home-made absorption device developed during the internship, measurement of the optical band gap of the samples showed that we achieve the ideal value of 1.7 eV for a nominal composition of ~20% Mg.