A thermal route to synthesize photovoltaic grade CuInSe2 films from printed CuO/In2O3 nanoparticle-based inks under Se atmosphere

In this work we present an alternative thermal route for the synthesis of CuInSe2 light absorber films for photovoltaic applications from printed CuO/In2O3 nanoparticle-based inks. We demonstrate the possibility of substituting highly toxic (H2Se) and explosive (H2) gases for the processing of this type of precursors, using more environmental friendly gases (elemental Se and Ar/H2 mixtures). We show that by using Ar/H2 mixtures with low H2 concentration, it is possible to reduce the oxide nanoparticles to their metallic form, thus priming the film for subsequent selenization. This reactive thermal process seems to be the critical step to obtain large CuInSe2 grains with photovoltaic activity. Optimizing the proposed thermal route, based on less toxic, safer, and more eco-friendly gases, we obtain a very promising 2.4% efficiency solar cell based on CuInSe2 films as the absorber layer.