Comparison of potassium-functionalized Cu2ZnSnS4 nanoparticles annealed in different reactive sulfide atmospheres

Kesterite Cu₂ ZnSnS₄ (CZTS) can be a promising, alternative material for thin-film solar cells, because it is earth-abundant, non-toxic and displays relevant physical properties. For future up-scaling possibilities and to decrease the environmental impact of the photovoltaic technology, solution-processing deposition methods are desired. This paper deals with CZTS absorber layers fabricated from CZTS nanoparticles that are functionalized with KCl, and investigates two different types of furnaces for the annealing process; a hydrogen sulfide (H₂S) flow furnace and a nitrogen atmosphere closed furnace. We find that more uniform grain growth is achieved when annealing in a closed furnace, while very large grains on the surface of the film are obtained when annealing in H₂S.