Single-step sulfo-selenization method to synthesize Cu ₂ZnSn(S_ySe_1-y)₄ absorbers from metallic stack precursors

Pentenary Cu₂ZnSn(S_ySe_1-y)₄ (kesterite) photovoltaic absorbers are synthesized by a one-step annealing process from copper-poor and zinc-rich precursor metallic stacks prepared by direct-current magnetron sputtering deposition. Depending on the chalcogen source - mixtures of sulfur and selenium powders, or selenium disulfide - as well as the annealing temperature and pressure, this simple methodology permits the tuning of the absorber composition from sulfur-rich to selenium-rich in one single annealing process. The impact of the thermal treatment variables on chalcogenide incorporation is investigated. The effect of the S/(S+Se) compositional ratio on the structural and morphological properties of the as-grown films, and the optoelectronic parameters of solar cells fabricated using these absorber films is studied. Using this single-step sulfo-selenization method, pentenary kesterite-based devices with conversion efficiencies up to 4.4 % are obtained. Not an ordinary pentenary! A straightforward sulfo-selenization process for the formation of pentenary Cu ₂ZnSn(S_ySe_1-y) solar-cell absorber films permits the tuning of the absorber composition from sulfur-rich to selenium-rich in a single annealing process. The resulting films, with compositions in the whole range of S/(S+Se) ratios, aim at pentenary-based solar cells of superior efficiency, which to date have been mostly limited to chalcogen-containing precursors.