Effects of pre-alloying process on the absorber quality for Cu₂ZnSnS₄ thin-film solar cells

Sulfide-kesterite Cu₂ZnSnS₄ absorber fabricated using magnetron sputtering method exhibits great application potential for its pure and flat precursors, great repeatability and efficient process. However, the elements distribution of metallic stacked precursors is not uniform vertically and limits the efficiency of Cu₂ZnSnS₄ solar cells. In present work, the precursor is pre-alloyed before sulfurization to make elements interdiffuse effectively and promotes the metal elements to transform into alloying phases. Due to the improved element distribution of the precursor, Cu₂ZnSnS₄ phase is preferentially formed during the growth process. By pre-alloying the precursor, the absorber performs better crystallinity, and the grain size of the bottom layer is improved effectively. Using this approach, the photovoltaic performance of Cu₂ZnSnS₄ solar cells is significantly improved, and the best cell is acquired with the efficiency of 7.28%.