Beyond 10% efficient Cu₂ZnSn(S,Se)₄ solar cells: Effects of the introduction of SnS powder during selenization process

Cu₂ZnSn(S,Se)₄ (CZTSSe) has received considerable attention as the promising absorber for thin-film solar cells. For traditional selenization process, the issues of Sn-loss, lower S/(S + Se) ratio, and unsuitable back contact interface extensively exist in CZTSSe solar cells. In present work, SnSe and SnS powder is introduced during selenization process, respectively. The effects of SnSe and SnS powder on CZTSSe films and the Mo/CZTSSe interface have been comprehensively studied. We discover that SnS not only can provide the Sn-contained vapor in selenization process but also offer S-vapor. Due to the presence of Sn-contained vapor, the number of voids in the CZTSSe absorber and Mo/CZTSSe interface decreases remarkably and the Sn-loss is effectively suppressed. The thickness of Mo(S,Se)₂ layer is significantly reduced, and the S/(S + Se) ratio in CZTSSe bulk obviously increases owing to the presence of S-vapor. As a consequence, the open-circuit voltage and fill factor of the solar cell significantly increase and the CZTSSe solar cell with efficiency of 10.07% (total area) is successfully fabricated.