Cu₂ZnSnS₄ (CZTS) is a promising photovoltaic absorber material, however, efficiency is largely hindered by potential fluctuation and a band tailing problem due to the abundance of defect complexes and low formation energy of an intrinsic Cu_Zn defect. Alternatives to CZTS by group I, II, or IV element replacement to circumvent this challenge has grown research interest. In this work, using a hybrid (HSE06) functional, we demonstrated the qualitative similarity of defect thermodynamics and electronic properties in Cu₂MgSnS₄ (CMTS) to CZTS. We show Sn_Mg to be abundant when in Sn- and Cu-rich condition, which can be detrimental, while defect properties are largely similar to CZTS in Sn- and Cu-poor. Under Sn- and Cu-poor chemical potential, there is a general increase in formation energy in most defects except Sn_Mg, Cu_Mg remains as the main contribution to p-type carriers, and Sn_Mg may be detrimental because of a deep defect level in the mid gap and the possibility of forming defect complex Sn_Mg+Mg_Sn. Vacancy diffusion is studied using generalized gradient approximation, and we find similar vacancy diffusion properties for Cu vacancy and lower diffusion barrier for Mg vacancy, which may reduce possible Cu-Mg disorder in CMTS. These findings further confirm the feasibility of CMTS as an alternative absorber material to CZTS and suggest the possibility for tuning defect properties of CZTS, which is crucial for high photovoltaic performance.

中文翻译：

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Cu2MgSnS4 中的缺陷特性和空位扩散

Cu ₂ ZnSnS ₄ (CZTS) 是一种很有前途的光伏吸收材料，然而，效率在很大程度上受到电位波动和由于缺陷复合物的丰度和本征 Cu Zn 缺陷的低形成能而导致的带拖尾问题的_阻碍。通过 I、II 或 IV 族元素替代 CZTS 的替代品来规避这一挑战已经引起了研究兴趣。在这项工作中，我们使用混合 (HSE06) 泛函证明了 Cu ₂ MgSnS ₄ (CMTS) 与 CZTS 中缺陷热力学和电子特性的定性相似性。我们展示 Sn _Mg在富 Sn 和 Cu 的条件下会很丰富，这可能是有害的，而缺陷特性在很大程度上类似于 Sn 和 Cu 贫乏的 CZTS。_{在 Sn 和 Cu 贫化学势下，除 Sn Mg}外，大多数缺陷的形成能普遍增加，Cu _Mg仍然是对 p 型载流子的主要贡献，而 Sn _Mg可能是有害的，因为缺陷能级较深在中间间隙和形成缺陷复合物 Sn _Mg + Mg _Sn的可能性. 使用广义梯度近似研究空位扩散，我们发现 Cu 空位具有相似的空位扩散特性，而 Mg 空位具有较低的扩散势垒，这可能会减少 CMTS 中​​可能出现的 Cu-Mg 紊乱。这些发现进一步证实了 CMTS 作为 CZTS 的替代吸收材料的可行性，并提出了调整 CZTS 缺陷特性的可能性，这对于高光伏性能至关重要。