Hybrid functional studies of electronic properties of Cu₂MgSnS₄ (CMTS) for photovoltaics

Cu₂ZnSnS₄ (CZTS) is a promising photovoltaic absorber material, efficiency is however largely hindered by potential fluctuation and band tailing problem due to abundance of defect and their complexes. Our previous work has establish CMTS should have a stable chemical potential range and desirable optical properties similar to CZTS. In this work, we examine the electronic properties of CMTS using HSE06 functional, our results shows 1) a general increase in formation energy in most defects except Mg_Sn in CMTS, mainly due to the change of ground state structure, 2) qualitative similarity of defect thermodynamics and electronic properties in CMTS to CZTS and 3) identified Cu_Mg as the main contribution to p-type carrier. These findings suggest CMTS may suppress potential fluctuation due to formation of detrimental Cu_Zn+Zn_Cu defect complex in CZTS, and alleviate the band tailing near CZTS and CdS interface, and further confirm the feasibility of CMTS as an alternative absorber material to CZTS, suggesting potential for tuning. Implications to alloy with CZTS will be discussed.