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  Fritsch, D.; Schorr, S.: Disorder induced band gap lowering in kesterite type Cu₂ZnSnSe₄ and Ag₂ZnSnSe₄: A first-principles and special quasirandom structures investigations. Journal of Physics: Condensed Matter 36 (2024), p. 375702/1-8

10.1088/1361-648X/ad52de
Open Accesn Version

Abstract:
Quaternary chalcogenides, i.e. Cu2ZnSnS4, crystallising in the kesterite crystal structure have already been demonstrated as potential building blocks of thin film solar cells, containing only abundant elements and exhibiting power conversion efficiencies of about 13 % so far. However, a correct determination of their ground state crystal structure has been hindered in the past by two structurally similar polymorphs, namely the kesterite and the stannite crystal structure. Additional complications arose from the later identified Cu-Zn disorder, present in virtually all thin film samples. Subsequently, is has been shown experimentally that this unavoidable Cu-Zn disorder leads to a band gap lowering in the respective samples. Additional theoretical investigations, mostly based on Monte-Carlo methods, tried to understand the atomistic origin of this disorder induced band gap lowering. Here, we present theoretical results from first-principles calculations based on density functional theory for the disorder induced band gap lowering in kesterite Cu2ZnSnSe4 and Ag2ZnSnSe4, where the Cu-Zn disorder is modelled via a supercell approach and special quasirandom structures. Results of subsequent analyses of structural, electronic, and optical properties will be discussed with respect to available experimental results, and will provide additional insight and knowledge towards the atomistic origin of the observed disorder induced band gap lowering in kesterite type materials.