Berlin 2024 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 4: Perovskite and Photovoltaics I (joint session HL/KFM)

HL 4.4: Vortrag

Montag, 18. März 2024, 10:15–10:30, EW 203

Explaining the tetragonal distortion of chalcopyrites and solving the puzzle of the peculiar bond length dependence in (Ag,Cu)(In,Ga)Se₂ — •Hans H. Falk¹, Stefanie Eckner¹, Konrad Ritter¹, Sergiu Levcenko¹, Timo Pfeiffelmann¹, Edmund Welter², Jes Larsen³, William N. Shafarman⁴, and Claudia S. Schnohr¹ — ¹Felix Bloch Institute for Solid State Physics, Leipzig University, Germany — ²Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany — ³Department of Materials Science and Engineering, Uppsala University, Sweden — ⁴Department of Materials Science and Engineering, University of Delaware, Newark, USA

(Ag,Cu)(In,Ga)Se₂ is a highly efficient thin film solar cell absorber. EXAFS studies of (Ag,Cu)InSe₂ and (Ag,Cu)GaSe₂ show that the element specific bond length of the common cation (In-Se or Ga-Se) decreases with increasing Ag content even though the lattice expands. This peculiar bond length dependence is not only counter-intuitive but also the opposite of what is commonly observed in other chalcopyrite alloys, like Cu(In,Ga)Se₂ and Ag(In,Ga)Se₂, where the bond length of the common cation (Cu-Se or Ag-Se) increases as the lattice expands. This puzzling difference in the behavior of the common cation bond lengths can be explained by minimizing the distortion energy (Keating potential) of bond angles and bond lengths. With simple calculations, focusing on the local tetrahedral neighborhood, we are able to reproduce both the tetragonal distortion and the bond length behavior of various chalcopyrite alloys, leading to a deepened understanding of these technologically relevant photovoltaic absorber materials.

Keywords: Tetragonal Distortion; Chalcopyrite; (Ag,Cu)(In,Ga)Se2; Extended X-Ray Absorption Fine Structure; Crystal Structure