SKM 2023 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 6: Perovskite and photovoltaics I (joint session HL/CPP)

CPP 6.9: Vortrag

Montag, 27. März 2023, 12:00–12:15, JAN 0027

Peculiar bond length dependence and its impact on the band gap bowing in (Ag,Cu)(In,Ga)Se₂ thin film alloys — •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, Germany — ³Department of Materials Science and Engineering, Uppsala University, Sweden — ⁴Department of Materials Science and Engineering, University of Delaware, USA

Incorporation of Ag into Cu(In,Ga)Se₂ thin film solar cells improves several of their properties. However, with increasing Ag content, the band gap of (Ag,Cu)GaSe₂ increases even though the lattice expands and the Ga-Se bond length is predicted to decrease. This is counterintuitive, since in other chalcopyrite alloys all bond lengths increase and the band gap decreases as the lattice expands. Therefore, we studied the element-specific average bond lengths of (Ag,Cu)GaSe₂, (Ag,Cu)InSe₂ and Ag(In,Ga)Se₂ using X-ray absorption spectroscopy for thin films grown on Mo-coated soda lime glass by a single stage co-evaporation process. As predicted, the Ga-Se bond length decreases with increasing Ag content in (Ag,Cu)GaSe₂. While the In-Se bond length of (Ag,Cu)InSe₂ shows the same behavior, Ag(In,Ga)Se₂ exhibits a dependence similar to that of Cu(In,Ga)Se₂, demonstrating that the peculiar behavior is related to mixing the group-I lattice site. Using the bond lengths we model the anion positions and estimate their effect on the band gap bowing.