Driving factors for the peculiar bond length dependence and tetragonal distortion of (Ag,Cu)(In,Ga)Se2 and other chalcopyrites
Date
2024-12-04
Journal Title
Journal ISSN
Volume Title
Publisher
JPhys Energy
Abstract
The chalcopyrite alloy (Ag,Cu)(In,Ga)Se2 is a highly efficient thin film solar cell absorber, reaching record efficiencies above 23%. Recently, a peculiar behavior in the bond length dependence of (Ag,Cu)GaSe2 was experimentally proven. The common cation bond length, namely Ga–Se, decreases with increasing Ag/(Ag + Cu) ratio even though the crystal lattice expands. This is opposite to the behavior observed for Cu(In,Ga)Se2, where all bond lengths increase with increasing lattice size. To better understand this peculiar bond length behavior, element-specific bond lengths of (Ag,Cu)InSe2 and Ag(In,Ga)Se2 alloys are determined using extended x-ray absorption fine structure spectroscopy. They show that the peculiar bond length dependence occurs only for (Ag,Cu) alloys, independent of the species of common cation (In or Ga). The bond lengths are used to determine the anion displacements and to estimate their contribution to the bandgap bowing. Again, both behaviors differ significantly depending on the type of alloyed cation. A valence force field approach, relaxing bond lengths and bond angles, is used to describe the structural distortion energy for a comprehensive set of I–III–VI2 and II–IV–V2 chalcopyrites. The model reveals bond angle distortions as main driving factor for the tetragonal distortion and reproduces the literature values with less than 10% deviation. In contrast, the peculiar bond length dependence is not reproduced, demonstrating that it originates from electronic effects beyond the scope of this structural model. Thus, a fundamental understanding of bond length behavior and tetragonal distortion is achieved for chalcopyrite materials, benefiting their technological applications such as high efficiency thin film photovoltaics.
Description
This article was originally published in JPhys Energy. The version of record is available at: https://doi.org/10.1088/2515-7655/ad967f.
© 2024 The Author(s). Published by IOP Publishing Ltd.
Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 license (https://creativecommons.org/licenses/by/4.0/). Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Keywords
chalcopyrite, extended x-ray absorption fine structure, thin film solar cells, tetragonal distortion, Keating potential, bandgap bowing, bond length behavior
Citation
Falk, Hans H, Stefanie Eckner, Konrad Ritter, Sergiu Levcenko, Timo Pfeiffelmann, Jes Larsen, William N Shafarman, and Claudia S Schnohr. “Driving Factors for the Peculiar Bond Length Dependence and Tetragonal Distortion of (Ag,Cu)(In,Ga)Se2 and Other Chalcopyrites.” Journal of Physics: Energy 7, no. 1 (January 31, 2025): 015004. https://doi.org/10.1088/2515-7655/ad967f.