Journal
JOURNAL OF ALLOYS AND COMPOUNDS
Volume 774, Issue -, Pages 803-812Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.jallcom.2018.10.026
Keywords
Semiconductors; Atomic scale structure; EXAFS; Synchrotron radiation; Order-disorder effects; CIGS
Categories
Funding
- German Federal Ministry for Economic Affairs and Energy [0325448E, 0324095E]
- Friedrich-Schiller-Universitat Jena under the ProChance Initiative [2.11.3-A1/2012-01]
- Department of Earth Sciences of the University of Florence
- ESRF
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The Cu-poor phases Cu(In,Ga)(3)Se(5 )and Cu(In,Ga)(5)Se-8 play an important role both for understanding the Cu-(In,Ga)-Se material system and for growing high-efficiency Cu(In,Ga)Se-2 thin film solar cells. Using extended X-ray absorption fine structure spectroscopy, we have studied the element-specific short-range structure of Cu(In,Ga)Se-2, Cu(In,Ga)(3)Se-5, and Cu(In,Ga)(5)Se-8 alloys spanning the entire compositional range. The materials feature different local atomic arrangements and the element-specific average bond lengths remain nearly constant despite significant changes of the lattice constants with increasing In to Ga ratio and decreasing Cu content. In particular, the average bond lengths of Cu-Se and Ga-Se are almost identical while the average In-Se bond length is significantly longer in all three phases. The distance between lattice sites with mixed site occupation therefore corresponds to the weighted average of different element-specific bond lengths rather than to the individual bond lengths themselves. Furthermore, the increasing number of vacancies with decreasing Cu content lead to both a significant unit cell contraction and a slight bond length expansion. The crystallographic long-range structure and the element-specific short-range structure thus describe different structural aspects that are certainly interrelated but obviously not identical. (C) 2018 Elsevier B.V. All rights reserved.
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