Date Published: May 22, 2017
Publisher: John Wiley and Sons Inc.
Author(s): Anna Miglio, Christophe P. Heinrich, Wolfgang Tremel, Geoffroy Hautier, Wolfgang G. Zeier.
Quaternary chalcopyrites have shown to exhibit tunable band gaps with changing anion composition. Inspired by these observations, the underlying structural and electronic considerations are investigated using a combination of experimentally obtained structural data, molecular orbital considerations, and density functional theory. Within the solid solution Cu2ZnGeS4−xSex, the anion bond alteration parameter changes, showing larger bond lengths for metal–selenium than for metal–sulfur bonds. The changing bonding interaction directly influences the valence and conduction band edges, which result from antibonding Cu–anion and Ge–anion interactions, respectively. The knowledge of the underlying bonding interactions at the band edges can help design properties of these quaternary chalcopyrites for photovoltaic and thermoelectric applications.
Quaternary chalcopyrites Cu2MIIMIVQ4 (MII = Zn, Fe; MIV = Sn, Ge; Q = S, Se) have attracted interest, nearly quite as much as the ternary analogues, as materials for multiple applications such as photovoltaics, photocatalysts, and thermoelectrics. Especially, the adjustable band gaps in the absorbance region of the solar spectrum lead to good photovoltaic and photocatalytic efficiencies.1, 2, 3, 4 In the field of thermoelectrics, the materials have been mostly studied due to their very low thermal conductivities5, 6, 7, 8, 9, 10 and recently discovered band convergence,11, 12, 13 leading to good mid‐temperature range efficiencies.
In summary, we have extended the description of influences of crystal structure and bonding interactions of chalcopyrites from the ternary to the quaternary compounds. While the d–p‐hybridization between the metal and anions determine the valence band edges, the Ge s–anion p interactions influence the conduction band edge. Using a combination of experimentally obtained structural data with molecular orbital considerations and density function theory, it is possible to understand occurring electronic changes in the quaternary chalcopyrites.
Synthesis and Structural Data: Synthesis as well as X‐ray diffraction data collection, and corresponding Rietveld refinements of the polycrystalline stannite‐type Cu2ZnGeS4−xSex had been reported elsewhere.10 For obtaining anion displacement and bond lengths, the refined atomic positions and lattice parameters had been used as input in the structural program VESTA 3.49
The authors declare no conflict of interest.