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Title: Density-functional theory computer simulations of CZTS 0.25Se 0.75 alloy phase diagrams

Here, density-functional theory simulations of CZTS, CZTSe, and CZTS 0.25Se 0.75 photovoltaic compounds have been performed to investigate the stability of the CZTS 0.25Se 0.75 alloy vs. decomposition into CZTS, CZTSe, and other secondary compounds. The Gibbs energy for vibrational contributions was estimated by calculating phonon spectra and thermodynamic properties at finite temperatures. It was demonstrated that the CZTS 0.25Se 0.75 alloy is stabilized not by enthalpy of formation but primarily by the mixing contributions to the Gibbs energy. The Gibbs energy gains/losses for several decomposition reactions were calculated as a function of temperature with/without intermixing and vibration contributions to the Gibbs energy. A set of phase diagrams was built in the multidimensional space of chemical potentials at 300 K and 900 K temperatures to demonstrate alloy stability and boundary compounds at various chemical conditions. It demonstrated for CZTS 0.25Se 0.75 that the chemical potentials for stability differ between typical processing temperature (~900 K) and operating temperature (300 K). This implies that as cooling progresses, the flux/concentration of S should be increased in MBE growth to maintain the CZTS 0.25Se 0.75 in a thermodynamically stable state to minimize phase decomposition.
Authors:
 [1] ;  [1] ;  [2] ;  [3] ;  [1]
  1. Univ. of California, San Diego, CA (United States). Dept. of Chemistry and Biochemistry
  2. International Business Machines Corp. (IBM), Yorktown Heights, NY (United States). Thomas J. Watson Research Center
  3. Duke Univ., Durham, NC (United States). Dept. of Mechanical Engineering and Materials Science
Publication Date:
Grant/Contract Number:
EE0006334
Type:
Accepted Manuscript
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 145; Journal Issue: 6; Journal ID: ISSN 0021-9606
Publisher:
American Institute of Physics (AIP)
Research Org:
International Business Machines Corp. (IBM), Yorktown Heights, NY (United States). Thomas J. Watson Research Center
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 14 SOLAR ENERGY; decomposition reactions; phonons; solar cells; density functional theory; zinc; entropy; Gibbs free energy; II-VI semiconductors; phase diagrams; chemical potential
OSTI Identifier:
1467855
Alternate Identifier(s):
OSTI ID: 1287751