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Title: Modification of defects and potential fluctuations in slow-cooled and quenched Cu 2ZnSnSe 4 single crystals

Recent literature reports have shown the ability to manipulate Cu-Zn cation ordering for Cu 2ZnSnSe 4 (CZTSe) via low temperature treatments. Theoretical arguments suggest that one of the major roadblocks to higher V OC—significant band tailing—could be improved with increased cation order; however, few direct measurements have been reported and significant device improvements have not yet been realized. This paper investigates electrical properties, defects, and devices from quenched and slow-cooled single crystals of CZTSe. The extent of disorder was characterized by Raman spectroscopy as well as x-ray diffraction, where the change in Cu-Zn order can be detected by a changing c/a ratio. Quenched samples show higher acceptor concentrations, lower hole mobilities, and a lower-energy photoluminescence (PL) peak than crystals cooled at slower rates, consistent with a reduction in the bandgap. In addition, samples quenched at the highest temperatures showed lower PL yield consistent with higher quantities of deep defects. Devices fabricated using slow-cooled CZTSe single crystals showed improved efficiencies, most notably with increased V OC; however, low temperature intensity-dependent photoluminescence measurements continue to indicate the existence of potential fluctuations. We discuss the possibility that potential fluctuations in slow-cooled samples may be related to the inability to achieve a long rangemore » order of the Cu-Zn sub-lattice resulting in local regions of high and low levels of cation order, and consequent local variations in the bandgap. Finally, the presence of significant potential fluctuations, even after the slow-cooling step, suggests the difficulty in eliminating band-tailing in this system, and thus, additional approaches may be needed for significant reduction of the V OC deficit.« less
Authors:
ORCiD logo [1] ;  [2] ;  [3] ;  [2] ;  [3] ; ORCiD logo [2]
  1. Univ. of Delaware, Newark, DE (United States). Inst. of Energy Conversion; IBM T. J. Watson Research Center, Yorktown Heights, NY (United States)
  2. Univ. of Delaware, Newark, DE (United States). Inst. of Energy Conversion
  3. IBM T. J. Watson Research Center, Yorktown Heights, NY (United States)
Publication Date:
Grant/Contract Number:
EE0006334
Type:
Accepted Manuscript
Journal Name:
Journal of Applied Physics
Additional Journal Information:
Journal Volume: 121; Journal Issue: 6; Journal ID: ISSN 0021-8979
Publisher:
American Institute of Physics (AIP)
Research Org:
IBM T. J. Watson Research Center, Yorktown Heights, NY (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Solar Energy Technologies Office (EE-4S)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; single crystals; photoluminescence; X-ray diffraction; crystal defects; carrier density; zinc; band gap; low temperature instruments; cluster analysis; electrostatics
OSTI Identifier:
1465326
Alternate Identifier(s):
OSTI ID: 1361769