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Title: Core Levels, Band Alignments, and Valence-Band States in CuSbS 2 for Solar Cell Applications

The earth-abundant material CuSbS 2 (CAS) has shown good optical properties as a photovoltaic solar absorber material, but has seen relatively poor solar cell performance. To investigate the reason for this anomaly, the core levels of the constituent elements, surface contaminants, ionization potential, and valence-band spectra are studied by X-ray photoemission spectroscopy. The ionization potential and electron affinity for this material (4.98 and 3.43 eV) are lower than those for other common absorbers, including CuInxGa (1-x)Se 2 (CIGS). Experimentally corroborated density functional theory (DFT) calculations show that the valence band maximum is raised by the lone pair electrons from the antimony cations contributing additional states when compared with indium or gallium cations in CIGS. The resulting conduction band misalignment with CdS is a reason for the poor performance of cells incorporating a CAS/CdS heterojunction, supporting the idea that using a cell design analogous to CIGS is unhelpful. These findings underline the critical importance of considering the electronic structure when selecting cell architectures that optimize open-circuit voltages and cell efficiencies.
Authors:
ORCiD logo [1] ;  [1] ;  [2] ;  [3] ;  [3] ;  [1] ;  [1] ;  [1] ; ORCiD logo [4] ; ORCiD logo [3] ;  [5]
  1. Univ. of Liverpool (United Kingdom)
  2. Univ. College London (United Kingdom)
  3. National Renewable Energy Lab. (NREL), Golden, CO (United States)
  4. Univ. College London (United Kingdom); Science and Technology Facilities Council (STFC), Harwell Campus, Oxford (United Kingdom). Diamond Light Source, Ltd.
  5. Stephenson Institute for Renewable Energy and Department of Physics, University of Liverpool, Liverpool L69 7ZF, U.K.
Publication Date:
Report Number(s):
NREL/JA-5K00-70595
Journal ID: ISSN 1944-8244; TRN: US1800233
Grant/Contract Number:
AC36-08GO28308
Type:
Accepted Manuscript
Journal Name:
ACS Applied Materials and Interfaces
Additional Journal Information:
Journal Volume: 9; Journal Issue: 48; Journal ID: ISSN 1944-8244
Publisher:
American Chemical Society (ACS)
Research Org:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; band alignments; copper antimony sulfide; CuSbS2; density of states; DFT; thin-film solar cells; XPS
OSTI Identifier:
1411518