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Title: Local Electronic Structure Changes in Polycrystalline CdTe with CdCl 2 Treatment and Air Exposure

Postdeposition CdCl 2 treatment of polycrystalline CdTe is known to increase the photovoltaic device efficiency. However, the precise chemical, structural, and electronic changes that underpin this improvement are still debated. In this work, spectroscopic photoemission electron microscopy was used to spatially map the vacuum level and ionization energy of CdTe films, enabling the identification of electronic structure variations between grains and grain boundaries (GBs). In vacuo preparation and inert transfer of oxide-free CdTe surfaces isolated the separate effects of CdCl 2 treatment and ambient oxygen exposure. Qualitatively, grain boundaries displayed lower work function and downward band bending relative to grain interiors, but only after air exposure of CdCl 2-treated CdTe. Analysis of numerous space charge regions at grain boundaries showed an average depletion width of 290 nm and an average band bending magnitude of 70 meV, corresponding to a GB trap density of 10 11 cm –2 and a net carrier density of 10 15 cm –3. Finally, these results suggest that both CdCl 2 treatment and oxygen exposure may be independently tuned to enhance the CdTe photovoltaic performance by engineering the interface and bulk electronic structure.
Authors:
 [1] ;  [2] ;  [2] ;  [2] ; ORCiD logo [1] ; ORCiD logo [1]
  1. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
  2. Colorado State Univ., Fort Collins, CO (United States). Department of Mechanical Engineering
Publication Date:
Report Number(s):
SAND-2018-2059J
Journal ID: ISSN 1944-8244; 662903
Grant/Contract Number:
AC04-94AL85000; FOA-0000654; NA0003525
Type:
Accepted Manuscript
Journal Name:
ACS Applied Materials and Interfaces
Additional Journal Information:
Journal Volume: 10; Journal Issue: 11; Journal ID: ISSN 1944-8244
Publisher:
American Chemical Society (ACS)
Research Org:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Solar Energy Technologies Office (EE-4S); USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CdTe; grain boundaries; local electronic structure; photoemission electron microscopy; photovoltaics
OSTI Identifier:
1441464