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Title: Local Electronic Structure Changes in Polycrystalline CdTe with CdCl2 Treatment and Air Exposure

Abstract

Postdeposition CdCl2 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 CdCl2 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 CdCl2-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 1011 cm–2 and a net carrier density of 1015 cm–3. Finally, these results suggest that both CdCl2 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];  [1];  [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:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Solar Energy Technologies Office; USDOE Office of Science (SC)
OSTI Identifier:
1441464
Report Number(s):
SAND-2018-2059J
Journal ID: ISSN 1944-8244; 662903
Grant/Contract Number:  
AC04-94AL85000; FOA-0000654; NA0003525
Resource Type:
Journal Article: 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)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CdTe; grain boundaries; local electronic structure; photoemission electron microscopy; photovoltaics

Citation Formats

Berg, Morgann, Kephart, Jason M., Munshi, Amit, Sampath, Walajabad S., Ohta, Taisuke, and Chan, Calvin. Local Electronic Structure Changes in Polycrystalline CdTe with CdCl2 Treatment and Air Exposure. United States: N. p., 2018. Web. doi:10.1021/acsami.7b18963.
Berg, Morgann, Kephart, Jason M., Munshi, Amit, Sampath, Walajabad S., Ohta, Taisuke, & Chan, Calvin. Local Electronic Structure Changes in Polycrystalline CdTe with CdCl2 Treatment and Air Exposure. United States. https://doi.org/10.1021/acsami.7b18963
Berg, Morgann, Kephart, Jason M., Munshi, Amit, Sampath, Walajabad S., Ohta, Taisuke, and Chan, Calvin. 2018. "Local Electronic Structure Changes in Polycrystalline CdTe with CdCl2 Treatment and Air Exposure". United States. https://doi.org/10.1021/acsami.7b18963. https://www.osti.gov/servlets/purl/1441464.
@article{osti_1441464,
title = {Local Electronic Structure Changes in Polycrystalline CdTe with CdCl2 Treatment and Air Exposure},
author = {Berg, Morgann and Kephart, Jason M. and Munshi, Amit and Sampath, Walajabad S. and Ohta, Taisuke and Chan, Calvin},
abstractNote = {Postdeposition CdCl2 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 CdCl2 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 CdCl2-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 1011 cm–2 and a net carrier density of 1015 cm–3. Finally, these results suggest that both CdCl2 treatment and oxygen exposure may be independently tuned to enhance the CdTe photovoltaic performance by engineering the interface and bulk electronic structure.},
doi = {10.1021/acsami.7b18963},
url = {https://www.osti.gov/biblio/1441464}, journal = {ACS Applied Materials and Interfaces},
issn = {1944-8244},
number = 11,
volume = 10,
place = {United States},
year = {Mon Mar 12 00:00:00 EDT 2018},
month = {Mon Mar 12 00:00:00 EDT 2018}
}

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Cited by: 8 works
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Works referenced in this record:

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Works referencing / citing this record:

Grain boundary passivation by CdCl2 treatment in CdTe solar cells revealed by Kelvin probe force microscopy
journal, October 2018