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Title: Cadmium Selective Etching in CdTe Solar Cells Produces Detrimental Narrow-Gap Te in Grain Boundaries

Abstract

Recent advances in design and processing technology have made possible commercialization of polycrystalline (px)-CdTe as a photovoltaic absorber. Grain boundaries (GBs) are the most prominent structural defects in these devices and undergo significant changes during device fabrication. However, the effects of device fabrication processes on these GBs are not entirely understood. Prevailing models of GBs in thin-film photovoltaics consider individual GBs to have homogeneous properties in their area. Here, using an aberration-corrected scanning transmission electron microscope (STEM)-based low-loss and core-loss electron energy-loss spectroscopy (EELS), we show that back-surface etching of CdTe leads to inhomogeneity within individual grain boundaries. We observe that etching the back surface leads to the conversion of a region of GBs from CdTe to an elemental Te, which has an only 0.33 eV band gap, as deep as 1 μm from the back surface. The presence of elemental Te in GBs this deep into the absorber layer will increase recombination in the absorber layer and limit the extractable open-circuit voltage, thus reducing device efficiency. However, additive methods for back contact formation such as deposition of Te, ZnTe, or other materials preserve the CdTe stoichiometry of the GBs. Thus, especially for the next generations of CdTe-based cells havingmore » longer minority carrier diffusion length and/or thinner absorber layers, additive back contacting methods are superior.« less

Authors:
ORCiD logo [1]; ORCiD logo [2];  [1]; ORCiD logo [3]; ORCiD logo [3];  [4];  [4];  [5]; ORCiD logo [1]
  1. Univ. of Utah, Salt Lake City, UT (United States)
  2. Idaho National Lab. (INL), Idaho Falls, ID (United States)
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS)
  4. Colorado State Univ., Fort Collins, CO (United States)
  5. Univ. of South Florida, Tampa, FL (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Colorado State Univ., Fort Collins, CO (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE Office of Enterprise Assessments (EA); USDOE Office of Energy Efficiency and Renewable Energy (EERE)
Contributing Org.:
University of South Florida; Oak Ridge National Laboratory; University of Utah
OSTI Identifier:
1631240
Alternate Identifier(s):
OSTI ID: 1670788
Grant/Contract Number:  
AC05-00OR22725; EE0008557
Resource Type:
Accepted Manuscript
Journal Name:
ACS Applied Energy Materials
Additional Journal Information:
Journal Volume: 3; Journal Issue: 2; Journal ID: ISSN 2574-0962
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; Etching; Grain; Layers; Electron energy loss spectroscopy; Grain boundaries

Citation Formats

Misra, Sudhajit, Aguiar, Jeffery A., Gardner, Sophia, Sang, Xiahan, Unocic, Raymond R., Munshi, Amit, Sampath, Walajabad S., Ferekides, Chris S., and Scarpulla, Michael A. Cadmium Selective Etching in CdTe Solar Cells Produces Detrimental Narrow-Gap Te in Grain Boundaries. United States: N. p., 2020. Web. doi:10.1021/acsaem.9b02224.
Misra, Sudhajit, Aguiar, Jeffery A., Gardner, Sophia, Sang, Xiahan, Unocic, Raymond R., Munshi, Amit, Sampath, Walajabad S., Ferekides, Chris S., & Scarpulla, Michael A. Cadmium Selective Etching in CdTe Solar Cells Produces Detrimental Narrow-Gap Te in Grain Boundaries. United States. https://doi.org/10.1021/acsaem.9b02224
Misra, Sudhajit, Aguiar, Jeffery A., Gardner, Sophia, Sang, Xiahan, Unocic, Raymond R., Munshi, Amit, Sampath, Walajabad S., Ferekides, Chris S., and Scarpulla, Michael A. Tue . "Cadmium Selective Etching in CdTe Solar Cells Produces Detrimental Narrow-Gap Te in Grain Boundaries". United States. https://doi.org/10.1021/acsaem.9b02224. https://www.osti.gov/servlets/purl/1631240.
@article{osti_1631240,
title = {Cadmium Selective Etching in CdTe Solar Cells Produces Detrimental Narrow-Gap Te in Grain Boundaries},
author = {Misra, Sudhajit and Aguiar, Jeffery A. and Gardner, Sophia and Sang, Xiahan and Unocic, Raymond R. and Munshi, Amit and Sampath, Walajabad S. and Ferekides, Chris S. and Scarpulla, Michael A.},
abstractNote = {Recent advances in design and processing technology have made possible commercialization of polycrystalline (px)-CdTe as a photovoltaic absorber. Grain boundaries (GBs) are the most prominent structural defects in these devices and undergo significant changes during device fabrication. However, the effects of device fabrication processes on these GBs are not entirely understood. Prevailing models of GBs in thin-film photovoltaics consider individual GBs to have homogeneous properties in their area. Here, using an aberration-corrected scanning transmission electron microscope (STEM)-based low-loss and core-loss electron energy-loss spectroscopy (EELS), we show that back-surface etching of CdTe leads to inhomogeneity within individual grain boundaries. We observe that etching the back surface leads to the conversion of a region of GBs from CdTe to an elemental Te, which has an only 0.33 eV band gap, as deep as 1 μm from the back surface. The presence of elemental Te in GBs this deep into the absorber layer will increase recombination in the absorber layer and limit the extractable open-circuit voltage, thus reducing device efficiency. However, additive methods for back contact formation such as deposition of Te, ZnTe, or other materials preserve the CdTe stoichiometry of the GBs. Thus, especially for the next generations of CdTe-based cells having longer minority carrier diffusion length and/or thinner absorber layers, additive back contacting methods are superior.},
doi = {10.1021/acsaem.9b02224},
journal = {ACS Applied Energy Materials},
number = 2,
volume = 3,
place = {United States},
year = {Tue Jan 28 00:00:00 EST 2020},
month = {Tue Jan 28 00:00:00 EST 2020}
}

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