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Title: Understanding the charge transport mechanisms through ultrathin SiOx layers in passivated contacts for high-efficiency silicon solar cells

Abstract

We report on the microscopic structure of the SiOx layer and the transport mechanism in polycrystalline Si (poly-Si) passivated contacts, which enable high-efficiency crystalline Si (c-Si) solar cells. Using electron beam induced current (EBIC) measurements, we accurately map nanoscale conduction-enabling pinholes in 2.2 nm thick SiOx layers in a poly-Si/SiOx/c-Si stack. These conduction enabling pinholes appear as bright spots in EBIC maps due to carrier transport and collection limitations introduced by the insulating 2.2 nm SiOx layer. Performing high-resolution transmission electron microscopy at a bright spot identified with EBIC reveals that conduction pinholes in SiOx can be regions of thin tunneling SiOx rather than a geometric pinhole. Additionally, selectively etching the underlying poly-Si layer in contacts with 1.5 and 2.2 nm thick SiOx layers using tetramethylammonium hydroxide results in pinhole-like etch features in both contacts. However, EBIC measurements for a contact with a thinner, 1.5 nm SiOx layer do not reveal pinholes, which is consistent with uniform tunneling transport through the 1.5 nm SiOx layer. Finally, we theoretically show that reducing the metal to the c-Si contact size from microns, like in the p-type passivated emitter rear contact, to tens of nanometers, like in poly-Si contacts, allows lowering of themore » unpassivated contact area by several orders of magnitude, thus resulting in excellent passivation, as has been demonstrated for these contacts.« less

Authors:
 [1];  [2];  [2];  [3];  [2];  [2];  [2];  [2];  [4];  [2]
  1. Colorado School of Mines, Golden, CO (United States); National Renewable Energy Lab. (NREL), Golden, CO (United States)
  2. National Renewable Energy Lab. (NREL), Golden, CO (United States)
  3. Univ. of California, Berkeley, CA (United States)
  4. Colorado School of Mines, Golden, CO (United States)
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Solar Energy Technologies Office (EE-4S)
OSTI Identifier:
1502791
Report Number(s):
NREL/JA-5900-72682
Journal ID: ISSN 0003-6951
Grant/Contract Number:  
AC36-08GO28308
Resource Type:
Accepted Manuscript
Journal Name:
Applied Physics Letters
Additional Journal Information:
Journal Volume: 114; Journal Issue: 8; Journal ID: ISSN 0003-6951
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; silicon solar cell; passivated contact; silicon oxide; tunneling; oxide pinhole; electron beam induced current

Citation Formats

Kale, Abhijit S., Nemeth, William, Guthrey, Harvey, Kennedy, Ellis, Norman, Andrew G., Page, Matthew, Al-Jassim, Mowafak, Young, David L., Agarwal, Sumit, and Stradins, Paul. Understanding the charge transport mechanisms through ultrathin SiOx layers in passivated contacts for high-efficiency silicon solar cells. United States: N. p., 2019. Web. doi:10.1063/1.5081832.
Kale, Abhijit S., Nemeth, William, Guthrey, Harvey, Kennedy, Ellis, Norman, Andrew G., Page, Matthew, Al-Jassim, Mowafak, Young, David L., Agarwal, Sumit, & Stradins, Paul. Understanding the charge transport mechanisms through ultrathin SiOx layers in passivated contacts for high-efficiency silicon solar cells. United States. doi:10.1063/1.5081832.
Kale, Abhijit S., Nemeth, William, Guthrey, Harvey, Kennedy, Ellis, Norman, Andrew G., Page, Matthew, Al-Jassim, Mowafak, Young, David L., Agarwal, Sumit, and Stradins, Paul. Wed . "Understanding the charge transport mechanisms through ultrathin SiOx layers in passivated contacts for high-efficiency silicon solar cells". United States. doi:10.1063/1.5081832. https://www.osti.gov/servlets/purl/1502791.
@article{osti_1502791,
title = {Understanding the charge transport mechanisms through ultrathin SiOx layers in passivated contacts for high-efficiency silicon solar cells},
author = {Kale, Abhijit S. and Nemeth, William and Guthrey, Harvey and Kennedy, Ellis and Norman, Andrew G. and Page, Matthew and Al-Jassim, Mowafak and Young, David L. and Agarwal, Sumit and Stradins, Paul},
abstractNote = {We report on the microscopic structure of the SiOx layer and the transport mechanism in polycrystalline Si (poly-Si) passivated contacts, which enable high-efficiency crystalline Si (c-Si) solar cells. Using electron beam induced current (EBIC) measurements, we accurately map nanoscale conduction-enabling pinholes in 2.2 nm thick SiOx layers in a poly-Si/SiOx/c-Si stack. These conduction enabling pinholes appear as bright spots in EBIC maps due to carrier transport and collection limitations introduced by the insulating 2.2 nm SiOx layer. Performing high-resolution transmission electron microscopy at a bright spot identified with EBIC reveals that conduction pinholes in SiOx can be regions of thin tunneling SiOx rather than a geometric pinhole. Additionally, selectively etching the underlying poly-Si layer in contacts with 1.5 and 2.2 nm thick SiOx layers using tetramethylammonium hydroxide results in pinhole-like etch features in both contacts. However, EBIC measurements for a contact with a thinner, 1.5 nm SiOx layer do not reveal pinholes, which is consistent with uniform tunneling transport through the 1.5 nm SiOx layer. Finally, we theoretically show that reducing the metal to the c-Si contact size from microns, like in the p-type passivated emitter rear contact, to tens of nanometers, like in poly-Si contacts, allows lowering of the unpassivated contact area by several orders of magnitude, thus resulting in excellent passivation, as has been demonstrated for these contacts.},
doi = {10.1063/1.5081832},
journal = {Applied Physics Letters},
number = 8,
volume = 114,
place = {United States},
year = {2019},
month = {2}
}

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