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Title: Scanning Kelvin Probe Microscopy: A Tool to Investigate Nano-Scale Doping Non-Uniformities in Poly-Si/SiOx Contacts: Preprint

Abstract

Monocrystalline Si (c-Si) solar cells with passivated contacts based on the ultrathin SiOx and doped polycrystalline Si (poly-Si) layers in a poly-Si/SiOx/c Si structure show high solar cell efficiencies that are ~26%. Excellent surface passivation using these contacts is achieved via the combined effects of chemical passivation of the SiOx/c-Si interface by the SiOx layer and field-effect passivation from the heavily doped poly-Si layer. These contacts give best performance only when annealed to temperatures higher than 850 degrees C. Structural changes in the SiOx layer and dopant diffusion from poly-Si into the underlying c-Si wafer occur during this step which are hard to investigate using conventional characterization techniques. In this work we investigate poly-Si/SiOx contacts with both a 1.5 (tunneling transport) and 2.2 (pinhole transport) nm SiOx layer using atomic force microscopy techniques. Conductive AFM on n+-poly-Si/SiOx/p-Si structures show significant spatial variations for both contact types, likely due to non-uniformities in the poly-Si layer itself. The electrical and structural variations deeper into the contact were revealed by scanning Kelvin probe microscopy after precisely etching away the poly-Si and SiOx layers and few nanometers of c-Si surface. This etching was performed using tetramethylammonium hydroxide and dilute HF solutions. The resulting surfacemore » potential maps appear similar for both contacts, and show less than 500 nm size heavily-doped regions. However, further etching of the c-Si surface reveals these heavily-doped regions to be less than 200 nm deep for the 2.2 nm SiOx contact and greater than 200 nm deep for the 1.5 nm SiOx contact.« less

Authors:
 [1];  [2];  [2];  [2];  [2];  [2];  [2];  [2];  [1]
  1. National Renewable Energy Laboratory (NREL), Golden, CO (United States)
  2. Colorado School of Mines
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Solar Energy Technologies Office
OSTI Identifier:
1575908
Report Number(s):
NREL/CP-5900-73161
DOE Contract Number:  
AC36-08GO28308
Resource Type:
Conference
Resource Relation:
Conference: Presented at the 46th IEEE Photovoltaic Specialists Conference (PVSC 46), 16-21 June 2019, Chicago, Illinois
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; solar energy; nanoscale doping; solar cells

Citation Formats

Kale, Abhijit, Nanayakkara, Sanjini U., Nemeth, William, Guthrey, Harvey, Page, Matthew, Al-Jassim, Mowafak, Young, David L., Stradins, Paul, and Agarwal, Sumit. Scanning Kelvin Probe Microscopy: A Tool to Investigate Nano-Scale Doping Non-Uniformities in Poly-Si/SiOx Contacts: Preprint. United States: N. p., 2019. Web.
Kale, Abhijit, Nanayakkara, Sanjini U., Nemeth, William, Guthrey, Harvey, Page, Matthew, Al-Jassim, Mowafak, Young, David L., Stradins, Paul, & Agarwal, Sumit. Scanning Kelvin Probe Microscopy: A Tool to Investigate Nano-Scale Doping Non-Uniformities in Poly-Si/SiOx Contacts: Preprint. United States.
Kale, Abhijit, Nanayakkara, Sanjini U., Nemeth, William, Guthrey, Harvey, Page, Matthew, Al-Jassim, Mowafak, Young, David L., Stradins, Paul, and Agarwal, Sumit. 2019. "Scanning Kelvin Probe Microscopy: A Tool to Investigate Nano-Scale Doping Non-Uniformities in Poly-Si/SiOx Contacts: Preprint". United States. https://www.osti.gov/servlets/purl/1575908.
@article{osti_1575908,
title = {Scanning Kelvin Probe Microscopy: A Tool to Investigate Nano-Scale Doping Non-Uniformities in Poly-Si/SiOx Contacts: Preprint},
author = {Kale, Abhijit and Nanayakkara, Sanjini U. and Nemeth, William and Guthrey, Harvey and Page, Matthew and Al-Jassim, Mowafak and Young, David L. and Stradins, Paul and Agarwal, Sumit},
abstractNote = {Monocrystalline Si (c-Si) solar cells with passivated contacts based on the ultrathin SiOx and doped polycrystalline Si (poly-Si) layers in a poly-Si/SiOx/c Si structure show high solar cell efficiencies that are ~26%. Excellent surface passivation using these contacts is achieved via the combined effects of chemical passivation of the SiOx/c-Si interface by the SiOx layer and field-effect passivation from the heavily doped poly-Si layer. These contacts give best performance only when annealed to temperatures higher than 850 degrees C. Structural changes in the SiOx layer and dopant diffusion from poly-Si into the underlying c-Si wafer occur during this step which are hard to investigate using conventional characterization techniques. In this work we investigate poly-Si/SiOx contacts with both a 1.5 (tunneling transport) and 2.2 (pinhole transport) nm SiOx layer using atomic force microscopy techniques. Conductive AFM on n+-poly-Si/SiOx/p-Si structures show significant spatial variations for both contact types, likely due to non-uniformities in the poly-Si layer itself. The electrical and structural variations deeper into the contact were revealed by scanning Kelvin probe microscopy after precisely etching away the poly-Si and SiOx layers and few nanometers of c-Si surface. This etching was performed using tetramethylammonium hydroxide and dilute HF solutions. The resulting surface potential maps appear similar for both contacts, and show less than 500 nm size heavily-doped regions. However, further etching of the c-Si surface reveals these heavily-doped regions to be less than 200 nm deep for the 2.2 nm SiOx contact and greater than 200 nm deep for the 1.5 nm SiOx contact.},
doi = {},
url = {https://www.osti.gov/biblio/1575908}, journal = {},
number = ,
volume = ,
place = {United States},
year = {2019},
month = {11}
}

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