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Title: Polycrystalline silicon passivated tunneling contacts for high efficiency silicon solar cells

Abstract

Abstract

Authors:
; ; ; ; ; ;
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
1247961
Report Number(s):
NREL/JA-5J00-64830
Journal ID: ISSN 0884-2914
DOE Contract Number:
AC36-08GO28308
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Materials Research; Journal Volume: 31; Journal Issue: 06; Related Information: Journal of Materials Research
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; photovoltaic; passivation; thin film

Citation Formats

Nemeth, Bill, Young, David L., Page, Matthew R., LaSalvia, Vincenzo, Johnston, Steve, Reedy, Robert, and Stradins, Paul. Polycrystalline silicon passivated tunneling contacts for high efficiency silicon solar cells. United States: N. p., 2016. Web. doi:10.1557/jmr.2016.77.
Nemeth, Bill, Young, David L., Page, Matthew R., LaSalvia, Vincenzo, Johnston, Steve, Reedy, Robert, & Stradins, Paul. Polycrystalline silicon passivated tunneling contacts for high efficiency silicon solar cells. United States. doi:10.1557/jmr.2016.77.
Nemeth, Bill, Young, David L., Page, Matthew R., LaSalvia, Vincenzo, Johnston, Steve, Reedy, Robert, and Stradins, Paul. 2016. "Polycrystalline silicon passivated tunneling contacts for high efficiency silicon solar cells". United States. doi:10.1557/jmr.2016.77.
@article{osti_1247961,
title = {Polycrystalline silicon passivated tunneling contacts for high efficiency silicon solar cells},
author = {Nemeth, Bill and Young, David L. and Page, Matthew R. and LaSalvia, Vincenzo and Johnston, Steve and Reedy, Robert and Stradins, Paul},
abstractNote = {Abstract},
doi = {10.1557/jmr.2016.77},
journal = {Journal of Materials Research},
number = 06,
volume = 31,
place = {United States},
year = 2016,
month = 3
}
  • We describe the design, fabrication and results of passivated contacts to n-type silicon utilizing thin SiO 2 and transparent conducting oxide layers. High temperature silicon dioxide is grown on both surfaces of an n-type wafer to a thickness <50 Å, followed by deposition of tin-doped indium oxide (ITO) and a patterned metal contacting layer. As deposited, the thin-film stack has a very high J0, contact, and a non-ohmic, high contact resistance. However, after a forming gas anneal, the passivation quality and the contact resistivity improve significantly. The contacts are characterized by measuring the recombination parameter of the contact (J0, contact)more » and the specific contact resistivity (ρ contact) using a TLM pattern. The best ITO/SiO 2 passivated contact in this study has J 0,contact = 92.5 fA/cm 2 and ρ contact = 11.5 mOhm-cm 2. These values are placed in context with other passivating contacts using an analysis that determines the ultimate efficiency and the optimal area fraction for contacts for a given set of (J0, contact, ρ contact) values. The ITO/SiO 2 contacts are found to have a higher J0, contact, but a similar ρ contact compared to the best reported passivated contacts.« less
  • We present a case that passivated contacts based on a thin tunneling oxide layer, combined with a transport layer with properly selected work function and band offsets, can lead to high efficiency c-Si solar cells. Passivated contacts contribute to cell efficiency as well as design flexibility, process robustness, and a simplified process flow. Material choices for the transport layer are examined, including transparent n-type oxides and n+-doped poly-Si. SiO2/n+-poly-Si full-area, induced-junction back surface field contacts to n-FZ and n-Cz Si are incorporated into high efficiency cells with deep, passivated boron emitters.
  • Recent high-efficiency silicon solar cells employ high-quality oxides both for surface passivation and as a rudimentary antireflection coating. This gives over 3% reflection at the cell front surface, even though the surface is microstructured. A double layer antireflection coating applied to cells with reduced SiO[sub 2] thickness reduces the cell reflection. However, although reflection is minimized by reducing the oxide thickness to values below 100 [angstrom], a rapid falloff in both open-circuit voltage and short-circuit current is observed experimentally once this thickness is reduced below 200 [angstrom]. The best compromise is found when oxide thickness is 250 [angstrom] which allowsmore » improved short-circuit current density without appreciable loss in open-circuit voltage.« less
  • Carrier recombination at the metal contacts is a major obstacle in the development of high-performance crystalline silicon homojunction solar cells. To address this issue, we insert thin intrinsic hydrogenated amorphous silicon [a-Si:H(i)] passivating films between the dopant-diffused silicon surface and aluminum contacts. We find that with increasing a-Si:H(i) interlayer thickness (from 0 to 16 nm) the recombination loss at metal-contacted phosphorus (n{sup +}) and boron (p{sup +}) diffused surfaces decreases by factors of ∼25 and ∼10, respectively. Conversely, the contact resistivity increases in both cases before saturating to still acceptable values of ∼ 50 mΩ cm{sup 2} for n{sup +} andmore » ∼100 mΩ cm{sup 2} for p{sup +} surfaces. Carrier transport towards the contacts likely occurs by a combination of carrier tunneling and aluminum spiking through the a-Si:H(i) layer, as supported by scanning transmission electron microscopy–energy dispersive x-ray maps. We explain the superior contact selectivity obtained on n{sup +} surfaces by more favorable band offsets and capture cross section ratios of recombination centers at the c-Si/a-Si:H(i) interface.« less