Hot Wire Chemical Vapor Deposition of Epitaxial Film Crystal Silicon for Photovoltaics

Howard M. Branz, Charles W. Teplin, Manuel J. Romero, Ina T. Martin, Qi Wang, Kirstin Alberi, David L. Young, Paul Stradins

Research output: Contribution to journalArticlepeer-review

39 Scopus Citations

Abstract

We have demonstrated that hot-wire chemical vapor deposition (HWCVD) is an excellent technique to produce high-quality epitaxial silicon at high rates, at substrate temperatures from 620 to 800 °C. Fast, scalable, inexpensive epitaxy of high-quality crystalline Si (c-Si) in this temperature range is a key element in creating cost-competitive film Si PV devices on crystalline seed layers on inexpensive substrates such as display glass and metal foil. We have improved both the quality and rate of our HWCVD Si epitaxy in this display-glass-compatible T range. We understand factors critical to high-quality epitaxial growth and obtain dislocation densities down to 6 × 10 4 cm-2 by techniques that reduce the surface oxygen contamination at the moment growth is initiated. We have also developed and validated a model of the HWCVD silicon growth rate, based on fundamentals of reaction chemistry and ideal gas physics. This model enables us to predict growth rates and calculate the sticking coefficient of the Si radicals contributing to film formation between 300 and 800 °C. We obtain efficiencies up to 6.7% with a 2.5-micron absorber layer grown on heavily-doped 'dead' Si wafers although these cells still lack hydrogenation and light trapping. Open-circuit voltages up to 0.57 V are obtained on 2-μm cells. Efficient film crystal silicon photovoltaics will require dislocation spacing more than 6 times the cell thickness, or else effective H passivation of the dislocations.

Original languageAmerican English
Pages (from-to)4545-4550
Number of pages6
JournalThin Solid Films
Volume519
Issue number14
DOIs
StatePublished - 2 May 2011

NREL Publication Number

  • NREL/JA-5200-49297

Keywords

  • Dislocations
  • Epitaxy
  • Film crystal silicon
  • Hot-wire deposition
  • Modeling
  • Photovoltaics
  • Silicon
  • Solar cells

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