Polycrystalline Silicon Passivated Tunneling Contacts for High Efficiency Silicon Solar Cells

William Nemeth, Matthew Page, Vincenzo LaSalvia, Steven Johnston, Robert Reedy Jr., David Young, Pauls Stradins

Research output: Contribution to journalArticlepeer-review

130 Scopus Citations

Abstract

We apply n-and p-type polycrystalline silicon (poly-Si) films on tunneling SiO x to form passivated contacts to n-type Si wafers. The resulting induced emitter and n+/n back surface field junctions of high carrier selectivity and low contact resistivity enable high efficiency Si solar cells. This work addresses the materials science of their performance governed by the properties of the individual layers (poly-Si, tunneling oxide) and more importantly, by the process history of the cell as a whole. Tunneling SiO x layers (<2 nm) are grown thermally or chemically, followed by a plasma enhanced chemical vapor deposition growth of p+ or n+ doped a-Si:H. The latter is thermally crystallized into poly-Si, resulting in grain nucleation and growth as well as dopant diffusion within the poly-Si and penetration through the tunneling oxide into the Si base wafer. The cell process is designed to improve the passivation of both oxide interfaces and tunneling transport through the oxide. A novel passivation technique involves coating of the passivated contact and whole cell with atomic layer deposited Al2O3 and activating them at 400 °C. The resulting excellent passivation persists after subsequent chemical removal of the Al2O3. The preceding cell process steps must be carefully tailored to avoid structural and morphological defects, as well as to maintain or improve passivation, and carrier selective transport. Furthermore, passivated contact metallization presents significant challenges, often resulting in passivation loss. Suggested remedies include improved Si cell wafer surface morphology (without micropyramids) and postdeposited a-Si:H capping layers over the poly-Si.

Original languageAmerican English
Pages (from-to)671-681
Number of pages11
JournalJournal of Materials Research
Volume31
Issue number6
DOIs
StatePublished - 28 Mar 2016

Bibliographical note

Publisher Copyright:
© 2016 Materials Research Society.

NREL Publication Number

  • NREL/JA-5J00-64830

Keywords

  • passivation
  • photovoltaic
  • thin film

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