SnO2-Catalyzed Oxidation in High-Efficiency CdTe Solar Cells

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23 Scopus Citations

Abstract

Interfaces at the front of superstrate CdTe-based solar cells are critical to carrier transport, recombination, and device performance, yet determination of the chemical structure of these nanoscale regions has remained elusive. This is partly due to changes that occur at the front interfaces during high temperature growth and substantive changes occurring during postdeposition processing. In addition, these buried interfaces are extremely difficult to access in a way that preserves chemical information. In this work, we use a recently developed thermomechanical cleaving technique paired with X-ray photoelectron spectroscopy to probe oxidation states at the SnO 2 interface of CdTe solar cells. We show that the tin oxide front electrode promotes the formation of nanometer-scale oxides of tellurium and sulfur. Most oxidation occurs during CdCl 2 /O 2 activation. Surprisingly, we show that relatively low-temperature anneals (180-260 °C) used to diffuse and activate copper acceptors in a doping/back contact process also cause significant changes in oxidation at the front of the cell, providing a heretofore missing aspect of how back contact processes can modify device transport, recombination, and performance. Device performance is shown to correlate with the extent of tellurium and sulfur oxidation within this nanometer-scale region. Mechanisms responsible for these beneficial effects are proposed.

Original languageAmerican English
Pages (from-to)13003-13010
Number of pages8
JournalACS Applied Materials and Interfaces
Volume11
Issue number13
DOIs
StatePublished - 3 Apr 2019

Bibliographical note

Publisher Copyright:
© 2019 American Chemical Society.

NREL Publication Number

  • NREL/JA-5K00-73453

Keywords

  • cadmium telluride
  • interfaces
  • passivation
  • photovoltaics
  • solar cells
  • tin oxide
  • X-ray photoelectron spectroscopy

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