Interfacial Characterization of Positive Bias Voltage Degradation in PV Modules

Katherine Hurst, Archana Sinha, Stephanie Moffitt, Jiadong Qian, David Miller, Peter Hacke, Laura Schelhas

Research output: Contribution to conferencePaperpeer-review

1 Scopus Citations

Abstract

Degradation from high system voltage is a prevailing failure mode in fielded photovoltaic modules, and the degradation mechanism is inherently dependent on the bias polarity. Here we report the effects of positive bias. Modules under positive bias demonstrated a significant photocurrent loss caused by two routes. First, delamination and discoloration of the silicon nitride layer, leading to optical loss determined by reflectance measurements. Second, chemical discoloration of the cell gridlines and encapsulant (EVA), which is linked to an electrochemical reaction at the silver electrodes. Chemical compositional analysis using X-ray photoemission spectroscopy demonstrated that the discoloration is attributed to Ag2S and/or Ag2O. Evidence of Ag ion migration from the cell grid into the encapsulant is observed after shallow depth profiling on the EVA surface. However, Ag was not detected at the EVA/glass interface, inferring limited Ag ion transport through the EVA. The source of sulfur is believed to be ambient air, which diffused into the module through the breathable backsheet.

Original languageAmerican English
Pages1985-1986
Number of pages2
DOIs
StatePublished - 14 Jun 2020
Event47th IEEE Photovoltaic Specialists Conference, PVSC 2020 - Calgary, Canada
Duration: 15 Jun 202021 Aug 2020

Conference

Conference47th IEEE Photovoltaic Specialists Conference, PVSC 2020
Country/TerritoryCanada
CityCalgary
Period15/06/2021/08/20

Bibliographical note

Publisher Copyright:
© 2020 IEEE.

NREL Publication Number

  • NREL/CP-5900-79506

Keywords

  • characterization
  • discoloration
  • encapsulant
  • gridline
  • ion migration
  • system voltage bias
  • XPS

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