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 language | American English |
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Pages | 1985-1986 |
Number of pages | 2 |
DOIs | |
State | Published - 14 Jun 2020 |
Event | 47th IEEE Photovoltaic Specialists Conference, PVSC 2020 - Calgary, Canada Duration: 15 Jun 2020 → 21 Aug 2020 |
Conference
Conference | 47th IEEE Photovoltaic Specialists Conference, PVSC 2020 |
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Country/Territory | Canada |
City | Calgary |
Period | 15/06/20 → 21/08/20 |
Bibliographical note
Publisher Copyright:© 2020 IEEE.
NREL Publication Number
- NREL/CP-5900-79506
Keywords
- characterization
- discoloration
- encapsulant
- gridline
- ion migration
- system voltage bias
- XPS