Quantifying Optical Loss of High-Voltage Degradation Modes in PV Modules Using Spectral Analysis

David Miller, Katherine Hurst, Archana Sinha, Joanna Bomber, Jiadong Qian, Stephanie Moffitt, Sona Ulicna, Laura Schelhas, Peter Hacke

Research output: NRELPresentation


The direct current bias for photovoltaic (PV) modules interconnected in series-strings may include both high voltage negative ("HV-") and positive ("HV+") polarity with respect to the electrical ground. Multiple degradation modes, resulting in quantifiable optical loss, were found to occur during HV-/HV+ sequential stress, including: corrosion of the external glass surface, encapsulant delamination (at its interfaces with the glass and the PV cell), internal haze formation (resulting from a chemical interaction between the glass and the encapsulant), corrosion and migration of the gridlines, and corrosion of the silicon nitride (SixNy) antireflective coating on the cell. The effects of these separate modes were examined using monolithic (e.g., glass or PV cell) and laminated-coupon (glass/encapsulant/glass or glass/encapsulant/cell/encapsulant/backsheet) specimens. Characterizations during and after unbiased accelerated testing at 85 degrees C/85% relative humidity included: spectrophotometry, optical microscopy, electron microscopy, and ellipsometry. For some module components (i.e., the glass and the SixNy coating), the optical performance was determined through iterative analysis of empirical measurements. Concentrating on just their spectral effect, a novel model was then developed to estimate the transfer of light to the PV cell and the return of light from the PV module with simultaneous degradation mechanisms, which was compared to a mini-module previously subjected to HV-/HV+ stress. The model suggests one-third of the current loss observed for the mini-module can be attributed to the optical degradation of the packaging materials. The dominant degradation modes include encapsulant delamination and corrosion of the SixNy coating. Recommendations are given so that the optical model may be improved relative to accelerated testing and validated relative to field aging.
Original languageAmerican English
Number of pages71
StatePublished - 2022

NREL Publication Number

  • NREL/PR-5K00-82324


  • antireflective coating
  • corrosion
  • damp heat
  • encapsulant
  • HV-/HV+ stress
  • IEC 62804
  • optical absorptance
  • optical reflectance
  • spectral performance


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