Correlation of UV Fluorescence Images with Performance Loss of Field-Retrieved Photovoltaic Modules

Fang Li, Viswa Sai Pavan Buddha, Eric J. Schneller, Nafis Iqbal, Dylan J. Colvin, Kristopher O. Davis, Govindasamy Tamizhmani

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


The ultraviolet fluorescence (UVF) imaging method has been widely used as a rapid and economic field inspection tool for investigating encapsulant discoloration of field-aged photovoltaic (PV) modules. In field-aged PV modules, encapsulant discoloration can result in a pronounced decrease in the short-circuit current. The spatial distribution of environmental stressors and therefore discoloration pattern over each cell of a module depends on the climate. In this article, we investigated the discoloration patterns (and their correlation with electrical parameters of modules and the extracted-cells from the modules) of ten modules produced at the same manufacturing facility and retrieved respectively from two distinct climates of Arizona (hot-dry; seven modules; 18 years of exposure) and Florida (hot-humid; three modules; ten years of exposure). In the Arizona modules, three distinct spatial patterns were observed in the UVF images: cell center region (intense browning); cell edge region (no browning); region between cell center; and cell edge region (light browning). However, in the Florida modules, only two distinct spatial distributions were observed: nonedge cell region (medium browning) and cell edge region (no browning). Furthermore, we employed a high-contrast UVF imaging technique to correlate the interdependence between the encapsulant discoloration pattern and the metallization/contact degradation pattern. For this correlative study, various experimental characterizations were carried out on both field-aged (Arizona and Florida) and unexposed modules and the cells extracted from the modules of the same model and they include: processed UVF and EL images, and I-V, TLM, optical microscopy, and XPS measurements.

Original languageEnglish (US)
Article number9445396
Pages (from-to)926-935
Number of pages10
JournalIEEE Journal of Photovoltaics
Issue number4
StatePublished - Jul 2021


  • Contact resistance
  • corrosion
  • encapsulant browning
  • performance degradation
  • short-circuit current
  • ultraviolet fluorescence imaging

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Electrical and Electronic Engineering


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