Sodium Accumulation at Potential-Induced Degradation Shunted Areas in Polycrystalline Silicon Modules

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We investigated potential-induced degradation (PID) in silicon mini-modules that were subjected to accelerated stressing to induce PID conditions. Shunted areas on the cells were identified with photoluminescence and dark lock-in thermography (DLIT) imaging. The identical shunted areas were then analyzed via time-of-flight secondary-ion mass spectrometry (TOFSIMS) imaging, 3-D tomography, and high-resolution transmission electron microscopy. The TOF-SIMS imaging indicates a high concentration of sodium in the shunted areas, and 3-D tomography reveals that the sodium extends more than 2 μm from the surface below shunted regions. Transmission electron microscopy investigation reveals that a stacking fault is present at an area identified as shunted by DLIT imaging. After the removal of surface sodium, tomography reveals persistent sodium present around the junction depth of 300 nm and a drastic difference in sodium content at the junction when comparing shunted and nonshunted regions.

Original languageAmerican English
Pages (from-to)1440-1445
Number of pages6
JournalIEEE Journal of Photovoltaics
Issue number6
StatePublished - Nov 2016

Bibliographical note

Publisher Copyright:
© 2011-2012 IEEE.

NREL Publication Number

  • NREL/JA-5K00-65733


  • 3-D tomography
  • Accelerated stress
  • dark lock-in thermography (DLIT)
  • polycrystalline silicon modules
  • potential-induced degradation (PID)
  • shunting
  • time-of-flight secondary-ion mass spectrometry (TOF-SIMS)


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