Metastability and Degradation of CdTe Solar Cells Investigated by nm-Scale Electrical Potential Imaging

Chun-Sheng Jiang, David Albin, M. Nardone, K. Howard, A. Danielson, A. Munshi, Tushar Shimpi, W. Sampath, Chuanxiao Xiao, Helio Moutinho, Mowafak Al-Jassim, Glenn Teeter

Research output: NRELPresentation


We report on investigations of reversible metastability and irreversible degradation of MZO/CdSeTe/CdTe devices from the perspective of electric field across the device using Kelvin probe force microscopy (KPFM). The device showed reversible transitions between the light-soak state (LSS) with the best device efficiency and the dark-soak state (DSS) with an inferior efficiency. However, it showed an irreversible degradation state (DgS) driven by long-hour light soaking at an elevated temperature. The nm-scale KPFM electric field imaging on cross-sections of the devices revealed different anomalous electric field profiles. The electric field at the LSS exhibits a main peak inside the CdSeTe layer but not at the MZO/CdSeTe heterointerface, demonstrating that working junction of the device is a buried homojunction (BHJ). At the DSS, a second electric field peak was observed at the MZO/CdSeTe interface with a similar strength to the main BHJ, which probably caused the decrease in fill factor at the DSS. At the DgS, the electric field peak at the MZO/CdSeTe interface increased significantly and a third electric field was measured at the back contact of the device. Device modeling using COMSOL and in alignment with both the electric field and device current-voltage curves suggest that a slightly low n-doped CdSeTe in the region near the MZO/CdSeTe interface caused the BHJ, and that either a loss of MZO doping or increase of the conduction band offset spike due to long-term stress caused the fill factor-dominated degradation and the increased electric field near the MZO/CdSeTe interface at the DgS. The former, MZO doping decrease, is more plausible by referring the related literature.
Original languageAmerican English
Number of pages12
StatePublished - 2022

Publication series

NamePresented at the 49th IEEE Photovoltaic Specialists Conference (PVSC 49), 5-10 June 2022, Philadelphia, Pennsylvania

NREL Publication Number

  • NREL/PR-5K00-83144


  • BHJ
  • buried homojunction
  • irreversible degradation
  • Kelvin probe force microscopy
  • KPFM
  • MZO/CdSeTe/CdTe
  • photovoltaic
  • PV
  • reversible metastability


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