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Keywords:

  • polymer solar cells;
  • bulk heterojunction;
  • electroabsorption;
  • effective bandgap;
  • energy level alignment
Thumbnail image of graphical abstract

Using charge modulated electroabsorption spectroscopy (CMEAS), for the first time, the energy level alignment of a polymer:fullerene bulk heterojunction photovoltaic cell is directly measured. The charge-transfer excitons generated by the sub-bandgap optical pumping are coupled with the modulating electric field and introduce subtle changes in optical absorption in the sub-bandgap region. This minimum required energy for sub-bandgap charge genreation is defined as the effective bandgap.