Do the Defects Make It Work? Defect Engineering in Pi-Conjugated Polymers and Their Solar Cells: Preprint

Brian Gregg

Research output: Contribution to conferencePaper


The charged defect density in common pi-conjugated polymers such as poly(3-hexylthiophene), P3HT, is around 1018 cm-3. Despite, or perhaps because of, this huge defect density, bulk heterojunction solar cells made from these polymers and a C60 derivative such as PCBM exhibit some of the highest efficiencies (~5%) yet obtained in solid state organic photovoltaic cells. We discuss defects inmolecular organic semiconductors and in pi-conjugated polymers. These defects can be grouped in two categories, covalent and noncovalent. Somewhat analogous to treating amorphous silicon with hydrogen, we introduce chemical methods to modify the density and charge of the covalent defects in P3HT by treating it with electrophiles such as dimethyl sulfate and nucleophiles such as sodium methoxide.The effects of these treatments on the electrical and photovoltaic properties and stability of organic PV cells is discussed in terms of the change in the number and chemical properties of the defects. Finally, we address the question of whether the efficiency of OPV cells requires the presence of these defects which function as adventitious p-type dopants. Their presence relieves the resistancelimitations usually encountered in cleaner organic semiconductors and can create built-in electric fields at junctions.
Original languageAmerican English
Number of pages6
StatePublished - 2008
Event33rd IEEE Photovoltaic Specialists Conference - San Diego, California
Duration: 11 May 200816 May 2008


Conference33rd IEEE Photovoltaic Specialists Conference
CitySan Diego, California

NREL Publication Number

  • NREL/CP-270-42565


  • defect densities
  • electrophiles
  • excitonic semiconductors
  • OPV
  • p-Type dopants
  • PV


Dive into the research topics of 'Do the Defects Make It Work? Defect Engineering in Pi-Conjugated Polymers and Their Solar Cells: Preprint'. Together they form a unique fingerprint.

Cite this