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

Conference · Thu May 01 00:00:00 EDT 2008

DOI:https://doi.org/10.1109/PVSC.2008.4922905· OSTI ID:929611

Wang, D; Reese, M; Kopidakis, N; Gregg, B A

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 in molecular 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 resistance limitations usually encountered in cleaner organic semiconductors and can create built-in electric fields at junctions.

• Research Organization: National Renewable Energy Lab. (NREL), Golden, CO (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC36-99-GO10337
• OSTI ID: 929611
• Report Number(s): NREL/CP-270-42565; TRN: US200813%%261
• Resource Relation: Conference: Presented at the 33rd IEEE Photovoltaic Specialists Conference, 11-16 May 2008, San Diego, California
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
36 MATERIALS SCIENCE
42 ENGINEERING
CHEMICAL PROPERTIES
DEFECTS
EFFICIENCY
ELECTRIC FIELDS
HETEROJUNCTIONS
HYDROGEN
ORGANIC SEMICONDUCTORS
PHOTOVOLTAIC CELLS
POLYMERS
SILICON
SODIUM
SOLAR CELLS
STABILITY
SULFATES
PV
OPV
EXCITONIC SEMICONDUCTORS
P-TYPE DOPANTS
ELECTROPHILES
DEFECT DENSITIES
Chemical and Biosciences
Solar Energy - Photovoltaics