Bilayer heterojunction polymer solar cells using unsubstituted polythiophene via oxidative chemical vapor deposition

Publication Type:

Journal Article

Source:

Sol. Energy Mater. Sol. Cells, Elsevier, Volume 99, p.190-196 (2012)

ISBN:

0927-0248

Keywords:

2012, 2013 and earlier, Bilayer heterojunction, Polymer solar cells, Unsubstituted polythiophene, vacuum deposition, vapor deposition

Abstract:

We demonstrate the use of a vacuum-based, vapor phase technique for the deposition of a donor polymer for use in polymer solar cells.
Unsubstituted polythiophene (PT), which is insoluble and infusible and
thus typically difficult to process, is easily prepared by oxidative
chemical vapor deposition (oCVD). The oCVD process results in a conductive
PT film that is heavily doped with FeCl3, which is used as the oxidizing
agent. A post-deposition methanol rinse sufficiently dedopes the film and
removes spent oxidant, leaving semiconducting PT with an optical bandgap
close to 2 eV. Drastic changes in the film color, absorption spectra, and
film composition confirm the dedoping process. The resulting
semiconducting PT is then applied as an electron donor in bilayer
heterojunction solar cells with a thermally evaporated C60 electron
acceptor layer, resulting in power conversion efficiencies up to 0.8%. The
absorption edge of the PT at ∼620 nm closely matches the edge present in
the external quantum efficiency spectra, indicating that the oCVD PT
contributes to the photocurrent of the devices. This demonstrates that the
oCVD technique can be used in the processing and design of polymer active
layers for polymer solar cells and hybrid small molecular organic solar
cells without solubility, temperature, or substrate considerations.