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- Title
Understanding the Reduced Efficiencies of Organic Solar Cells Employing Fullerene Multiadducts as Acceptors.
- Authors
Faist, Mark A.; Shoaee, Safa; Tuladhar, Sachetan; Dibb, George F. A.; Foster, Samuel; Gong, Wei; Kirchartz, Thomas; Bradley, Donal D. C.; Durrant, James R.; Nelson, Jenny
- Abstract
The use of fullerenes with two or more adducts as acceptors has been recently shown to enhance the performance of bulk-heterojunction solar cells using poly(3-hexylthiophene) (P3HT) as the donor. The enhancement is caused by a substantial increase in the open-circuit voltage due to a rise in the fullerene lowest unoccupied molecular orbital (LUMO) level when going from monoadducts to multiadducts. While the increase in the open-circuit voltage is obtained with many different polymers, most polymers other than P3HT show a substantially reduced photocurrent when blended with fullerene multiadducts like bis-PCBM ( bis adduct of Phenyl-C61-butyric acid methyl ester) or the indene C60 bis-adduct ICBA. Here we investigate the reasons for this decrease in photocurrent. We find that it can be attributed partly to a loss in charge generation efficiency that may be related to the LUMO-LUMO and HOMO-HOMO (highest occupied molecular orbital) offsets at the donor-acceptor heterojunction, and partly to reduced charge carrier collection efficiencies. We show that the P3HT exhibits efficient collection due to high hole and electron mobilities with mono- and multiadduct fullerenes. In contrast the less crystalline polymer Poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl (PCDTBT) shows inefficient charge carrier collection, assigned to low hole mobility in the polymer and low electron mobility when blended with multiadduct fullerenes.
- Publication
Advanced Energy Materials, 2013, Vol 3, Issue 6, p744
- ISSN
1614-6832
- Publication type
Article
- DOI
10.1002/aenm.201200673