Energy Level Modulation of HOMO, LUMO, and Band‐Gap in Conjugated Polymers for Organic Photovoltaic Applications

Bong‐Gi Kim; Xiao Ma; Chelsea Chen; Yutaka Ie; Elizabeth W. Coir; Hossein Hashemi; Yoshio Aso; Peter F. Green; John Kieffer; Jinsang Kim

doi:10.1002/adfm.201201385

journal article Sep 14, 2012

Energy Level Modulation of HOMO, LUMO, and Band‐Gap in Conjugated Polymers for Organic Photovoltaic Applications

Bong‐Gi Kim Xiao Ma

Chelsea Chen Yutaka Ie

Elizabeth W. Coir Hossein Hashemi

Yoshio Aso Peter F. Green

John Kieffer Jinsang Kim

Advanced Functional Materials Vol. 23 No. 4 pp. 439-445 · Wiley

View at Publisher Save 10.1002/adfm.201201385

Abstract

AbstractTo devise a reliable strategy for achieving specific HOMO and LUMO energy level modulation via alternating donor‐acceptor monomer units, we investigate a series of conjugated polymers (CPs) in which the electron withdrawing power of the acceptor group is varied, while maintaining the same donor group and the same conjugated chain conformation. Through experiment and DFT calculations, good correlation is identified between the withdrawing strength of the acceptor group, the HOMO and LUMO levels, and the degree of orbital localization, which allows reliable design principles for CPs. Increasing the acceptor strength results in an enhanced charge transfer upon combination with a donor monomer and a more pronounced decrease of the LUMO level. Moreover, while HOMO states remain delocalized along the polymer chain, LUMO states are strongly localized at specific bonds within the acceptor group. The degree of LUMO localization increases with increasing polymer length, which results in a further drop of the LUMO level and converges to its final value when the number of repeat units reaches the characteristic conjugation length. Based on these insights we designed PBT8PT, which exhibits 6.78% power conversion efficiency after device optimization via the additive assisted annealing, demonstrating the effectiveness of our predictive design approach.

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References

Details

Published: Sep 14, 2012
Vol/Issue: 23(4)
Pages: 439-445
License: View

Authors

The Institute of Scientific and Industrial Research, Osaka University, 8-1, Mihogaoka, Ibaraki, Osaka 567-0047, Japan, CREST, Japan Science and Technology Agency (JST), Japan, Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan, and Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan

The Institute of Scientific and Industrial Research, Osaka University, 8-1, Mihogaoka, Ibaraki, Osaka 567-0047, Japan, CREST, Japan Science and Technology Agency (JST), Japan, Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan, and Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan

P

Peter F. Green

Department of Materials Science and Engineering, Biointerfaces Institute, University of Michigan, Ann Arbor, MI 48109, USA; National Renewable Energy Laboratory, 15013 Denver W Pkwy, Golden, CO 80401, USA

Macromolecular Science and Engineering; Department of Materials Science and Engineering; Chemical Engineering, University of Michigan, Ann Arbor, Michigan 48109

Cite This Article

Bong‐Gi Kim, Xiao Ma, Chelsea Chen, et al. (2012). Energy Level Modulation of HOMO, LUMO, and Band‐Gap in Conjugated Polymers for Organic Photovoltaic Applications. Advanced Functional Materials, 23(4), 439-445. https://doi.org/10.1002/adfm.201201385

Energy Level Modulation of HOMO, LUMO, and Band‐Gap in Conjugated Polymers for Organic Photovoltaic Applications

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