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

• DOI: 10.1002/adfm.201201385
• Publication Date: 2012-09-15T03:36:07Z
• Authors: Bong‐Gi Kim; Xiao Ma; Chelsea Chen; Yutaka Ie; Elizabeth W. Coir; Hossein Hashemi; Yoshio Aso; Peter F. Green; John Kieffer; Jinsang Kim
• Keywords: HOMO/LUMO; Acceptor

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