TY - JOUR
T1 - Characterization of the polymer energy landscape in polymer:fullerene bulk heterojunctions with pure and mixed phases
AU - Sweetnam, Sean
AU - Graham, Kenneth R.
AU - Ngongang Ndjawa, Guy O.
AU - Heumüller, Thomas
AU - Bartelt, Jonathan A.
AU - Burke, Timothy M.
AU - Li, Wentao
AU - You, Wei
AU - Amassian, Aram
AU - McGehee, Michael D.
N1 - Publisher Copyright:
© 2014 American Chemical Society.
Copyright:
Copyright 2014 Elsevier B.V., All rights reserved.
PY - 2014/10/8
Y1 - 2014/10/8
N2 - Theoretical and experimental studies suggest that energetic offsets between the charge transport energy levels in different morphological phases of polymer:fullerene bulk heterojunctions may improve charge separation and reduce recombination in polymer solar cells (PSCs). In this work, we use cyclic voltammetry, UV-vis absorption, and ultraviolet photoelectron spectroscopy to characterize hole energy levels in the polymer phases of polymer:fullerene bulk heterojunctions. We observe an energetic offset of up to 150 meV between amorphous and crystalline polymer due to bandgap widening associated primarily with changes in polymer conjugation length. We also observe an energetic offset of up to 350 meV associated with polymer:fullerene intermolecular interactions. The first effect has been widely observed, but the second effect is not always considered despite being larger in magnitude for some systems. These energy level shifts may play a major role in PSC performance and must be thoroughly characterized for a complete understanding of PSC function.
AB - Theoretical and experimental studies suggest that energetic offsets between the charge transport energy levels in different morphological phases of polymer:fullerene bulk heterojunctions may improve charge separation and reduce recombination in polymer solar cells (PSCs). In this work, we use cyclic voltammetry, UV-vis absorption, and ultraviolet photoelectron spectroscopy to characterize hole energy levels in the polymer phases of polymer:fullerene bulk heterojunctions. We observe an energetic offset of up to 150 meV between amorphous and crystalline polymer due to bandgap widening associated primarily with changes in polymer conjugation length. We also observe an energetic offset of up to 350 meV associated with polymer:fullerene intermolecular interactions. The first effect has been widely observed, but the second effect is not always considered despite being larger in magnitude for some systems. These energy level shifts may play a major role in PSC performance and must be thoroughly characterized for a complete understanding of PSC function.
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U2 - 10.1021/ja505463r
DO - 10.1021/ja505463r
M3 - Article
AN - SCOPUS:84907919634
VL - 136
SP - 14078
EP - 14088
IS - 40
ER -