Delocalization and dielectric screening of charge transfer states in organic photovoltaic cells

B. Bernardo, D. Cheyns, B. Verreet, R. D. Schaller, B. P. Rand, N. C. Giebink

Research output: Contribution to journalArticle

157 Citations (Scopus)

Abstract

Charge transfer (CT) states at a donor-acceptor heterojunction have a key role in the charge photogeneration process of organic solar cells, however, the mechanism by which these states dissociate efficiently into free carriers remains unclear. Here we explore the nature of these states in small molecule-fullerene bulk heterojunction photovoltaics with varying fullerene fraction and find that the CT energy scales with dielectric constant at high fullerene loading but that there is a threshold C 60 crystallite size of ∼4 nm below which the spatial extent of these states is reduced. Electroabsorption measurements indicate an increase in CT polarizability when C 60 crystallite size exceeds this threshold, and that this change is correlated with increased charge separation yield supported by CT photoluminescence transients. These results support a model of charge separation via delocalized CT states independent of excess heterojunction offset driving energy and indicate that local fullerene crystallinity is critical to the charge separation process.

Original languageEnglish
Article number3245
JournalNature Communications
Volume5
DOIs
Publication statusPublished - Feb 3 2014

Fingerprint

Fullerenes
Photovoltaic cells
photovoltaic cells
Charge transfer
Screening
screening
charge transfer
fullerenes
polarization (charge separation)
Heterojunctions
heterojunctions
Crystallite size
Energy Transfer
thresholds
crystallinity
Photoluminescence
Permittivity
solar cells
permittivity
photoluminescence

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)
  • Chemistry(all)
  • Physics and Astronomy(all)

Cite this

Delocalization and dielectric screening of charge transfer states in organic photovoltaic cells. / Bernardo, B.; Cheyns, D.; Verreet, B.; Schaller, R. D.; Rand, B. P.; Giebink, N. C.

In: Nature Communications, Vol. 5, 3245, 03.02.2014.

Research output: Contribution to journalArticle

Bernardo, B. ; Cheyns, D. ; Verreet, B. ; Schaller, R. D. ; Rand, B. P. ; Giebink, N. C. / Delocalization and dielectric screening of charge transfer states in organic photovoltaic cells. In: Nature Communications. 2014 ; Vol. 5.
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