Vibrational energy nediates charge separation in organic photovoltaic materials

Ryan D. Pensack, Kyle M. Banyas, John B. Asbury

Research output: Contribution to journalArticle

11 Scopus citations

Abstract

Charge separation and charge trapping following photoinduced electron transfer from the conjugated polymer, poly (2-methoxy-5-ethylhexyloxy-1,4- phenylenecyanovinylene (CN-MEH-PPV), to the electron accepting functionalized fullerene, 6,6-phenyl $\hbox{C}-{61}$ -butyric acid methyl ester (PCBM), is directly measured using ultrafast vibrational spectroscopy. Our group previously demonstrated that the vibrational frequency of the carbonyl (CO) stretch of PCBM is sensitive to the location of the molecules relative to the interfaces formed between PCBM clusters and CN-MEH-PPV. The correlation between the carbonyl frequency and the proximity of PCBM molecules to the interfaces enables the time evolution of the frequency of the bleach peak to be interpreted in terms of dissociation of charge transfer states into charge separated states. Temperature-dependent measurements of the rate of this charge separation process indicate that excess vibrational energy in hot charge transfer states resulting from the electron transfer reaction enables electrons to escape their Coulombic potentials at the interfaces on ultrafast timescales. Furthermore, temperature-dependent measurements on longer timescales indicate that after the initial charge separation reaction, electrons enter shallow trap states that, on the basis of the radial variation of vibrational frequencies, lie in the interior of PCBM clusters. The vibrational spectra suggest that these interior regions have higher intermolecular order in comparison to the interfaces.

Original languageEnglish (US)
Article number5423990
Pages (from-to)1776-1783
Number of pages8
JournalIEEE Journal on Selected Topics in Quantum Electronics
Volume16
Issue number6
DOIs
StatePublished - Nov 1 2010

All Science Journal Classification (ASJC) codes

  • Atomic and Molecular Physics, and Optics
  • Electrical and Electronic Engineering

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