Long-lived charge carrier generation in ordered films of a covalent perylenediimide-diketopyrrolopyrrole-perylenediimide molecule

Patrick E. Hartnett, Scott M. Dyar, Eric A. Margulies, Leah E. Shoer, Andrew W. Cook, Samuel W. Eaton, Tobin J. Marks, Michael R. Wasielewski

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Abstract

The photophysics of a covalently linked perylenediimide-diketopyrrolopyrrole-perylenediimide acceptor-donor-acceptor molecule (PDI-DPP-PDI, 1) were investigated and found to be markedly different in solution versus in unannealed and solvent annealed films. Photoexcitation of 1 in toluene results in quantitative charge separation in τ = 3.1 ± 0.2 ps, with charge recombination in τ = 340 ± 10 ps, while in unannealed/disordered films of 1, charge separation occurs in τ < 250 fs, while charge recombination displays a multiexponential decay in ∼6 ns. The absence of long-lived, charge separation in the disordered film suggests that few free charge carriers are generated. In contrast, upon CH2Cl2 vapor annealing films of 1, grazing-incidence X-ray scattering shows that the molecules form a more ordered structure. Photoexcitation of the ordered films results in initial formation of a spin-correlated radical ion pair (electron-hole pair) as indicated by magnetic field effects on the formation of free charge carriers which live for ∼4 μs. This result has significant implications for the design of organic solar cells based on covalent donor-acceptor systems and shows that long-lived, charge-separated states can be achieved by controlling intramolecular charge separation dynamics in well-ordered systems. This journal is

Original languageEnglish
Pages (from-to)402-411
Number of pages10
JournalChemical Science
Volume6
Issue number1
DOIs
Publication statusPublished - Jan 1 2015

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ASJC Scopus subject areas

  • Chemistry(all)

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