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Characterization of Interfacial Structure in Polymer-Fullerene Bulk Heterojunctions via 13C {2H} Rotational Echo Double Resonance NMR

Published

Author(s)

Ryan C. Nieuwendaal, Dean M. DeLongchamp, Martin Heeney, Jan Hummelen, Chad R. Snyder, Ronald L. Jones, Sebastian Engmann, Lee J. Richter, Zhuping Fei, Alex Sieval

Abstract

We introduce a new application of solid state NMR measurements towards characterizing the donor-acceptor interfaces within bulk heterojunction (BHJ) films. Rotational echo double resonance (REDOR) is used to measure dipolar couplings between 13C nuclei on the acceptor phenyl-C61-butyric acid methyl ester (PCBM) fullerene cage, which is ≈18% isotopically enriched with 13C, and beta hydrogens on the donor poly(3-hexyl thiophene) (P3HT) main chain, which are >95% isotopically enriched with 2H. The 13C − 2H dipolar couplings are used for constraining possible models of molecular packing in the amorphous mixed phase of a P3HT=PCBM BHJ. The films studied are highly mixed (>80%) and have a maximum length scale of composition nonuniformity of ≈6 nm in the mixed phase, as demonstrated by 1H spin diffusion NMR and supported by TEM. The REDOR results show that despite the lack of phase separation at lengthscales greater than ≈6 nm, neat P3HT and PCBM clusters exist on ≈3 nm size scales, and, for the average PCBM molecule, the number of nearest neighbors P3HTs is two.
Citation
Physical Review Letters
Volume
121

Keywords

Solid-state NMR, Polymer, Organic electronics, Composite, Bulk Heterojunction, Interface, Thin film

Citation

Nieuwendaal, R. , DeLongchamp, D. , Heeney, M. , Hummelen, J. , Snyder, C. , Jones, R. , Engmann, S. , Richter, L. , Fei, Z. and Sieval, A. (2018), Characterization of Interfacial Structure in Polymer-Fullerene Bulk Heterojunctions via 13C {2H} Rotational Echo Double Resonance NMR, Physical Review Letters, [online], https://doi.org/10.1103/PhysRevLett.121.026101 (Accessed April 19, 2024)
Created July 13, 2018, Updated November 10, 2018