Chad Snyder - Measuring the Extent of Phase Separation in Poly-3-Hexylthiophene/Phenyl-C61-Butyric Acid Methyl Ester Photovoltaic Blends with 1H Spin Diffusion NMR Spectroscopy

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  R.C. Nieuwendaal, C.R. Snyder, R.J. Kline, E.K. Lin, D.L.   VanderHart, and D.M. DeLongchamp, Chemistry of Materials  22 (9), 2930-2936 (2010).


  We demonstrate that 1H spin diffusion NMR is a valuable method to   estimate the domain size distribution in bulk heterojunction   (BHJ) active layers composed of poly-3-hexylthiophene (P3HT) and   phenyl-C61-butyric acid methyl ester (PCBM). Bulk samples were   annealed at several temperatures, and a distribution of domain   sizes was observed that ranged over hundreds of nanometers.   Unannealed samples exhibited a large amount of PCBM in small   domains (1 to 5 nm) and smaller amounts in moderate (tens of nm)   and large (>100 nm) domains. Annealing the samples at 100 °C   had no effect on the morphology as evidenced from 1H spin   diffusion NMR, grazing-incidence diffraction, and calorimetry,   but phase separation was observed after annealing at 150 °C. Even   with this higher temperature processing, the 1H NMR showed   conclusively that phase separation remained incomplete; this   finding was confirmed with photoluminescence quenching   measurements.

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