How to measure absolute P3HT crystallinity via13C CPMAS NMR.
We outline the details of acquiring quantitative13C cross-polarization magic angle spinning (CPMAS) nuclear magnetic resonance on the most ubiquitous polymer for organic electronic applications, poly(3-hexylthiophene) (P3HT), despite other groups' claims that CPMAS of P3HT is strictly nonquantitative. We lay out the optimal experimental conditions for measuring crystallinity in P3HT, which is a parameter that has proven to be critical in the electrical performance of P3HT-containing organic photovoltaics but remains difficult to measure by scattering/diffraction and optical methods despite considerable efforts. Herein, we overview the spectral acquisition conditions of the two P3HT films with different crystallinities (0.47 and 0.55) and point out that because of the chemical similarity of P3HT to other alkyl side chain, highly conjugated main chain polymers, our protocol could straightforwardly be extended to other organic electronic materials. Variable temperature1H NMR results are shown as well, which (i) yield insight into the molecular dynamics of P3HT, (ii) add context for spectral editing techniques as applied to quantifying crystallinity, and (iii) show why T1ρH, the1H spin-lattice relaxation time in the rotating frame, is a more optimal relaxation filter for distinguishing between crystalline and noncrystalline phases of highly conjugated alkyl side-chain polymers than other relaxation times such as the1H spin-spin relaxation time, T2H, and the spin-lattice relaxation time in the toggling frame, T1xzH. A 7 ms T1ρHspin lock filter, prior to CPMAS, allows for spectroscopic separation of crystalline and noncrystalline13C nuclear magnetic resonance signals. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.
National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD, 20899, USA.
Ryan C
RC
Nieuwendaal
13C CPMAS; P3HT; crystallinity; morphology; organic electronics; paracrystallinity; polymer; solid-state NMR