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Vibrational Neutron Scattering Spectra for Undoped and Doped P3HT

Citation

Harrelson, Thomas; Li, Jun; Moule, Adam (2018), Vibrational Neutron Scattering Spectra for Undoped and Doped P3HT, Dryad, Dataset, https://doi.org/10.25338/B8HC7K

Abstract

Doped semiconducting polymers have garnered vast research interest in photovoltaic, transistor, thermoelectric, and sensor applications. P3HT is a canonical semiconducting polymer that self-assembles into a mixture of crystalline and amorphous domains. Doping P3HT can increase the observed conductivity by several orders of magnitude. The vibrations of the polymer are sensitive to the local morphology of the film, and the morphology of the film changes upon doping. Vibrational neutron spectroscopy is a method for identifying vibrational modes/phonons over a large energy range (1 meV - 500 meV). Each peak in the spectra represents a specific vibrational mode, which can be used to correlate local structure in the material. We present spectra for undoped regioregular P3HT (rr-P3HT), undoped regiorandom P3HT (rra-P3HT), undoped deuterated rr-P3HT, rr-P3HT doped with F4TCNQ at 5% mole ratio, rr-P3HT doped with F4TCNQ at 17% mole ratio, and rr-P3HT doped with I2 at 10% mole ratio.

Methods

The samples were coarse powders that were placed into the sample holder of the neutron instrument. Thus, the resulting spectra are powder averages of the vibrations. Most samples are not deuterated, which means that those spectra are incoherent scattering spectra. The deuterated spectrum is primarily coherent scattering, and should be treated differently. The data was taken at the VISION spectrometer at the Spallation Neutron Source at Oak Ridge National Laboratory. The data was collected by cooling the sample to ~5 K, then opening the shutter allowing pulses of neutrons to interact with the sample at known time points. Scattering neutrons hit the analyzer crystals, which only reflect scattered neutrons with a known wavelength toward the detector. The detector records the time at which a scattered neutron hits the detector, allowing the energy loss of the scattered neutron to be calculated through time-of-flight analysis. The sample was run long enough to sufficiently reduce the signal to noise ratio. The data is displayed in 3 columns: Energy loss (in meV), Intensity, error. Most text file contains 2 sets of data: the first one is the results from the forward scattering analyzers, the second from the back scattering analyzers. The forward scattering data comes from low momentum transfer scattering events, and the back scattering data comes from high momentum transfer scattering events. If a text file contains only one spectrum, it is the forward scattering data.