Fully conjugated block copolymers, consisting of covalently bonded donor and acceptor blocks, can serve as the active layer in organic photovoltaics and other organic electronic devices. The use of Resonant Soft X-ray Scattering (RSoXS) allows for studies into the molecular orientation and domain spacing of the polymers by tuning the X-ray energy and polarization to examine various components of block copolymers. Using the conjugated block copolymer system of poly(3-hexylthiophene)-block-poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(thiophen-5-yl)-2,1,3-benzothiadiazole]-2′,2″-diyl), P3HT-b-PFTBT, and PFTBT derivatives, we can examine the effects of various polymer blocks on the differences of morphology between the donor and acceptor. Polarized Soft X-Ray Scattering (PSoXS) allows us to quantify the type and the degree of orientation of chains within block copolymer domains in thin films. Further examination of the anisotropy in PSoXS data provides a clear signature of the block copolymer microstructure. Radial distribution and Fourier transform calculations of model polymer structures corroborate this concept of block copolymer domains. Simulated scattering helps predict size, orientation, inhomogeneity, and interfacial width within conjugated block copolymers. Based on our early finding, we believe that within our P3HT-b-PFTBT block copolymer films, the crystalline P3HT blocks orient parallel to the block copolymer interface, and we confirm that the domain spacing extracted from PSoXS scales with the end-to-end distance of the blocks. Additionally, there is a correlation between block copolymer device performance and the strength of the anisotropy of the film, as measured by the PSoXS data.

Polarized soft X-ray scattering reveals chain orientation and domain size of conjugated block copolymer lamellae

255th National Meeting (2018)

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