Polarized Soft X-ray Scattering Reveals Chain Orientation within Nanoscale Polymer Domains

Abstract

Fully conjugated donor−acceptor block copolymers can serve as the active layer in organic photovoltaics and other organic electronic devices. Self-assembly into periodic domains and crystallization of the constituent blocks are crucial to enable control of the multiscale structure and consequently electronic properties. Resonant soft X-ray scattering (RSoXS) is an invaluable tool to characterize such materials, where tuning the X-ray energy and polarization reveals molecular orientation and domain spacing. Here, anisotropic soft X-ray scattering data reveal the type and degree of orientation within conjugated block copolymers composed of poly(3-hexylthiophene-2,5-diyl) and various push−pull copolymers. The maximum anisotropy is observed at the scattering vector corresponding to the spacing between block copolymer domains, which scales with the end-to-end distance of the blocks, as expected. Furthermore, the anisotropy in RSoXS data reveals that the crystalline P3HT blocks orient, on average, parallel or nearly parallel to the block copolymer interface; the average tilt angle between P3HT chains and domain interfaces can be extracted from the dependence of the anisotropy with polar angle. We interpret this angle to correspond to the average tilt of rings in the unit cell, potentially within a chiral mesostructure. Results are corroborated with scattering calculations based on simple model structures.

Chemical and Morphological Origins of Improved Ion Conductivity in Perfluoro Ionene Chain Extended Ionomers

“…Resonant soft X-ray scattering (RSoXS) has recently seen widespread use in many carbon-based materials such as carbon nanotubes, 27 liquid crystals, [28][29][30] proteins, 31,32 and polymers. [33][34][35][36][37][38] To date, RXS has not been applied to PFSA ionomers. Here, we showcase RXS at energies near the sulfur K-edge, around 2470 eV, which is ideal for studying proton-conducting ionomers for several reasons.…”

Control of aggregated structure of photovoltaic polymers for high‐efficiency solar cells

“…Present understanding of the aggregated structure greatly benefits from the advances in characterization tools of soft matters. [45,47,416] For instance, R-SoXS has been a very powerful tool to analyze the structural parameters (domain size, [417,418] domain purity, [419] type and degree of orientation [420,421] ) of polymers blends in solid films. Use of other techniques (e.g., in situ neutron scattering [422] and cryo-TEM [423] ) will help to understand how the aggregated structure forms in solution state.…”

Wide bandgap polymer donors for high efficiency non-fullerene acceptor based organic solar cells

“…59 Resonant soft X-ray scattering (RSoXS) is another evolving method to investigate multi-component, multi-phase systems like the active layer of an OSC, where the contrast of the donor and acceptor components can be tuned by selection of the incident X-ray energy to quantitatively reveal molecular orientation, domain purity, and domain spacing. 59,60,63,64 5) Exciton dissociation, collection, and recombination: The trend of photocurrent density J ph (J ph = J L -J D , where J L is the current density under illumination and J D is the current density in dark) versus effective voltage (V eff = V-V 0 ), gives insights into the charge generation and exciton dissociation characteristics of the device. Here V 0 is called the compensation voltage or the voltage at which J ph = 0 and V is the applied voltage.…”