How Halogenation Impacts the Polymer Backbone Conformation: Learning from Combination of Solid‐State MAS NMR and X‐Ray Scattering

Abstract

Over the past decade, halogenated semiconducting polymers have attracted considerable interest due to their outstanding optoelectronic properties. Thus, in most of today's organic photovoltaic devices benchmark organic semiconductors are halogenated materials, either electron donor polymers or non‐fullerene acceptor (NFA) small molecules. However, the nature and position of the substituted halogen atoms in halogenated semiconducting polymers impact, through self‐assembly modification, their optoelectronic properties in a way that is difficult to predict. Yet, the solid‐state self‐assembling of these materials has been shown to be a key parameter toward high charge transport properties and photovoltaic efficiencies. In this context, there is still a need to develop analytical methods that will enable an atomic‐scale structural characterization of these materials as a function of the halogenation. In this study, the solid‐state nuclear magnetic resonance (NMR) under magic angle spinning (MAS) is explored as a tool to investigate the local structure and supramolecular organization of a series of conjugated polymers, specially designed for this study. Through a comprehensive study using complementary techniques, including MAS–NMR, small and wide‐angle X‐ray scattering, and molecular modeling investigations, the molecular conformation of these polymers in relation to their chemical composition, is successfully determined.

Importance of Short-Range Order in Governing Thin Film Morphology and Electronic Properties of Polymeric Organic Semiconductors

“…Specifically, magnetic resonance spectroscopy (NMR and EPR) techniques allow site-specific compositions and structures in both the ordered and disordered regions of OSC materials to be identified and distinguished. ,− The short-range interactions at subnanometer to nanometer distances measured by these techniques also facilitate structure elucidation of OSC thin films. To this end, the emerging NMR crystallography approaches make use of the combined ssNMR, X-ray scattering, and modeling techniques, which are likely to be well-suited to characterize single-component OSCs and organic photovoltaic blends. ,− In a bottom-up strategy, it is first important to resolve the local order in single-component OSCs and then extend it to the study of complex OSC blends. Therefore, we turned our attention to systematically characterize the local order and disorder in polymeric OSCs.…”

Fluorinated Conjugated Polymers Enabled Enhanced Detectivity in Organic Near-Infrared Photodetectors

“…Conjugated polymers (CPs) are an important component of bulk-heterojunctional OPDs in which structure modification of CPs can adjust their molecular aggregation, charge transport, and optoelectronic properties. − CPs possess unique semiconductor properties, and understanding how to control their optoelectronic performance is critical for designing CPs with improved photoresponse characteristics. A large number of studies in the field of organic electronics show that the halogenation strategy is an ideal method to improve the optoelectronic properties of CPs. − Fluorine (F) substitution, in particular, can not only adjust the energy level structure of CPs but also improve their crystallinity, trap density, and mobility. − Bai et al found that in D-A-type CPs, fluorination of electron-donating units can suppress density of trap states in the active layer, effectively enhancing performance of OPDs . Additionally, Park et al studied the effect of fluorinated alkyl chains in CPs on J dark and D* of OPDs.…”