Controlling the Interaction of Light with Polymer Semiconductors

Hellmann, Christoph; Paquin, Francis; Treat, Neil D.; Bruno, Annalisa; Reynolds, Luke X.; Haque, Saif A.; Stavrinou, Paul N.; Silva, Carlos; Stingelin, Natalie

doi:10.1002/adma.201300881

Cited by 46 publications

(66 citation statements)

References 26 publications

(20 reference statements)

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“…37 When blending the three polymers with high molecular weight PEO (viscosity averaged molecular weight M v = 900 kg mol -1 ), following the procedures reported in Refs. 20 and 38, we find that adding PEO to the P3HT homopolymer leads to a substantially enhanced 0-0/0-1 peak ratio in both absorption and emission, entirely consistent with earlier observations 20 and characteristic of a transition from inter-to intra-molecular coupling 26,29,31 similar changes in neat P3HT were previously attributed to polar solvent induced planarization in solution prior to aggregation. 39,40 In contrast, blending the block copolymer P3HT-b-PEO with PEO has a negligible effect on the optical response of this P3HT copolymer.…”

Section: Results and Disucssionsupporting

confidence: 90%

“…This difference was tentatively attributed to a change in the torsional backbone order of P3HT. 20 Here, we aim at combining these two approacheschemical modification and blending -to control the molecular order of the active material and, thus, functionality. For this, we use model systems with the same conjugated backbone based on polythiophene chains -the P3HT homopolymer, the diblock copolymer poly(3-hexylthiophene)-block-poly(ethylene oxide) (P3HT-b-PEO), 25 and the graft polymer poly[3but(ethylene oxide)thiophene] (P3BEOT; for chemical structures see Figure 1b,c insets) -and their blends with PEO.…”

Section: Introductionmentioning

confidence: 99%

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Managing Local Order in Conjugated Polymer Blends via Polarity Contrast

et al. 2019

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The optoelectronic landscape of conjugated polymers is intimately related to their molecular arrangement and packing, with minute changes in local order, such as chain conformation and torsional backbone order/disorder, frequently having a substantial effect on macroscopic properties. While many of these local features can be manipulated via chemical design, the synthesis of a series of compounds is often required to elucidate correlations between chemical structure and macromolecular ordering. Here, we show that blending semiconducting polymers with insulating commodity plastics enables controlled manipulation of the semiconductor backbone planarity. The key is to create a polarity difference between the semiconductor backbone and its side chains, while matching the polarity of the side chains and the additive. We demonstrate the applicability of this approach through judicious comparison of regioregular poly(3-hexylthiophene) (P3HT) with two of its more polar derivatives, namely the diblock copolymer poly(3hexylthiophene)-block-poly(ethylene oxide) (P3HT-b-PEO) and the graft polymer poly[3-but(ethylene oxide)thiophene] (P3BEOT), as well as their blends with poly(ethylene oxide) (PEO). Proximity between polar side chains and a similarly polar additive reduces steric hindrance between individual chain segments by essentially 'expelling' the side chains away from the semiconducting backbones. This process, which has been shown to be facilitated via exposure to polar environments

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Section: Results and Disucssionsupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Managing Local Order in Conjugated Polymer Blends via Polarity Contrast

et al. 2019

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“…Paquin et al (36) and Parkinson et al (37) both have revealed a dynamic evolution from an initial vibrationally hot excited state (low symmetry) to a geometrically relaxed state (high symmetry) (i.e., dynamic torsional planarization of the backbones) for P3HT, which results in a dynamic and strong decrease of the relative 0-0 intensity within ∼10 ps. With time-resolved absorption measurements, Ade and coworkers have reported the interchain coupling involves a dynamic process evolving from J-like to H-like within a few hundreds of picoseconds for P3HT in polyethylene oxide matrix * (38). In the H-aggregate model (25,36), the 0-0 transition from the first excited state to the ground state is symmetry forbidden and the emission can be described by a modified Franck-Condon progression:…”

Section: Resultsmentioning

confidence: 99%

Impact of backbone fluorination on nanoscale morphology and excitonic coupling in polythiophenes

Haws

Fei

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Fluorination represents an important strategy in developing highperformance conjugated polymers for photovoltaic applications. Here, we use regioregular poly(3-ethylhexylthiophene) (P3EHT) and poly(3-ethylhexyl-4-fluorothiophene) (F-P3EHT) as simplified model materials, using single-molecule/aggregate spectroscopy and molecular dynamic simulations, to elucidate the impacts of backbone fluorination on morphology and excitonic coupling on the molecular scale. Despite its high regioregularity, regioregular P3EHT exhibits a rather broad distribution in polymer chain conformation due to the strong steric hindrance of bulky ethylhexyl side chains. This conformational variability results in disordered interchain morphology even between a few chains, prohibiting long-range effective interchain coupling. In stark contrast, the experimental and molecular dynamic calculations reveal that backbone fluorination of F-P3EHT leads to an extended rod-like single-chain conformation and hence highly ordered interchain packing in aggregates. Surprisingly, the ordered and close interchain packing in F-P3EHT does not lead to strong excitonic coupling between the chains but rather to dominant intrachain excitonic coupling that greatly reduces the molecular energetic heterogeneity.fluorinated polythiophenes | photophysics | single-molecule spectroscopy | morphology | organic electronics M orphology and excitonic coupling are among the most important factors dictating the functions and performance of conjugated polymers (CPs) in a variety of optoelectronic applications (1-4). To tune and optimize the morphological and optoelectronic properties of CPs, chemical structure modification of the backbone and side chains is one of the main and most effective approaches (5-7). It has been revealed that the position, size, and length of side chains dramatically affect the morphology and optoelectronic properties of CPs. In the efforts to develop high-performance photovoltaic CPs, the introduction of fluorine atoms onto aromatic comonomers, i.e., the fluorination of polymer backbone, offers a very appealing strategy to tune the electronic properties, morphology, and photochemical stability (6-8). It is proposed that the inherent electronwithdrawing nature of fluorine atoms lowers the highest energy occupied molecular orbital energy levels, thereby increasing the open-circuit voltage in photovoltaics. In addition, the strong electronegativity might induce F-S and F-H interactions and potentially modifies the molecular conformation and intermolecular organization (6). Furthermore, it has been shown that fluorination often leads to enhanced thermal and oxidative stability (9-11). Given a combination of these desirable properties, fluorine-containing CPs have led to most of the best-performing polymer-based solar cells to date (12-15).For typical CPs, the primarily created exciton is Coulombically bound upon photoexcitation mainly due to the low dielectric constant and strong electron-phonon interaction in polymers. The interchain and intrachain morp...

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“…A large redshift of the absorption maxima to 550–600 nm in the spin‐coated films is generally observed because of the planarization of the π‐conjugated chain; however, the disordered packing means that the side‐by‐side interchain interaction dominates the electronic properties of the films (weak H ‐aggregation model) . This situation can be changed if the polymer chains form highly ordered and planar structures, then the head‐to‐tail interaction could be strong enough to determine the optical properties, as observed in highly crystalline nanofibers, single crystals, or crystallized films in a poly(ethylene oxide) matrix, where a more significant redshift of the absorption to 640 nm is observed ( J ‐aggregation). These recent results suggest that the same π‐conjugated polymers can show completely different optical properties depending on the structural order and the packing of the main chains in the films…”

Section: Methodsmentioning

confidence: 99%