Polymorphism of Crystalline Molecular Donors for Solution-Processed Organic Photovoltaics

Poll, Thomas S. van der; Zhugayevych, Andriy; Chertkov, Eli; Bakus, Ronald C.; Coughlin, Jessica E.; Teat, Simon J.; Bazan, Guillermo C.; Tretiak, Sergei

doi:10.1021/jz5012675

Cited by 25 publications

(33 citation statements)

References 39 publications

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“…Their responses to film processing solvent/additive conditions should help assess processing-morphology generalities for OSC polymers. [51][52][53][54][55] Simple changes in molecular structure [52][53][54] or processing solvent [55] can dramatically affect crystal packing. [47,48] However, while this description is qualitatively correct, depending on the poly mer and processing, crystalline characteristics can vary.…”

Section: Introductionmentioning

confidence: 99%

In Situ Analysis of Solvent and Additive Effects on Film Morphology Evolution in Spin‐Cast Small‐Molecule and Polymer Photovoltaic Materials

Manley

Strzalka

Fauvell

et al. 2018

Advanced Energy Materials

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indicate the realistic possibility of new soft matter technologies. Note that these highperformance laboratory devices are often produced via spin-coating, a reliable fabrication process that enables rapid prototyping and basic research. However, the transition to high throughput film fabrication processes such as blade-coating, roll-to-roll printing, and others will require understanding of film morphology-forming mechanisms operative in spin-coating processes that optimize organic device performance. [13] Traditionally, optimizing device performance relied on empirical screening of spin-casting para meters such as solvent, processing additive, and spin speed, followed by postprocessing analysis of which morphologies are produced by which coating conditions. [14][15][16] For OSC film morphology, grazing incidence wide-angle X-ray scattering (GIWAXS) is especially powerful for monitoring crystallinity, orientation, donor-acceptor intermixing, [14][15][16][17][18] and developing an ex post facto understanding basis for otherwise completely empirical "recipes." While informative, postdeposition analysis can miss important temporal characteristics of film growth processes which can only be identified by in situ techniques. In situ film growth studies utilizing GIWAXS and other techniques during film deposition and drying have been employed by several groups, including our own, to understand crystalline morphology development in organic electronic thin films. [19,20] Characterizing morphology during the film formation process can elucidate important mechanistic pathways and inform rational solution processing parameter optimization.Several recent studies have reported in situ optical and X-ray analyses of organic film growth by roll-to-roll printing, [21] blade To elucidate the details of film morphology/order evolution during spin-coating, solvent and additive effects are systematically investigated for three representative organic solar cell (OSC) active layer materials using combined in situ grazing incidence wide angle x-ray scattering (GIWAXS) and optical reflectance. Two archetypical semiconducting donor (p-type) polymers, P3HT and PTB7, and semiconducting donor small-molecule, p-DTS(FBTTh 2 ) 2 are studied using three neat solvents (chloroform, chlorobenzene, 1,2-dichlorobenzene) and four processing additives (1-chloronaphthalene, diphenyl ether, 1,8-diiodooctane, and 1,6-diiodohexane). In situ GIWAXS identifies several trends: 1) for neat solvents, rapid crystallization occurs that risks kinetically locking the material into multiple crystal structures or crystalline orientations; and 2) for solvent + additive processed films, morphology evolution involves sequential transformations on timescales ranging from seconds to hours, with key divergences dependent on additive/ semiconductor molecular interactions. When π-planes dominate the additive/semiconductor interactions, both polymers and small molecule films follow similar evolutions, completing in 1-5 min. When side chains dominate the additive/semiconductor...

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Section: Introductionmentioning

confidence: 99%

In Situ Analysis of Solvent and Additive Effects on Film Morphology Evolution in Spin‐Cast Small‐Molecule and Polymer Photovoltaic Materials

Manley

Strzalka

Fauvell

et al. 2018

Advanced Energy Materials

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“…Such astrategy would lead to amolecule with increased solubility through the participation of the twisted conformation, while possessing aplanar topology in the solid state with long-range order. [16] Though both molecules have the same number of hexyl groups,t he solubility of TT in CHCl 3 (25 mg mL À1 )i ss ubstantially higher than that of CT (14 mg mL À1 ). In both, identical wings (blue) are connected through different dithiophene linkers (red).…”

mentioning

confidence: 99%

“…Forb oth, the outer wings are essentially planar, which is consistent with previous single crystal characterization of structurally-related molecules. [16] Though both molecules have the same number of hexyl groups,t he solubility of TT in CHCl 3 (25 mg mL À1 )i ss ubstantially higher than that of CT (14 mg mL À1 ). We attribute this increased solubility to the non-planar molecular topology of TT.…”

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confidence: 99%

Topological Transformation of π‐Conjugated Molecules Reduces Resistance to Crystallization

et al. 2017

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Tw oe lectronically delocalized molecules were designed as models to understand howm olecular shape impacts the tradeoff between solubility and crystallization tendencies in molecular semiconductors.T he more soluble compound TT contains an on-planar bithiophene central fragment, whereas CT has ap lanar cyclopentadithiophene unit. Calorimetry studies show that CT can crystallizem ore easily than TT.H owever,a bsorption spectroscopys hows that the initially amorphous TT film can eventually form crystals in which the molecular shape is significantly more planar.T wo thermally reversible polymorphs for TT were observed by XRD and grazing-incidence wide-angle X-rays cattering (GIWAXS) measurements.T hese findings are relevant within the context of designing soft semiconductors that exhibit high solubility and atendency to providestable organized structures with desirable electronic properties.

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“…In the context of this research, it became clear that molecular packing within (semi‐/poly‐) crystalline layers or single crystals plays a central role for charge transport. Thus, charge transport is not only governed by the molecular structure of the OSC but also by substituents, which includes the number and position as well as length and flexibility of the solubilizing side chains, often giving rise to multiple polymorphs with different performance . Interestingly, many of these solubilizing chains are branched, or even chiral, creating a plethora of stereoisomers and diastereomers within one material batch, especially in polymers .…”

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confidence: 99%

Impact of 2‐Ethylhexyl Stereoisomers on the Electrical Performance of Single‐Crystal Field‐Effect Transistors

Leowanawat

Burschka

et al. 2018

Advanced Materials

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Many organic semiconductors (OSCs) inherit chiral alkyl chains, which ensure the desirable high solubility for solution-processing but may also lead to disorder, inhomogeneous film-formation, as well as interfacial defects due to the presence of mixtures of stereoisomers or diastereomers, which impair their peak performance. Here, single-crystal field-effect transistors (SCFETs) of a diketopyrrolopyrrole-based organic semiconductor with chiral 2-ethylhexyl substituents by sublimation in air and organic ribbon mask method are fabricated. Devices of the mesomer (R/S), both enantiomers (R/R, S/S), as well as mixtures of these three stereoisomers measured under ambient conditions exhibit all appreciable p-channel charge carrier mobilities of > 0.1 cm V s despite different packing arrangement in the R/S, R/R (or S/S), and racemate crystal structures. These results suggest a surprising tolerance for isomeric impurities. The highest literature-reported p-channel mobility so far for a diketopyrrolopyrrole-based OSC of 3.4 cm V s (I /I of 1 × 10 ) is, however, only obtained for the pure R/S mesomer, illustrating the inherent potential of stereochemical purity. These results on SCFETs are further substantiated by studies on organic thin-film transistors (OTFTs) of pure and mixed thin films of the different stereoisomers.

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Polymorphism of Crystalline Molecular Donors for Solution-Processed Organic Photovoltaics

Cited by 25 publications

References 39 publications

In Situ Analysis of Solvent and Additive Effects on Film Morphology Evolution in Spin‐Cast Small‐Molecule and Polymer Photovoltaic Materials

In Situ Analysis of Solvent and Additive Effects on Film Morphology Evolution in Spin‐Cast Small‐Molecule and Polymer Photovoltaic Materials

Topological Transformation of π‐Conjugated Molecules Reduces Resistance to Crystallization

Impact of 2‐Ethylhexyl Stereoisomers on the Electrical Performance of Single‐Crystal Field‐Effect Transistors

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