Aggregation in a High-Mobility n-Type Low-Bandgap Copolymer with Implications on Semicrystalline Morphology

Steyrleuthner, Robert; Schubert, Marcel; Howard, Ian A.; Klaumünzer, Bastian; Schilling, Kristian; Chen, Zhihua; Saalfrank, Peter; Laquai, Frédéric; Facchetti, Antonio; Neher, Dieter

doi:10.1021/ja306844f

Cited by 399 publications

(692 citation statements)

References 129 publications

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“…2B). P(NDI2OD-T2) has a strong tendency to preaggregate in low-polar solvents, even at low concentrations (20). Similar to what is observed in neat P(NDI2OD-T2) films, aggregation is strongly promoted also for the blends with the formation of aggregate species, exhibiting a main absorption band at ∼710 nm and a shoulder at ∼790 nm (Fig.…”

Section: Resultssupporting

confidence: 69%

“…2B). This structured low-energy absorption represents a clear spectroscopic fingerprint of the formation of aggregate species and was attributed to the interaction of chain segments (20). The optical characteristics of nonaggregate chains are observed only when solvent molecules with large and highly polarizable aromatic cores such as chloronaphthalene are used to dissolve the polymer, resulting in unstructured absorption centered at 620 nm.…”

Section: Resultsmentioning

confidence: 99%

“…However, film morphologies with predominantly edge-on oriented polymer chains were observed to yield lower performance in both diodes and top-gated OFETs because of the reduced out-of-plane mobility and larger injection barrier (16)(17)(18)(19). In a recent publication, Neher and coworkers also showed that this polymer has a strong tendency to aggregate, which greatly affects the bulk optical and electrical properties (20,21). Control of the preaggregation of this polymer in solution has shown great promise for the optimization of all-polymer solar cells in which P(NDI2OD-T2) is used as a fullerene replacement (22,23).…”

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Experimental evidence that short-range intermolecular aggregation is sufficient for efficient charge transport in conjugated polymers

Wang

Fabiano

Himmelberger

et al. 2015

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

176

200

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Efficiency, current throughput, and speed of electronic devices are to a great extent dictated by charge carrier mobility. The classic approach to impart high carrier mobility to polymeric semiconductors has often relied on the assumption that extensive order and crystallinity are needed. Recently, however, this assumption has been challenged, because high mobility has been reported for semiconducting polymers that exhibit a surprisingly low degree of order. Here, we show that semiconducting polymers can be confined into weakly ordered fibers within an inert polymer matrix without affecting their charge transport properties. In these conditions, the semiconducting polymer chains are inhibited from attaining longrange order in the π-stacking or alkyl-stacking directions, as demonstrated from the absence of significant X-ray diffraction intensity corresponding to these crystallographic directions, yet still remain extended along the backbone direction and aggregate on a local length scale. As a result, the polymer films maintain high mobility even at very low concentrations. Our findings provide a simple picture that clarifies the role of local order and connectivity of domains.organic electronics | conjugated polymers | aggregation | charge transport C onjugated polymers have received significant scientific attention as the active material in devices for printed and flexible organic electronics (1, 2). Owing to their versatile chemical synthesis, inexpensive processability from solution, and unique mechanical flexibility, these materials are in fact promising for a vast array of devices in future low-cost and distributed technologies, such as integrated systems for electronic labels targeting safety, security, and surveillance applications (3). The rational design of new organic semiconductors has been guided by a thorough investigation of their limitations in charge transport, leading to the development of high-performance materials for next-generation electronic applications such as low-cost displays, solar cells, sensors, and logic circuits (4, 5). For more than a decade research has primarily focused on increasing the long-range order and the crystallinity of conjugated polymers as a strategy to improve the solid-state charge transport properties. As a result, the charge carrier mobility has increased by several orders of magnitude through the design and synthesis of highly ordered polymers. However, recent studies have suggested that the key to designing high-mobility polymers is not to increase their crystallinity but rather to improve their tolerance for disorder by allowing more efficient intra-and intermolecular charge transport pathways (6). This observation explains why mobility values obtained from recently designed seemingly disordered organic semiconductors often exceed those of polymers having a high degree of crystallinity (∼1 cm 2 ·V -1 ·s -1 ) (7-10). Indeed, polymers may exhibit little longrange order, as measured by X-ray diffraction (XRD), and yet display a remarkable degree of short-range or...

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Section: Resultssupporting

confidence: 69%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

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Experimental evidence that short-range intermolecular aggregation is sufficient for efficient charge transport in conjugated polymers

Wang

Fabiano

Himmelberger

et al. 2015

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

176

200

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“…The reference polymer P(NDI2OD-T2) is well-known to form self-aggregates in chloroform due to strong interchain stacking of more planar polymer backbone, which leads to a red-shifted ICT band. 28 Incorporation of the large PDI units in the random copolymers reduced the planarity of the polymer backbone as well as interchain aggregation. 35 Consequently, the ICT band was shifted to lower wavelength.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…15,16,20 However, it exhibited a strong tendency to form aggregates in specific organic solvents that resulted in large-scale phase separation instead of the desirable pure donor/acceptor microphase separation. 28 Consequently, the earlier reports on the all-PSC measurements of P3HT/P(NDI2OD-T2) blend showed very low device efficiency value (PCE, 0.2%). 29,30 Later studies showed that the aggregation in P(NDI2OD-T2) could be suppressed significantly in the early stage of film formation by using more polar aromatic solvents.…”

Section: ■ Introductionmentioning

confidence: 84%

Improved All-Polymer Solar Cell Performance of n-Type Naphthalene Diimide–Bithiophene P(NDI2OD-T2) Copolymer by Incorporation of Perylene Diimide as Coacceptor

et al. 2016

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Naphthalene diimide−bithiophene P(NDI2OD-T2) is a well-known donor−acceptor polymer, previously explored as n-type material in all-polymer solar cells (all-PSCs) and organic field effect transistor (OFETs) applications. The optical, bulk, electrochemical, and semiconducting properties of P(NDI2OD-T2) polymer were tuned via random incorporation of perylene diimide (PDI) as coacceptor with naphthalene diimide (NDI). Three random copolymers containing 2,2′-bithiophene as donor unit and varying compositions of naphthalene diimide (NDI) and perylene diimide (xPDI, x = 15, 30, and 50 mol % of PDI) as two mixed acceptors were synthesized by Stille coupling copolymerization. Proton NMR spectra recorded in CDCl 3 showed that the π−π stacking induced aggregation among the naphthalene units could be successfully disrupted by the random incorporation of bulky PDI units. The newly synthesized random copolymers were investigated as electron acceptors in BHJ all-PSCs, and their performance was compared with P(NDI2OD-T2) as reference polymer. An enhanced PCE of 5.03% was observed for BHJ all-PSCs (all-polymer solar cells) fabricated using NDI-Th-PDI30 as acceptor and PTB7-Th as donor, while the reference polymer blend with the same donor polymer exhibited PCE of 2.97% efficiency under similar conditions. SCLC bulk carrier mobility measured for blend devices showed improved charge mobility compared to reference polymer, with PTB7-Th:NDI-Th-PDI30 blend device exhibiting the high hole and electron mobility of 4.2 × 10 −4 and 1.5 × 10 −4 cm 2 /(V s), respectively. This work demonstrates the importance of molecular design via random copolymer strategy to control the bulk crystallinity, compatibility, blend morphology, and solar cell performance of n-type copolymers.

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Organic Photovoltaic Morphology

Collins

Bokel

DeLongchamp

2014

Organic Photovoltaics

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Aggregation in a High-Mobility n-Type Low-Bandgap Copolymer with Implications on Semicrystalline Morphology

Cited by 399 publications

References 129 publications

Experimental evidence that short-range intermolecular aggregation is sufficient for efficient charge transport in conjugated polymers

Experimental evidence that short-range intermolecular aggregation is sufficient for efficient charge transport in conjugated polymers

Improved All-Polymer Solar Cell Performance of n-Type Naphthalene Diimide–Bithiophene P(NDI2OD-T2) Copolymer by Incorporation of Perylene Diimide as Coacceptor

Organic Photovoltaic Morphology

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