Organic Thin-Film Transistors with Phase Separation of Polymer-Blend Small-Molecule Semiconductors: Dependence on Molecular Weight and Types of Polymer

Ohe, Takahiro; Kuribayashi, Miki; Tsuboi, Ami; Satori, Kotaro; Itabashi, Masao; Nomoto, Kazumasa

doi:10.1143/apex.2.121502

Cited by 45 publications

(42 citation statements)

References 18 publications

(20 reference statements)

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“…[33] In particular, differences with regard to the solution's film formation properties are anticipated as viscosity is expected to significantly change with the molecular weight. [35] Therefore, we decided to test solutions with four different molecular weights of polystyrene. [34] These differences have, for instance, been shown in a study on spin-cast devices, where blending with a low molecular weight polymer has not led to vertical stratification of the two components, while higher molecular weights have produced a multilayer structure with good device performance.…”

Section: Optimization Of C8-btbt:polystyrene Blendmentioning

confidence: 99%

High‐Mobility, Solution‐Processed Organic Field‐Effect Transistors from C8‐BTBT:Polystyrene Blends

Haase

Rocha

Hauenstein

et al. 2018

Adv Elect Materials

103

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record values exceeding 10 cm 2 V −1 s −1 have been reported. [3][4][5][6][7][8] Though these results are promising, some of these reported values suffer from overestimation, [9,10] require significant engineering efforts, [3] complex fabrication procedures, [4] or employ nonscalable fabrication techniques, [5] ultimately highlighting the need for alternative and potentially more industry-relevant processing methods. We believe that adjustments to existing solution coating methods rather than intensive technology engineering could result in a feasible and simple approach.Ink properties such as the solvents' boiling point, [11] solubility parameters, [12] or the solute concentration [13] can be tuned in order to control crystal growth and packing in a manner that provides favorable electrical characteristics. Such ink engineering has recently been shown to generate high mobility devices based on C8-BTBT. [14] In particular, a distinct increase of performance by utilizing a solvent mixture rather than a single solvent has been reported for a range of semiconductors, including TIPS-pentacene [15,16] or diketopyrrolopyrrole (DPP)-based polymers. [17] This approach has frequently been combined with another effective method -the addition of a polymer additive to the printing solution. This combination has been shown to significantly reduce the device-to-device variations and yielded improved transistor performances when applied to high-mobility small molecules, like TIPS-pentacene, [18] diF-TES-ADT, [8,19,20] or even C8-BTBT. [5,7,21,22] In this study, we explore various blends of the high-mobility semiconductor C8-BTBT with the inert polymer polystyrene (PS) with the objective of improving device-to-device uniformity and investigating the effect on device characteristics. We report improved film formation that results in the reduction of deviceto-device variations and the reliable fabrication of high-mobility organic field-effect transistors by a scalable, meniscus-guided coating method, and demonstrate OFETs based on C8-BTBT, that to the best of our knowledge show the highest intrinsic mobility so far reported. Results and Discussion Discussion of C8-BTBT-Based Devices in LiteratureIn the literature, the blending of C8-BTBT and PS led to improvements in the effective mobility of organic field-effect Organic field-effect transistors based on aligned small molecule semiconductors have shown high charge carrier mobilities in excess of 10 cm 2 V −1 s −1 . This makes them a viable alternative to amorphous inorganic semiconductors especially if a high reproducibility can be achieved. Here, the optimization of high mobility organic field-effect transistors based on the organic semiconductor 2,7-dioctyl[1]benzothieno[3,2-b] benzothiophene (C8-BTBT) via the addition of a polymer additive to the printing solution is reported. Specifically, films and devices are compared based on solutions of the neat semiconductor and the blend with polystyrene and shear-coated devices with excellent device characteristics and gate-voltage-ind...

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Section: Optimization Of C8-btbt:polystyrene Blendmentioning

confidence: 99%

High‐Mobility, Solution‐Processed Organic Field‐Effect Transistors from C8‐BTBT:Polystyrene Blends

Haase

Rocha

Hauenstein

et al. 2018

Adv Elect Materials

103

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“…[184][185][186]193,200,201,203] In contrast, the strong intermolecular interactions made by the rigid conjugated building blocks of polymeric OSC molecules make these molecules less soluble than common insulating polymers such as PS and PMMA. Evaporation of solvent molecules from the film/air interface increases the solute concentration near this interface.…”

Section: Wileyonlinelibrarycommentioning

confidence: 99%

Effective Use of Electrically Insulating Units in Organic Semiconductor Thin Films for High‐Performance Organic Transistors

Kang

Qiu

et al. 2016

Adv Elect Materials

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The electrical properties of organic semiconductors (OSCs), whether they are conjugated small molecules or polymers, can be tailored by incorporating electrically insulating units (EIUs), which are organic moieties consisting of nonconjugated units. EIUs can be introduced to a thin film by synthetically connecting them to the otherwise conjugated OSC molecules or by blending them in as separate EIU molecules with the OSCs during the thin‐film fabrication process. The engineered EIUs are capable of imparting various additional functions to the OSC thin film and improving their electrical properties. In this review article, a comprehensive overview of various effects of EIUs on OSC thin films and their consequent electrical performance when used as active layers in organic field‐effect transistors (OFETs) is provided. A broad range of studies of the synthetic approaches of incorporating EIUs, such as those using side chains, block copolymers, and conjugation‐break spacers, and of the blending approaches with organic insulators is discussed. Finally, a brief summary and perspectives for future research in this field are presented.

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“…The effective degrees of polymerization (N i ) in terms of the number of lattice sites were calculated to be 1, 8, 846, and 6 for toluene, PaMS (1 kDa), PaMS (100 kDa), and TIPS, respectively, taking the molecular volume of one solvent molecule to represent one lattice site. Figure 1 shows the ternary phase diagram calculated for M PaMS = 1 kDa, for which no (considerable) phase separation was observed during casting, [9,10] and M PaMS = 100 kDa, for which extensive phase separation during spin-coating was demonstrated. [10] Upon spin-coating a typical blend solution (f 1 % 0.99) the volume of the solvent rapidly decreases, which, beyond a critical value, quenches the system into the coexistence region yielding two phases, defined by the binodal compositions.…”

Section: Resultsmentioning

confidence: 99%

“…[7] Besides processing conditions and substrate effects, also molecular parameters determine whether the desired phase-separated morphology is obtained. For poly(a-methylstyrene)/triisopropylsilylpentacene (PaMS/TIPS) O-TFT blends, for instance, several authors [9,10] reported vertical phase separation into a layered geometry in ascast films for sufficiently high molecular weight of PaMS (of the order of 10 2 kDa). In contrast, for low PaMS molecular weights (of the order of 1 kDa) phase separation and significant TIPS crystallization was only obtained after subsequent annealing at T > T g .…”

Section: Introductionmentioning

confidence: 99%

Surface‐Directed Spinodal Decomposition of Solvent‐Quenched Organic Transistor Blends

Michels

2010

ChemPhysChem

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This paper describes the first example of the application of a combination of the Flory-Huggins and Cahn-Hilliard theories to model and simulate microstructure evolution in solution-processed functional blend layers of organic semiconductors, as used in organic electronics devices. Specifically, the work considers phase separation of the active blend components of organic transistors based on triisopropylsilylpentacene (TIPS-pentacene) and poly(α-methylstyrene) (PαMS). By calculation and estimation of relevant physical parameters, it is shown that the vertically phase-separated structure observed in as-cast blend layers containing PαMS of a sufficiently high molecular weight (of the order of 10(2) kDa) evolves via surface-directed spinodal decomposition. The surface-directed effect can already be triggered by small differences in substrate- and/or air-interface interaction energies of the separating phases. During phase separation, which commences at the interfaces, bulk features of the TIPS-enriched phase formed by thermal noise collapse to give the experimentally observed trilayer structure of TIPS-PαMS-TIPS. The reported near absence of solution-state phase separation of as-cast blend layers containing a low molecular weight PαMS (of the order of 1 kDa) is also reproduced.

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Organic Thin-Film Transistors with Phase Separation of Polymer-Blend Small-Molecule Semiconductors: Dependence on Molecular Weight and Types of Polymer

Cited by 45 publications

References 18 publications

High‐Mobility, Solution‐Processed Organic Field‐Effect Transistors from C8‐BTBT:Polystyrene Blends

High‐Mobility, Solution‐Processed Organic Field‐Effect Transistors from C8‐BTBT:Polystyrene Blends

Effective Use of Electrically Insulating Units in Organic Semiconductor Thin Films for High‐Performance Organic Transistors

Surface‐Directed Spinodal Decomposition of Solvent‐Quenched Organic Transistor Blends

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