Control of Polymorphism and Morphology in Solution Sheared Organic Field‐Effect Transistors

Low‐voltage organic field‐effect transistors (OFETs) are of great interest for organic electronics applications that require low power consumption such as wearable electronics, biomedical applications, or mobile electronics. In this work, an approach leading to transistors fabricated from solution with high charge carrier mobilities operating at voltages < 1 V is presented. By blending the small‐molecule semiconductor 6,13‐bis(triisopropylsilyl‐ethynyl)pentacene (TIPS‐pentacene) with polystyrene it is possible to achieve good film coverage and uniformity as well as ultrathin semiconductor films. This reduction in thickness relative to neat films results in a high fraction of the high‐mobility polymorph of TIPS‐pentacene and excellent film morphologies with continuous highly crystalline domains. OFETs using SiO2 as the dielectric with average hole mobilities as high as 8.3 cm2 V−1 s−1 and maximum mobilities of up to 12.3 cm2 V−1 s−1 which favorably compares with the previous record for TIPS‐pentacene, especially when considering the simplicity of the approach, are demonstrated. By depositing the optimized semiconductor blends on solution‐based polymer dielectric layers of polyvinylphenol, cross‐linked with 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride, a record‐high mobility of 4.2 cm2 V−1 s−1 for solution‐processed, ultralow‐voltage OFET devices (operating at <1 V) is obtained.

Section: Film Characterizationsupporting

confidence: 84%

Section: Film Characterizationsupporting

confidence: 84%

Solution Coating of Small Molecule/Polymer Blends Enabling Ultralow Voltage and High‐Mobility Organic Transistors

Rocha

Haase

Zheng

et al. 2018

“…[36] A different trend is reported for TIPS-pentacene blended with poly(α-methyl styrene) (PαMS), where the highest mobility values are obtained when the blend contained a higher fraction of the small molecule semiconductor. Indeed, large differences in terms of device characteristics have been reported for blends of dibenzotetrathiafulvalene (DB-TTF) mixed to various ratios with PS with the best performance being achieved for majority polymer blends.…”

Section: Optimization Of C8-btbt:polystyrene Blendmentioning

confidence: 96%

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

Haase

Rocha

Hauenstein

et al. 2018

102

101

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...

“…Further, by tuning the deposition parameters, such as temperature, speed or solution, it is possible to modulate the thin-film morphology. [28] This method has proven to be useful to deposit uniform and reproducible crystalline semiconducting thin-films giving high-performance devices on inorganic Si/SiOx substrates [29] as well as on flexible plastic ones [30], in particular when the semiconductor was blended with insulating polymers.…”

Section: Introductionmentioning

confidence: 99%

Morphology Influence on the Mechanical Stress Response in Bendable Organic Field‐Effect Transistors with Solution‐Processed Semiconductors

Lai

Temiño

Cramer

et al. 2017

Self Cite

The results not only demonstrate that the response to bending is reliant on the morphological properties of the films, but also that it can be tuned according to the bar-shearing direction. The employment of the proposed approach for the development of devices with different extent of response to mechanical deformation, from bending sensors to strain-insensitive devices for applications needing electrical stability upon deformation, can be thus foreseen.