COMMUNICATION © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com (1 of 8) 1605685 Ultrahigh Mobility in Solution-Processed Solid-State Electrolyte-Gated Transistors Benjamin Nketia-Yawson, Seok-Ju Kang, Grace Dansoa Tabi, Andrea Perinot, Mario Caironi, Antonio Facchetti, and Yong-Young Noh* B. Nketia-Yawson, Dr. S.-J. Kang, G. D. Tabi, Prof. Y.-Y. Noh Department of Energy and Materials Engineering Dongguk University 30 Pildong-ro, 1-gil, Jung-gu Seoul 04620, Republic of Korea E-mail: yynoh@dongguk.edu A. Perinot, Dr. M. Caironi Center for Nano Science and Technology @PoliMi Istituto Italiano di Tecnologia Via Pascoli 70/3, Milano 20133, Italy A. Perinot Politecnico di Milano Dipartimento di Fisica P.za L. da Vinci 32, Milano 20133, Italy Dr. A. Facchetti Polyera Corporation 8045 Lamon Avenue, Skokie, IL 60077, USA DOI: 10.1002/adma.201605685 Solution-processed field-effect transistors (FETs), particularly those based on organic semiconductors, have been actively investigated to realize lightweight and flexible electronics manufactured with cost-effective mass production processes, such as high-throughput and large-area printing. [1] Significant progress has enabled organic FETs (OFETs) with charge-carrier mobilities (μ’s) exceeding 10 cm 2 V -1 s -1 via the development of novel semiconducting polymers, [2–4] optimization of the semiconducting film microstructure, [4] and the use of gate die- lectrics, leading to high-quality semiconductor–dielectric inter- faces. [5–8] However, the performance of OFETs still lags behind those of their large-area compatible inorganic counterparts, such as metal oxide semiconductors, thereby critically nar- rowing the set of potential applications. A further less explored opportunity for the improvement of μ in OFETs, though the potential was reported a long time ago, [9] derives from the con- trol of the charge-carrier density within the transistor channel. By increasing the charge-carrier density, more states are filled within the density of states when the gate bias is applied, pre- venting traps from hindering charge transport. [9–11] One typical example to this regard is molecular doping of the semicon- ductor layer, and a few reports have demonstrated substantial μ improvement for small additions of dopant. [12,13] However, this approach is limited in scope because high doping concentra- tions, which are desirable in the attempt to improve channel conductivity, can increase both the OFET off-current and even- tually decrease the mobility by disrupting the semiconducting film morphology. [13] An alternative approach to enhance charge-carrier density relies on the use of gating media characterized by very high specific capacitance such as high-k materials, [5,14,15] ultrathin layers, [15,16] and electrolytes. [17–24] All these approaches have con- siderable advantages and limitations. Among the latter mate- rials, ion-gel dielectrics have been widely investigated, as they exhibit very high specific capacitance values above 1 μF cm -2 for films that are thick and potentially printable using conventional methodologies. [17–23] In fact, the high capacitance is due to the formation, upon polarization of the gel, of a very thin electric double layer (EDL) at the electrolyte–semiconductor interface following ion migration within the electrolyte and subsequent accumulation of carriers in the semiconductor. [24] Typically, the aggregation of ions into clusters/micelles within ion liquids and the electrolyte slows down cations and anions migration and therefore increases the time required to achieve full gating of the semiconductor through the EDL. [25,26] Previous reports by Watanabe and co-workers revealed that about 30–50% of the total ions in the bulk ionic liquid, such as 1-ethyl-3-methylim- idazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]) (Figure 1a), contribute to ion conduction. [27–29] One key strategy to enhance the ion dispersion (Figure 1b), thus improving the migration of cations and anions and reducing the EDL forma- tion time in ion gels, is to blend them with another polymer dielectric in order to hamper the ion-aggregate formation. [26] Importantly this approach, which results in a solid rather than in a gel film, will also allow the direct deposition of a conductive top-gate electrode by any methods such as thermal evaporation and printing, thus enabling the fabrication of FETs with a more robust gate electrode/insulator interface contact compared with conventional side-gated or direct top-gated metal-stitched ion- gel transistors. [17–21,30,31] Here, we report a solid-state electrolyte gate insulators (SEGIs) medium formed by a controlled blend consisting of the high-k polymer poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) and the ion gel based on poly(vinylidene fluo- ride-co-hexafluoropropylene) (P(VDF-HFP)) with [EMIM][TFSI] (Figure 1a), achieving remarkable FET performance in top gate/ bottom contacts (TGBC) devices for an ample set of common conjugated polymers (Figure 1c). Our engineered SEGIs enable large charge-carrier mobilities owing to: i) the formation of a robust gate electrode and gate dielectric interface thanks to the solid-state nature of the dielectric film and ii) an enhanced charge-carrier density in the transistor channel thanks to the high-k polymer component and the facile movement of well-dis- persed ions in the gate dielectric layer, allowing high capacitance values of >4 μF cm -2 to be achieved. Furthermore, the broad potential of our SEGI approach is validated beyond OFETs by Adv. Mater. 2017, 1605685 www.advancedsciencenews.com www.advmat.de