Combining Aqueous Solution Processing and Printing for Fabrication of Flexible and Sustainable Tin Dioxide Ion‐Gated Transistors

Abstract

to obtain high-performance crystalline films, these oxides are processed at high temperatures (>350 °C), which are not compatible with flexible electronics. [1a,4] Additionally, the brittle nature of crystalline metal oxides limits their applications in flexible electronics. [4a] SnO 2 is a promising metal oxide for electronics applications due to its abundance, electrical conductivity, and optical transparency, which make it interesting for thin-film transistors, gas sensors, and transparent electrodes. [5] SnO 2 films can be processed via several techniques, such as sputtering, evaporation, pulsed laser deposition, and various solution processing methods. [6] Among these, a single step, low temperature process in aqueous solution would meet the requirements for sustainable and cost-effective flexible electronics. [1a,7] Field effect transistors (FETs) based on SnO 2 films, deposited using physical and chemical methods, exhibited a high field-effect mobility (>100 cm 2 V −1 s −1 ) at an operating voltage below 5 V. [8] Sb-doped SnO 2 showed a mobility of ≈550 cm 2 V −1 s −1 , when the material was deposited by vaporliquid-solid growth, [8d] and ≈158 cm 2 V −1 s −1 , when radio frequency magnetron sputtering was used. [8e] The high mobility of SnO 2 is due to the large overlap of the spherical Sn 5s orbitals in the SnO 2 electronic structure. [8a,9] The charge carrier density (electrons) in SnO 2 can be tuned by creating oxygen vacancies (i.e. deviation of SnO 2 stoichiometry), by unintentional (i.e. impurities during the growth of SnO 2 ) and intentional doping (i.e. metallic dopants such as Ta, Sb on SnO 2 ). [10] By tuning the charge carrier density, the transistor mode of operation can be switched from enhancement to depletion mode. Ohta et al., fabricated FETs based SnO 2 films grown by pulsed laser deposition (400 °C) and investigated the electron transport properties at different thicknesses. The film thickness was found to affect the crystallinity and charge carrier concentration, as well as the performance and operation mode of the transistors. [11] Jang et al., deposited SnO 2 films by UV-ozone assisted solgel (300 °C), which were used as active layers in FETs on flexible polyimide substrates. [12] Lim et al., fabricated flexible SnO 2 FETs on polyethersulfone substrate by direct current reactive magnetron sputtering at room temperature, which did not show Ion-gated transistors (IGTs) are extensively used in chemo-and bio-sensors as well as intelligent sensors, that is, with neuromorphic computing functionality, exploiting their ion to electron convertibility. Metal oxides are attractive as active channel materials in IGTs because of their low-temperature solution processability, ambient stability, and tunable optoelectronic properties. SnO 2 is a low-cost material widely used in thin-film transistors, gas sensors, and transparent electrodes. In this work, films of crystalline SnO 2 nanorods are prepared on flexible substrates using a controlled aqueous growth technique, at 95 °C. The top ...

Electrical and mechanical stability of flexible, organic electrolyte-gated transistors based on iongel and hydrogels

“…Au source and drain electrodes (channel width/length ( W / L ) = 4000 μm/10 μm) were patterned on Si/SiO 2 and PET substrates by photolithography and lift-off, as reported elsewhere. 6 The DPP-DTT solution (2.5 mg mL −1 ) in CHCl 3 was prepared and stirred overnight at room temperature. DPP-DTT films (thickness 65 ± 5 nm) were obtained by spin coating the prepatterned substrates (1000 rpm, 1 min), followed by heating at 100 °C for 20 min on a hotplate.…”

“…We chose Au as the bottom electrode and conductive carbon paper coated with activated carbon as the top electrode. This material, which has a high surface area, high capacitance, and wide electrochemical stability window, is commonly used as a gate electrode in EGTs, 4,7,29,30 and can be directly laminated on the gel electrolyte without the need of thermal evaporation. The Nyquist plots (imaginary component, Z i , versus the real component of impedance, Z r ) show tilted straight lines that are related to the typical behavior of electrolytes in contact with the electrodes.…”

“…3,4 A variety of materials are used for EGTs gating media, including aqueous saline solutions, ionic liquids, polymer electrolytes, polyelectrolytes, iongels and hydrogels. [5][6][7] These materials differ in their physical state (e.g., solid, gel, or liquid), electrochemical stability, ionic conductivity, and mechanical properties. Aqueous electrolytes, which are used in most bioelectronic applications, have the disadvantages of limited electrochemical stability (B1.2 V) and rapid evaporation, leading to device degradation.…”

“…3,4 A variety of materials are used for EGTs gating media, including aqueous saline solutions, ionic liquids, polymer electrolytes, polyelectrolytes, iongels and hydrogels. 5–7 These materials differ in their physical state ( e.g. , solid, gel, or liquid), electrochemical stability, ionic conductivity, and mechanical properties.…”

Improvement in Optoelectronic Properties of Bismuth Sulphide Thin Films by Chromium Incorporation at the Orthorhombic Crystal Lattice for Photovoltaic Applications

“…The capture and transmission of charge carriers inside semiconductor networks have always been fundamental problems that have to be addressed in order to ensure efficient charge separation. To increase the overall effectiveness of light energy conversion, several strategies to enhance photoinduced charge separation and electron transfer processes have been put forward [ 11 , 12 , 13 ]. Additionally, it is a popular issue right now to concentrate future research efforts on the creation and use of unique nanostructures for the advancement of next-generation solar cells [ 14 , 15 , 16 ].…”