A new type of nitrogen dioxide (NO2) gas sensor based on copper phthalocyanine (CuPc) thin film transistors (TFTs) with a simple, low‐cost UV–ozone (UVO)‐treated polymeric gate dielectric is reported ...here. The NO2 sensitivity of these TFTs with the dielectric surface UVO treatment is ≈400× greater for NO2 = 30 ppm than for those without UVO treatment. Importantly, the sensitivity is ≈50× greater for NO2 = 1 ppm with the UVO‐treated TFTs, and a limit of detection of ≈400 ppb is achieved with this sensing platform. The morphology, microstructure, and chemical composition of the gate dielectric and CuPc films are analyzed by atomic force microscopy, grazing incident X‐ray diffraction, X‐ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy, revealing that the enhanced sensing performance originates from UVO‐derived hydroxylated species on the dielectric surface and not from chemical reactions between NO2 and the dielectric/semiconductor components. This work demonstrates that dielectric/semiconductor interface engineering is essential for readily manufacturable high‐performance TFT‐based gas sensors.
Highly sensitive nitrogen dioxide gas sensors based on organic thin‐film transistors (OTFTs) having a low‐cost UV–ozone‐treated polymeric gate dielectric are fabricated. The enhanced sensing performance originates from UV–ozone‐induced hydroxylated species on the dielectric surface. This work demonstrates that simple dielectric–semiconductor interface engineering can be utilized to realize OTFT‐based gas sensors with excellent sensitivity and selectivity.
Hardware implementation of artificial synapse/neuron by electronic/ionic hybrid devices is of great interest for brain‐inspired neuromorphic systems. At the same time, printed electronics have ...received considerable interest in recent years. Here, printed dual‐gate carbon‐nanotube thin‐film transistors with very high saturation field‐effect mobility (≈269 cm2 V−1 s–1) are proposed for artificial synapse application. Some important synaptic behaviors including paired‐pulse facilitation (PPF), and signal filtering characteristics are successfully emulated in such printed artificial synapses. The PPF index can be modulated by spike width and spike interval of presynaptic impulse voltages. The results present a printable approach to fabricate artificial synaptic devices for neuromorphic systems.
Printed dual‐gate carbon‐nanotube thin‐film transistors with very high saturation field‐effect mobility are proposed for artificial synapse application. Important synaptic behaviors including paired‐pulse facilitation and signal filtering characteristics are successfully emulated. The PPF index can be modulated by spike interval and spike width of presynaptic voltages. This work presents a printable approach to fabricate synaptic devices for neuromorphic system applications.
Noncovalent conformational locks are broadly employed to construct highly planar π‐conjugated semiconductors exhibiting substantial charge transport characteristics. However, current chalcogen‐based ...conformational lock strategies for organic semiconductors are limited to S···X (X = O, N, halide) weak interactions. An easily accessible (minimal synthetic steps) and structurally planar selenophene‐based building block, 1,2‐diethoxy‐1,2‐bisselenylvinylene (DESVS), with novel Se···O noncovalent conformational locks is designed and synthesized. DESVS unique properties are supported by density functional theory computed electronic structures, single crystal structures, and experimental lattice cohesion metrics. Based on this building block, a new class of stable, structurally planar, and solution‐processable conjugated polymers are synthesized and implemented in organic thin‐film transistors (TFT) and organic photovoltaic (OPV) cells. DESVS‐based polymers exhibit carrier mobilities in air as high as 1.49 cm2 V−1 s−1 (p‐type) and 0.65 cm2 V−1 s−1 (n‐type) in TFTs, and power conversion efficiency >5% in OPV cells.
Noncovalent “Se···O” conformational locks for high‐performance conjugated polymers: an easily accessible and structurally planar selenophene‐based building block with novel Se···O noncovalent conformational locks is designed and synthesized, which affords polymer thin‐film transistors with charge‐carrier mobilities in air as high as 1.49 cm2 V−1 s−1 (p‐type) and 0.65 cm2 V−1 s−1 (n‐type), and organic photovoltaic cells with power conversion efficiency >5%.
Flexible transparent display is a promising candidate to visually communicate with each other in the future Internet of Things era. The flexible oxide thin‐film transistors (TFTs) have attracted ...attention as a component for transparent display by its high performance and high transparency. The critical issue of flexible oxide TFTs for practical display applications, however, is the realization on transparent and flexible substrate without any damage and characteristic degradation. Here, the ultrathin, flexible, and transparent oxide TFTs for skin‐like displays are demonstrated on an ultrathin flexible substrate using an inorganic‐based laser liftoff process. In this way, skin‐like ultrathin oxide TFTs are conformally attached onto various fabrics and human skin surface without any structural damage. Ultrathin flexible transparent oxide TFTs show high optical transparency of 83% and mobility of 40 cm2 V−1 s−1. The skin‐like oxide TFTs show reliable performance under the electrical/optical stress tests and mechanical bending tests due to advanced device materials and systematic mechanical designs. Moreover, skin‐like oxide logic inverter circuits composed of n‐channel metal oxide semiconductor TFTs on ultrathin, transparent polyethylene terephthalate film have been realized.
Ultrathin, flexible, and transparent oxide thin‐film transistors for skin‐like displays are transferred to an ultrathin flexible substrate using an inorganic based laser liftoff process. The transferred transistor arrays with high mobility of ≈40 cm2 V−1 s−1 adhere to both fabric and human skin and operate stably without significant degradation of their characteristics. Finally, skin‐like oxide logic inverters are successfully manipulated to verify the dynamic responses on an ultrathin plastic substrate.
Here, a simple, nontoxic, and inexpensive “water‐inducement” technique for the fabrication of oxide thin films at low annealing temperatures is reported. For water‐induced (WI) precursor solution, ...the solvent is composed of water without additional organic additives and catalysts. The thermogravimetric analysis indicates that the annealing temperature can be lowered by prolonging the annealing time. A systematic study is carried out to reveal the annealing condition dependence on the performance of the thin‐film transistors (TFTs). The WI indium‐zinc oxide (IZO) TFT integrated on SiO2 dielectric, annealed at 300 °C for 2 h, exhibits a saturation mobility of 3.35 cm2 V−1 s−1 and an on‐to‐off current ratio of ≈108. Interestingly, through prolonging the annealing time to 4 h, the electrical parameters of IZO TFTs annealed at 230 °C are comparable with the TFTs annealed at 300 °C. Finally, fully WI IZO TFT based on YOx dielectric is integrated and investigated. This TFT device can be regarded as “green electronics” in a true sense, because no organic‐related additives are used during the whole device fabrication process. The as‐fabricated IZO/YOx TFT exhibits excellent electron transport characteristics with low operating voltage (≈1.5 V), small subthreshold swing voltage of 65 mV dec−1 and the mobility in excess of 25 cm2 V−1 s−1.
A water‐induced metal‐oxide precursor route is used to fabricate low‐temperature thin‐film transistors (TFTs). For water‐induced TFTs, the annealing temperature can be lowered by prolonging the annealing time. Fully water‐induced InZnO/YOx TFTs exhibit excellent performance with operating voltage of 1.5 V and mobility of 25 cm2 V−1 s−1.
Following the unprecedented rise in photovoltaic power conversion efficiencies during the past five years, metal‐halide perovskites (MHPs) have emerged as a new and highly promising class of ...solar‐energy materials. Their extraordinary electrical and optical properties combined with the abundance of the raw materials, the simplicity of synthetic routes, and processing versatility make MHPs ideal for cost‐efficient, large‐volume manufacturing of a plethora of optoelectronic devices that span far beyond photovoltaics. Herein looks beyond current applications in the field of energy, to the area of large‐area electronics using MHPs as the semiconductor material. A comprehensive overview of the relevant fundamental material properties of MHPs, including crystal structure, electronic states, and charge transport, is provided first. Thereafter, recent demonstrations of MHP‐based thin‐film transistors and their application in logic circuits, as well as bi‐functional devices such as light‐sensing and light‐emitting transistors, are discussed. Finally, the challenges and opportunities in the area of MHPs‐based electronics, with particular emphasis on manufacturing, stability, and health and environmental concerns, are highlighted.
Their extraordinary electrical and optical properties combined with the abundance of their raw materials, have driven metal‐halide perovskites (MHPs) to the forefront of functional electronic materials research, with envisioned applications spanning across several technology sectors. The recent advances in the use of MHPs in the area of transistors and transistor‐related applications are summarized.
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Solution processing, including printing technology, is a promising technique for oxide thin‐film transistor (TFTs) fabrication because it tends to be a cost‐effective process with high composition ...controllability and high throughput. However, solution‐processed oxide TFTs are limited by low‐performance and stability issues, which require high‐temperature annealing. This high thermal budget in the fabrication process inhibits oxide TFTs from being applied to flexible electronics. There have been numerous attempts to promote the desired electrical characteristics of solution‐processed oxide TFTs at lower fabrication temperatures. Recent techniques for achieving low‐temperature (<350 °C) solution‐processed and printed oxide TFTs, in terms of the materials, processes, and structural engineering methods currently in use are reviewed. Moreover, the core techniques for both n‐type and p‐type oxide‐based channel layers, gate dielectric layers, and electrode layers in oxide TFTs are addressed. Finally, various multifunctional and emerging applications based on low‐temperature solution‐processed oxide TFTs are introduced and future outlooks for this highly promising research are suggested.
Solution‐processed oxide thin‐film transistors (TFTs) conventionally require high‐temperature annealing, which may hinder their potential application in flexible devices. To solve this problem, this review provides the latest approaches for achieving low‐temperature (<350 °C) solution‐processed and printed oxide TFTs in terms of the materials, processes, and structural engineering methods, and perspectives for emerging flexible applications.
Solution‐processed copper(I) thiocyanate (CuSCN) typically exhibits low crystallinity with short‐range order; the defects result in a high density of trap states that limit the device's performance. ...Despite the extensive electronic applications of CuSCN, its defect properties are not understood in detail. Through X‐ray absorption spectroscopy, pristine CuSCN prepared from the standard diethyl sulfide‐based recipe is found to contain under‐coordinated Cu atoms, pointing to the presence of SCN− vacancies. A defect passivation strategy is introduced by adding solid I2 to the processing solution. At small concentrations, the iodine is found to exist as I− which can substitute for the missing SCN− ligand, effectively healing the defective sites and restoring the coordination around Cu. Computational study results also verify this point. Applying I2‐doped CuSCN as a p‐channel in thin‐film transistors shows that the hole mobility increases by more than five times at the optimal doping concentration of 0.5 mol.%. Importantly, the on/off current ratio and the subthreshold characteristics also improve as the I2 doping method leads to the defect‐healing effect while avoiding the creation of detrimental impurity states. An analysis of the capacitance‐voltage characteristics corroborates that the trap state density is reduced upon I2 addition.
X‐ray absorption spectroscopy reveals the under‐coordination environment around Cu+ centers in copper(I) thiocyanate (CuSCN), pointing to the presence of SCN− vacancies. Iodine doping is then introduced as a defect passivation strategy. I− can fill in the vacancy sites and effectively heal the defect states. Transistor application shows that the hole transport is significantly improved.
Directional solution coating by the Chinese brush provides a facile approach to fabricate highly oriented polymer thin films by finely controlling the wetting and dewetting processes under ...directional stress. The biggest advantage of the Chinese brush over the normal western brush is the freshly emergent hairs used, whose unique tapered structure renders a dynamic balance of the liquid within the brush by multiple forces when interacting with the liquid. Consequently, the liquid is steadily held within the brush without any unexpected leakage, making the liquid transfer proceed in a well‐controllable manner. It is demonstrated that the Chinese brush coating enables the crystallization of the polymer and the self‐assembly of conjugated backbones to proceed in a quasi‐steady state via a certain direction, which is attributed to the controllable receding of the three‐phase contact line during the dewetting process by the multiple parallel freshly emergent hairs. The as‐prepared polymer thin films exhibit over six times higher charge‐carrier mobility compared to the spin‐coated films, which therefore provides a general approach for high‐performance organic thin‐film transistors.
Directional solution coating by the Chinese brush provides a facile approach to fabricate highly oriented polymer thin films by finely controlling the wetting and dewetting processes under the direction stress, and the as‐prepared polymer thin films exhibit over six times higher charge‐carrier mobility compared to the equivalent spin‐coated films. Therefore, a general approach is provided for high‐performance organic thin‐film transistors.
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