P-type Cu(2)O/SnO bilayer thin film transistors processed at low temperatures

Enhanced photoactive performance of three-layer structured Ag/Cu2O/TiO2 composites with tunable crystal microstructures

Ag particle-decorated Cu2O/TiO2 composite films effectively photodegrade MO solution under irradiation.

Cuprous Oxide Nanoparticles: Synthesis, Characterization, and Their Application for Enhancing the Humidity-Sensing Properties of Poly(dioctylfluorene)

In this paper, we report on the synthesis—via the wet chemical precipitation route method—and thin film characteristics of inorganic semiconductor, cuprous oxide (Cu₂O) nanoparticles, for their potential application in enhancing the humidity-sensing properties of semiconducting polymer poly(9,9-dioctylfluorene) (F8). For morphological analysis of the synthesized Cu₂O nanoparticles, transmission electron microscope (TEM) and scanning electron microscope (SEM) micrographs are studied to investigate the texture, distribution, shape, and sizes of Cu₂O crystallites. The TEM image of the Cu₂O nanoparticles exhibits somewhat non-uniform distribution with almost uniform shape and size having an average particle size of ≈24 ± 2 nm. Fourier transformed infrared (FTIR) and X-ray diffraction (XRD) spectra are studied to validate the formation of Cu₂O nanoparticles. Additionally, atomic force microscopy (AFM) is performed to analyze the surface morphology of polymer-inorganic (F8-Cu₂O) nanocomposites thin film to see the grain sizes, mosaics, and average surface roughness. In order to study the enhancement in sensing properties of F8, a hybrid organic–inorganic (F8-Cu₂O) surface-type humidity sensor Ag/F8-Cu₂O/Ag is fabricated by employing F8 polymer as an active matrix layer and Cu₂O nanoparticles as a dopant. The Ag/F8-Cu₂O/Ag device is prepared by spin coating a 10:1 wt% solution of F8-Cu₂O nanocomposite on pre-patterned silver (Ag) electrodes on glass. The inter-electrode gap (≈5 μm) between Ag is developed by photolithography. To study humidity sensing, the Ag/F8-Cu₂O/Ag device is characterized by measuring its capacitance (C) as a function of relative humidity (%RH) at two different frequencies (120 Hz and 1 kHz). The device exhibits a broad humidity sensing range (27–86%RH) with shorter response time and recovery time, i.e., 9 s and 8 s, respectively. The present results show significant enhancement in the humidity-sensing properties as compared to our previously reported results of Ag/F8/Ag sensor wherein the humidity sensing range was 45–78%RH with 15 s and 7 s response and recovery times, respectively. The improvement in the humidity-sensing properties is attributed to the potential use of Cu₂O nanoparticles, which change the hydrophobicity, surface to volume ratio of Cu₂O nanoparticles, as well as modification in electron polarizability and polarity of the F8 matrix layer.

Recent Advances in Hole-Transporting Layers for Organic Solar Cells

Global energy demand is increasing; thus, emerging renewable energy sources, such as organic solar cells (OSCs), are fundamental to mitigate the negative effects of fuel consumption. Within OSC’s advancements, the development of efficient and stable interface materials is essential to achieve high performance, long-term stability, low costs, and broader applicability. Inorganic and nanocarbon-based materials show a suitable work function, tunable optical/electronic properties, stability to the presence of moisture, and facile solution processing, while organic conducting polymers and small molecules have some advantages such as fast and low-cost production, solution process, low energy payback time, light weight, and less adverse environmental impact, making them attractive as hole transporting layers (HTLs) for OSCs. This review looked at the recent progress in metal oxides, metal sulfides, nanocarbon materials, conducting polymers, and small organic molecules as HTLs in OSCs over the past five years. The endeavors in research and technology have optimized the preparation and deposition methods of HTLs. Strategies of doping, composite/hybrid formation, and modifications have also tuned the optical/electrical properties of these materials as HTLs to obtain efficient and stable OSCs. We highlighted the impact of structure, composition, and processing conditions of inorganic and organic materials as HTLs in conventional and inverted OSCs.

Atomically Thin Tin Monoxide-Based p-Channel Thin-Film Transistor and a Low-Power Complementary Inverter

Atomically thin oxide semiconductors are significantly expected for next-generation cost-effective, energy-efficient electronics. A high-performance p-channel oxide thin-film transistor (TFT) was developed using an atomically thin p-type tin monoxide, SnO channel with a thickness of ∼1 nm, which was grown by a vacuum-free, solvent-free, metal-liquid printing process at low temperatures, as low as 250 °C in an ambient atmosphere. By performing oxygen-vacancy defect termination for the bulk-channel and back-channel surface of the ultrathin SnO channel, the presented p-channel SnO TFT exhibited good device performances with a reasonable TFT mobility of ∼0.47 cm2 V-1 s-1, a high on/off current ratio of ∼106, low off current of <10-12 A, and a subthreshold swing of ∼2.5 V decade-1, which was improved compared with the conventional p-channel SnO TFTs. We also fabricated metal-liquid printing-based n-channel oxide TFTs such as n-channel SnO2 and In2O3-TFTs and developed ultrathin-channel oxide-TFT-based low-power complementary inverter circuits with the developed p-channel SnO TFTs. The full swing of voltage-transfer characteristics with a voltage gain of ∼10 and a power dissipation of <4 nW for p-SnO/n-SnO2 and ∼120 and <2 nW for p-SnO/n-In2O3-CMOS inverters were successfully demonstrated.

High Performance of Solution-Processed Amorphous p-Channel Copper-Tin-Sulfur-Gallium Oxide Thin-Film Transistors by UV/O3 Photocuring

The development of p-type metal-oxide semiconductors (MOSs) is of increasing interest for applications in next-generation optoelectronic devices, display backplane, and low-power-consumption complementary MOS circuits. Here, we report the high performance of solution-processed, p-channel copper-tin-sulfide-gallium oxide (CTSGO) thin-film transistors (TFTs) using UV/O₃ exposure. Hall effect measurement confirmed the p-type conduction of CTSGO with Hall mobility of 6.02 ± 0.50 cm² V^-1 s^-1. The p-channel CTSGO TFT using UV/O₃ treatment exhibited the field-effect mobility (μ_FE) of 1.75 ± 0.15 cm² V^-1 s^-1 and an on/off current ratio (I_ON/I_OFF) of ∼10⁴ at a low operating voltage of -5 V. The significant enhancement in the device performance is due to the good p-type CTSGO material, smooth surface morphology, and fewer interfacial traps between the semiconductor and the Al₂O₃ gate insulator. Therefore, the p-channel CTSGO TFT can be applied for CMOS MOS TFT circuits for next-generation display.

Lanthanum Doping Enabling High Drain Current Modulation in a p-Type Tin Monoxide Thin-Film Transistor

Effects of lanthanum (La) loading on the structural, optical, and electrical properties of tin monoxide (SnO) films were examined as a p-type semiconducting layer. La loading up to 1.9 atom % caused the texturing of the tetragonal SnO phase with a preferential orientation of (101), which was accompanied by the smoother surface morphology. Simultaneously, the incorporated La cation suppressed the formation of n-type SnO₂ in the La-doped SnO film and widened its optical band gap. These variations allowed the 1.9 atom % La-loaded SnO film to have a high hole mobility and carrier density, compared with the La-free control SnO film. The superior semiconducting property was reflected in the p-type thin-film transistor (TFT). The control SnO TFTs exhibited the field-effect mobility (μ_SAT) and I_ON/OFF ratio of 0.29 cm² V^-1 s^-1 and 5.4 × 10², respectively. Enhancement in the μ_SAT value and I_ON/OFF ratio was observed for the TFTs with the 1.9 atom % La-loaded SnO channel layer: they were improved to 1.2 cm² V^-1 s^-1 and 7.3 × 10³, respectively. The reason for this superior performance was discussed on the basis of smoother morphology, suppression of disproportionation conversion from Sn²⁺ to Sn + Sn⁴⁺, and reduced gap-state density.

Polyol Reduction: A Low-Temperature Eco-Friendly Solution Process for p-Channel Copper Oxide-Based Transistors and Inverter Circuits

An optimized polyol reduction method was proposed for p-type Cu_xO deposition using a spin-coating method at low temperatures. The film characterizations and the electrical properties of integrated thin-film transistors (TFTs) were investigated as a function of annealing temperature and polyol type. The Cu_xO TFTs derived from propylene glycol showed the optimal performance with an average field-effect hole mobility of 0.15 cm² V^-1 s^-1, an on/off current ratio of ∼10⁴, and a threshold voltage of -7 V at a low temperature of 220 °C. Considering few investigations on the operational/air stability of solution-processed p-type oxide TFTs, we carried out systematical studies and revealed different roles of O₂ and H₂O on the device performance. The low activation energy (0.16 eV) for hole transport and high voltage gain (37) of the composed complementary inverter highlight great potential for the construction of all oxide-based transparent flexible electronics and circuits.

Room-Temperature Solution-Synthesized p-Type Copper(I) Iodide Semiconductors for Transparent Thin-Film Transistors and Complementary Electronics

Here, room-temperature solution-processed inorganic p-type copper iodide (CuI) thin-film transistors (TFTs) are reported for the first time. The spin-coated 5 nm thick CuI film has average hole mobility (µFE ) of 0.44 cm2 V-1 s-1 and on/off current ratio of 5 × 102 . Furthermore, µFE increases to 1.93 cm2 V-1 s-1 and operating voltage significantly reduces from 60 to 5 V by using a high permittivity ZrO2 dielectric layer replacing traditional SiO2 . Transparent complementary inverters composed of p-type CuI and n-type indium gallium zinc oxide TFTs are demonstrated with clear inverting characteristics and voltage gain over 4. These outcomes provide effective approaches for solution-processed inorganic p-type semiconductor inks and related electronics.

Facile fabrication of electrolyte-gated single-crystalline cuprous oxide nanowire field-effect transistors

Oxide semiconductors are considered to be one of the forefront candidates for the new generation, high-performance electronics. However, one of the major limitations for oxide electronics is the scarcity of an equally good hole-conducting semiconductor, which can provide identical performance for the p-type metal oxide semiconductor field-effect transistors as compared to their electron conducting counterparts. In this quest, here we present a bulk synthesis method for single crystalline cuprous oxide (Cu2O) nanowires, their chemical and morphological characterization and suitability as active channel material in electrolyte-gated, low-power, field-effect transistors (FETs) for portable and flexible logic circuits. The bulk synthesis method used in the present study includes two steps: namely hydrothermal synthesis of the nanowires and the removal of the surface organic contaminants. The surface treated nanowires are then dispersed on a receiver substrate where the passive electrodes are structured, followed by printing of a composite solid polymer electrolyte (CSPE), chosen as the gate insulator. The characteristic electrical properties of individual nanowire FETs are found to be quite interesting including accumulation-mode operation and field-effect mobility of 0.15 cm(2) V(-1) s(-1).

Recent Developments in p-Type Oxide Semiconductor Materials and Devices

The development of transparent p-type oxide semiconductors with good performance may be a true enabler for a variety of applications where transparency, power efficiency, and greater circuit complexity are needed. Such applications include transparent electronics, displays, sensors, photovoltaics, memristors, and electrochromics. Hence, here, recent developments in materials and devices based on p-type oxide semiconductors are reviewed, including ternary Cu-bearing oxides, binary copper oxides, tin monoxide, spinel oxides, and nickel oxides. The crystal and electronic structures of these materials are discussed, along with approaches to enhance valence-band dispersion to reduce effective mass and increase mobility. Strategies to reduce interfacial defects, off-state current, and material instability are suggested. Furthermore, it is shown that promising progress has been made in the performance of various types of devices based on p-type oxides. Several innovative approaches exist to fabricate transparent complementary metal oxide semiconductor (CMOS) devices, including novel device fabrication schemes and utilization of surface chemistry effects, resulting in good inverter gains. However, despite recent developments, p-type oxides still lag in performance behind their n-type counterparts, which have entered volume production in the display market. Recent successes along with the hurdles that stand in the way of commercial success of p-type oxide semiconductors are presented.

Exploring Two-Dimensional Transport Phenomena in Metal Oxide Heterointerfaces for Next-Generation, High-Performance, Thin-Film Transistor Technologies

In the last decade, metal oxides have emerged as a fascinating class of electronic material, exhibiting a wide range of unique and technologically relevant characteristics. For example, thin-film transistors formed from amorphous or polycrystalline metal oxide semiconductors offer the promise of low-cost, large-area, and flexible electronics, exhibiting performances comparable to or in excess of incumbent silicon-based technologies. Atomically flat interfaces between otherwise insulating or semiconducting complex oxides, are also found to be highly conducting, displaying 2-dimensional (2D) charge transport properties, strong correlations, and even superconductivity. Field-effect devices employing such carefully engineered interfaces are hoped to one day compete with traditional group IV or III-V semiconductors for use in the next-generation of high-performance electronics. In this Concept article we provide an overview of the different metal oxide transistor technologies and potential future research directions. In particular, we look at the recent reports of multilayer oxide thin-film transistors and the possibility of 2D electron transport in these disordered/polycrystalline systems and discuss the potential of the technology for applications in large-area electronics.

Recent advances in hybrid Cu2O-based heterogeneous nanostructures

Hybrid Cu2O-based heterogeneous nanostructures possess novel synergistic properties that arise from the integrated interaction between the disparate components, thereby showing promising potential for various important applications including solar cells, carbon monoxide oxidation, photocatalysts, field emission, sensors, templates and so on. With the rapid progress in nanomaterials science and nanotechnology, hybrid Cu2O-based heterogeneous nanostructures with well-controlled compositions, shapes and sizes have been rationally designed and synthesized. This review attempts to summarize the important advances in the development of different types of hybrid Cu2O-based heterogeneous nanostructures, such as hybrid Cu2O-metal nanostructures, hybrid Cu2O-metal oxide nanostructures and hybrid Cu2O-carbon nanostructures. The correlations between the improved performances and interfacial structures of the hybrid Cu2O-based heterogeneous nanostructures are discussed based on some important and representative examples. Several key scientific issues and perspective research directions in this field are also given.

Low temperature processed complementary metal oxide semiconductor (CMOS) device by oxidation effect from capping layer

In this report, both p- and n-type tin oxide thin-film transistors (TFTs) were simultaneously achieved using single-step deposition of the tin oxide channel layer. The tuning of charge carrier polarity in the tin oxide channel is achieved by selectively depositing a copper oxide capping layer on top of tin oxide, which serves as an oxygen source, providing additional oxygen to form an n-type tin dioxide phase. The oxidation process can be realized by annealing at temperature as low as 190°C in air, which is significantly lower than the temperature generally required to form tin dioxide. Based on this approach, CMOS inverters based entirely on tin oxide TFTs were fabricated. Our method provides a solution to lower the process temperature for tin dioxide phase, which facilitates the application of this transparent oxide semiconductor in emerging electronic devices field.