Low-Temperature and Solution-Processable Zinc Oxide Transistors for Transparent Electronics

High-Performance Self-Powered Quantum Dot Infrared Photodetector with Azide Ion Solution Treated Electron Transport Layer

The demand for self-powered photodetectors (PDs) capable of NIR detection without external power is growing with the advancement of NIR technologies such as LIDAR and object recognition. Lead sulfide quantum dot-based photodetectors (PbS QPDs) excel in NIR detection; however, their self-powered operation is hindered by carrier traps induced by surface defects and unfavorable band alignment in the zinc oxide nanoparticle (ZnO NP) electron-transport layer (ETL). In this study, an effective azide-ion (N3 -) treatment is introduced on a ZnO NP ETL to reduce the number of traps and improve the band alignment in a PbS QPD. The ZnO NP ETL treated with azide ions exhibited notable improvements in carrier lifetime and mobility as well as an enhanced internal electric field within the thin-film heterojunction of the ZnO NPs and PbS QDs. The azide-ion-treated PbS QPD demonstrated a increase in short-circuit current density upon NIR illumination, marking a responsivity of 0.45 A W-1, specific detectivity of 4 × 1011 Jones at 950 nm, response time of 8.2 µs, and linear dynamic range of 112 dB.

Structural, Optical, and Magnetic Properties of Pure and Ni-Fe-Codoped Zinc Oxide Nanoparticles Synthesized by a Sol-Gel Autocombustion Method

Pure and Ni-Fe-codoped Zn1 - 2xNixFexO (x = 0.01, 0.02, 0.03, and 0.04) nanoparticles were effectively synthesized using a sol-gel autocombustion procedure. The structural, optical, morphological, and magnetic properties were determined by using X-ray diffraction (XRD), ultraviolet-visible (UV-vis), scanning electron microscopy, and vibrating sample magnetometer techniques. The XRD confirmed the purity of the hexagonal wurtzite crystal structure. XRD analysis further indicated that Fe and Ni successfully substituted the lattice site of Zn and generated a single-phase Zn1-2xNixFexO magnetic oxide. In addition, a significant morphological change was observed with an increase in the dopant concentration by using high-resolution scanning electron microscopy. The UV-vis spectroscopy analysis indicated the redshift in the optical band gap with increasing dopant concentration signifying a progressive decrease in the optical band gap. The vibrating sample magnetometer analysis revealed that the doped samples exhibited ferromagnetic properties at room temperature with an increase in the dopant concentration. Dopant concentration was confirmed by using energy-dispersive X-ray spectroscopy. The current results provide a vital method to improve the magnetic properties of ZnO nanoparticles, which may get significant attention from researchers in the field of magnetic semiconductors.

Solar-based photocatalytic ozonation employing novel S-scheme ZnO/Cu2O/CuO/carbon xerogel photocatalyst: effect of pH, salinity, turbidity, and temperature on salicylic acid degradation

This paper proposes the study of a solar-based photocatalytic ozonation process for the degradation of salicylic acid (SA) using a novel S-scheme ZnO/Cu2O/CuO/carbon xerogel photocatalyst. The incorporation of CuO and Cu2O aims to enhance charge mobility through the formation of p-n heterojunctions with ZnO, whereas the carbon xerogel (XC) was selected due to its eco-friendly nature, capacity to stabilize S-scheme heterojunctions as a solid-state electron mediator, and ability to function as a reducing agent under high temperatures. The characterization of the composites demonstrates that the presence of the XC during the calcination step led to the reduction of a fraction of the CuO into Cu2O, forming a ternary semiconductor heterojunction system. In terms of photocatalysis, the XC/ZnO-CuxO 5% composite achieved the best efficiency for salicylic acid degradation, mainly due to the stabilization of the S-scheme charge transfer pathway between the ZnO/CuO/Cu2O semiconductors by the XC. The total organic carbon (TOC) removal during heterogeneous photocatalysis was 80% for the solar-based process and 68% for the visible light process, after 300 min. The solar-based photocatalytic ozonation process was highly successful regarding the degradation of SA, achieving a 75% increase in the apparent reaction rate constant when compared to heterogeneous photocatalysis. Furthermore, a 78% TOC removal was achieved after 150 min, which is half the time required by the heterogeneous photocatalysis to obtain the same result. Temperature, salinity, and turbidity had major effects on the efficiency of the photocatalytic ozonation process; the system's pH did not cause any major performance variation, which holds relevance for industrial applications.

Kraft lignin-based carbon xerogel/zinc oxide composite for 4-chlorophenol solar-light photocatalytic degradation: effect of pH, salinity, and simultaneous Cr(VI) reduction

Considering the ever-increasing need for efficient wastewater treatment, this study focused on the development of new kraft lignin-based carbon xerogel/zinc oxide (XCL/ZnO w) photocatalysts. The inclusion of the carbon xerogel is expected to cause an improvement in charge transfer throughout the photoactivation process, consequently enhancing its overall photocatalytic efficiency. Characterization shows that the materials developed are composed of both zinc oxide and carbon xerogel. The addition of the lignin-based carbon xerogel caused a significant morphological modification to the composite materials, resulting in a greater specific surface area. Regarding the photocatalytic efficiency, the optimized composite (XCL/ZnO 1.0) displayed superior efficiency to the pure zinc oxide, especially when calcined at 700 °C, with an increase of 20% in the overall photodegradation capacity for the 4-chlorophenol (4CP) molecule. The XCL/ZnO 1.0 also displayed better performance than its tannin counterpart, previously reported in the literature, obtaining a 60% increase in the apparent reaction rate constant. The XCL/ZnO 1.0 also displayed better performance for the simultaneous hexavalent chrome (Cr (VI)) reduction/4CP oxidation reaction. Salinity and system pH had a significant influence on the efficiency of the 4CP photodegradation, as higher values of salinity and lower pHs caused a decrease in the overall efficiency of the process. At last, chronoamperometry and open-circuit potential tests confirmed the superiority of the XCL/ZnO 1.0 over the pure ZnO, highlighting the beneficial impact of the carbon xerogel on the charge transport dynamics of the composite.

Additive manufacturing of Zn with submicron resolution and its conversion into Zn/ZnO core-shell structures

Electrohydrodynamic redox 3D printing (EHD-RP) is an additive manufacturing (AM) technique with submicron resolution and multi-metal capabilities, offering the possibility to switch chemistry during deposition "on-the-fly". Despite the potential for synthesizing a large range of metals by electrochemical small-scale AM techniques, to date, only Cu and Ag have been reproducibly deposited by EHD-RP. Here, we extend the materials palette available to EHD-RP by using aqueous solvents instead of organic solvents, as used previously. We demonstrate deposition of Cu and Zn from sacrificial anodes immersed in acidic aqueous solvents. Mass spectrometry indicates that the choice of the solvent is important to the deposition of pure Zn. Additionally, we show that the deposited Zn structures, 250 nm in width, can be partially converted into semiconducting ZnO structures by oxidation at 325 °C in air.

Spin-Coating and Aerosol Spray Pyrolysis Processed Zn1-xMgxO Films for UV Detector Applications

A series of Zn_1-xMg_xO thin films with x ranging from 0 to 0.8 were prepared by spin coating and aerosol spray pyrolysis deposition on Si and quartz substrates. The morphology, composition, nano-crystalline structure, and optical and vibration properties of the prepared films were studied using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), and optical and Raman scattering spectroscopy. The optimum conditions of the thermal treatment of samples prepared by spin coating were determined from the point of view of film crystallinity. The content of crystalline phases in films and values of the optical band gap of these phases were determined as a function of the chemical composition. We developed heterostructure photodetectors based on the prepared films and demonstrated their operation in the injection photodiode mode at forward biases. A device design based on two Zn_1-xMg_xO thin films with different x values was proposed for extending the operational forward bias range and improving its responsivity, detectivity, and selectivity to UV radiation.

High-Performance Indium–Tin Oxide (ITO) Electrode Enabled by a Counteranion-Free Metal–Polymer Complex

Although multicomponent inorganic thin films (metal-oxides, -carbides, -nitrides, and -chalcogenides) have been synthesized by polymer-assisted deposition (PAD), synthesis of high-performance transparent conducting oxides (TCOs) has been rarely reported. TCO requires (i) removal of impurities, (ii) high-density oxide film, (iii) homogeneity in crystal structures and film morphology, and (iv) controllable elemental doping. This study performs a systematic investigation on preparation of stable multicomponent metal-polymer complex solutions by removing the counteranions in the solution. This study also proposes accurate acid-base titration for each metal species in order to minimize the amount of PEI, thus maximizing the density of the film. As a representative TCO, Sn-doped In₂O₃ (ITO) films have been achieved. The ITO film has an excellent sheet resistance (24.5 Ω/sq) at 93% optical transparency, with a figure of merit of 2.1 × 10^-2 Ω^-1, which is comparable to the best.

Modulation of intrinsic defects in vertically grown ZnO nanorods by ion implantation

Intrinsic defects created by chemically inert gas (Xe) ion implantation in vertically grown ZnO nanorods are studied by optical and X-ray absorption spectroscopy (XAS). The surface defects produced due to dynamic sputtering by ion beams control the fraction of O and Zn with ion fluence, which helps in tuning the optoelectronic properties. The forbidden Raman modes related to Zn interstitials and oxygen vacancies are observed because of the weak Fröhlich interaction, which arises due to disruption of the long-range lattice order. The evolution of the lattice disorder is identified by O K-edge and Zn K-edge scans of XAS. The hybridization strength between the O 2p and Zn 4p states increases with ion fluence and modulates the impact of intrinsic defects. The ion irradiation induced defects also construct intermediate defects bands which reduce the optical bandgap. Density functional theory (DFT) calculations are used to correlate the experimentally observed trend of bandgap narrowing with the origin of electronic states related to Zn interstitial and O vacancy defects within the forbidden energy gap in ZnO. Our finding can be beneficial to achieve enhanced conductivity in ZnO by accurately varying the intrinsic defects through ion irradiation, which may work as a tuning knob to control the optoelectronic properties of the system.

Engineering the Interfacial Microenvironment via Surface Hydroxylation to Realize the Global Optimization of Electrochemical CO2 Reduction

The adsorption and activation of CO₂ on the electrode interface is a prerequisite and key step for electrocatalytic CO₂ reduction reaction (eCO₂ RR). Regulating the interfacial microenvironment to promote the adsorption and activation of CO₂ is thus of great significance to optimize overall conversion efficiency. Herein, a CO₂-philic hydroxyl coordinated ZnO (ZnO-OH) catalyst is fabricated, for the first time, via a facile MOF-assisted method. In comparison to the commercial ZnO, the as-prepared ZnO-OH exhibits much higher selectivity toward CO at lower applied potential, reaching a Faradaic efficiency of 85% at -0.95 V versus RHE. To the best of our knowledge, such selectivity is one of the best records in ZnO-based catalysts reported till date. Density functional theory calculations reveal that the coordinated surficial -OH groups are not only favorable to interact with CO₂ molecules but also function in synergy to decrease the energy barrier of the rate-determining step and maintain a higher charge density of potential active sites as well as inhibit undesired hydrogen evolution reaction. Our results indicate that engineering the interfacial microenvironment through the introduction of CO₂-philic groups is a promising way to achieve the global optimization of eCO₂ RR via promoting adsorption and activation of CO₂.

On-Substrate Joule Effect Heating by Printed Micro-Heater for the Preparation of ZnO Semiconductor Thin Film

Fabrication of printed electronic devices along with other parts such as supporting structures is a major problem in modern additive fabrication. Solution-based inkjet printing of metal oxide semiconductor usually requires a heat treatment step to facilitate the formation of target material. The employment of external furnace introduces additional complexity in the fabrication scheme, which is supposed to be simplified by the additive manufacturing process. This work presents the fabrication and utilization of micro-heater on the same thermal resistive substrate with the printed precursor pattern to facilitate the formation of zinc oxide (ZnO) semiconductor. The ultraviolet (UV) photodetector fabricated by the proposed scheme was successfully demonstrated. The performance characterization of the printed devices shows that increasing input heating power can effectively improve the electrical properties owing to a better formation of ZnO. The proposed approach using the on-substrate heating element could be useful for the additive manufacturing of functional material by eliminating the necessity of external heating equipment, and it allows in-situ annealing for the printed semiconductor. Hence, the integration of the printed electronic device with printing processes of other materials could be made possible.

Various Coating Methodologies of WO3 According to the Purpose for Electrochromic Devices

Solution-processable electrochromic (EC) materials have been investigated widely for various applications, such as smart windows, reflective displays, and sensors. Among them, tungsten trioxide (WO₃) is an attractive material because it can form a film via a solution process and relative low temperature treatment, which is suitable for a range of substrates. This paper introduces the slot-die and electrostatic force-assisted dispensing (EFAD) printing for solution-processable methods of WO₃ film fabrication. The resulting films were compared with WO₃ films prepared by spin coating. Both films exhibited a similar morphology and crystalline structure. Furthermore, three different processed WO₃ film-based electrochromic devices (ECDs) were prepared and exhibited similar device behaviors. In addition, large area (100 cm²) and patterned ECDs were fabricated using slot-die and EFAD printing. Consequently, slot-die and EFAD printing can be used to commercialize WO₃ based-ECDs applications, such as smart windows and reflective displays.