One-Step Coating of Full-Coverage CsPbBr₃ Thin Films via Mist Deposition for All-Inorganic Perovskite Solar Cells

In this work, one-step coating of CsPbBr₃ thin films using the mist deposition method is demonstrated. The CsPbBr₃ layer is composed of large grains with an average size of approximately 1.4 μm, and it fully covers the substrate surface, unlike the layers prepared by conventional one-step spin-coating methods, so that efficient carrier transport is realized. Carbon-based CsPbBr₃ perovskite solar cells (PSCs) fabricated using the mist deposition method exhibit a stabilized power conversion efficiency of 7.7%, which is a record value for carbon-based CsPbBr₃ PSCs prepared via a one-step solution process

Fabrication of CsPbBr₃ Thick Films by Using a Mist Deposition Method for Highly Sensitive X-ray Detection

X-ray imaging is a valuable technique used for medical imaging and non-destructive inspection of industrial products. However, the radiation may put humans at risk of developing cancer. Consequently, highly sensitive X-ray detectors, which enable X-ray imaging at a low dose rate, are required. Metal halide perovskite materials have demonstrated excellent X-ray detection performance including a high sensitivity owing to their high absorption coefficient, high carrier mobility, and long carrier lifetime. However, perovskite thick films with a large area, which is essential to realize the application of such materials to X-ray imaging devices have not been extensively investigated. To this end, in this study, a polymer is employed as a buffer layer to avoid film exfoliation, which makes it difficult to fabricate perovskite thick films, and a 110-μm-thick CsPbBr₃ film is successfully obtained using a scalable solution method. In addition, an X-ray detector based on the CsPbBr₃ thick film is fabricated, which demonstrates a sensitivity of 11, 840 μC Gyair⁻¹ cm⁻². This sensitivity is approximately 600 times higher than that of the existing commercial a-Se X-ray detectors

Fabrication of (101)-oriented CsPbBr₃ thick films with high carrier mobility using a mist deposition method

CsPbBr₃ is a promising candidate for highly sensitive flat-panel X-ray detectors due to its excellent optoelectronic properties. Thus, a method of preparing thick CsPbBr₃ films (>10 μm) over large areas (>10 × 10 cm²) is required. Herein, we report the fabrication of thick CsPbBr₃ films using a scalable mist deposition method. In this method, the film thickness was controlled and up-scaled by the number of deposition cycles. The obtained CsPbBr₃ films were composed of highly (101)-oriented columnar crystals and had a high carrier mobility of 13 cm² V⁻¹ s⁻¹, which is comparable to that for single crystals

Epitaxial Growth and Bandgap Control of Ni1-xMgxO Thin Film Grown by Mist Chemical Vapor Deposition Method

Wide-bandgap oxide semiconductors have received significant attention as they can produce devices with high output and breakdown voltage. p-Type conductivity control is essential to realize bipolar devices. Therefore, as a rare wide-bandgap p-type oxide semiconductor, NiO (3.7 eV) has garnered considerable attention. In view of the heterojunction device with Ga2O3 (4.5–5.0 eV), a p-type material with a large bandgap is desired. Herein, we report the growth of a Ni1-xMgxO thin film, which has a larger bandgap than NiO, on α-Al2O3 (0001) substrates that was developed using the mist chemical vapor deposition method. The Ni1-xMgxO thin films epitaxially grown on α-Al2O3 substrates showed crystallographic orientation relationships identical to those of NiO thin films. The Mg composition of Ni1-xMgxO was easily controlled by the Mg concentration of the precursor solution. The Ni1-xMgxO thin film with a higher Mg composition had a larger bandgap, and the bandgap reached 3.9 eV with a Ni1-xMgxO thin film with x = 0.28. In contrast to an undoped Ni1-xMgxO thin film showing insulating properties, the Li-doped Ni1-xMgxO thin film had resistivities of 101–105 Ω∙cm depending on the Li precursor concentration, suggesting that Li effectively acts as an acceptor

Formation of a photocatalytic WO3 surface layer on electrodeposited Al–W alloy coatings by selective dissolution and heat treatment

In this study, we explored the feasibility of WO3 surface layer formation on electrodeposited Al–W alloy coatings by selective dissolution and heat treatment, with the aim of providing corrosion-resistant Al–W alloy coatings with photocatalytic self-cleaning properties under visible light illumination. The selective dissolution of Al and oxidation of residual W was carried out by immersing Al–W alloy films in an aqueous solution of nitric acid. A nanostructured H2WO4·H2O surface layer was formed on the alloy film by this process. The H2WO4·H2O layer was dehydrated to WO3 by heat treatment, yielding a multilayered WO3/Al–W alloy film with an approximately 300 nm thick WO3 layer. The WO3/Al–W alloy film exhibited photocatalytic self-cleaning, as demonstrated by the photodegradation of stearic acid and methylene blue. We also confirmed that selective dissolution and heat treatment did not significantly diminish the corrosion resistance of the Al–W alloy films

Epitaxial growth of undoped and Li-doped NiO thin films on α-Al2O3 substrates by mist chemical vapor deposition

Undoped and Li-doped NiO thin films were grown on α-Al₂O₃ (0 0 0 1) substrates by mist chemical vapor deposition. Both undoped and Li-doped NiO thin films grew bi-epitaxially on the substrates with crystallographic orientation relationships of NiO(1 1 1)[ 1 0] || α-Al₂O₃(0 0 0 1)[0 1  0] and NiO(1 1 1)[1  0] || α-Al₂O₃(0 0 0 1)[0 1  0]. In the Li-doped NiO thin film, a periodic structure was observed, in accordance with a mirror-symmetrical oxygen layer on the terraces of the substrate. Both undoped and Li-doped NiO thin films exhibited high transmittance (>80%) in the visible-light region and optical bandgaps of 3.7–3.8 eV. The undoped NiO thin film showed insulating properties and a resistivity of 10⁶ Ω cm or higher. In contrast, the Li-doped NiO thin films had resistivities of 10¹–10⁵ Ω cm, depending on the Li precursor concentration. Furthermore, they exhibited positive Seebeck coefficients, indicating their p-type conductivity. These results indicate that Li dopants effectively act as acceptors in NiO thin films

Hole mobility improvement in Cu2O thin films prepared by the mist CVD method

A high-mobility Cu₂O thin film was fabricated using the mist chemical vapor deposition (CVD) method. This was achieved by suppressing the contamination from nitrogen impurities and optimum growth conditions to obtain single-phase Cu₂O without CuO. A 600 nm Cu₂O thin film was obtained using ethylenediaminetetraacetic acid as a complexing agent in dry-air growth atmosphere for 120 min. The resulting thin film had a resistivity of 2.8 × 10² Ω ･ cm, carrier concentration of 1.2 × 10¹⁵ cm⁻³ and hole mobility of 19.3 cm² ･ V⁻¹. This hole mobility improved by two or more orders of magnitude compared to that of previous Cu₂O thin film obtained by the mist CVD method

Growth and Electrical Properties of Epitaxial ZnO Films Prepared by Chemical Bath Deposition Using a Flow Reactor

Deposition methods using aqueous solutions have been developed as cost-effective routes to form transparent ZnO semiconductor films. Chemical bath deposition (CBD) employing a solution of zinc nitrate and hexamethylenetetramine is one of the most popular methods to grow ZnO using aqueous solutions. However, the electrical properties of ZnO films grown by CBD have not been extensively studied. In this study, epitaxial ZnO films were prepared by CBD using a flow reactor under various deposition conditions, and the temperature and reactant concentrations required for the growth of a transparent ZnO film with a smooth surface were determined. The electrical properties of the transparent ZnO films were examined by resistivity and Hall effect measurements. The optimum flow rate of the reaction solution, leading to the fastest growth of ZnO, was also identified. The ZnO film grown at such flow rate exhibited the highest electrical mobility. The carrier concentration and mobility of the ZnO film grown under the optimized conditions were 1.2 × 10¹8 cm⁻³ and 21 cm² V⁻¹ s⁻¹, respectively

Mist CVD of vanadium dioxide thin films with excellent thermochromic properties using a water-based precursor solution

Mist chemical vapor deposition (mist CVD), which is capable of producing oxide films over large areas at a high productivity and low cost, has been proposed as a fabrication method for VO₂ thin films for smart windows. However, the thermochromic properties of the VO₂ films previously prepared by mist CVD are not sufficient for application in smart windows. In this study, to obtain a high-quality VO₂ film, we investigated the effects of the solvent of the precursor solution on the resulting film in mist CVD. Films consisting of a single phase of VO₂ were obtained when a water-based precursor solution was used. In contrast, V₂O₃ films are formed when a methanol-based precursor solution is used. The VO₂ film deposited from water solution exhibited high visible transmittance along with a large change in the infrared transmittance with temperature change. The high quality of the VO₂ film indicates that mist CVD is an effective method for the fabrication of VO₂-based smart windows

Aluminum Barrel Plating on Steel Bolts Using Chloroaluminate Ionic Liquids

Al electroplating using ionic liquids (ILs) has been extensively studied for various potential applications, including corrosion-resistant coatings. When Al electroplating is to be performed commercially for many small objects, adopting the barrel plating method is reasonable for improving productivity and reducing manufacturing costs. However, little is known about the barrel-plating conditions for the formation of Al coatings. In this study, the barrel plating conditions for forming Al coatings on steel bolts using ILs composed of 1-ethyl-3-methylimidazolium chloride (EMIC) and aluminum chloride (AlCl₃) were investigated. Hull cell tests showed that the IL with an AlCl₃/EMIC molar ratio of 1.2 has a higher covering power than the IL with a higher AlCl₃ ratio. Barrel plating using the IL with an AlCl₃ ratio of 1.2 enabled complete coverage of the bolt with the Al coating. The uniformity of the Al coating on the bolts was further improved by adjusting the rotation speed of the barrel. Furthermore, a simple pretreatment procedure for steel bolts was proposed to obtain an electrodeposited Al coat that adheres well to steel bolts