UV-O3 Treatment Research Articles

Enhanced Performance of Polymer Solar Cells by Ultraviolet-Ozone Treatment of MoOX Films with non-Thermal Annealing Treatment of MoOX Films

Molybdenum oxide (MoOX) is a commonly used hole extraction material (HEL) in polymer solar cells (PSCs). Here, we perform ultraviolet ozone treatment (UVO, non-thermal annealing treatment) on MoOX film (by spin-coated (NH4)6Mo7O24-4H2O solution on the ITO top) prepared by solution processing to develop hole extraction materials for efficient PSC. After UVO treatment of MoOX films (US-MoOX), the (NH4)6Mo7O24-4H2O molecules decompose to form a denser and higher energy levels MoOX film. Compared with E-MoOX films (vacuum evaporated MoO3 powder), US-MoOX films have similar square resistance and electrical conductivity to E-MoOX films, and the photovoltaic performance of US-MoOX-based PSCs is comparable to that of E-MoOX-based PSCs and higher than that of PEDOT:PSS-based PSCs. Therefore, US-MoOX-based PSCs show the advantages of combining high photovoltaic performance with solution processing. In addition, US-MoOX-based PSCs have the advantage of not requiring thermal annealing treatment. The results indicate that US-MoOX films are promising HEL materials for the practical production of PSCs.

Vanadyl Sulfate Based Hole‐Transporting Layer Enables Efficient Organic Solar Cells

Comprehensive SummaryIt remains an urgent task to develop alternative hole‐transporting layer (HTL) materials beyond commonly used PEDOT:PSS to increase the shelf‐life of organic solar cells (OSCs). Inorganic metal oxide type materials, such as NiOx, CoOx and VOx, with suitable work functions have attracted numerous research attention recently. In this work, more abundant and easily accessible oxygenated salt, vanadyl sulfate (VOSO4) has been demonstrated to be excellent choice as HTL for OSCs. The VOSO4‐based HTL can be readily processed by spin‐coating from the precursor solution with subsequent thermal annealing and UVO treatment. As a consequence, a high power conversion efficiency (PCE) of 18.72% can be achieved for PM8:L8‐BO based OSCs with the VOSO4‐based HTL. High transmittance, smooth film surface, suitable energy level and high conductivity were revealed to contribute to the high OSC performance. More importantly, compared to device with PEDOT:PSS, VOSO4‐based OSCs exhibit improved stability when stored in the N2 filled glove box. After being stored for 600 h, VOSO4‐based device can retain 89% of its initial efficiency. Notably, VOSO4 can be used as general HTL in PM6:BTP‐BO‐4Cl and PM6:IT‐4F based OSCs, yielding high PCEs of 17.87% and 13.85%, respectively.

Effect of UV-O3 treatment on the performance of UV detector based on zinc oxide/molybdenum disulfide nanosheet heterostructures

UV photodetectors based on ZnO nanostructures, using a metal-semiconductor-metal (MSM) configuration, are popular due to their simple fabrication. However, they experience high dark currents and slow photoresponse speeds. This is due to a high recombination rate for photogenerated electrons and holes as well as low charge carrier mobility attributable to ZnO's inherent defects. In this study, MoS2 nanosheets was employed to cover the surface of ZnO nanorods, creating a unique architecture that focuses the impact of MoS2 solely on light absorption and charge transfer on the ZnO surface. Subsequently, a 15-min UV-O3 exposure is applied to the ZnO/MoS2 structure. The ZnO/MoS2UVo heterostructure exhibits remarkable results, including a six-fold increase in sensitivity compared to pure ZnO, Additionally, the Detectivity increases by 265 %, while the Responsivity and Quantum Efficiency rise by up to 102 %. These enhancements are attributed to the reduction of dark current coming from the reduction of oxygen vacancies as sulfur edge atoms from MoS2 fill these vacancies. Furthermore, additional dark current reduction post UV-O3 treatment is due to both the reduced ZnO oxygen vacancies and the formation of a thin MoO3 passivation layer on the ZnO NR surface. Despite these achievements, the study acknowledges the presence of multiple junctions between ZnO, MoS2, and MoO3, which still pose challenges for efficient charge transfer to the electrodes.

Ultraviolet-Ozone Treatment: An Effective Method for Fine-Tuning Optical and Electrical Properties of Suspended and Substrate-Supported MoS2

Ultraviolet-ozone (UV-O3) treatment is a simple but effective technique for surface cleaning, surface sterilization, doping, and oxidation, and is applicable to a wide range of materials. In this study, we investigated how UV-O3 treatment affects the optical and electrical properties of molybdenum disulfide (MoS2), with and without the presence of a dielectric substrate. We performed detailed photoluminescence (PL) measurements on 1–7 layers of MoS2 with up to 8 min of UV-O3 exposure. Density functional theory (DFT) calculations were carried out to provide insight into oxygen-MoS2 interaction mechanisms. Our results showed that the influence of UV-O3 treatment on PL depends on whether the substrate is present, as well as the number of layers. Additionally, 4 min of UV-O3 treatment was found to be optimal to produce p-type MoS2, while maintaining above 80% of the PL intensity and the emission wavelength, compared to pristine flakes (intrinsically n-type). UV-O3 treatment for more than 6 min not only caused a reduction in the electron density but also deteriorated the hole-dominated transport. It is revealed that the substrate plays a critical role in the manipulation of the electrical and optical properties of MoS2, which should be considered in future device fabrication and applications.

Modulating the Properties of SnO2 Thin Film by Post-Deposition UV-Ozone Treatment

AbstractTin(IV) oxide (SnO2) is a metal oxide renowned for its excellent optoelectronic properties. With the use of simple post-processing methods, the characteristics of SnO2 may be easily modified. In the current work, SnO2 thin films were prepared using the spray pyrolysis technique and were subjected to post-UV-ozone (UVO) treatment for different durations. Characterization techniques including x-ray diffraction, Raman spectroscopy, scanning electron microscopy, energy-dispersive spectroscopy, UV–visible spectroscopy, and photoluminescence spectroscopy were employed to assess the effects of UVO treatment. It was found that UVO treatment had no significant impact on the film's structural characteristics. However, after exposure to UVO, the bandgap was seen to decrease from 3.04 eV to 2.84 eV. Also, photoluminescence investigations revealed that UVO treatment increased the defects in the films with a decrease in the ratio between band-to-band emission and defect emissions. The results indicate that UVO treatment is an effective strategy for tuning the optical properties of SnO2 thin films by precisely managing the bandgap.

Work function tuning of directly grown graphene via ultraviolet–ozone treatment for electrode application in organic photovoltaic devices

Graphene is an efficient electrode material for flexible optoelectronic devices because of its high transmittance and electrical conductivity. A graphene film directly grown using plasma-enhanced chemical vapor deposition is suitable for electrode applications because it can be prepared on a glass substrate at relatively low temperatures without a transfer process from a metal catalyst. However, to obtain efficient optoelectronic devices using graphene electrodes, surface modification is necessary. Herein, we tuned the work function of a graphene electrode using ultraviolet (UV)-O3 treatment. The power conversion efficiency of organic photovoltaic devices was significantly increased by the UV-O3 treatment of the graphene anode. To investigate the origin of the improved device performance, the interface between the graphene anode and tetraphenyldibenzoperiflanthene (DBP) donor layer was analyzed via in situ ultraviolet photoelectron spectroscopy. The energy offset between the Fermi level of graphene and the highest occupied molecular orbital level of DBP was significantly reduced because of the increased work function. The results indicate that the electronic structure modification of graphene is of significant importance for fabricating efficient optoelectronic devices.

Resistive random access memory based on graphene oxide with UV-O3 treatment

Resistive random access memory based on graphene oxide with UV-O3 treatment

Janus 3D graphene based evaporator with controllable wettability for highly efficient solar desalination

Interfacial solar desalination has been widely favored as a convenient technology to relieve the prominent lack of clean water. However, it remains urgent and challenging to develop materials that can simultaneously reduce heat loss and provide effective channels for water transport without salt accumulation. In this work, we developed a free-standing Janus 3D graphene based evaporator modified by a wettability-controllable UV-O3 treatment method. The upper hydrophilic layer of the Janus 3DG plays the role of continuous water supplement for evaporation, while the bottom hydrophobic layer could support material floating on the water surface to ensure effective light absorption and contribute to heat loss reduction. Taking advantage of the synergistic effect of the structure, Janus 3DG delivers a stable water evaporation rate of 1.71 kg m−2 h−1 under 1 kW m−2 illumination, a highly efficient conversion efficiency of 94.1 % and exhibits excellent salt-resistance in high concentration simulated seawater (10 wt%) without salt accumulation. The Janus 3DG had satisfactory availability for solar desalination and wastewater purification. Our study establishes and validates a simple method for fabricating an efficient solar-driven evaporator for desalination.

Engineering cell morphology using maskless 2D protein micropatterning on 3D nanostructures

Mechanical cues such as the 2-Dimensional (2D) and 3-Dimensional (3D) shape of cellular microenvironments affect several cellular processes including adhesion and proliferation. Recent studies provide controlled conditions to recapitulate the 2D and 3D microenvironments to understand the mechanisms of cellular response to these mechanical cues. Microengineering surfaces such as micropatterning techniques are widely used to modulate 2D cell shapes. Additionally, nanostructured surfaces are used to modulate 3D substrate nanotophography. By confining cells to micropatterns, cells reorganize their cytoskeleton architecture to the microenvironment by remodeling the actin and microtubule fibers. In this study, we present a micropatterning technique on nanostructured surfaces based on a maskless laser-assisted technique to study the cellular response to 3D nano-topographies in a controlled 2D microenvironment. We used a two-step dry and wet etching technique to fabricate transparent (SiO2) 3D nanostructured surfaces. Next, we micropatterned extracellular matrix proteins directly on the fabricated nanostructures by maskless micropatterning (PRIMO, Alvéole) system mounted on an inverted microscope. Briefly, UVO treatment was performed to clean the surface followed by surface incubation with Poly-L-Lysine. Subsequently, the surface was passivated with m-PEG-SVA, and a photosensitizer reagent (PLPP) applied to the surface to remove the PEG layer upon UV exposure. After UV illumination and washing the surface, nanopillars were incubated with ECM proteins (Fibronectin and Gelatin). Next, we demonstrated the 2D control of cell and nuclear shape on 3D nanostructured surfaces for an epithelial-like cell line (U2OS, ATCC) by seeding them on Fibronectin/Gelatin micropatterns of various geometries. We then used fluorescent microscopy to characterize the organization of intracellular components such as the nucleus and cytoskeletal elements. Moreover, we analyzed the spreading of cells over time, the effect of 2D micropattern geometry on cell morphology, and cytoskeleton reorganization on various 2D and 3D configurations.

Improved Tunneling Property of p+Si Nanomembrane/n+GaAs Heterostructures through Ultraviolet/Ozone Interface Treatment

Here, heterostructures composed of p+Si nanomembranes (NM)/n+GaAs were fabricated by ultraviolet/ozone (UV/O3, UVO) treatment, and their tunneling properties were investigated. The hydrogen (H)-terminated Si NM was bonded to the oxygen (O)-terminated GaAs substrate, leading to Si/GaAs tunnel junctions (TJs). The atomic-scale features of the H-O-terminated Si/GaAs TJ were analyzed and compared to those of Si/GaAs heterojunctions with no UVO treatment. The electrical characteristics demonstrated the emergence of negative differential resistance, with an average peak-to-valley current ratio of 3.49, which was examined based on the band-to-band tunneling and thermionic emission theories.

UV Ozone based rapid low temperature fabrication of flexible dye sensitized solar cells

Herein, we have developed a multilayer TiO2 film thickness of around 4 µm at lower temperature (120 °C) by spin coating and doctor blade technique on polyethylene terephthalate (ITO-PET) substrate. Further, the additional processing step Ultravoilet-Ozone (UVO3) treatment was performed on TiO2 electron transport layer (ETL) to enhance the performance of FDSSCs. UVO3 treatment significantly improved the crystallinity and charge transport characteristic of ETL by removing the organic impurities. The photovoltaic devices based on 4 h of UVO3 treated TiO2 film exhibited superior device performance with an overall power conversion efficiency (PCE) of 2.53% compared to 1.43% (without UVO3 treatment). Electrochemical impedance measurement indicated that TiO2 layer treated with UVO3 decreased series resistance, electron recombination and improved electron life substantially. The improved device properties, simple preparation procedure and low processing cost, enable this FDSSCs fabrication method to be a credible alternative of conventional techniques.

Low-Temperature Chemical Sintered TiO2 Photoanodes Based on a Binary Liquid Mixture for Flexible Dye-Sensitized Solar Cells

A chemically sintered and binder-free paste of TiO2 nanoparticles (NPs) was prepared using a binary-liquid mixture of 1-octanol and CCl4. The 1:1 (v/v) complex of CCl4 and 1-octanol easily interacted chemically with the TiO2 NPs and induced the formation of a highly viscous paste. The as-prepared binary-liquid paste (<bold>P</bold>BL)-based TiO2 film exhibited the complete removal of the binary-liquid and residuals with the subsequent low-temperature sintering (~150°C) and UV-O3 treatment. This facilitated the fabrication of TiO2 photoanodes for flexible dye-sensitized solar cells (f-DSSCs). For comparison purposes, pure 1-octanol-based TiO2 paste (<bold>P</bold>O) with moderate viscosity was prepared. The <bold>P</bold>BL-based TiO2 film exhibited strong adhesion and high mechanical stability with the conducting oxide coated glass and plastic substrates compared to the <bold>P</bold>O-based film. The corresponding low-temperature sintered <bold>P</bold>BL-based f-DSSC showed a power conversion efficiency (PCE) of 3.5%, while it was 2.0% for <bold>P</bold>O-based f-DSSC. The <bold>P</bold>BL<bold>-</bold>based low- and high-temperature (500°C) sintered glass-based rigid DSSCs exhibited the PCE of 6.0 and 6.3%, respectively, while this value was 7.1% for a 500°C sintered rigid DSSC based on a commercial (or conventional) paste.

Defect Engineering in Thickness-Controlled Bi2O2Se-Based Transistors by Argon Plasma Treatment.

We present a simple, effective, and controllable method to uniformly thin down the thickness of as-exfoliated two-dimensional Bi2O2Se nanoflakes using Ar+ plasma treatment. Atomic force microscopy (AFM) images and Raman spectra indicate that the surface morphology and crystalline quality of etched Bi2O2Se nanoflakes remain almost unaffected. X-ray photoelectron spectra (XPS) indicate that the O and Se vacancies created during Ar+ plasma etching on the top surface of Bi2O2Se nanoflakes are passivated by forming an ultrathin oxide layer with UV O3 treatment. Moreover, a bottom-gate Bi2O2Se-based field-effect transistor (FET) was constructed to research the effect of thicknesses and defects on electronic properties. The on-current/off-current (Ion/Ioff) ratio of the Bi2O2Se FET increases with decreasing Bi2O2Se thickness and is further improved by UV O3 treatment. Eventually, the thickness-controlled Bi2O2Se FET achieves a high Ion/Ioff ratio of 6.0 × 104 and a high field-effect mobility of 5.7 cm2 V-1 s-1. Specifically, the variation trend of the Ion/Ioff ratio and the electronic transport properties for the bottom-gate Bi2O2Se-based FET are well described by a parallel resistor model (including bulk, channel, and defect resistance). Furthermore, the Ids-Vgs hysteresis and its inversion with UV irradiation were observed. The pulsed gate and drain voltage measurements were used to extract trap time constants and analyze the formation mechanism of different hysteresis. Before UV irradiation, the origin of clockwise hysteresis is attributed to the charge trapping/detrapping of defects at the Bi2O2Se/SiO2 interface and in the Bi2O2Se bulk. After UV irradiation, the large anticlockwise hysteresis is mainly due to the tunneling between deep-level oxygen defects in SiO2 and p++-Si gate, which implies the potential in nonvolatile memory.

Current advancement of flexible dye sensitized solar cell: A review

In the last two decades, research on dye-sensitized solar cells (DSSCs) has shown tremendous improvement with promising findings. It has become one of the alternative options in replacing conventional silicon-based photovoltaics. Recently, a study towards the flexible form of solar cells has gained the attention of researchers. The features possess in DSSC such as high flexibility, light weight and environmentally friendly have made DSSC suitable for such purposes compared to rigid glass substrates. However, the biggest challenge faced by plastic-type substrates is temperature, where plastic substrates only withstand up to 150 °C before melting. In the DSSC fabrication process, temperatures as high as 400–500 °C are critically required for the purpose of material crystallization. With insufficient temperature during this process, poor interconnection between nanoparticles and increased electrode resistance will occur, thereby lowering the performance of plastic based DSSC. Here, we discuss the approaches that researchers have performed in solving the problem. Such approaches include the use of doctor blades, electrophoretic deposition, hydrothermal, peel and stick technique, and pulse laser deposition methods. In addition, this paper also discusses the most recent method which is additional procedure using Titanium(IV) tetraisopropoxide or UV-O3 treatment in the preparation of flexible DSSC. Several types of photoanode materials such as titanium dioxide, zinc oxide and graphene are also discussed in this paper.

Fabrication of Elastomer Films with Nano-micro Hierarchical Wrinkled Structure

Instabilities are commonly manifested in our daily lives, such as in water jets breaking into isolated drops, wave patterns at the sea surface, sand dunes, cloud waves, ruptures of paint from a wall, and wrinkles on human skin. Previously, we have fabricated hierarchical concentric wrinkled-structures by 3D-stretching method combining UVO and plasma treatments. The hierarchical structure has been achieved via structural transfer. However, the fabrication of hierarchical structures requires a complicated transcription process. In this study, we examined the fabrication of hierarchical wrinkled-structures by 3D-stretching method continuous plasma and UVO treatment.

Amphiphilic Perforated Honeycomb Films for Gravimetric Liquid Separation

AbstractThe separation of oil and water is an important technology for solving a wide range of water‐related problems such as purification of industrial wastewater. Herein, the fabrication of an extremely thin oil–water separation membrane is reported by precisely controlling the wettability of a honeycomb (HC) porous membrane. The developed membrane can easily separate water and oil by gravity and capillary force. The method of wettability control by UV–O3 treatment and the resultant change in the separated liquid are discussed. Amphiphilic perforated HC films with controlled wettability can be used in membranes that can separate different liquids according to their densities when the initial liquid added to the surface of the HC film is changed.

Reducing the Threshold Voltage Instability of β-Ga2O3 Nanobelt Field-Effect Transistors Using Ozone Treatment

β-Ga2O3 is a promising semiconducting material for next-generation power devices owing to its wide bandgap (4.8 eV), high breakdown electric field (8 MV/cm), and good thermal stability. β-Ga2O3 has a monoclinic crystal structure with weak covalent bonding along the direction of (100), so bulk β-Ga2O3 can be exfoliated into ultra-thin flakes, which can be integrated with van der Waals materials. An example of the application is metal-insulator-semiconductor field-effect transistors (MISFETs) using h-BN as a gate dielectric. H-BN has an atomically flat surface without dangling bond, minimizing interfacial states between the channel and insulator layer. Moreover, the high thermal conductivity of h-BN (30 W/m·K along the c-plane) makes heat management easier (cf. SiO2: 1.4 W/m·K). Therefore, β-Ga2O3/h-BN MISFETs are expected to enhance device performance with a synergetic effect of both materials.However, there are remaining reliability issues about the gate-bias stress instability (BSI), the temporary or permanent degradation of electrical properties from gate bias stress (ex. threshold voltage, field-effect mobility, on/off ratio). β-Ga2O3 FETs have been developed for high voltage operation in harsh environments, so that suppression of BSI is required. BSI is mainly attributed to charge trapping in the channel, channel/dielectric interface, or dielectric layer under gate-bias stress. In this work, we tried to reduce bias-stress instability of β-Ga2O3/h-BN MISFETs by UV-O3 treatment. Numerous reports demonstrated the annealing of oxygen-related defects by UV-O3 treatment in oxide-based materials. Therefore, UV-O3 treatment was expected to also work on β-Ga2O3.First, β-Ga2O3 (200-300 nm) and h-BN (40-50 nm) flakes were exfoliated from each bulk crystal with adhesive tape. H-BN flake was dry-transferred on SiO2/p++Si substrate, and subsequently β-Ga2O3 flake was stacked on h-BN. The source, drain, and gate electrodes (Ti/Au 50 nm/100 nm) were defined by e-beam lithography, followed by e-beam evaporation and lift-off processes. Bias-stress characteristics were systematically measured by Measure-Stress-Measure (MSM) method—repeating the sequence of 1) IDS-VGS, 2) VGS stress, 3) IDS-VGS sweep. β-Ga2O3/h-BN MISFET was UV-O3 treated using a commercial UV-O3 cleaning system (PSD-UV, Novascan Technologies, Ames, IA, USA). By following bias-stress characteristics measurement, we could observed reduced shifts of electrical properties regarding as annealing effect on oxygen-related defect by UV-O3 treatment. This work grants facile way to achieve β-Ga2O3 FETs stable to stress and open up new opportunities for the practical implementation of β-Ga2O3 power device. The details of methods and results will be presented at the conference.

Optimization of ultraviolet/ozone (UVO3) process conditions for the preparation of gelatin coated polystyrene (PS) microcarriers

The aim of this study was to develop gelatin coated polystyrene (PS) microcarriers with good cell adhesion and proliferation properties. PS microspheres, prepared using oil-in water (o/w) solvent evaporation method, were loaded with oxygen containing functional groups using an ultraviolet/ozone (UVO3) system. Using water-soluble carbodiimide chemistry, gelatin was subsequently immobilized on UVO3 treated PS microspheres. The amount of immobilized gelatin was found to be directly proportional to the surface carboxyl (COOH) concentration on PS microspheres. Face Centered Central Composite Design (FCCD) was employed to optimize the process conditions of UVO3 treatment to maximize the surface COOH concentration on PS microspheres for allowing higher gelatin immobilization. Statistical results revealed that, the optimized process conditions were ozone flow rate of ∼64,603 ppm, exposure time of ∼60 minutes and sample amount of 5.05 g. Under these conditions, the surface COOH concentration on PS microspheres was ∼1,505 nmol/g with the corresponding amount of immobilized gelatin was ∼2,725 µg/g. Characterization analyses strongly suggest that the optimized UVO3 treatment and successive gelatin immobilization have successfully improved surface wettability and dispersion stability of PS microspheres. Moreover, gelatin coated PS microcarriers were also proven as able to support the growth of CHO-K1 cells in high cell density culture.

Improved osteogenesis of human adipose-derived stromal cells on hydroxyapatite-mineralized graphene film

This study investigated whether hydroxyapatite (HAp)-mineralized graphene (GR) film could support osteogenic differentiation of human adipose-derived, stromal cell (hASCs) in vitro. GR was produced by a chemical vapor deposition (CVD) method and the physical and chemical characteristics of the GR film, which was functionalized with HAp mineralization following ultraviolet-ozone (GR_UVO) treatment, were subsequently validated. Results of scanning electron microscopy, x-ray photoelectron spectroscopy and Raman spectroscopy showed GR_UVO for 5 min yielded applicable GR coverage (97.98 ± 0.85%), conversion of chemical composition ratio (29.78% C–O, 18.34% C=O and 8.49% O–C=O) and degree of oxidation, (I 2D/I G ratios 2.22) with maximal density of HAp-GR layer. In vitro-cell proliferation, viability and adhesion of hASCs after being cultured on HAp-mineralized, GR-coated glass (HAp/GR) with the optimized GR_UVO treatment (5 min) demonstrated a significant increment of proliferation (1.56 ± 0.1 vs 1–1.13 ± 0.1, p< 0.05) without changing in viability (94.83 ± 1% to 95.3 ± 1.6%, p= 0.9651) compared with the control (intact glass). There were no differences in F-actin and vinculin on day 1 (p= 0.1422 and 0.5025, respectively) and on day 4 (p= 0.3787 and 0.9208) of culture. Osteogenic differentiation of hASCs was significantly improved on the HAp/GR with increasing of osteogenesis-related genes (Runx2 and Osteocalcin). The hASCs culture with the HAp/GR glass promoted phospho-SMAD1/5/9 and SMAD4 expression with increased patterns of BMP/Smad signal-related genes, regardless of differentiation induction or not. These results demonstrated that HAp-mineralized GR film prepared by CVD method and optimal ultraviolet treatment promoted osteogenic differentiation of hASCs, which BMP/Smad signaling was involved.

Highly efficient and stable quantum dot light-emitting devices with a low-temperature tin oxide electron transport layer

UVO treatment is proposed to decompose the residual tin hydroxide in an SnO2 ETL film. With UVO treatment, efficient and stable QLEDs are fabricated with a low-temperature SnO2 transport layer.