UV-ozone Treatment Research Articles

Postdeposition UV-Ozone Treatment: An Enabling Technique to Enhance the Direct Adhesion of Gold Thin Films to Oxidized Silicon.

We found that continuous films of gold (Au) on oxidized silicon (SiO2) substrates, upon treatment with ultraviolet (UV)-ozone, exhibit strong adhesion to the SiO2 support. Importantly, the enhancement is independent of micro- or nanostructuring of such nanometer-thick films. Deposition of a second Au layer on top of the pretreated Au layer makes the adhesion stable for at least 5 months in environmental air. Using this treatment method enables us to large-scale fabricate various SiO2-supported Au structures at various thicknesses with dimensions spanning from a few hundreds of nanometers to a few micrometers, without the use of additional adhesion layers. We explain the observed adhesion improvement as polarization-induced increased strength of Auδ−Siδ+ bonds at the Au–SiO2 interface due to the formation of a gold oxide monolayer on the Au surface by the UV-ozone treatment. Our simple and enabling method thus provides opportunities for patterning Au micro/nanostructures on SiO2 substrates without an intermediate metallic adhesion layer, which is critical for biosensing and nanophotonic applications.

Iridescent and Glossy Effect on Polymer Surface Using Micro-/Nanohierarchical Structure: Artificial Queen of the Night Tulip Petals.

Many petals in nature have a hierarchical structure that imparts various optical properties. Among these, the petals of the Queen of the Night tulip exhibit an iridescent and glossy color due to the diffraction and scattering of light. Herein, we report a bioinspired micro-/nanohierarchical structure that mimics Queen of the Night tulip petal surfaces. Using a method that combined soft lithography and UV-ozone treatment, we fabricated nanoscale line patterns with a linewidth of 600 nm on microwrinkles of 15 μm width and 3 μm height. Using optical microscopy in the dark-field mode and monochromatic light diffraction measurements, we found that these hierarchical structures on a poly(dimethylsiloxane) (PDMS) substrate synergistically improved the scattering and diffraction effects, unlike the pristine, nano-, and microstructures. In addition, using a dye-colored PDMS material, we fabricated artificial Queen of the Night petals with iridescent and glossy effects. They show great potential for a range of applications, such as coloring, smart displays, dynamic gratings, and light-control devices.

UV-ozone induced surface passivation to enhance the performance of Cu2ZnSnS4 solar cells

Interface property has been considered one of the most critical factors affecting the performance of semiconductor devices. In this work, we demonstrate an efficient surface passivation for the interface between Cu2ZnSnS4 (CZTS) and CdS buffer layer by using UV-ozone treatment at room temperature. The passivation led to a significant enhancement of short circuit current density (Jsc) of the device from 11.70 mA/cm2 to 18.34 mA/cm2 and thus efficiency of the CZTS solar cells from 3.18% to 5.55%. The study of surface chemistry has revealed that the UV-ozone exposure led to formation of a Sn–O rich surface on CZTS, which passivates the dangling bonds and forms an ultra-thin energy barrier layer at the interface of CZTS/CdS. The barrier is considered to be responsible for the reduction of non-radiative recombination loss in the solar cells as confirmed by photoluminescence (PL) measurement. The elongated lifetime of minority carriers in the CZTS solar cells by time-resolved PL has further verified the interface passivation effect induced by UV-ozone treatment. This work provides a fast, simple yet very effective approach for surface passivation of CZTS film to boost the performance of CZTS solar cells.

Removal of Surface Oxygen Vacancies Increases Conductance Through TiO2 Thin Films for Perovskite Solar Cells.

We report that UV–ozone treatment of TiO2 anatase thin films is an efficient method to increase the conductance through the film by more than 2 orders of magnitude. The increase in conductance is quantified via conductive scanning force microscopy on freshly annealed and UV–ozone-treated TiO2 anatase thin films on fluorine-doped tin oxide substrates. The increased conductance of TiO2 anatase thin films results in a 2% increase of the average power conversion efficiency (PCE) of methylammonium lead iodide-based perovskite solar cells. PCE values up to 19.5% for mesoporous solar cells are realized. The additional UV–ozone treatment results in a reduced number of oxygen vacancies at the surface, inferred from X-ray photoelectron spectroscopy. These oxygen vacancies at the surface act as charge carrier traps and hinder charge extraction from the adjacent material. Terahertz measurements indicate only minor changes of the bulk conductance, which underlines the importance of UV–ozone treatment to control surface-based defects.

Solvent mediated inclusion of metal oxide into block copolymer nanopatterns: Mechanism of oxide formation under UV-Ozone treatment

Uniform, periodic and ordered iron oxide nanopatterns can be generated by selective metal ion inclusion into microphase separated polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymer (BCP) thin films. After solvent mediated metal ion inclusion into the PEO block, an ultraviolet-ozone (UVO) treatment was used to remove the polymer and oxidize the metallic ions to their oxides. This paper provides an in-depth study of the UVO processing steps as a function of exposure time. Surface wettability, topography, morphology, compositional and interfacial changes were analysed by contact angle measurement, microscopic and spectroscopic techniques through the UVO treatment. It was found that the UVO treatment initially cross-links the polymer network followed by oxidation and removal of the polymer simultaneously. It was also found that if short UVO exposure times are used, a post calcination treatment can be used to generate similar patterns. The iron oxide nanopatterns created due to strong coordination bond between metallic ions and free electron pairs of O atoms in the PEO and these interactions are responsible for the final pattern mimicking the original self-assembled BCP morphology. The film thicknesses, surface roughness, the size/shape of the iron oxides and patterns, the amount of residual polymers were also investigated regarding the UVO exposure time.

Photocatalytic Template Removal by Non-Ozone-Generating UV Irradiation for the Fabrication of Well-Defined Mesoporous Inorganic Coatings.

The processing of mesoporous inorganic coatings typically requires a high-temperature calcination step to remove organic precursors that are essential during the material assembly. Lowering the fabrication energy costs and cutting back on the necessary resources would provide a greater scope for the deployment in applications such as architectural glass, optical components, photovoltaic cells, and energy storage, as well as further compatibilize substrates with low temperature stability. Organic removal methods based on UV–ozone treatment are increasing in popularity, but concerns remain regarding large-scale ozone generation and usage of mercury-containing UV lamps. To this end, we present a method that relies on non-ozone-generating UV radiation at 254 nm (UV254) and incorporation of small amounts of photocatalytic material in the formulation, here demonstrated with TiO2 nanocrystals. At concentrations as low as 5 wt % relative to the main inorganic aluminosilicate material, the TiO2 nanocrystals catalyze a “cold combustion” of the organic components under UV254 irradiation to reveal a porous inorganic network. Using block copolymer-based co-assembly in conjunction with photocatalytic template removal, we produce well-defined mesoporous inorganic thin films with controlled porosity and refractive index values, where the required processing time is governed by the amount of TiO2 loading. This approach provides an inexpensive, flexible, and environmentally friendly alternative to traditional organic removal techniques, such as UV–ozone degradation and thermal calcination.

Facilitating electron collection of organic photovoltaics by passivating trap states and tailoring work function

The low-temperature solution-processed ZnO normally has intrinsic oxygen vacancies and various surface defects such as organic residues and surface adsorbates. When ZnO film is used in organic solar cells as electron selective layer, these defects will serve as bimolecular recombination centers for light induced charge carriers and trap electrons, leading to an unsatisfied device performance. Herein, we demonstrate an effective way to employ a simple combination of UV-ozone (UVO) and dipole treatment to passivate the ZnO layer, and the electronic property of ZnO layer is great improved upon eliminating the residual hydrocarbons and passivating surface traps. The reengineered uniform ZnO films play a major role on the facilitated charge transfer and decreased contact resistance, resulting in an enhanced device efficiency. The optimized ZnO transport layer also regulates the upper active layer depositing and morphology, and consequently increases the dissociation of photo-excitons and suppresses charge recombination.

A low-temperature-annealed and UV-ozone-enhanced combustion derived nickel oxide hole injection layer for flexible quantum dot light-emitting diodes.

Sol-gel derived nickel oxide (NiOx) has been extensively investigated as the hole injection layer (HIL) for many optoelectronic devices because of its advantages of high environmental stability and low cost fabrication. Conventional sol-gel synthesis of NiOx requires high annealing temperature to convert precursors into crystal lattices, which limits its application in flexible devices. To address this issue, a low-temperature (150 °C) combustion method is used to synthesize NiOx. Besides, UV-ozone treatment is further performed to improve the electrical properties of low-temperature-grown NiOx, which leads to the formation of nickel oxyhydroxide (NiO(OH)) surface dipoles and Ni vacancies and thus modifies the energy structure and increases the conductivity of NiOx. Moreover, the formation of surface NiO(OH) induces a vacuum level shift and thus reduces the hole injection barrier. Owing to the enhanced hole injection, solution-processed green QLEDs with optimized UV-ozone treated NiOx HILs exhibit maximum current efficiencies of 45.8 cd A-1 and external quantum efficiencies of 10.9%, which outperform those of the devices with poly(3,4-ethylene dioxythiophene) : poly(4-styrenesulfonate) (PEDOT:PSS) HILs. Meanwhile, these devices also show better long-term stability with a 3.2-fold longer half-life time than that of the PEDOT:PSS-based devices. The demonstrated low-temperature-annealed and UV-ozone enhanced NiOx HILs would enable the realization of flexible QLEDs with high brightness, efficiency and stability.

High Performance Single Crystalline Diamond Normally-Off Field Effect Transistors

High performance normally-off hydrogen-terminated diamond (H-diamond) MOSFETs were fabricated on single crystalline diamond grown in our lab. The device with 2- $\mu \text{m}$ gate length shows threshold voltage of −1.0 V, and a drain current of 51.6 mA/mm at $V_{\mathrm{ GS}}= {V}_{\mathrm{ DS}} = -4.5$ V and an on-resistance of $65.39~ \Omega \cdot $ mm. The transconductance keeps increasing when $\text{V}_{\mathrm{ GS}}$ shifts from $\text{V}_{\mathrm{ TH}}$ toward more negative direction, and reaches the record high value of 20 mS/mm at $\text{V}_{\mathrm{ GS}}$ of −4.5 V, which benefitted from the almost constant mobility of the holes in the gate voltage range of −4 V $ V. The critical device process to realize these low on-resistance normally-off MOSFETs consists of 2-min UV ozone treatment of the H-diamond surface and thermal oxidation of aluminum film in the air to form an alumina gate dielectric.

Water Quality Assessment of Major Drinking Waters in Natural Parks

The purpose of this study is to evaluate water quality characteristics of main drinking waters in natural parks, for providing the basic information of water quality and to propose the appropriate management method. to maintain the water quality standards. As a result of the analysis, microorganisms were mostly detected in the nature of natural park. And some sites are currently using UV sterilizer and ozone treatment, and it is considered appropriate to extend the use to other main drinking water. It is also good to boil drinking water at home. Turbidity is expected to improve through environmental cleanup. Overall, the main drinking water in the natural park is suitable for water quality standards, and it is considered that maintenance such as cleaning is necessary.

Impact of Substrate Characteristics on Stretchable Polymer Semiconductor Behavior.

Stretchable conductive polymer films are required to survive not only large tensile strain but also stay functional after the reduction in applied strain. In the deformation process, the elastomer substrate that is typically employed plays a critical role in response to the polymer film. In this study, we examine the role of a polydimethylsiloxane (PDMS) elastomer substrate on the ability to achieve stretchable PDPP-4T films. In particular, we consider the adhesion and near-surface modulus of the PDMS tuned through UV/ozone (UVO) treatment on the competition between film wrinkling and plastic deformation. We also consider the role of PDMS tension on the stability of films under cyclic strain. We find that increasing the near-surface modulus of the PDMS and maintaining the PDMS in tension throughout the cyclic strain process promote plastic deformation over film wrinkling. In addition, the UVO treatment increases film adhesion to the PDMS resulting in a significantly reduced film folding and delamination. For a 20 min UVO-treated PDMS, we show that a PDPP-4T film root-mean-square roughness is consistently below 3 nm for up to 100 strain cycles with a strain range of 40%. In addition, although the film is plastically deforming, the microstructural order is largely stable as probed by grazing incidence X-ray scattering and UV-visible spectroscopy. These results highlight the importance of neighboring elastomer characteristics on the ability to achieve stretchable polymer semiconductors.

UV- ozone treated graphene oxide/ PEDOT:PSS bilayer as a novel hole transport layer in highly efficient and stable organic solar cells

Abstract The utilization of UV-ozone (UVO) treated graphene oxide (GO)/PEDOT:PSS bilayer as hole transport layer (HTL) in solution processed organic solar cells (OSCs) is demonstrated. The HTLs were treated with UVO for 0, 5, 10 and 15 min. The 10 min treated OSC showed the best performance and displayed power conversion efficiency (PCE) of 5.24%, much higher than the untreated OSC device. This enhanced performance is mainly driven by improvements in the short circuit current (∼10.82 mA/cm2) as well as the fill factor (∼57%) that is ascribed to the moderate reduction of GO and increased work function (WF) of PEDOT:PSS after UVO treatment, which improved the contact conditions between the HTL and photoactive layer. Consequently, extraction efficiency of the photogenerated holes is increased, while recombination probability of holes and electrons in the photoactive layer is decreased. Moreover, the UVO-reduction of GO and consequently increased conductivity of reduced-GO (r-GO) has been modeled and proved using the density functional theory (DFT) simulation. Meanwhile, the 15 min UVO-treated OSC device showed severe reduction in the PCE that dropped to 2.11%, possibly due to various factors such as decomposition of chemical bonds, significant increase in the series resistance and pronounced drop in the photovoltaic performance parameters.

A Nondestructive Surface Zwitterionization of Polydimethylsiloxane for the Improved Human Blood-inert Properties.

Polydimethylsiloxane (PDMS) is extensively used in the field of biomaterials. However, its hydrophobicity still limits its range of applications and makes it prone to biofouling. Various techniques are currently utilized to overcome this limitation, but most of them reduce some of the PDMS prime characteristics, such as its mechanical strength and optical transparency. In this work, we employed an original two-step coating process to bypass harsh treatments on PDMS like UV-ozone or plasma treatment. A pre-coating step of tannic acid-Fe(III) complex was performed prior to the zwitterionization of the PDMS with poly(glycidyl methacrylate-co-sulfobetaine methacrylate) or poly(GMA-co-SBMA) by a "grafting-to" approach. Successful coating was evidenced by a decrease of the water-contact angle from 118° to 79°. The process was optimized, and the optimized coating condition led to a significant improvement of the PDMS biocompatibility while maintaining its mechanical property and optical transparency. In addition, a 90% reduction of Escherichia coli attachment and fibrinogen plasma protein, an 80% reduction of red blood cells and cells from whole-blood attachment, and a 60% reduction of platelets adhesion were measured. We further tested the potential of the zwitterionic PDMS material as a storage vessel for platelet-rich plasma under physiological conditions. Platelet activation was decreased from 10.95% using virgin PDMS to 3.35% with the coated sample in a period of 2 days.

High-Performance Flexible Schottky Diodes Based on Sputtered InGaZnO

High-performance flexible InGaZnO-based Schottky diodes are fabricated on polyethylene terephthalate (PET) and polyimide (PI) substrates at room temperature without any thermal treatment. The diode performance improves significantly by either oxygen plasma or UV-ozone treatment on Pd anode. X-ray photo-electron spectroscopy indicates that both treatments lead to Pd surface oxidation. The oxygen plasma treatment results in more complete oxidation, and thus ensures better oxygen stoichiometry at the Schottky interface and a higher anode work function. This leads to high performance with on/off ratios of $7.3 \times 10^{6}$ and $2.6 \times 10^{4}$ , barrier heights of 0.79 and 0.76 eV, and ideality factors of 1.22 and 1.19 on PET and PI, respectively. Interestingly, these flexible diodes show improved performance after storing in ambient air for two years, and fittings on the reverse currents indicate an improved barrier uniformity. The flexible diode on PET after a two-year storage achieves a high on/off ratio of 2 107, a large barrier height of 0.80 eV, a close to unity ideality factor of 1.09, a high breakdown voltage of −7.5 V, and robust performance upon outward or inward bending, which is, to the best of our knowledge, the highest performance in reported flexible diodes to date.

Addition Effect of Pyreneammonium Iodide to Methylammonium Lead Halide Perovskite‐2D/3D Heterostructured Perovskite with Enhanced Stability

AbstractDespite the eminent performance of the organometallic halide perovskite solar cells (PSCs), the poor stability for humidity and ultraviolet irradiation is still major problem for the commercialization of PSCs. Herein, a novel functional organic compound 1‐(ammonium acetyl)pyrene is successfully introduced for preparing the 2D/3D heterostructured MAPbI3 perovskite. Because of the functional organic pyrene group with high humidity resistance and strong absorption in the ultraviolet region, the 2D/3D perovskite film shows notable stability with no degradation in ≈60% relative humidity after even six months and exhibits a high ultraviolet irradiation stability which keeps nearly no degradation after 1 h in the UV Ozone treatment. Planar PSCs are fabricated in the ≈60% relative humidity air outside glovebox. The champion efficiency of (PEY2PbI4)0.02MAPbI3 perovskite solar cells is 14.7% with nearly no hysteresis which is equal performance of 3D MAPbI3 devices (15.0%). This work presents a new direction for enhancing the solar cells' performance and stability by incorporating a functional organic aromatic compound into the perovskite layer.

Low temperature solution deposited niobium oxide films as efficient electron transport layer for planar perovskite solar cell

In high efficient planar perovskite solar cells (PSC), electron transportation layer (ETL) plays an important role in its photovoltaic performance. Except for TiO2, Nb2O5 has also been considered as ideal electron selective layer material for planar perovskite solar cell due to its excellent optical transmittance and similar Femi level with TiO2. Herein, we report niobium oxide film deposited by a simple and low temperature solution method, as an effective alternative to high temperature sintered TiO2 film in the regular architecture of PSC. Nb2O5 modification of FTO has successfully tuned the surface work function from 4.59 eV to 4.28 eV without obviously affecting the surface roughness and optical transmittance, which could significantly decrease energy level offset and improve the open voltage. Appropriate UV ozone treatment could adjust the surface hydrophilicity of Nb2O5 film benefiting the growth of perovskite films on low temperature solution deposited Nb2O5 coated FTO substrate. Relatively high efficiency over 17% with less J–V hysteresis has been achieved by optimizing the precursor solution, spin rate, annealing temperature and UV ozone treatment time. The results indicate low temperature solution deposited Nb2O5 film can be a low cost and easy-prepared ETL material for high performance PSC.

Mechanical Reliability of Flexible Encapsulated Organic Solar Cells: Characterization and Improvement.

The encapsulation of organic photovoltaic (OPV) devices can help mitigate the degradation induced by environmental factors like water and oxygen and thus potential to increase OPV lifetime. Because flexibility is an important parameter for targeted OPV applications, this paper proposes a fundamental study on the impact of the roll-to-roll flexible encapsulation process. Both performance and mechanical reliability of encapsulated devices have been scouted. Furthermore, it has been demonstrated that a relatively simple peeling technique allows understanding the role of the interfaces inside a multilayered OPV device supported by a flexible poly(ethylene terephthalate) substrate. For this purpose, the peeling strengths between each layer were measured using a series of partial devices. This provided a quantitative analysis of the mechanical strength or quality of each interface. Two interfaces revealed pronounced weaknesses: active layer with hole transporting layer and transparent conducting electrode with electron transporting layer. Among various surface treatments applied to improve these interfaces, an optimized UV-ozone (UVO3) treatment proved to modify substantially the surface properties of used zinc oxide (ZnO) and thus improved its adhesion to the neighboring layers. The physicochemical and structural changes of ZnO have been confirmed by IR spectroscopy and contact angle measurements. It has also been shown that better interfaces within the device improve the overall performance of the devices and their resilience to roll-to-roll encapsulation.

Improvement of OLED performance by tuning of silver oxide buffer layer composition on silver grid surface using UV-ozone treatment

In this study, silver grid/Ag2O and AgOx/MoO3 transparent conductive electrodes (TCEs) were fabricated and implemented in organic light-emitting diodes (OLEDs). The effects of ultraviolet (UV)-ozone treatment time on the silver grids are discussed. With a treatment duration of 15 s, the Ag2O thin films do not grow completely and current-voltage characteristics are poor. However, a 30 s UV-ozone treatment yielded good-quality Ag2O thin films. The Ag2O thin films were reconverted into the AgOx phase with further increases in UV-ozone exposure time. The Ag2O work function is nearly 5.0 eV, which decreases the injection barrier of the silver grids (∼4.7 eV) and MoO3 (∼5.3 eV). Nevertheless, excessive treatment time leads to the production of AgOx thin films and an increase in the work function to 5.3 eV, the same as the highest occupied molecular orbital energy of MoO3, which causes a work function mismatch. The work function mismatch between the Ag grids and the MoO3 layer results in a high injection barrier, decreasing OLED performance. The electrical properties of the electrodes and devices apparently depend on the composition of the silver oxide buffer layer, as determined using X-ray photoelectron spectroscopy. The surface and optical properties of the TCEs were also investigated. The results show that the OLED devices with the proposed TCEs have better roll off and current efficiency compared to traditional ITO-based devices.

Carbon nanotube heat transfer fluids for solar radiant heating of buildings

Solar-based radiant heating systems represent a sustainable, and relatively low-cost, technology to raise the temperature of the interior thermal mass of our buildings. Through the use of direct absorption solar thermal collectors, the same working fluid which absorbs the solar energy can be used to transfer the energy for storage in the thermal mass of the structure using a network of pipes embedded in concrete floors. This study investigates a promising working fluid which can be used in such systems – one which is based on multi-walled carbon-nanotubes suspended in normal base fluids. A major stumbling block affecting the wide spread use of carbon-nanotube nanofluids is their low dispersion stability at elevated temperatures, which significantly reduces the absorption capabilities of the nanofluids and could lead to clogging of the pumps used to circulate the fluids. In this paper, we report on a scalable UV-ozone (UVO) treatment technique to produce highly stable dispersions for the elevated temperatures experienced by working fluids in radiant heating systems. To probe suitability of UVO treated multi-walled carbon-nanotube (MWCNTs) for solar-assisted radiant heating systems, this paper investigates the effects of exposure time and temperature on stability, optical absorbance properties, the extent of functionalisation, and the photothermal conversion performance of UVO-treated MWCNT nanofluids. No agglomeration or degradation of the MWCNTs was observed at elevated temperatures (up to 150 °C), highlighting the stability of proposed nanofluids.

Simple and versatile UV-ozone oxide for silicon solar cell applications

Semiconductor surface clean is sometimes perceived as costly but long recognized as pivotal in determining the final semiconductor device performance and yield. In this contribution, we investigated the effectiveness of crystalline silicon surface cleaning by a simple UV-ozone process in comparison to the industry standard RCA clean for silicon photovoltaic applications. We present a unique method of processing the silicon surface effectively by UV-ozone cleaning. Despite being simple, UV-ozone cleaning results in a superior surface passivation quality that is comparable to high-quality RCA clean. When used as a stack dielectric—UV-ozone oxide overlaid by aluminum oxide—the thickness of UV-ozone oxide plays an important role in determining the passivation quality. Of all treatment times, 15 min of UV-ozone treatment results in an outstanding passivation quality, achieving the effective carrier lifetime of 3 ms and saturation current density of 5 fA/cm2. In addition, we present a simple and effective technique to extract values of electron/hole capture cross-section for the purpose of analyzing the interface passivation quality from already measured surface recombination parameters of saturation current density, interfacial trap density and total fixed charge, instead of measuring on the separately prepared metal-insulated-semiconductor (MIS) samples by the techniques: frequency-dependent parallel conductance or deep-level transient spectroscopy.