Visible Light Transparency Research Articles

Computational Screening of p -Type Transparent Conducting Oxides Using the Optical Absorption Spectra and Oxygen-Vacancy Formation Energies

Although n-type transparent conducting oxides (TCOs) with visible-light transparency and electric conductivity have been used in industry for decades, their p-type counterparts have not been commercialized. To search for promising p-type TCOs, computational screening was applied by several research groups in the last decade. However, screening of a wide material space is mainly based on the approximated physical quantities, such as underestimated band gaps, and band-alignment techniques. In particular, it is unlikely that band alignments can predict the dopability of a wide range of insulators because they do not include information about the chemical potentials of the constituent elements. In this study, we use optical absorption spectra calculated with dielectric dependent hybrid functionals and the formation energies of oxygen vacancies as screening parameters. Oxygen vacancies are known to act as hole killers when seeking p-type TCOs, and indeed, only 156 out of the 845 oxides are found to have benign oxygen vacancies for p-type doping. As a result, we identify six potential p-type TCOs from 845 oxides: ${\mathrm{Na}}_{3}{\mathrm{Ag}\mathrm{O}}_{2}$, ${\mathrm{Rb}}_{2}{\mathrm{Pb}}_{2}{\mathrm{O}}_{3}$, ${\mathrm{Cs}}_{2}{\mathrm{Pb}}_{2}{\mathrm{O}}_{3}$, $\mathrm{Cs}\mathrm{Cu}\mathrm{O}$, ${\mathrm{K}}_{2}{\mathrm{Pb}}_{2}{\mathrm{O}}_{3}$, and ${\mathrm{B}}_{6}\mathrm{O}$. ${\mathrm{Na}}_{3}{\mathrm{Ag}\mathrm{O}}_{2}$, ${\mathrm{Rb}}_{2}{\mathrm{Pb}}_{2}{\mathrm{O}}_{3}$, and ${\mathrm{Cs}}_{2}{\mathrm{Pb}}_{2}{\mathrm{O}}_{3}$ are identified as potential p-type TCOs, while $\mathrm{Cs}\mathrm{Cu}\mathrm{O}$, ${\mathrm{K}}_{2}{\mathrm{Pb}}_{2}{\mathrm{O}}_{3}$, and ${\mathrm{B}}_{6}\mathrm{O}$ were previously proposed. By analyzing the electronic structures and point-defect properties of ${\mathrm{Na}}_{3}{\mathrm{Ag}\mathrm{O}}_{2}$, $\mathrm{Cs}\mathrm{Cu}\mathrm{O}$, and ${\mathrm{K}}_{2}{\mathrm{Pb}}_{2}{\mathrm{O}}_{3}$ in detail, we find that they show p-type conductivity, even without external doping, which validates the use of the formation energies of oxygen vacancies as descriptors of the p-type dopability of oxides.

Multi-functional terahertz metamaterials based on nano-imprinting.

This paper reports a multi-functional terahertz (THz) metamaterial based on a nano-imprinting method. The metamaterial is composed of four layers: 4 L resonant layer, dielectric layer, frequency selective layer, and dielectric layer. The 4 L resonant structure can achieve broadband absorption, while the frequency selective layer can achieve transmission of specific band. The nano-imprinting method combines electroplating of nickel mold and printing of silver nano-particle ink. Using this method, the multilayer metamaterial structures can be fabricated on ultrathin flexible substrates to achieve visible light transparency. For verification, a THz metamaterial with broadband absorption in low frequency and efficient transmission in high frequency is designed and printed. The sample's thickness is about 200 µm and area is 65 × 65 mm2. Moreover, a fiber-based multi-mode terahertz time-domain spectroscopy system was built to test its transmission and reflection spectra. The results are consistent with the expectations.

Cover Feature: Importance of Electron Mediator Transparency: Photocatalytic Hydrogen Production from Polyoxometalate using Dye‐double‐layered Photocatalysts (ChemCatChem 4/2023)

The Cover Feature shows the photocatalytic hydrogen production by dual Ru(II)-dye sensitized layered niobate oxide with intercalated Pt cocatalyst in the presence of redox-reversible M-substituted polyoxometalate anions (M-POM, M = VIV, MnII). In their Research Article, A. Kobayashi and co-workers found that the photocatalytic activity is remarkably higher in MnII-POM aq. than that in VIV-POM aq. despite their comparable redox potentials. Their experimental results suggest that the visible-light transparency of surface-immobilized M-POM is the key factor for the photocatalytic H2 production activity. More information can be found in the Research Article by A. Kobayashi and co-workers.

In-situ synthesis of Pt-CsxWO3/SiO2 composite aerogel with synergistic effect of near-infrared shielding and low thermal conductivity for energy-saving window applications

In order to obtain high-performance energy-saving window material, Pt-CsxWO3/SiO2 composite aerogels were prepared by in-situ solvothermal synthesis and ambient pressure drying method. The relationship among the near-infrared shielding ability, thermal conductivity, thermal insulation performance and microstructure of Pt-CsxWO3/SiO2 composite aerogel was investigated. The as-prepared composite aerogel after heat-treatment at 450 ​°C exhibits low thermal conductivity (0.1090 ​W/(m·k)) of SiO2 aerogel and near-infrared shielding ability at the same time due to its high pore volume (0.537–0.796 ​cm3/g), specific surface area (113.968–141.284 ​m2/g) and W5+ content. The near-infrared shielding rate at 1500 ​nm of the composite aerogel could attain to 84% when the visible light transmittance is 72%. As Pt-CsxWO3/SiO2 composite aerogel has the synergistic effect of near-infrared shielding and low thermal conductivity, the composite aerogel heat-treated at 450 ​°C has excellent visible light transparency and thermal insulation performance. This research provides a new idea for developing high efficient energy-saving window glasses.

Transparent broadband absorber based on a multilayer ITO conductive film.

Present study reports a novel visible-light transparent, microwave broadband absorbing metamaterial. The designed structure is implemented using three different sizes of indium tin oxide (ITO) conductive film patch arrays, which is capable of achieving a reflection coefficient ≤ -10 dB from 2.2 to 18 GHz in simulations. Moreover, a fractional bandwidth of about 156.4% and the absorber thickness of only 0.088 times the cutoff wavelength (the lowest absorption frequency) was achieved. Changing the angle of incidence ensures a good absorption effect with large angle stability, and the absorber has good transmission in the visible range. In accordance with the simulation, a sample with a size of 299 × 299 mm was fabricated, and its wave absorption performance was assessed. The experimental results and the various incidence angles in the simulation of the TE and TM modes correspond well, allowing for the realization of large angle broadband absorption at frequencies ranging from 2.2 to 18 GHz. Thus, it has been found that the structure has good optical transparency and broadband radar absorption capability, both of which will have a wide range of applications in the fields of multi-spectrum stealth and electromagnetic compatibility.

Synthesis and transparent conductivity of crack-free La:BaSnO3 epitaxial flexible sheets.

La-doped BaSnO3 (LBSO), which exhibits both high electron mobility and visible-light transparency, is a promising transparent electrode/transistor material that does not require expensive elements such as indium. However, because a high crystal orientation is necessary for high mobility, the development of a synthetic technique is crucial for next-generation optoelectronic applications. One promising method for achieving this is the lift-off and transfer method. Epitaxial films are first deposited on single-crystal substrates, peeled off from the substrates, and subsequently transferred onto other substrates. However, such transferred sheets typically contain a high density of cracks. Therefore, LBSO sheets with flexibility, high mobility, and transparency have not yet been reported. In this study, we successfully synthesized crack-free LBSO epitaxial sheets via a lift-off and transfer method using a water-soluble Sr3Al2O6 sacrificial layer and amorphous (a-)Al2O3 protection layer. The LBSO sheet simultaneously exhibited a high electron mobility of 80 cm2 V-1 s-1 and a wide optical bandgap of 3.5 eV owing to the epitaxial crystallinity of the sheet. Moreover, two types of LBSO sheets were prepared, flat and rolled sheets, by tuning the lift-off process. The flat sheet had a lateral size of 5 mm × 5 mm, whereas the rolled sheet had a tube shape with a height of 5 mm and a diameter of 1 mm. Such large crack-free area and flexibility were achieved in LBSO sheets owing to the use of the a-Al2O3 protection layer.

RuO2-decorated CsxWO3 composite nanorods as transparent photothermal negative electrode material for enhancing supercapacitor performance in acid electrolyte

With the development of wearable and portable electronics, flexible transparent photothermal supercapacitors which improve the performance via the utilization of sunlight have received increasing attention. The high performance electrode materials, particularly those for negative electrodes in acid electrolytes, are needed. Herein, we developed a novel flexible transparent photothermal supercapacitor using RuO2-decorated CsxWO3 nanorods as the negative electrode material for acid electrolytes. It was demonstrated that the resulting electrodes possessed good pseudocapacitive performance in the potential window of −0.5–0.0 V in 1 M H2SO4 and the appropriate decoration of RuO2 on CsxWO3 nanorods could raise the pseudocapacitance effectively. Also, the fabricated all-solid-state supercapacitor was shown to possess high visible light transparency, flexibility, capacitive performance and stability. Its electrochemical performances could be remarkably enhanced by simulated sunlight illumination because the photothermal conversion-induced temperature increase might reduce the electrolyte and charge-transfer resistances effectively. Further kinetic analysis revealed that the enhanced capacitance was contributed by both the diffusion-limited and surface-limited processes. Accordingly, the strategy to improve the capacitive performance of CsxWO3 nanorods by RuO2 decoration was successful and made the resulting composite have great potential as the negative electrode material for transparent photothermal supercapacitors.

Biodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate) films coated with tannic acid as an active food packaging material

Non-biodegradable plastic packaging waste, such as polyethylene and polypropylene, is increasing, resulting in environmental pollution. In this study, we prepared ecofriendly food packaging films using poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB-4HB), a microbially produced biodegradable aliphatic polyester, as a replacement for non-degradable packaging films. The films were prepared using hot-pressing and surface-modified to be hydrophilic via N2 plasma treatment. Finally, the films were coated with tannic acid (TA) by dip-coating. The effects of these treatments were investigated, and the antioxidant and antibacterial properties of the P3HB-4HB film were evaluated. We found that the TA coating improved the film’s mechanical and thermal properties, which had been reduced by the N2 plasma treatment. Importantly for packaging applications, the TA coating did not affect the visible-light transparency. The films were used to store bananas, and lower weight loss and browning were observed compared to those of non-packaged bananas, demonstrating the promise of the prepared films.

In situ facile one-step solvothermal synthesizing hexagonal ammonium tungsten bronze (NH4)0.33WO3 to tap NIR light absorption ability by controlling crystallinity

Tungsten bronze (TB) has potentially high visible light transparency and excellent near-infrared (NIR) shielding ability. To fully dig out the concealed optical properties of TB with specific chemical components, in this work, hexagonal ammonium tungsten bronze (h-ATB) (NH4)0.33WO3 was fabricated by a one-step solvothermal reaction. Through X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and ultraviolet–visible–near infrared (UV–vis–NIR) spectroscopy to characterize h-ATB, which unraveled that controlling crystallinity could adjust the optical property of h-ATB. In particular, when the crystallinity of the h-ATB is over 95%, it exhibits the attractive NIR light shielding capability, which is in line with the predicted optical property via the first principle calculation based on density functional theory (DFT). Given the result, this work can provide a feasible research idea to explore the hidden optical properties of TB.

NIR band-pass filters for CMOS image sensors constructed with NIR absorbing dyes and plasmonic nanoparticles.

Two NIR band-pass filters for CMOS image sensors are developed by incorporating NIR absorption dye and silver nanodisks simultaneously in a transparent polymer, one of which blocks the NIR near the wavelength of 750 nm and the other near 950 nm. They offer low NIR transmittance while maintaining high visible light transparency even at a thin film thickness of 500 nm. By superimposing the proposed NIR band-pass filters, an NIR cutoff filter with a thickness of 1 µm is formed that shields the NIR at wavelengths longer than 680 nm while remaining transparent in the visible range.

Realizing translucency in aluminosilicate glass at ultralow temperature via cold sintering process

Glass with high visible-light transparency is widely considered as the most important optical material, which typically requires a processing temperature higher than 1000 °C. Here, we report a translucent aluminosilicate glass that can be prepared by cold sintering process (CSP) at merely 300 °C. After eliminating structural pores in hexagonal faujasite (EMT)-type zeolite by heat treatment, the obtained highly active nanoparticles are consolidated to have nearly full density by adding NaOH solution as liquid aids. However, direct densification of EMT powder cannot remove the structural pores of zeolite completely, leading to an opaque compact after the CSP. It is proved that the chemical reaction between the NaOH- and zeolite-derived powders is highly beneficial to dissolution-precipitation process during sintering, leading to the ultra-low activation energy of 27.13 kJ/mol. Although the addition of 5 M NaOH solution greatly promotes the densification via the reaction with aluminosilicate powder, lower or higher concentration of solvent can deteriorate the transmittance of glass. Additionally, the CSP-prepared glass exhibits a Vickers hardness of 4.3 GPa, reaching 60% of the reported value for spark plasma sintering (SPS)-prepared sample.

(Invited, Digital Presentation) Ion Implantation for Amorphous-InGaZnO Sheet Resistance Control Technique

Amorphous indium-gallium-zinc oxide (a-IGZO) attracts much attention for next-generation flat-panel displays due to the large band gap, visible light transparency, printability, thickness-uniformity and low-temperature in film deposition. Using a-IGZO films, thin-film-transistors (TFTs) are realized, which show superior behavior compared with amorphous Si-based TFT. In order to further improve a-IGZO TFT performance via source-drain resistance reduction, plasma treatment, excimer laser annealing and ion implantation methods as the sheet resistance reduction techniques were investigated. Among them, the ion implantation methods have depth control ability through insulator layers and good verticality.In our previous work we elucidated that a-IGZO sheet resistance reduction can be attributed to oxygen vacancy (Vo) generated by noble gas implantation. However, there is still much room for clarifying and improving the implantation method, since it is difficult to measure the gas itself and vacancies profiles in a-IGZO due to small ionization cross sections and small existence ratio. In addition many injectable ion species in a-IGZO are not investigated in detail.In this work, we carried out one of the conventional ion boron (B+) or noble gas neon ion (Ne+) implantations and investigations in 50-nm-thick a-IGZO film on glass. Electron transport properties of B+ or Ne+ implanted a-IGZO films as a function of the a-IGZO depth were investigated by room temperature Hall measurements combined with wet etchings. In case of Ne+ implanted a-IGZO film, we estimated Vo relation density depth profile consistent with the electron concentration depth profile in a-IGZO and implanted Ne density depth profile, since the Ne itself cannot be a donor. In case of B+ implanted a-IGZO film, the Vo concentration profile is not agreement with electron concentration profile only, but also agreement the B profiles at the deep position in the a-IGZO. On the other hand, bonding analyses by X-ray photoelectron spectroscopy (XPS) were carried out. From the XPS results, we find that Vo increases after the Ne+ implantation in a-IGZO and Boron-Oxygen bonding is dominant for the implanted B+ in a-IGZO, which indicates also that boron itself contribute the a-IGZO resistance reduction. Based on the knowledges obtained by the Hall measurements and the XPS results, we carried out a-IGZO TFT processes with gate length L g = 4-10 um and channel width 10 um via the appropriate ion energies and doses of B+ or Ne+ implantation. The TFTs show off current 10-12 A/mm, on/off ratio ~108 in the case of the both ions from relations between gate voltage and drain current. In addition, we investigated the device scalability. The electrical channel length (L eff) is not the same as the L g, and is determined by the carrier profile at the gate edges. L eff = L g - ΔL is obtained by the transmission line method (TLM). From TLM results, we find that the ΔL < 1 um in case of the B+ implantations and ΔL ~ 1 um in case of the Ne+ implantations. In summary, we elucidated that a-IGZO sheet resistance reduction can be attributed to Vo or boron itself.In addition, a-IGZO TFT processes with the ion implantations were carried out, which indicate good on/off ratios and microfabrication possibilities for industrial application. We expect that the B+ or Ne+ implantations in a-IGZO films are useful as resistance control technique for a-IGZO device processing.This work is supported by Beam and Plasma Technology Laboratories Research and Development Division NISSIN ELECTRIC CO., LTD. in the large number of sample preparations and analyses.

Infrared‐Reflective Transparent Hyperbolic Metamaterials for Use in Radiative Cooling Windows

AbstractPassive multilayer coatings for windows have potential to improve energy consumption for indoor temperature regulation. The coatings should block the solar IR energy (800–2500 nm) while maintaining visible light transparency (400–700 nm) to prevent unwanted heating of the interior of a building or a vehicle. It should also efficiently radiate thermal energy to prevent excessive heating. Although solar energy management and radiative cooling techniques have been investigated individually, the combination of the two, a transparent radiative cooler, has emerged only recently. This study theoretically and experimentally demonstrates a transparent radiative cooling window using a combination of planar hyperbolic metamaterials and a uniform layer of polydimethylsiloxane, resulting in high visible transparency (&gt;60%), IR reflectivity (&gt;89%), and thermal emissivity (&gt;95%). Daytime temperature experiments confirm that the cooling window efficiently lowers the interior temperature by as much as 7 °C.

Pressure Engineering Promising Transparent Oxides with Large Conductivity Enhancement and Strong Thermal Stability.

Transparent conducting oxides (TCO) with high electrical conductivity and high visible light transparency are desired for a wide range of high-impact engineering. Yet, usually, a compromise must be made between conductivity and transparency, limiting the practical application of a TCO to the next level. Furthermore, TCO performance is highly sensitive to composition, so conventional synthesis methods, such as chemical doping, cannot unravel the mysteries of the quantitative structure-performance relationship. Thus, improving the fundamental understanding or creating materials-by-design has limited success. Here, a strategy is proposed to modulate the lattice and electronic and optical properties precisely by applying pressure on a TCO. Strikingly, after compression-decompression treatment on the indium titanium oxides (ITiO), a highly transparent and metastable phase with two orders of magnitude enhancement in conductivity is synthesized from an irreversible phase transition. Moreover, this phase possesses previously unattainable filter efficiency on hazardous blue light up to 600°C, providing potential for healthcare-related applications with strong thermal stability up to 200°C. These results demonstrate that pressure engineering is a clean and effective tool for tailoring functional materials that are not achievable by other means, providing an exciting alternative property-tuning dimension in materials science.

Semitransparent polymer solar cell/triboelectric nanogenerator hybrid systems: Synergistic solar and raindrop energy conversion for window-integrated applications

Development of photovoltaic (PV)-derived hybrid power systems can overcome the weather-dependent electricity production and increase the amount of dispatchable renewable energy generation. Herein, monolithic hybrid devices are developed via rational integration of high-performance semitransparent polymer solar cells (ST-PSCs) and liquid−solid triboelectric nanogenerators (TENGs). High-performance PSCs with efficiencies of 17.4% for rigid and 15.7% for flexible devices are achieved. Further electrode modifications and integration of transparent TENGs synergistically balance the above-bandgap photon harvesting and transparency in a broad wavelength range (380 − 1000 nm), yet significantly reduce the transmittance in the near-infrared wavelength range (1000 − 2500 nm) of hybrid devices. The hybrid devices simultaneously provide high visible light transparency, good color fidelity, efficient heat resistance and possibility to integrate on rigid and flexible substrates. The hybrid devices attain a high solar conversion efficiency of 10.1% under 1 sun, indicating efficient light-to-electricity conversion (a maximum electrical power output: 101 W m−2) on sunny days. The hybrid devices can also generate a maximum electrical power output of 2.62 W m−2 through waterdrop energy conversion, implying complementary green electricity production on rainy days. The controlled ambient temperature and specific transmittance windows provided by the hybrid devices sustain plant growth and highlight their great potential in agricultural applications. Gratifyingly, this work demonstrates the first example of ST-PSC/TENG hybrid systems for scaling up renewable power generation in different weather conditions, considering architectural and agricultural applications.

Flexible and Semi-Transparent Silicon Solar Cells as a Power Supply to Smart Contact Lenses.

Supplying electric power to wearable IoT devices, particularly smart contact lenses (SCLs), is one of the main obstacles to widespread adoption and commercialization. In the present study, we have successfully designed, fabricated, and characterized semi-transparent, self-supported, and flexible single crystalline silicon solar cells using a single-sided micromachining procedure. Optical, mechanical, and electrical simulations, together with the practical measurements, verify the application of our developed solar cells to be mounted on a limited-footprint and flexible SCL. The 15 μm-thick silicon solar cells conformally fit on a dome-shaped contact lens (ROC = 8 mm) without any mechanical and electrical degradation. This homojunction photovoltaic device containing an array of micro-holes exhibits a V oc, J sc, and maximum power density of 504 mV, 6.48 mA cm-2, and 1.67 mW cm-2, respectively, at 25% visible light transparency under an AM1.5 one sun condition. Furthermore, the measurements were conducted under low-intensity indoor light conditions and resulted in a maximum power output of 25 and 42 μW cm-2 for the 50 and 25% transparent solar cells, respectively.

High-Performance Semitransparent Organic Solar Cells: From Competing Indexes of Transparency and Efficiency Perspectives.

Semitransparent organic solar cells (ST‐OSCs) offer potentially more opportunities in areas of self‐powered greenhouses and building‐integrated photovoltaic systems. In this work, the effort to use a combination of solution‐processable gold nanobipyramids (AuNBPs)‐based hole transporting layer and a low/high dielectric constant double layer optical coupling layer (OCL) for improving the performance of ST‐OSCs over the two competing indexes of power conversion efficiency (PCE) and average visible transmittance (AVT) is reported. The fabrication and characterization of the ST‐OSCs are guided, at design and analyses level, using the theoretical simulation and experimental optimization. The use of a low/high dielectric constant double layer OCL helps enhancing the visible light transparency while reflecting the near‐infrared (NIR) photons back into the photoactive layer for light harvesting. NIR absorption enhancement in the ST‐OSCs is realized through the AuNBPs‐induced localized surface plasmon resonance (LSPR). The weight ratio of the polymer donor to nonfullerene acceptor in the bulk heterojunction is adjusted to realize the maximum NIR absorption enhancement, enabled by the AuNBPs‐induced LSPR, achieving the high‐performance ST‐OSCs with a high PCE of 13.15% and a high AVT of 25.9%.

Phase stability, phonon, electronic, and optical properties of not-yet-synthesized CsScS2, CsYS2, and APmS2 (A= Li, Na, K, Rb, Cs) materials: Insights from first-principles calculations

Transparent conducting materials (TCMs) combine two exclusive properties, electrical conductivity and visible-light transparency; which make them a unique class of materials. They are required in a wide range of applications in modern life ranging from touchscreen-based devices, flat panel displays, light-emitting diodes (LED), and solar cells. Most of the commercially and widely used TCMs are n-type, whereas the development of high-performance p-type TCMs remains an outstanding challenge in the actual time. Herein, using the newly developed SCAN meta-GGA and the hybrid HSE06 functionals, we have explored the structural stability and physical properties of not-yet-synthesized ternary materials CsScS2, CsYS2, and APmS2 (A = Li, Na, K, Rb, Cs) to identify promising p-type TCMs. As result, the calculated formation energy, phase diagram and phonon dispersion curves confirm that these materials are thermodynamically stable and feasible to synthesize experimentally. All these materials, have large optical band gaps (larger than 3.4 eV), small hole effective masses (except for LiPmS2), and have no absorption and weak reflectivity of the visible light. Our work demonstrates that these compounds have suitable properties for p-type TCMs applications.

Ab initio analysis of MxLa1−xB6 as a solar radiation shielding material

The optical properties and solid solubility of La atoms substituted with another atom were comprehensively investigated using ab initio calculations to improve the optical properties of LaB6. The results confirm that f electrons have little effect on optical properties at low energy, and PrxLa1−xB6, NdxLa1−xB6, SmxLa1−xB6, and GdxLa1−xB6 exhibit comparable optical properties. In addition, monovalent and divalent atoms are relatively easy to form solid solutions with LaB6. In actual applications, as solar radiation shielding materials, SrLa5B36 and EuLa4B30 exhibit satisfactory optical properties, combining transparency in visible light with absorption properties in near-infrared light.

Benzotriazole-containing fluorinated acrylic polymer coatings with high thermal stability, low surface energy, high visible-light transparency, and UV-blocking performance

Benzotriazole-containing fluorinated acrylic polymer coatings with high thermal stability, low surface energy, high visible-light transparency, and UV-blocking performance