Color Neutrality Research Articles

Heat-Insulating Black Electrochromic Device Enabled by Reversible Nickel-Copper Electrodeposition.

An electrochromic device (ECD), which can switch between black and transmissive states under electrical bias, is a promising candidate for smart windows due to its color neutrality and excellent durability. Most of the black ECDs are achieved through a reversible electrodeposition and dissolution mechanism; however, they typically suffer from relatively poor cycling stability and a slow coloration/bleaching time. Herein, we present a heat-insulating black ECD with a gel electrolyte that operates via reversible Ni-Cu electrodeposition and dissolution. With the adoption of a Cu alloying strategy and a compatible gel electrolyte, this two-electrode ECD (5.0 cm × 2.5 cm) can achieve a cycling stability of 1500 cycles with transmittance modulation up to 55.2% in short coloration (6.2 s) and bleaching times (13.2 s) at a wavelength of 550 nm. Additionally, the ECD can be switched from the transparent state (visible light transmittance: 0.566) to the opaque state (visible light transmittance: 0.003) within 1 min, reaching transmittance less than 5% across the visible-near-infrared spectrum (400-2000 nm) to efficiently block solar heat. Besides, in the voltage-off state, the black Ni-Cu alloy film can be sustained for more than 60 min (at room temperature, λ = 550 nm). Under infrared irradiation (170 W/m2) for 30 min, the black ECD blocks up to 35.0% of infrared radiation, which not only effectively prevents the heat transmission for energy management but also finds potential applications for promoting indoor human health and indoor farming.

Highly Visible‐Transparent and Color‐Neutral Perovskite Solar Cells for Self‐Powered Smart Windows

Electrochromic smart windows can reduce the energy consumption of buildings by managing the light and heat transmission. However, they need external power to work, raising the installation cost and compromising the aesthetics of the buildings. Self‐powered smart windows without external power sources have great potential in practical applications. Transparent solar cells can be integrated with smart windows and serve as their power sources. High optical transmittance, good color neutrality, and high power conversion efficiency (PCE) are required for the transparent solar cells to meet the optical and power requirements of self‐powered smart windows. Herein, an efficient MAPbCl3‐based transparent perovskite solar cell (TPSC) using a solvent‐assisted two‐step approach is developed. The transparency and color‐neutrality of the TPSCs are optimized through delicately selecting and pairing the charge transport layers and transparent electrodes. The TPSCs achieve a PCE up to 1.06% and average visible transmittance up to 72%. Self‐powered smart windows powered by the TPSCs show fast and reversible modulation of visible light from 55% to 5% without external power input. This work demonstrates the prospect of deploying TPSCs in a self‐powered smart window for energy saving and sustainable buildings.

Simultaneous Enhanced Device Efficiency and Color Neutrality in Semitransparent Organic Photovoltaics Employing a Synergy of Ternary Strategy and Optical Engineering

AbstractPower conversion efficiency (PCE) and color rendering index (CRI) are two important parameters for realizing the potential application of semitransparent organic photovoltaics (ST‐OPVs) into the field of building‐integrated photovoltaics (BIPVs). Herein, to extend the PCE limit while showing desirable neutral‐colored perception, formally in a trade‐off relationship, of ST‐OPVs, new ternary photoactive layers composed of polymer donor PM6‐Ir1, non‐fullerene acceptor BTP‐eC9, and fullerene acceptor PC71BM as the third component are employed, which are effective to improve opaque device efficiency while modulating CRI in relevant ternary blends. Furthermore, multifunctional ST‐OPVs are realized via simultaneously optimizing the content of PC71BM in acceptors and employing a simple photonic reflector, leading to not only excellent neutral color perception with a CRI of 96.5 but also a PCE of 14.09% with an average visible transmittance higher than 20%. Vivid backgrounds can be clearly seen through the 1‐DBR‐based ternary ST‐OPVs. Overall, these results represent the best‐performing multifunctional ST‐OPVs, and this synergistic effect can pave the road for ST‐OPVs as promising BIPVs of high device performance and good color neutrality.

Electronic properties and ion migration of “in vacuo” lithiated nanoporous WO3:Mo thin films

Electrochromic (EC) glazing helps manage daylight and solar heat gains in building, thereby allowing a reduction in energy consumption caused by heating, cooling, and artificial lighting. This study relates the optical and electronic properties of nanoporous amorphous molybdenum-doped tungsten trioxide thin films (WO3:Mo) in the pristine state and upon lithiation. When such a film is used as a cathode in EC devices, the color neutrality can be improved with respect to pure WO3, and electrochromic transmission control can be achieved in the full spectral range of solar radiation. In situ x-ray photoelectron spectroscopy reveals that the coloration mechanism is related to the reduction of W6+ to W5+ and Mo6+ to Mo5+. In the initial stages of lithiation, Mo is preferably reduced followed by the reduction of W. Ultraviolet photoelectron spectroscopy highlights systematic trends in the position of the valence band edge and in work function. The occurrence of peaks at 2.2 and 0.8 eV is observed and is related to the formation of partially delocalized Mo5+ and W5+ midgap states. Visible/near-infrared spectrophotometry shows initial absorption mainly in the visible spectral range, followed by absorption in the near infrared. Both absorption bands can be associated with the midgap states due to the occurrence of Mo5+ and W5+, respectively. Lithiation of bilayers composed of WO3:Mo and WO3 shows that the Mo5+ states, which are energetically lower, trap preferentially the transferred charges. Furthermore, our results suggest that lithium ions diffuse rather freely in the direction perpendicular to the substrate. These findings pave the way to next-generation EC devices with color neutral and broadband modulation of spectral transmission and in principle also with dual-band modulation of visible and near-infrared light.

Ultrathin Solar Cell With Magnesium-Based Optical Switching for Window Applications

Photovoltaic windows that can be switched between transparent and energy harvesting mode can be realized by using ultrathin solar absorbers embedded in an optical nanocavity. In the present work, we use a 5 nm thick amorphous germanium absorber integrated in a magnesium-based thin film optical cavity, which switches from an absorptive to a transparent state due to hydrogen absorption. We analyze the influence of the mirror layer thickness on the light absorption, photocurrent generation, and transmission as well as color neutrality of the device. The optical properties are studied by 1-D transfer-matrix method by changing Mg thickness between 0 and 100 nm, then compared to the experimental results of fabricated devices. When the thickness of Mg increases, the switchable average transparency varies between 25% and 0%, while the power conversion efficiency rises up to 2.3%. The applicability of the device is tested by modeling the annual power generation in realistic scenarios. The influence of the cardinal orientation and the seasons on the switchable photovoltaic window implemented in a building facade with the abovementioned parameters is analyzed for different switching scenarios.

Topological confinement of vortices in two-flavor dense QCD

We find a novel confinement mechanism in the two-flavor dense quark matter proposed recently, that consists of the 2SC condensates and the P-wave diquark condensates of d-quarks. This quark matter exhibiting color superconductivity as well as superfluidity is classified into two phases; confined and deconfined phases of vortices. We establish that the criterion of the confinement is color neutrality of Aharonov-Bohm (AB) phases: vortices exhibiting color non-singlet AB phases are confined by the so-called AB defects to form color-singlet bound states. In the deconfined phase, the most stable vortices are non-Abelian Alice strings, which are superfluid vortices with fractional circulation and non-Abelian color magnetic fluxes therein, exhibiting color non-singlet AB phases. On the other hand, in the confined phase, these non-Abelian vortices are confined to either a baryonic or mesonic bound state in which constituent vortices are connected by AB defects. The baryonic bound state consists of three non-Abelian Alice strings with different color magnetic fluxes with the total flux canceled out connected by a domain wall junction, while the mesonic bound state consists of two non-Abelian Alice strings with the same color magnetic fluxes connected by a single domain wall. Interestingly, the latter contains a color magnetic flux in its core, but this can exist because of color neutrality of its AB phase.

Reversible Electrodeposition of Ni and Cu for Dynamic Windows

Reversible metal electrodeposition is a promising method for constructing dynamic windows with electronically switchable transparency. Through the reduction of lighting, heating, and cooling costs, these windows reduce energy consumption. Here, we design new electrolytes for reversible metal electrodeposition on tin-doped indium oxide electrodes based on the co-electrodeposition of Ni and Cu. We determined that synergistic effects between Ni and Cu facilitate spectroelectrochemical reversibility in contrast to the individual electrodeposition of these metals. The most reversible electrolytes contain chloride to improve electrodeposition kinetics and sulfamate ions to prevent the formation of dendrites. In addition to improving the color neutrality of the electrodeposits, nickel sulfamate in the electrolytes serves as a source of sulfamate ions that is soluble without added acid. After investigating the functions of the different electrolyte components, we then evaluated the performance of 25 cm2 two-electrode Ni-Cu dynamic windows.

Design, Development, and Characterization of Low Distortion Advanced Semitransparent Photovoltaic Glass for Buildings Applications

Aesthetic appearance of building-integrated photovoltaic (BIPV) products, such as semitransparent PV (STPV) glass, is crucial for their widespread adoption and contribution to the net-zero energy building (NZEB) goal. However, the visual distortion significantly limits the aesthetics of STPV glass. In this study, we investigate the distortion effect of transparent periodic-micropattern-based thin-film PV (PMPV) panels available in the market. To minimize the visual distortion of such PMPV glass panel types, we design and develop an aperiodic micropattern-based PV (APMP) glass that significantly reduces visual distortion. The developed APMP glass demonstrates a haze ratio of 3.7% compared to the 10.7% of PMPV glass. Furthermore, the developed AMPV glass shows an average visible transmittance (AVT) of 58.3% which is around 1.3 times higher than that of AMPV glass (43.8%). Finally, the measured CIELAB values (L* = 43.2, a* = −1.55, b* = −2.86.) indicate that our developed AMPV glass possesses excellent color neutrality, which makes them suitable for commercial applications. Based on the characterization results, this study will have a significant impact on the areas of smart window glasses that can play a vital role in developing a sustainable environment and enhancing the aesthetical appearance of net-zero energy buildings (NZEB).

Optical properties of in vacuo lithiated nanoporous WO3:Mo thin films as determined by spectroscopic ellipsometry

Incorporation of Mo into pure WO3 thin films is of interest for electrochromic devices, as it improves colour neutrality in the dark state. Existing literature still lacks reliable quantitative data on the complex dielectric function of such coatings. In this study, we deposited WO3 and MoxW1−xO3 thin films by magnetron sputtering and subsequently characterised them by X-ray photoelectron spectrometry (XPS), grazing incidence X-ray diffraction (GIXRD) and scanning electron microscopy (SEM). In vacuo-lithiation was performed to incorporate lithium inside the thin films. The lithiated films were evaluated with variable-angle spectroscopic ellipsometry (VASE) from 340 to 990 nm and with transmission measurements from 330 to 2100 nm. The ellipsometric data were analysed with a straightforward model composed of the sum of Tauc-Lorentz and Lorentz oscillators dispersion laws. One Lorentz oscillator positioned around 1.3 eV is associated with the reduction of W6+ to W5+ by lithium incorporation. One Lorentz oscillator positioned around 2.3 eV is associated with additional states in the band-gap due to the presence of Mo in the lithiated film. The proposed model allows a better comprehension of the involved electronic transitions and allows to determine the refractive index and extinction coefficient of the materials precisely.

Optical simulations to inform the design of UV-absorbing organic materials and solar cells

Organic solar cells are ideal for semi-transparent applications given their “peaky” absorption, which allows them to selectively absorb photons outside the visible range while transmitting visible light. Such devices embody a fundamental tradeoff between transparency and power generation that must be optimized to fit the requirements of each potential application—for example, powering electrically dimmable smart windows. To inform the design of organic ultraviolet-absorbers and solar cells that target such applications, we computer-generate sets of optical constants with a range of absorption coefficients and absorption cutoff wavelengths that mimic those of real organic semiconductors. We then perform optical transfer-matrix simulations to determine the absorption and transmission spectra of full-stack photovoltaic cells, inserting these computer-generated optical constants to describe the photoactive absorbing layers. We find that solar cells having absorbers with a cutoff wavelength of 420 nm produce the most power without degrading transparency or color neutrality, and that absorption coefficients up to 5 × 105 cm−1 are needed to fully absorb the targeted wavelengths within practical photoactive layer thicknesses <300 nm in the absence of a reflecting electrode.

Large‐Area Electrochromic Devices on Flexible Polymer Substrates with High Optical Contrast and Enhanced Cycling Stability

AbstractLarge‐area electrochromic devices (ECDs) based on a cathodically‐coloring, side chain‐modified poly(3,4‐ethylene dioxythiophene) (PEDOT) derivative and anodically‐coloring Prussian blue (PB) are assembled by a customized sheet‐to‐sheet (S2S) lamination process. The ECDs with two complementary switching “half‐cells”, based on flexible PET‐ITO substrates, offer enhanced optical properties in terms of visible light transmission change (4–53%), contrast ratio (CR = 93.4) and color neutrality (L* = 77.9, a* = −5.9, b* = −0.6) in the bleached state. The cycling stability is monitored for up to 10 000 switching cycles (97% charge retention). The reported optical, electrochemical, and in operando (in situ) spectroelectrochemical data are obtained from small laboratory‐scale ECDs (active area: 5 × 5 cm2). These results, the homogeneity of the large‐area devices and the scalability of the S2S lamination process are confirmed by measurements on the large ECDs with an active area of 45 × 65 cm2. This large‐area electrochromic film technology with high optical contrast and enhanced cycling stability offers an excellent perspective for further development and scale‐up towards pilot production and the commercialization of flexible ECDs upon their unique materials and processing characteristics.

Color-neutral, semitransparent organic photovoltaics for power window applications

Semitransparent organic photovoltaic cells (ST-OPVs) are emerging as a solution for solar energy harvesting on building facades, rooftops, and windows. However, the trade-off between power-conversion efficiency (PCE) and the average photopic transmission (APT) in color-neutral devices limits their utility as attractive, power-generating windows. A color-neutral ST-OPV is demonstrated by using a transparent indium tin oxide (ITO) anode along with a narrow energy gap nonfullerene acceptor near-infrared (NIR) absorbing cell and outcoupling (OC) coatings on the exit surface. The device exhibits PCE = 8.1 ± 0.3% and APT = 43.3 ± 1.2% that combine to achieve a light-utilization efficiency of LUE = 3.5 ± 0.1%. Commission Internationale d'eclairage chromaticity coordinates of (0.38, 0.39), a color-rendering index of 86, and a correlated color temperature of 4,143 K are obtained for simulated AM1.5 illumination transmitted through the cell. Using an ultrathin metal anode in place of ITO, we demonstrate a slightly green-tinted ST-OPV with PCE = 10.8 ± 0.5% and APT = 45.7 ± 2.1% yielding LUE = 5.0 ± 0.3% These results indicate that ST-OPVs can combine both efficiency and color neutrality in a single device.

Fabrication of mesoporous double-layer antireflection coatings with near-neutral color and application in crystalline silicon solar modules

Single-layer antireflection (SLAR) coatings have been applied in crystalline silicon solar modules for a decade, which evolved from open-pore silica at an early stage into closed-pore structures nowadays in industry. For improving photovoltaic and aesthetic characteristics of solar modules, not only AR properties but also color neutrality of AR coatings need to be intensively studied. In this work, the double-layer antireflection (DLAR) coatings were designed and their residual color was studied by comparing with conventional SLAR and DLAR coatings under both normal and oblique incidences. According to the design, we fabricated the mesoporous DLAR coatings, which exhibited a high average transmittance of Tave = 99.02% at visible wavelengths from 380 nm to 780 nm and a low chroma value of C = 3.35. Applying the mesoporous DLAR coatings to the crystalline silicon mini-modules, the power conversion efficiency was increased by 2.40% on average in relative terms. Besides the power output gain, durable DLAR coatings with neutral color are of great significance for not only imparting a natural and sheer-black appearance to photovoltaic modules without unwanted blueish color, but also finding practical applications in consumer electronics, building glazing, and display windows.

Hadronization and Charm-Hadron Ratios in Heavy-Ion Collisions.

Understanding the hadronization of the quark-gluon plasma (QGP) remains a challenging problem in the study of strong-interaction matter as produced in ultrarelativistic heavy-ion collisions (URHICs). The large mass of heavy quarks renders them excellent tracers of the color neutralization process of the QGP when they convert into various heavy-flavor (HF) hadrons. We develop a 4-momentum conserving recombination model for HF mesons and baryons that recovers the thermal and chemical equilibrium limits and accounts for space-momentum correlations (SMCs) of heavy quarks with partons of the hydrodynamically expanding QGP, thereby resolving a long-standing problem in quark coalescence models. The SMCs enhance the recombination of fast-moving heavy quarks with high-flow thermal quarks in the outer regions of the fireball. We also improve the hadrochemistry with "missing" charm-baryon states, previously found to describe the large Λ_{c}/D^{0} ratio observed in proton-proton collisions. Both SMCs and hadrochemistry, as part of our HF hydro-Langevin-recombination model for the strongly coupled QGP, importantly figure in the description of recent data for the Λ_{c}/D^{0} ratio and D-meson elliptic flow in URHICs.

Controlling the Optical Properties of Dynamic Windows Based on Reversible Metal Electrodeposition

We describe physicochemical strategies that allow for control of the transmission and color of dynamic windows based on reversible metal electrodeposition. The electrolyte composition and voltage profile used for Bi and Cu electrodeposition significantly affect the color of the devices as quantified by La*b* space colorimetry (L = lightness, a* = red/green coordinate, b* = yellow/blue coordinate). First, in terms of electrolyte composition, we find that although increasing the Cu ion concentration improves the maximum attainable opacity of the devices, it decreases the color neutrality of the windows. Second, we demonstrate that altering the electrodeposition voltage profile affects the average size of the metal electrodeposits, which in turn dictates device color during tinting. Through a combination of SEM-EDX imaging and Mie theory calculations, we develop a model that satisfactorily predicts the relationship between electrodeposit morphology and color neutrality. By using pulsed electrodeposition to f...

New Roll‐to‐Roll Processable PEDOT‐Based Polymer with Colorless Bleached State for Flexible Electrochromic Devices

AbstractConjugated electrochromic (EC) polymers for flexible EC devices (ECDs) generally lack a fully colorless bleached state. A strategy to overcome this drawback is the implementation of a new sidechain‐modified poly(3,4‐ethylene dioxythiophene) derivative that can be deposited in thin‐film form in a customized high‐throughput and large‐area roll‐to‐roll polymerization process. The sidechain modification provides enhanced EC properties in terms of visible light transmittance change, Δτv = 59% (ΔL* = 54.1), contrast ratio (CR = 15.8), coloration efficiency (η = 530 cm² C−1), and color neutrality (L* = 83.8, a* = −4.3, b* = −4.1) in the bleached state. The intense blue‐colored polymer thin films exhibit high cycle stability (10 000 cycles) and fast response times. The design, synthesis, and polymerization of the modified 3,4‐ethylene dioxythiophene derivative are discussed along with a detailed optical, electrochemical, and spectroelectrochemical characterization of the resulting EC thin films. Finally, a flexible see‐through ECD with a visible light transmittance change of Δτv = 47% (ΔL* = 51.9) and a neutral‐colored bleached state is developed.

Effects of fluctuations and color neutrality in a finite volume

AbstractWe investigate properties of strongly interacting matter in a schematic model based on the combined degrees of freedom of a noninteracting hadronic phase and a noninteracting deconfined phase. It is found that, in a finite system, both phases contribute to the thermodynamic state due to fluctuations and that signatures of critical behavior, such as the divergence of statistical quantities, are dampened. The constraint of color neutrality leads to a volume‐dependent shift of the effective critical temperature, which follows a scaling law, independent of the baryochemical potential. According to the model, observable baryon number susceptibilities at a given T and μB strongly depend on the system size. Finally, we compare hadronization conditions from the model with hadrochemical fits to experimental collider data, where a qualitatively similar system size dependence is extracted.

Color neutral nanocomposite nickel-tantalum oxide for electrochromic windows

Electrochromic windows can darken on demand to limit the solar gains entering a building to reduce the risk of overheating, while preserving the view towards the exterior. Yet, the switching speed and contrast as well as the durability of commercial products still need to be improved. Novel materials are investigated to address these shortcomings. Since gel or polymer electrolytes limit the durability of electrochromic glazing, all-solid state, inorganic devices are considered. The optical properties of doped nickel oxides were studied in order to obtain a color neutral anodic electrochromic oxide. The addition of tantalum was shown to increase the light transmittance and to provide a coating with better color neutrality compared to nickel vanadium oxides. The study of the crystalline structure by X-ray diffraction suggests that a nickel oxide-tantalum pentoxide nanocomposite is formed. These results are encouraging to use nickel tantalum oxide as an anodic electrochromic oxide.

Fine-Tuning the Color Hue of π-Conjugated Black-to-Clear Electrochromic Random Copolymers

A family of dioxythiophene (DOT)-based conjugated random copolymers, capable of reversibly switching between a neutral black and an oxidized transmissive state, are reported for electrochromic (EC) applications. By replacing 3,4-ethylenedioxythiophene (EDOT) in the previous generation of a core donor–acceptor–donor (D–A–D) terheterocycle with a methyl-alkylated 3,4-propylenedioxythiophene (ProDOT), we enhance the solubility of precursors and monomers in this new generation of broadly absorbing electrochromic polymers (ECPs). By adjusting the newly designed terheterocycle monomer feed ratio, we obtain three polymers with varying hues of color neutrality (a* and b* < ±10) throughout the entire switching voltage range and with integrated contrasts 45–49% throughout the visible region (380–700 nm). The a* values of the polymers ranged between −8 (green hue) and +5 (red hue), with their b* values ranging between −4 and −7 (blue hue) in their neutral states; additionally, the a* and b* values are all below ±8 i...

Design of Reversible Electroplating Cells for Energy-Saving Windows

Dynamic windows, which allow electronic control over visible light and solar irradiation, enable responsive environments free of glare and unwanted heat. Electronic control over visible light transmittance and solar heat gain coefficients will allow dynamic windows to be integrated with algorithms to optimize for energy efficiency and comfort. The implementation of this technology increases building energy efficiency by 10% compared to traditional, static low-emissivity windows. Dynamic windows based on reversible metal electrodeposition (RME) represent an exciting, new class of electrochromic devices. These RME windows function like a battery by electrochemical movement of metallic ions between a transparent conducting working electrode and a metal mesh or ion-intercalation counter electrode. Metals are ideal light-modulators for dynamic windows because they can be color neutral, inert, photostable, and opaque at 20-30 nanometer thicknesses. Our team has demonstrated metal-based dynamic windows that boast cheap processing, fast switching (<1 minute), and stable performance over thousands of cycles on the 100 cm2 scale. Our current RME windows use an acidic, aqueous halide-based liquid electrolyte that presents technical barriers to device scalability. Due to the inherent voltage drop across the indium tin oxide (ITO) electrode under operating conditions, the electrolyte must exhibit a wide voltage range for uniform metal deposition without undesired side reactions. In an acidic aqueous system, the hydrogen evolution reaction (HER) and ITO oxidation potential set a firm boundary on the voltage range in which the windows can operate. Finally, a liquid electrolyte limits the size of the window due to hydrostatic pressure build up in a vertically oriented window. These design constraints set parameters for developing an electrolyte for RME windows with improved scale and durability. We explore a non-aqueous, non-halide electrolyte that meets these design constraints and is capable of reversibly depositing metals (e.g. Ag and Cu) for RME dynamic windows. The addition of various gel-inducing polymers and electrolyte additives allows us to design windows with reduced hydrostatic pressure build up and improved durability. Utilizing a combination of electrochemical and materials characterization techniques, we present a detailed study of the kinetic and transport properties as well as the morphological and optical effects of this electrolytic system. From these results, we successfully engineered a 400 cm2 window demonstrating fast, uniform transmission change with high optical contrast (~60%), color neutrality, and high cycle life. Developing a strong understanding of reversibly electroplating metals using multivalent metallic ions with variable sizes yields valuable insight to batteries where reversible plating is critical for operation and durability. Further, insights gained from electrolyte-electrode interfaces and interactions in these RME windows can be used to improve fuel cell and battery performance. Reversible Metal Electrodeposition Operating Principle and Schematic: Figure 1