Optical Haze Values Research Articles

An energy-efficient and low-driving-voltage flexible smart window enhanced by POSS and CsxWO3

Smart windows with controllable visible and near-infrared (NIR) light transmittance are highly desirable for energy-saving buildings. Herein, we propose a hybrid polymer dispersed liquid crystal (PDLC) film for smart window applications, which combines dopants of polyhedral oligomeric silsesquioxane (POSS) and cesium tungsten bronze (Cs x WO 3 ). The low surface free energy of POSS and NIR absorption of Cs x WO 3 endow the film with enhanced electro-optical performance (ultra-low driving voltages, high contrast ratio and low optical haze value) and maneuverable light modulation in visible and NIR range. A model house equipped with the proposed film as smart windows reveals its outstanding light shielding and temperature regulating abilities that the indoor temperature rises less than 5 o C after irradiation for 10min under the experimental conditions. The research provides new opportunities for further development of energy-efficient smart windows, especially for cooling energy saving in buildings. • A hybrid PDLC film is proposed that can modulate the light passage in both visible and near-infrared ranges. • Cs x WO 3 is introduced to absorb the near-infrared radiation. • Both Cs x WO 3 and POSS can enhance the electro-optical properties of PDLC. • The as-fabricated film can regulate indoor temperature if used as smart windows.

Diphylleia grayi-Inspired Intelligent Hydrochromic Adhesive Film.

Diphylleia grayi-inspired hydrochromic nano/microstructured films have received much attention for its promising smart hydrochromic applications owing to their simple and low-cost but energy-effective strategy. A new type of water-switchable glazing film patterned with various nano/micro air-hole inverse opal arrays is introduced by selectively removing nano/microsphere polystyrene arrays embedded in the surface of polydimethylsiloxane (PDMS) films. Using the significant contrast ratio of the bleaching and the scattering states, we have optimized the switching properties of Mie scattered patterns. As a result, we obtained a single inverse opal layer-embedded PDMS adhesive film with hexagonally close-packed 1 μm air-hole arrays as an optimum scattered film. The differences of diffusive transmittance and optical haze values between the dry and the wet states of the best scattered film reached 44.93% (ΔTD.T = 59.11-14.18%) and 54.88% (ΔH = 69.42-14.54%), respectively. In addition, using the best-optimized inverse opal layer-embedded PDMS film, we fabricated a perfectly imitated Diphylleia grayi structure for camouflage application and an intelligent hydrochromic window device. The dynamic water modulation of the scattered opaque and nonscattered transparent state of the inverse opal-patterned PDMS adhesive film can provide an advanced platform structure in the area of hydrochromic technology for smart windows, camouflage, and clear umbrellas for rainy days.

The Role of Mixed Reaction Promoters in Polyol Synthesis of High Aspect Ratio Ag Nanowires for Transparent Conducting Electrodes

In recent years, thin silver nanowires (Ag NWs) with diameters smaller than 150 nm have been synthesized by implementation of NaCl or FeCl3 as reaction promoters and high molecular weight polyvinylpyrrolidone (PVP) as the capping agent. However, the yield of Ag NWs still remains low, mostly due to the insufficient aspect ratio (AR) of the synthesized nanostructures and the production of Ag nanoparticles, which is an undesirable by product. This study proposes a modified technique to alleviate the problem by using a mixture of FeCl3/CuCl2 as the reaction promoter and two different types of PVP with molecular weight of 360 k and 40 k as the capping agents. The appropriate mixtures of FeCl3/CuCl2 (molar ratio of 1.48:1.45) and PVP 360 k/40 k (molar ratio of 2:1) allow for the rapid synthesis of NWs with diameter of about 110 nm and length of up to 50 μm. It is revealed that the ARs of the synthesized NWs are much greater. The NWs are then used for the fabrication of transparent conductive films (TCFs). The obtained TCF prepared by a scalable, in-house, and cost-efficient spray apparatus possesses a transmittance of 91%, sheet resistance of 10 Ω/sq, and optical haze value of 6.6%. In fact, the AR of the NWs is increased as much as 1135%, and further the figure␣of merit of the TCFs is improved by as much as 2785%.

Improved FTO/NiOx Interfaces for Inverted Planar Triple-Cation Perovskite Solar Cells

Front electrodes of fluorine-doped tin oxide (FTO) thin films and hole-transporting layers of nickel oxide thin films have been combined to fabricate 1.063 cm2 inverted planar solar cells with cesium-containing triple-cation perovskites as absorber layers. Using atmospheric pressure chemical vapor deposition, FTO layers were obtained with low sheet resistance, decreased root-mean-square roughness, increased transmission, and reduced optical haze values compared with a widely used commercial FTO substrate. Cell performance outperformed the equivalent cells fabricated using the commercial FTO. With full illumination under maximum power point tracking, a stabilized power conversion efficiency of 13.78% was obtained for the champion device.

Micro-Segregated Liquid Crystal Haze Films for Photovoltaic Applications: A Novel Strategy to Fabricate Haze Films Employing Liquid Crystal Technology.

Herein, a novel strategy to fabricate haze films employing liquid crystal (LC) technology for photovoltaic (PV) applications is reported. We fabricated a high optical haze film composed of low-molecular LCs and polymer and applied the film to improve the energy conversion efficiency of PV module. The technique utilized to fabricate our haze film is based on spontaneous polymerization-induced phase separation between LCs and polymers. With optimized fabrication conditions, the haze film exhibited an optical haze value over 95% at 550 nm. By simply attaching our haze film onto the front surface of a silicon-based PV module, an overall average enhancement of 2.8% in power conversion efficiency was achieved in comparison with a PV module without our haze film.

The coated porous polyimide layers for optical scattering films

We have investigated the optical scattering characteristic of the air-void micro-structure of air-voids of the porous polyimide (PI) layer prepared from a simple polyimide-precursor coating and the immersion precipitation method. For the careful control or tune of the generated pore-structure, the content of polar aprotic solvent in polar protic non-solvent bath was adjusted during the pore-generation process. To account the correlation between the generated micro-structure of a porous polymer layer and its optical scattering property, the optical haze values were calculated and compared with the measured total transmittance and diffuse transmittance values. And the calculated average optical haze value decreased from 0.88 to 0.53 as increasing the content of polar aprotic solvent in the coagulation bath. In addition, the light scattering mechanism was proposed for a prepared porous polymer film consisting of air-voids inside the polymer media and the rough surface at the ambient interface. Finally, for an analytical explanation, we also introduced Mie scattering and Scalar surface scattering which explains the light scattering inside pore structure as well as at the rough surface, respectively. Based on our systematic approach, it can be said that the net power of light scattering was the sum of Mie scattering and the surface scattering.

Optical and electrical studies of sputter-deposited transparent and conducting ITO/Ag/ITO multilayer on Kapton® substrate for transparent flexible electronic applications

Transparent and conducting thin films on flexible substrates have enormous applications in the areas of space, solar, displays, etc. We hereby report the sputter deposition of transparent and conducting ITO/Ag/ITO (IAI) thin films on commercially available flexible Kapton® substrate at a lower substrate temperature. IAI multilayer has been deposited by magnetron sputtering system using an alloy In:Sn (90%:10%) and Ag targets at room temperature without breaking the vacuum. The optimized IAI coating shows high transmittance (∼81.3% at λ = 650 nm) along with very low resistance (8.36 Ω/□). Optical haze value of IAI on Kapton was measured and found to be <7%. The figure of merit of IAI coating on Kapton® has been calculated using the Haacke’s formula ϕ=T10Rs. At λ = 650 nm ϕ=15×10-3Ω-1 was observed. Our findings give worthful insight into the sputter deposition of transparent conducting IAI coating on flexible Kapton® substrate for flexible electronics applications.

Efficient light-trapping with quasi-periodic uniaxial nanowrinkles for thin-film silicon solar cells

Self-organizing nanopatterns can enable economically competitive, industrially applicable light-harvesting platforms for thin-film solar cells. In this work, we present transparent solar cell substrates having quasi-periodic uniaxial nanowrinkle patterns with high optical haze values. The self-organized nanowrinkle template is created by controlled heat-shrinking of metal-deposited pre-stretched polystyrene sheets. A scalable UV-nanoimprinting method is used to transfer the nanopatterns to glass substrates on which single-junction hydrogenated amorphous silicon p-i-n solar cells are subsequently fabricated. The structural and optical analyses of the solar cell show that the nanowrinkle pattern is replicated throughout the solar cell structure leading to enhanced absorption of light. The efficient broadband light-trapping in the nanowrinkle solar cells results in very high 18.2mA/cm2 short-circuit current density and 9.5% energy-conversion efficiency, which respectively are 35.8% and 39.7% higher than the values obtained in flat-substrate solar cells. The cost- and time-efficient technique introduces a promising new approach to customizable light-management strategies in thin-film solar cells.

Optical haze of transparent and conductive silver nanowire films

Contemporary nanostructured transparent electrodes for use in solar cells require high transmittance and high conductivity, dictating nanostructures with high aspect ratios. Optical haze is an equally important yet unstudied parameter in transparent electrodes for solar cells that is also determined by the geometry of the nanostructures that compose the electrode. In this work, the effect of the silver nanowire diameter on the optical haze values in the visible spectrum was investigated using films composed of wires with either small diameters (~60 nm) or large diameters (~150 nm). Finite difference time domain (FDTD) simulations and experimental transmittance data confirm that smaller diameter nanowires form higher performing transparent conducting electrode (TCE) films according to the current figure of merit. While maintaining near constant transmittance and conductivity for each film, however, it was observed experimentally that films composed of silver nanowires with larger diameters have a higher haze factor than films with smaller diameters. This confirms the FDTD simulations of the haze factor for single nanowires with similarly large and small diameters. This is the first record of haze properties for Ag NWs that have been simulated or experimentally measured, and also the first evidence that the current figure of merit for TCEs is insufficient to evaluate their performance in solar cell devices.

Light scattering by residual pores in transparent zirconia ceramics

We studied the effects of residual pores on the transparency of cubic zirconia ceramics by applying Mie scattering theory. The optical haze value H, defined as the diffuse transmission divided by the total forward transmission, was calculated as a function of the pore size (rpore) and the porosity of residual pores (Vpore) with sample thickness (t) = 1 mm. Even a small amount of pores critically affect the transparency; Vpore < 5 ppm is required to maintain H value within 1%, when rpore = 0.05 µm is assumed. The theoretical study also revealed that the acceptable amount of residual pores for H = 1% gradually degreases with an increase in the refractive index of the materials.