Visible Transmittance Research Articles

Semitransparent Near‐Infrared Organic Photodetectors: Flexible, Large‐Area, and Physical‐Vapor‐Deposited for Versatile Advanced Optical Applications

AbstractOrganic photodetectors (OPDs) have experienced remarkable performance improvements over the past decade thanks to significant advancements in organic material synthesis and device architecture engineering. In this study, high‐performance near‐infrared (NIR) OPDs with versatile advanced properties, including large detection areas, mechanical flexibility, and high transparency are realized. By incorporating a thin photo‐absorbing layer, functional blocking layers with a large energy gap, and semitransparent electrodes, the OPDs achieve an average visible transmittance (AVT) of up to 53.4% and color rendering index (CRI) of up to 95 within the human vision photopic response window of 380–780 nm. Both the small (6.44 mm2) and large (256 mm2) detection‐area semitransparent OPDs demonstrate an impressive external quantum efficiency (EQE) of 34% and 36%, and specific detectivity (D*) of 1.4 × 1013 and 1.1 × 1012 Jones, respectively, comparable to silicon‐based inorganic photodetectors. As application demonstrations, OPDs with rigid and flexible substrates are employed for NIR imaging and biosensing, respectively. Notably, the flexible semitransparent OPDs are utilized as signal receivers in conjunction with semitransparent NIR organic light‐emitting diodes (OLEDs) operating as signal producers, demonstrating the feasibility of invisible optical communication. These OPDs represent the best‐performing see‐through devices with flexibility, making them promising candidates for integratable, bio‐compatible, and invisible optical‐sensing applications.

Zwitterionic hydrogel smart windows: Radiative cooling, privacy protection and energy savings

Current thermochromic smart windows based on lower critical solution temperature (LCST) behavior can achieve solar regulation and energy saving by modulating solar transmission at the cost of visibility at higher temperature. To tackle this issue, a new concept of smart window based on the upper critical solution temperature (UCST) characteristic of zwitterionic hydrogel has been developed, giving daytime luminous transparency, all day radiative cooling and nighttime privacy protection. This design rule is suitable for energy saving smart windows for regions where cooling demand is dominant. The UCST smart window panel provides moderate luminous transmission (Tlum) of 37.1 % and low near-infrared transmission (TNIR) of 20.3 % during the daytime, all day near unity long-wave infrared emissivity (ƐLWIR) of 0.96 facing outdoor to promote radiative cooling with outer space, low ƐLWIR 0.19 facing indoor to suppress heat transfer, and low visible transmission (Tvis) of 1.4 % at night mode for privacy protection. Energy-saving simulations demonstrate that compared to commercial low-emissivity (low-E) windows in three climate zones (zone 0, 1, 2), the UCST smart window achieves an impressive annual energy-saving up to 30.7 %. This work introduces a novel conceptual design specifically tailored for climate zones where cooling demands prevail, offering a combination of moderate luminous transparency, suppressed NIR transmission, excellent radiative cooling with outdoor environment and reduced heat transfer with indoor combining with an added privacy protection feature.

Analyzing the effectiveness of building integrated Photovoltaics (BIPV) to reduce the energy consumption in Dubai

In Dubai, 38.9 % of the total energy consumption is related to buildings, and the high-rise building sector is key to energy efficiency. BIPV (Building Integrated Photovoltaic) can be a very efficient alternative in Dubai because of building load reduction and power generation. This paper aims to investigate energy efficiency according to the number of floors with BIPV application. As a methodology, an analysis model for office use was used with the curtain wall with a floor height of 3.6 m, floor area of 400 m2, and a window area ratio to wall area ratio of 80 %. Energy Plus Version 9.0 and TRNSYS were used as evaluation tools. The physical properties of windows and doors in the analysis model were assumed to be low-E double-glazed glass with a Solar Radiation Gain Coefficient (SHGC) of 0.564, a visible light transmittance of 47.2 %, and a thermal transmittance of 1.760 W/m2K. The result showed that when the alternatives of the window replacement type, exterior wall finishing type, and hybrid type BIPV system are applied, heating and cooling energy consumption is reduced by 13.2 % to 32.8 %. It was proven that applying BIPV was effective in high-rise office buildings. It is practical to replace windows and apply light-transmitting amorphous thin film Photovoltaic (PV) double-layered, double-layered Low-E, or triple Low-E windows, replace exterior wall finishing materials with crystalline PV, or use a mixture of both. The simulation results show that applying a roof-top BAPV (Building-Applied Photovoltaic) system is only practical for low-rise buildings.

Multi-objective optimization for visual, thermal, and cooling energy performance of building envelope design in the composite climate of Jaipur (India)

Climate-responsive passive envelope features such as windows, louvers, and shading have significant impact on a building's energy and economic performance. This paper presents a multi-objective optimization (MOO) approach to enhance energy, visual and thermal performances of a building by considering a wide range of numerous design possibilities. A residential apartment building located in a semi-arid composite climate (Köppen climate classification: Bsh) of Jaipur, India is considered for the analysis. The multi-objective optimization approach involves three steps: firstly, developing a base simulation model using Rhinoceros software, and then performing multi-objective optimization by Octopus plugin, and finally applying multi-criteria decision-making to select the optimal values of thermal conductivity, window-to-wall ratio of south and west façades, solar heat gain coefficient, visual light transmittance, window sill height, louvers depth, distance between slits, slits angle, external shade depth, and shade (slits) count. The optimized results reported a six-fold Useful Daylight Illuminance (UDI) improvement, 72% cooling energy demand reduction, and 34% thermal comfort enhancement from the worst-case scenario. The presented approach can aid designers in selecting optimal envelope features during building design, refurbishment, and renovation or for green field development.

Solid Additive Dual-Regulates Spectral Response Enabling High-Performance Semitransparent Organic Solar Cells.

Semi-transparent organic solar cells (ST-OSCs) possess significant potential for applications in vehicles and buildings due to their distinctive visual transparency. Conventional device engineering strategies are typically used to optimize photon selection and utilization at the expense of power conversion efficiency (PCE); moreover, the fixed spectral utilization range always imposes an unsatisfactory upper limit to its light utilization efficiency (LUE). Herein, a novel solid additive named1,3-diphenoxybenzene (DB) is employed to dual-regulate donor/acceptor molecular aggregation and crystallinity, which effectively broadens the spectral response of ST-OSCsin near-infrared region. Besides, more visible light is allowed to pass through the devices, which enables ST-OSCs to possess satisfactory photocurrent and high average visible transmittance (AVT) simultaneously. Consequently, the optimal ST-OSC based on PP2+DB/BTP-eC9+DB achieves a superior LUE of 4.77%, representing the highest value within AVT range of 40-50%, which also correlates with the formation of multi-scale phase-separated morphology. Such results indicate that the ST-OSCs can simultaneously meet the requirements for minimum commercial efficiency and plant photosynthesis when integrated with the roofs of agricultural greenhouses. This work emphasizes the significance of additives to tune the spectral response in ST-OSCs, and charts the way for organic photovoltaics in economically sustainable agricultural development.

Efficient Bifacial Semitransparent Perovskite Solar Cells Using Down‐Conversion 2D Perovskite Nanoplatelets–Poly(Methyl Methacrylate) Composite Film

Semitransparent perovskite solar cells (ST‐PSCs) hold significant appeal for various applications in smart windows, multijunction tandem devices, bifacial and chargeable devices, etc. Unfortunately, to possess high transparency, the perovskite layer in the ST‐PSCs must be kept relatively thin (<400 nm), which in turn causes insufficient light absorption and thus inferior device performance. Herein, a 2D perovskite nanoplatelets (NPLs)/poly(methyl methacrylate) (PMMA) composite thin layer is applied in the ST‐PSCs to solve these problems. Thanks to its dual function of down‐conversion (DC) effect, converting high‐energy UV photons into low‐energy visible photons to enhance the photocurrent, and interfacial passivation, reducing the nonradiative recombination at the interface, the 2D NPLs–PMMA‐based devices with the different average visible transmittance (AVT) values of perovskite film demonstrate significantly improved power‐conversion efficiency (PCE) compared to the pristine devices, and remarkable UV stability, retaining over 77% of initial PCE after aging under continuous UV illumination for 280 h. More importantly, the full bifacial ST‐PSCs using a transparent MoO3/Au/MoO3 rear electrode exhibits a record PCE of 14.26% and 10.65% with a whole device AVT of 19.4% and 26.9%, respectively, which are among the highest performing ST‐PSCs of the kind reported to date.

All-Inorganic Hydrothermally Processed Semitransparent Sb2S3 Solar Cells with CuSCN as the Hole Transport Layer.

An inorganic wide-bandgap hole transport layer (HTL), copper(I) thiocyanate (CuSCN), is employed in inorganic planar hydrothermally deposited Sb2S3 solar cells. With excellent hole transport properties and uniform compact morphology, the solution-processed CuSCN layer suppresses the leakage current and improves charge selectivity in an n-i-p-type solar cell structure. The device without the HTL (FTO/CdS/Sb2S3/Au) delivers a modest power conversion efficiency (PCE) of 1.54%, which increases to 2.46% with the introduction of CuSCN (FTO/CdS/Sb2S3/CuSCN/Au). This PCE is a significant improvement compared with the previous reports of planar Sb2S3 solar cells employing CuSCN. CuSCN is therefore a promising alternative to expensive and inherently unstable organic HTLs. In addition, CuSCN makes an excellent optically transparent (with average transmittance >90% in the visible region) and shunt-blocking HTL layer in pinhole-prone ultrathin (<100 nm) semitransparent absorber layers grown by green and facile hydrothermal deposition. A semitransparent device is fabricated using an ultrathin Au layer (∼10 nm) with a PCE of 2.13% and an average visible transmittance of 13.7%.

Boosting the Performances of Semitransparent Organic Photovoltaics via Synergetic Near-Infrared Light Management.

Semitransparent organic photovoltaics (ST-OPVs) offer promising prospects for application in building-integrated photovoltaic systems and greenhouses, but further improvement of their performance faces a delicate trade-off between the two competing indexes of power conversion efficiency (PCE) and average visible transmittance (AVT). Herein, the authors take advantage of coupling plasmonics with the optical design of ST-OPVs to enhance near-infrared absorption and hence simultaneously improve efficiency and visible transparency to the maximum extent. By integrating core-bishell PdCu@Au@SiO2 nanotripods that act as optically isotropic Lambertian sources with near-infrared-customized localized surface plasmon resonance in an optimal ternary PM6:BTP-eC9:L8-BO-based ST-OPV, it is shown that their interplay with a multilayer optical coupling layer, consisting of ZnS(130nm)/Na3AlF6(60nm)/WO3(100nm)/LaF3(50nm) identified from high-throughput optical screening, leads to a record-high PCE of 16.14% (certified as 15.90%) along with an excellent AVT of 33.02%. The strong enhancement of the light utilization efficiency by ≈50% as compared to the counterpart device without optical engineering provides an encouraging and universal pathway for promoting breakthroughs in ST-OPVs from meticulous optical design.

A compact frequency-selective absorber with optical transparency

This article proposes a new method for designing an optical transparent frequency-selective surface absorber using indium tin oxide (ITO) conductive film with different sheet resistances. This novel optical transparent frequency-selective absorber exhibits excellent optical transparency, ensuring a visible light transmittance exceeding 76%. Simultaneously, it exhibits broadband absorption characteristics covering the entire X-Ku band, with an absorption rate exceeding 90%. Due to the simplicity of the design, the overall structure is easily processable, and the desired product can be rapidly fabricated using laser etching equipment without adding any lumped elements in the design. Simulation and experimental results indicate that the S11–10 dB frequency range of the frequency-selective absorber is 7.7–18.4 GHz, with a transmission frequency range below −3 dB between 26.7–29.4 GHz. The findings suggest that this structure holds potential applications in microwave stealth design requiring optical transparency and high-throughput satellite communication scenarios.

Continuous modulation of VO2 film’s phase transition threshold and transmittance via n-AZO/n-VO2 heterojunction

To solve the irreconcilable contradiction between the phase transition threshold and the optical property of VO2 film, an n-AZO/n-VO2 heterojunction, in which AZO is Al-doped ZnO, was constructed with the radio frequency (RF) magnetron sputtering and the post annealing. The effects of annealing on the composition and properties of vanadium oxide films have been investigated, as well as the effects of annealing and AZO layer thickness on the phase transition performance of the n-AZO/n-VO2 heterojunction. The results indicate that the V2O5 film will gradually transform into VO2 (M) through V6O13 and VO2 (B) during the reduction annealing at 500 °C. The phase transition temperature (Tc) of VO2 (M) film increases with the annealing temperature. In the heterojunction formed by the ohmic contact between AZO and VO2 layers, the free electrons will be injected into the VO2 layer from AZO layer, which reduces the heterojunction’s Tc from 69.2 to 41.5 °C. The first-principles calculations were performed with the Vienna Ab initio Simulation Package (VASP) to assist in the influence mechanism explanation. In addition to modulating Tc, the AZO layer in the heterojunction also plays an antireflection role, increasing the maximum visible transmittance of VO2 film by ∼ 10 %.

Optical and electrical properties of Ni+2 doped nanocrystalline Bi2S3 thin films prepared by chemical bath deposition method

Nickel (Ni+2) doped nanocrystalline Bi2S3 thin films are deposited on the glass substrate from the solutions containing Bismuth Nitrate, Ethylenediamine Tetraacetic acid (EDTA) and Thioacetamide at a bath deposition temperature of 318K. The optical, surface morphological and electrical properties of Ni-doped Bi2S3 thin films prepared at three different doping concentration are investigate by using ultraviolet–visible transmission spectra (UV–Vis), Scanning electron microscopy (SEM), Energy Dispersive X-ray (EDAX) and thermo-e.m.f. techniques. The optical band gap energies are found in between 2.32-2.43 eV. The SEM images show that the prepared films are continuous, dense and distributed over the entire area with good uniformity. The electrical conductivity of the films are in the order of 10-2 Ω-1 m-1 . The films are n-type as determined from the Hot Probe method. Photoconductivity studies reveal that photocurrent increases with the increase in Ni doping concentrations. Due to the absorption of photons, free electron-hole pairs (EHP) are produce.

Flexible Embedded Metal Meshes by Sputter-Free Crack Lithography for Transparent Electrodes and Electromagnetic Interference Shielding.

A facile and novel fabrication method is demonstrated for creating flexible poly(ethylene terephthalate) (PET)-embedded silver meshes using crack lithography, reactive ion etching (RIE), and reactive silver ink. The crack width and spacing in a waterborne acrylic emulsion polymer are controlled by the thickness of the polymer and the applied stress due to heating and evaporation. Our innovative fabrication technique eliminates the need for sputtering and ensures stronger adhesion of the metal meshes to the PET substrate. Crack trench depths over 5 μm and line widths under 5 μm have been achieved. As a transparent electrode, our flexible embedded Ag meshes exhibit a visible transmission of 91.3% and sheet resistance of 0.54 Ω/sq as well as 93.7% and 1.4 Ω/sq. This performance corresponds to figures of merit (σDC/σOP) of 7500 and 4070, respectively. For transparent electromagnetic interference (EMI) shielding, the metal meshes achieve a shielding efficiency (SE) of 42 dB with 91.3% visible transmission and an EMI SE of 37.4 dB with 93.7% visible transmission. We demonstrate the highest transparent electrode performance of crack lithography approaches in the literature and the highest flexible transparent EMI shielding performance of all fabrication approaches in the literature. These metal meshes may have applications in transparent electrodes, EMI shielding, solar cells, and organic light-emitting diodes.

Transparent Near‐IR Dye‐Sensitized Solar Cells: Ultrafast Spectroscopy Reveals the Effects of Driving Force and Dye Aggregation

AbstractIn the context of developing transparent near‐IR absorbing dye‐sensitized solar cells, diketopyrrolopyrrole (DPP) cyanine dyes have recently emerged as an alternative to strongly aggregating linear cyanines. In our efforts to increase both the power conversion efficiency (PCE) and the average visible transmittance (AVT), a thienylated version, called TB202, that shows a red‐shifted absorption with respect to our champion dye TB207 was designed. However, the lower energy LUMO level of TB202 brings along a lower driving force (−ΔG) for carrier injection, which we recently identified as the main parameter limiting the PCE to 1.5 % in the best device conditions. In the present paper, we publish a detailed account of the effect of the de‐aggregating cheno‐deoxycholic acid (CDCA) for both TB207 and TB202. Both transient absorption (TAS) and fluorescence up‐conversion (FLUPS) data are presented, which allow to quantitively compare the effect of −ΔG and the CDCA concentration, in terms of the kinetic competition of ensemble averaged carrier injection and monomer‐to‐aggregate energy transfer (ET) rates. A comprehensive picture emerges on how ET is reduced by higher CDCA concentrations, leading in the best device conditions to injection efficiencies in the range of 65 % for TB207 and only 35 % for TB202.

Growth and Leaf Color of Coleus under Light Conditions Modified by Translucent Agrivoltaic Panels and Light-Emitting Diodes in a Greenhouse

Dye-sensitized solar cells (DSSCs) can be used as greenhouse glazing materials in agrivoltaic systems because they are translucent, have different colors, and can produce electricity. However, the light quality of DSSCs differs from that of sunlight, and the visible light transmittance is low. Therefore, we compared the plant shape, growth, and leaf color of coleus, a highly photosensitive plant, under transparent glass and red-colored DSSCs. Coleus ‘Highway Rose’ was grown in transparent (T, the control), shaded (S), and DSSC (D) chambers maintained at 23 ± 2 °C. The DSSC chambers were additionally illuminated with blue (B), green (G), white (W), B+G, and R+B+W light-emitting diodes (LEDs) (D+L) at 60 μmol·m−2·s−1 photosynthetic photon flux density for 15 h from 05:00 to 20:00. The coleus generally exhibited good growth under the T treatment. However, the light quality of DSSCs differed from that of sunlight, and the visible light transmittance decreased. Coleus exhibited increased growth and leaf color characteristics under the supplemental B lighting treatments (D+L(RBW), D+L(B), D+L(BG), and D+L(W)). Supplemental lighting with B LEDs using DSSCs improved plant morphology growth and leaf color. On the other hand, supplemental G lighting reinforced the shade avoidance syndrome. Moreover, DSSCs could aid in reducing the energy required to control the environment.

A novel poly(vinyl alcohol)/silica composite film with “spherical crystal interlocking structure” and its barrier and enhancement mechanism

Using the semi-crystalline poly(vinyl alcohol) (PVA) as the polymer matrix and silica nanoparticles (SNPs) as the reinforcing filler, composite films with excellent water vapor barrier, high tensile strength, visible light transmission and ultraviolet (UV) shielding performances were constructed via a simple heat treatment process, during which the films underwent dehydration cross-linking and isothermal recrystallization to form a "spherical crystal interlocking structure". Both the dosage and average particle size of SNPs significantly affected the barrier property, and the optimal values were 7 wt% and 15 nm, respectively. The heat treatment further improved the water resistance, mechanical strength, and barrier property to a great extent. Moreover, different theoretical models including Guggenheim Anderson de Boer (GAB), Brunauer Emmett and Teller (BET), Hailwood-Horribon (H-H) model, crystallinity model and Fick's law model were successfully used to explain the water vapor barrier mechanism. The water vapor permeability (WVP) of the optimized composite film was reduced to 2.20 × 10−12 g·m/(m2·Pa·s) at 37°C and 65% RH, while the tensile strength was increased up to 116.8 MPa. In addition, the absorption rate of ultraviolet of the film after heat treatment increased from 13% to 92.0%, while the transmittance of visible light remained above 78%.

Transparent photothermal films with high optical selectivity for anti/de-icing

A variety of transparent photothermal films with enhanced ultraviolet and near-infrared solar radiation absorption has been investigated to operate in cold environments in recent years. However, the enhancement of solar energy harvesting has to excessively sacrifice the transmittance of visible light in most existing anti-frosting and anti/de-icing systems, which leads to a widespread constraint in the applications requiring high transparency. In this study, a new type of transparent photothermal film, PMMA-iAg, was proposed and optimally designed. The polymethyl methacrylate (PMMA) is doped with indium tin oxide (ITO) nanospheres and silver nanocylinders (AgNCs). Effects of the particle doping concentration ratio and volume fraction fv on the light transfer of the PMMA-iAg film have been systematically studied. An evaluation parameter of “deviation from the ideal spectrum” σT is established to assess the photothermal performance and transparency simultaneously. The results show that the present PMMA-iAg film can achieve a UV and NIR absorbance of 93% and a visible transmittance Tp of 80%. Moreover, the PMMA-iAg films can absorb more high-energy light (UV) instead of letting them transmit. In particular, the effect of ice-drops on the transmittance and haze of the transparent photothermal film was investigated at different projected surface coverage ratios fa and wettability. The results indicate that ice-covered films with both hydrophilic and super-hydrophobic surfaces achieve outstanding transmittance. The ice-covered films with super-hydrophilic surfaces have a remarkably low haze. This work provides guidance for designing efficient transparent photothermal films for the application of anti/de-icing.

Trade-Off Judgement for Daylighting and Energy Consumption in the High and Large Space of the University Gymnasium in Beijing

Taking the high and large space of the University of Science and Technology Beijing Gymnasium as this research object, this paper analyzes the influence of different window positions, window-to-wall ratio (WWR), solar heat gain coefficient (SHGC), heat transfer coefficient (K), and visible light transmittance (VT) on the total indoor energy consumption in winter and summer and obtains the relationship between the daylight factor and VT formed when the window is opened per unit area. Through energy consumption simulation, the variation law and calculation formula for indoor total energy consumption are obtained. The results show that the SHGC and K of the exterior window have a significant influence on the total energy consumption. By using the energy consumption simulation of different types of exterior windows, it is concluded that the SHGC of the south-facing window is negatively correlated with the variation of air conditioning energy consumption per unit area Δe1,w, while the others are positively correlated. Moreover, the SHGC and K of the skylight have the most significant influence on the Δe1,w. The total energy consumption decreases and then increases with the increase in the window area, and there is a lowest point, so the right side of the lowest point is less than or equal to 105% of the lowest total energy consumption as a reasonable window area zone. Finally, a progressive optimization method for weighing daylighting and energy consumption in university gymnasiums in Beijing is proposed.

Fabrication of carbon dots-embedded luminescent transparent wood with ultraviolet blocking and thermal insulating capacities towards smart window application

To expand functions of transparent wood (TW) including fluorescence, ultraviolet blocking, heat preservation and insulation, we adopted carbon quantum dots (CQDs) to prepare luminescent transparent wood. CQDs with yellow/red fluorescence (YCD/RCD) were prepared by chitosan and o-phenylenediamine. Afterwards, Balsa woods were pretreated to obtain wood frameworks (DW/LW), which were further combined with epoxy resin for achieving transparent woods (DW-TW/LW-TW). Results showed LW retained more lignin, the LW-TW blocked more ultraviolet light, displaying the better visible transmission and mechanical strength than DW-TW. After adding YCD and RCD to LW-TW, the yellow and red fluorescence transparent woods with outstanding mechanical and ultraviolet blocking properties were prepared, especially the red fluorescence transparent wood (RTW). Specifically, the tensile strength and elongation at break of RTW reached up to 19.39 MPa and 5.35 %, respectively. Moreover, RTW could block 78.8 % of UV-B light and 78 % of UV-A light, respectively. Besides, RTW possessed excellent visible transmission (70.3 %) and UV blocking (88.87 %). Significantly, both RTW and YTW displayed outstanding water repellency, excellent durability, good thermal stability and insulation. Predictably, luminescent transparent woods certainly will enhance the adaptability of wood, and broaden its applications in green decoration, lighting setup, sensor and other fields.

Crystal growth, structural, optical, mechanical characterization and quantum chemical analysis by DFT of an organic nonlinear optical single crystal 4-Hydroxy pyridinium succinate for photonic and optoelectronic devices

A new organic nonlinear optical single crystal 4-Hydroxypyridinium Succinate was synthesized and grown successfully by slow evaporation method using methanol as solvent at ambient temperature. Single crystal X –ray diffraction studies on the grown crystal reveals that 4HPS crystallizes into orthorhombic structure with the non-centrosymmetric space group (Pna21). In structural point of view, the 4-Hydroxypyridinium cation is bonded to the hydrogen succinate anion by direct electron conjugation through nitrogen atom. In addition, the UV visible transmittance spectrum implies that the crystal has high transparency domain in the entire UV visible region with a lower cut-off wavelength of 286 nm. The various functional groups present in the crystal and their frequency assignments are derived from FTIR spectral analysis. The Photoluminescence spectrum brings forth that the grown crystal has violet emission property. The microhardness measurements testify that the crystal belongs to soft material category with reasonable hardness parameters. The compound was found to be thermally stable up to 188 °C without any weight loss from the TGA and DTG traces. The detailed quantum chemical calculation done by density functional theory (DFT) indicates the Homo –Lumo energy gap of the molecule is 3. 956 eV and 4. 289 eV for α and β wave functions respectively. The Laser induced damage threshold of the crystal investigated using Nd: YAG laser of 1064 nm radiation was found to be 21. 93 Gw/cm2. The second harmonic generation efficiency of the 4HPS crystal was confirmed by the emission of green light under Kurtz and Perry powder test.

Transparent energy-saving windows based on broadband directional thermal emission

Abstract Passive radiative cooling has emerged as a sustainable energy-saving solution, characterized by its energy-free operation and absence of carbon emissions. Conventional radiative coolers are designed with a skyward orientation, allowing for efficient heat dissipation to the cold heat sink. However, this design feature presents challenges when installed on vertical surfaces, as nearby objects obstruct heat release by blocking the cooler’s skyward view. Here, we introduce a directional radiative cooling glass (DRCG) designed to facilitate efficient heat dissipation through angular selective emission. The DRCG is constructed as a multilayer structure incorporating epsilon-near-zero materials, specifically Si3N4 and Al2O3, layered on an indium-tin-oxide thermal reflector. This innovative design restricts thermal emission to specific angular ranges, known as the Berreman mode. Additionally, the transparent layers enable a visible transmittance exceeding 84 %. Theoretical simulations validate the enhanced cooling performance of the DRCG, exhibiting a temperature reduction of over 1.5 °C compared with conventional glass in hot urban environments characterized by a nearby object temperature exceeding 60 °C and a sky view factor of 0.25. Furthermore, outdoor experiments demonstrate that employing the DRCG as a window enhances space-cooling performance by ∼1.5 °C. These findings underscore the potential of transparent energy-saving windows in mitigating the urban heat island effect.