Smart Window Applications Research Articles

A Thermoresponsive Lead‐Free Organic‐Inorganic Hybrid Perovskite as a Dielectric Switch

AbstractThermochromic perovskites, renowned for their tunable bandgap, high absorption coefficient, and reversible color changes, emerge as promising candidates for applications in smart windows. These advancements not only have the potential to enhance occupant comfort but also contribute significantly to reducing energy consumption in buildings. Here, we present a two‐dimensional lead‐free organic‐inorganic hybrid perovskite [Cyclobutylammonium]2CuCl4 which shows phase transitions from C2/c to P21/c to P21/c space group at 319.5 K and 348.8 K, respectively. Accompanying these transitions is a fascinating, reversible thermochromic behavior that is dependent on the phase structure. This behavior manifests as a vibrant sequence transitioning from yellow to brown and finally to a slightly dark brown. Most importantly, the demonstrated ability to switch stably between high and low dielectric states indicates the enormous potential of this material as a dielectric switch. This non‐toxic thermoresponsive perovskite, characterized by its appropriate transition temperatures, reversible phase structure‐dependent thermochromism, and stable dielectric switching behavior, is expected to generate significant interest within the fields of thermoresponsive and dielectric switching materials. The integration of these features not only positions this perovskite as a noteworthy subject of scientific inquiry but also opens avenues for practical applications in diverse fields.

Recent Advances in Smart Windows Based on Photo-Responsive Liquid Crystals Featuring Phase Transition.

A smart window is an optical dimming device with intelligent functions that can control its relevant performances through external stimuli, achieving functions such as privacy protection and temperature regulation. Light is an ideal stimulus for regulating smart windows, which is noninvasive and allows self-adaptable manipulation of materials. This review highlights recent significant achievements in smart windows constructed by photo-responsive liquid crystals (LCs) systems that can undergo the transition between different phases. The smart windows based on photo-responsive LCs are used in a plethora of areas, including privacy protection, absorption glass, building decoration, energy saving, and climate modulation applications. The review concludes with a brief perspective on some significant challenges and opportunities for the future development of photo-responsive smart windows, which is crucial for expanding the applications of smart windows and improving their performances.

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.

Towards Room Temperature Thermochromic Coatings with controllable NIR-IR modulation for solar heat management & smart windows applications

Solar heat management & green air-conditioning are among the major technologies that could mitigate heat islands phenomenon while minimizing significantly the CO2 global foot-print within the building & automotive sectors. Chromogenic materials in general, and thermochromic smart coatings especially are promising candidates that consent a noteworthy dynamic solar radiation Infrared (NIR-IR) regulation and hence an efficient solar heat management especially with the expected increase of the global seasonal temperature. Within this contribution, two major challenging bottlenecks in vanadium oxide based smart coatings were addressed. It is validated for the first time that the NIR-IR modulation of the optical transmission (∆TTRANS = T(T〈TMIT) − T(T〉TMIT) of Vanadium oxide based smart coatings can be controlled & tuned. This upmost challenging bottle-neck controllability/tunability is confirmed via a genuine approach alongside to a simultaneous drastic reduction of the phase transition temperature TMIT from 68.8 °C to nearly room temperature. More precisely, a substantial thermochromism in multilayered V2O5/V/V2O5 stacks equivalent to that of standard pure VO2 thin films but with a far lower transition temperature, is reported. Such a multilayered V2O5/V/V2O5 thermochromic system exhibited a net control & tunability of the optical transmission modulation in the NIR-IR (∆TTRANS) via the nano-scaled thickness’ control of the intermediate Vanadium layer. In addition, the control of ∆TTRANS is accompanied by a tremendous diminution of the thermochromic transition temperature from the elevated bulk value of 68.8 °C to the range of 27.5–37.5 ºC. The observed remarkable and reversible thermochromism in such multilayered nano-scaled system of V2O5/V/V2O5 is likely to be ascribed to a noteworthy interfacial diffusion, and an indirect doping by alkaline ions diffusing from the borosilicate substrate. It is hoped that the current findings would contribute in advancing thermochromic smart window technology and their applications for solar heat management in glass windows in general, skyscraper especially & in the automotive industry. If so, this would open a path to a sustainable green air-conditioning with zero-energy input.

Thin films based on electrochromic materials for energy storage performance and smart windows applications: a review

Thin films based on electrochromic materials for energy storage performance and smart windows applications: a review

Mask-inspired moisture-transmitting and durable thermochromic perovskite smart windows

Thermochromic perovskite smart windows (TPWs) are a cutting-edge energy-efficient window technology. However, like most perovskite-based devices, humidity-related degradation limits their widespread application. Herein, inspired by the structure of medical masks, a unique triple-layer thermochromic perovskite window (MTPW) that enable sufficient water vapor transmission to trigger the thermochromism but effectively repel detrimental water and moisture to extend its lifespan is developed. The MTPW demonstrates superhydrophobicity and maintains a solar modulation ability above 20% during a 45-day aging test, with a decay rate 37 times lower than that of a pristine TPW. It can also immobilize lead ions and significantly reduce lead leakage by 66 times. Furthermore, a significant haze reduction from 90% to 30% is achieved, overcoming the blurriness problem of TPWs. Benefiting from the improved optical performance, extended lifespan, suppressed lead leakage, and facile fabrication, the MTPW pushes forward the wide applications of smart windows in green buildings.

Surface induced effects on the dielectric and optical properties of polymer-stabilized cholesteric liquid crystal composites

Polymer-stabilized cholesteric liquid crystal is one of the most coveted systems in the ever-expanding field of liquid crystal due to its wider potential application in smart windows, optical shutters, tunable lenses, etc. The dispersion of polymer into liquid crystal by introducing a small amount of chiral dopant prepared polymer-stabilized cholesteric liquid crystal. In this work, two samples of polymer- cholesteric liquid crystal were prepared. Surface treatment is applied on one composite while another sample is prepared without any treatment on the indium tin-oxide coated glass substrates. Frequency and temperature-dependent dielectric parameters are observed for both samples. The dielectric studies revealed that after surface treatment, the permittivity of the sample significantly increased. AC conductivity of the sample also increased. The photoluminescence spectra also show improvement in the intensity with the surface-treated sample.

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.

Photo- and electrochemical properties of newly synthesized thioxathone-viologen-fluorene ternary compound and its electrochromic device

External stimuli-responsive materials exhibit widespread potential applications in sensors, smart windows, displays, and opto-electronic molecular devices. In this study, we report light-/electrochemically induced chromic behaviors of newly synthesized ternary compound in the device. This compound is composed of a light-harvesting unit of thioxathone (TX), an electron donor of fluorene (FL), and an electron mediator of viologen (VIO), and thus it can act as a photochromic species with an intramolecular electron transfer under irradiation. The precursors of TX and FL substituents give off broad emissions at approximately 437 and 310 − 330 nm, respectively. Both emissions are largely quenched in the TX-VIO-FL ternary compound, which is caused by an intramolecular transduction of energy from the excited singlet FL and TX to the electroactive VIO substituent. Based on cyclic voltammogram of TX-VIO-FL modified electrodes, two reversible waves are observed at around − 0.44 and − 0.89 V (vs Hg/Hg2Cl2), attributed to the electron transport processes of TX-VIO2+-FL ↔ TX-VIO+•-FL and TX-VIO+•-FL ↔ TX-VIO0-FL, respectively. Sandwiched type of photo-/electrochromic devices are constructed, displaying a good transmittance and reversible viologen color change behavior under irradiation or an applied bias of − 2.6 V.

Role of 4f electrons and 3d-4f hybridization in metal-insulator transition in RE (La, Nd, Sm, Eu, Dy and Er)-doped vanadium dioxide for thermochromic applications

Vanadium dioxide is a promising thermochromic material for novel applications to smart optoelectronic devices due to its reversible insulator-to-metal transition which is accompanied by rapid variation in its optical properties. In this work, rare-earth (La, Nd, Sm, Eu, Dy and Er) dopants substituting vanadium site were investigated in detail to control the phase transition temperature (TMIT) and optical properties of VO2. It is found that TMIT is mainly related to the nature of 3d-4f hybridization in RE-doped VO2(M1): the direct overlapping of 3d-4f orbitals contributes to V–V dimerization, but it is less pronounced to lower TMIT; the indirect 3d-4f interaction via O-2p makes 4f electrons itinerant to egπ states to assist MIT from M1 to R phase at lower temperatures. The dominating nature of 3d-4f hybridization varies with changing RE dopant's ionic radius and electronegativity. Er offered the lowest TMIT with a decreasing rate of 12.8 °C/at. % due to effective 4f-O2p-3d hybridization. RE dopants were also found effective in changing optical properties by scaling Eg1 and Eg2 bandgaps of VO2. Hence, the fashion of 3d-4f interaction in RE-doped VO2 is found to play important role in modulating thermochromic properties of VO2 for smart window applications and smart optoelectronics devices.

Graphene and Graphene Derived Nanomaterials as Versatile Candidates for Organic Solar Cells and Smart Windows Applications – A Review

AbstractGraphene and related materials have been employed in several applications till date due to the unique set of properties. Research in the area of organic solar cells and smart windows are important to meet the increasing global energy demands and to realize the future goal of zero energy buildings. Here, we present a summary of the important research progress in application of graphene and related materials in organic solar cells and smart windows. This review starts by introducing the need of photovoltaic technology including organic solar cells and smart windows. The remaining sections are broadly divided into two sections – the first one briefly introduces organic cells and their different types, and the next section focuses on the different chromogenic technologies used in smart windows. After a brief overview of graphene, the application of graphene and related materials in organic cells and smart windows are presented. In the end, some of the major challenges and possible research directions are also outlined. Hopefully, this review will shed light on the recent trends and directions to achieve enhancement in performance of organic solar cells and smart windows with integration of graphene and provide overview for researchers about this novel field.

Spatially confined growth of VO2(M) nanoparticles with improved thermochromic property

In the pursuit of VO2-based energy efficient smart window, high-temperature annealing is a common way to prepare well-crystallized VO2 nanoparticles (NPs) with reduced defect density. However, it is usually accompanied by the formation of oversized VO2 NPs due to Ostwald ripening, making unsatisfactory optical performances of VO2-based films. In this work, we reported a spatial confinement route via incorporating commercial fumed silica (FS) as space barrier during the process of annealing ultrafine γ-VOOH NPs, and the size of the obtained VO2 NPs could be reduced to ∼50 nm. Moreover, VO2 films based on the multilevel spatial confinement strategy exhibit outstanding optical performances with balanced solar regulation efficiency (ΔTsol ∼ 17.82 %) and luminous transmittance (Tlum ∼ 51.74 %). A simple dipping process could be carried out to enable a hydrophobic self-cleaning surface of the obtained VO2 films, which was meaningful for smart window applications. VO2@SiO2 core-shell structure, referring to a strong spatial confinement strategy, was also prepared via coating γ-VOOH NPs with SiO2 followed by annealing treatment. The top-level optical performances with ΔTsol of 20.46 % and Tlum of 44.26 % of VO2@SiO2/PVP films were achieved successfully. The spatial confinement strategy may inspire more facile and efficient processes for development of high-performance VO2 films for various applications.

Viologen-based solution-processable ionic porous polymers for electrochromic applications.

Electrochromic porous thin films are promising for applications in smart windows and energy-efficient optical displays. However, their generally poor processing ability and excessive processing times remain grand challenges. Herein, we report the design and convenient synthesis of core-altered N-arylated viologens with aldehyde groups (πV-CHO) as new building blocks to prepare soluble, viologen-embedded ionic porous polymers. We also demonstrate that these polymers can be easily solution-processed by drop-coating to fabricate high-quality electrochromic films with tunable optoelectronic properties in a cost-effective fashion. The prepared films exhibit excellent electrochromic performance, including a low driving voltage (1.2-1.4 V), fast switching times (0.8-1.7 s), great coloration efficiency (73-268 cm2 C-1), remarkably high optical contrast up to 95.6%, long cycling stability, and tunable oxidation and reduction colors. This work sheds important light on a new molecular engineering approach to produce redox-active polymers with combined properties of intrinsic porosity, reversible and tunable redox activity, and solution processability. This provides the materials with an inherently broad utility in a variety of electrochemical devices for energy storage, sensors, and electronic applications.

Acid–base regulated inclusion complexes of β-cyclodextrin with 1-[2-(4-fluorophenyl)-2-oxoethyl]-4,4′-bipyridinium dichloride displaying multistimuli-responsive chromic behaviors and photomodulable fluorescence

Two inclusion complexes of β-cyclodextrin with a viologen derivative display multistimuli-responsive chromic behaviors and photomodulable fluorescence, which endows them with various applications.

Tunable insulator-metal transition in epitaxial VO2 thin films via strain and defect engineering.

The Metal to Insulator Transition (MIT) in materials, particularly vanadium dioxide (VO2), has garnered significant research interest due to its potential applications in smart windows, memristors, transistors, sensors, and optical switches. The transition from an insulating, monoclinic phase to a conducting, tetragonal phase involves changes in optical and electrical properties, opening avenues in adaptive radiative coolers, optical memories, photodetectors, and optical switches. VO2 exhibits MIT close to 68 °C, thereby requiring tuneable transition temperatures (T c) in VO2 thin films for practical device applications. In this work, we explore the role of strain and defect engineering in tuning the MIT temperature in epitaxial VO2 thin films deposited on c-cut sapphire using Pulsed Laser Deposition (PLD). The study involves tuning the metal-to-insulator transition (MIT) by varying growth parameters, mainly temperature and oxygen partial pressure. Strain engineering along the b-axis helped tune the transition temperature from 65 °C to 82 °C with the out-of-plane b-strain varying from -0.71% to -0.44%. Comprehensive structural and property analyses, including X-ray diffraction (XRD), Reciprocal Space Mapping (RSM), X-ray Photoelectron Spectroscopy (XPS), Raman spectroscopy, and resistivity-temperature (R-T) measurements, were performed to correlate structural properties with T c. Additionally, density functional theory (DFT) calculations were performed using Quantum Espresso within the generalized gradient approximation of the revised Perdew-Burke-Ernzerhof (PBEsol) functional to provide theoretical validity to the experimentally obtained results. Our study provides critical insights into the interplay between strain and oxygen vacancies and their effect on the physical properties of VO2 thin films with DFT calculations supporting the experimental findings.

Kirkendall effect induced ultrafine VOOH nanoparticles and their transformation into VO2(M) for energy-efficient smart windows.

Vanadium dioxide (VO2) has received widespread attention for application in energy-efficient smart windows because of its distinct thermochromic property in the near-infrared region during the reversible metal-insulator phase transition. In this study, lepidocrocite VOOH ultrafine nanoparticles (NPs) with a diameter less than 30 nm were prepared by a mild and efficient hydrothermal method, and the Kirkendall effect played a vital role in the growth of the VOOH NPs. It was found that VOOH could be transformed into VO2via a subsequent annealing treatment during which the size and morphology of VOOH are well preserved even though the annealing temperature is up to 500 °C. The ultrafine VO2 NPs are crucial for achieving excellent nanothermochromic performance with a luminous transmittance (Tlum) up to 56.45% and solar modulation ability (ΔTsol) up to 14.95%. The environmental durability is well improved by coating VO2 NPs with an SiO2 shell as confirmed via progressive oxidation and acid corrosion experiments. Meanwhile, the Tlum of the VO2@SiO2 film is further increased from 56.45% to 62.29% while the ΔTsol remained unchanged. This integrated thermochromic performance presents great potential for the development of VO2-based smart windows.

N-Type redox-tuneable conducting polymer optical nanoantennas.

Conducting polymers can be dynamically switched between being optically metallic (negative real permittivity) and dielectric (positive real permittivity) by varying their redox state. This has enabled nanoantennas with plasmonic resonances that can be reversibly turned on/off, opening for applications in dynamic metaoptics, reflective displays, and smart windows. However, previous reports on conducting polymer plasmonics were limited to p-type polymers. Here, we show that a highly conducting n-type polymer, called poly(benzodifurandione) (PBFDO), can also provide optically metallic properties and be used to make dynamic optical nanoantennas. The doped version of the polymer becomes metallic at wavelengths above around 700 nm, leading to plasmonic extinction peaks for nanodisks made from the material. These peaks can be reversibly switched off and on electrically or chemically by varying the doping level of the polymer. The study extends the field of dynamic polymer plasmonics to n-type materials and broadens the application areas of PBFDO.

LCST ion gels fabricating "all-in-one" smart windows: thermotropic, electrochromic and power-generating.

Smart windows always respond to single stimuli, which cannot satisfy various needs in practical applications. Smart windows that integrate thermotropic, electrochromic and power-generating functions in one device is highly challenging yet important in satisfying on-demand light modulation and energy efficiency in practical applications. Herein, a thermoresponsive lower critical solution temperature (LCST) ion gel was fabricated via a facile in situ polymerization of butyl acrylate in a conventional ionic liquid to explore "all in one" smart windows. The ion gel-assembled smart windows are thermotropic and electrochromic with a reliable adjustment of light transparency as well as power-generating, enabled by the ionic Soret effect of ionic liquids. Additionally, the ion gels demonstrated self-defensive robust mechanical properties, thermal insulating and antifogging properties. With such an interdisciplinary and comprehensive study of the ion gels, the LCST ion gels could fulfil the requirements of genius windows with high energy-saving potential and exceptional climate adaptability, such as shut-down of light transmission in summer, daily solar energy collection, and colour changes on demand. It conceptually updates smart windows from an energy saving to an energy supplier in buildings. It is the first time to explore the "all in one" smart windows based on integrated multifunctional ionic liquids, which could greatly bridge the gap between the materials and buildings to accelerate practical applications of smart windows.

Boosting the electrochromic performance of P-doped WO3 films via electrodeposition for smart window applications.

Electrochromic smart windows have attracted more attention from researchers due to their potential applications for energy conservation in buildings. As the most key component, the electrochromic layer is still limited by the complexity of the preparation process and poor performance, such as lower stability, slow response time, and low coloration efficiency. In this study, as a simple and expedient method, electrodeposition is successfully used to prepare amorphous WO3 films doped with P. By optimizing the amount of P in the PW-2 film, a large optical modulation of 80.8% at 550 nm is achieved, and the P-doped amorphous WO3 film also shows a fast response time, a high CE, and good cycling stability. The mechanism of the P-doped amorphous WO3 films to improve the electrochromic properties is as follows. Firstly, by appropriate phosphorus doping, the stress of the film is released, and the binding force is improved. Secondly, the films possess proper cracks, which accelerate the diffusion of ions. Thirdly, the films make the nanoparticles more uniform, and provide more active sites. Furthermore, the electrochromic smart windows based on the P-doped amorphous WO3 film display a large temperature difference of 11 °C, which indicates good solar thermal regulation ability, and promises practical applications for building energy conservation.

Polymerisation of twist-bend nematic textures for electro-optical applications.

Polymer-stabilised liquid crystals (PSLCs) have recently been used to maintain the focal conic domains (FCDs) typical of the smectic A phase in the nematic phase for smart window applications. The newly discovered twist-bend nematic phase of bent-shaped dimers also exhibits FCDs due to its pseudo-layered structure. The variety of topological defects in the NTB phase is arguably even greater than in the smectic A phase, but the NTB phase is often metastable and usually crystallises at room temperature, which hinders its use in electro-optical applications. Here we show how different textures (FCDs, rope-like texture, double helices) of the NTB phase can be polymerised and then maintained in the nematic phase, at room temperature. This allows us to combine in PSLCs the optical properties of these defects, the thermal stability of the nematic phase and its reversible response to an electric field. We also show that the polymerised FCDs of the NTB phase could be used in smart glass applications and that the polymerised rope-like texture could be of interest for optical modulators and beam steering. In addition, the polymerisation of double helices could help to better understand their formation and structure in the NTB phase. More fundamentally, our work shows that despite the lack of density modulation, the textures of the NTB phase, thanks to its periodic character, can be exploited in the same way as those of the smectic A phase.