Self-powered Smart Window Research Articles

Double-Shell Encapsulation of Lead-Free Tin Halide Perovskite for Self-Powered Smart Windows.

Luminescent solar concentrators (LSC) have the potential application in building integrated photovoltaic (BIPV). 0D tin-based perovskites are a promising embedding phosphor in LSC due to the large Stokes shift and high photoluminescence quantum yield. But the instability and uncontrollable crystal growth are severe limiting their successful utilization in device fabrication. To tackle these issues, double-shell encapsulated configurations are presented, soft ligands of hypophosphorous acid and hard-shell of hollow mesoporous silica are simultaneously suppressing the oxidation of Sn2+ and restricting crystal growth within nano-matrix. The stable phosphor is subsequently embedded into LSC for harvesting solar energy and the resulting output power efficiently drives the combined electrochromic glass under natural light. These fabricated devices also offer the self-adaptable switch on/off functionality to regulate light absorption with variable solar irradiation intensity in real time. This approach is anticipated to open new avenues for utilizing lead-free perovskite nanomaterials in self-powered smart windows for BIPV.

Self-Powered Dual-Band Electrochromic Supercapacitor Devices for Smart Window Based on Ternary Dielectric Triboelectric Nanogenerator.

A dual-band electrochromic supercapacitor device (DESCD) can be driven by an external power supply to modulate solar radiation, which is a promising energy-saving strategy and has broad application prospects in smart windows. However, traditional power supplies, such as batteries, supercapacitors, etc., usually face limited lifetimes and potential environmental issues. Hence, we propose a self-powered DESCD based on TiO2/WO3 dual-band electrochromic material and a ternary dielectric rotating triboelectric nanogenerator (TDR-TENG). The TDR-TENG can convert mechanical energy from the environment into electrical energy to obtain a high output of 840 V, 23.9 µA, and 327 nC. The as-prepared TDR-TENG can drive the TiO2/WO3 film to store energy with a high dual-band modulation amplitude of 41.6% in the visible (VIS) region and 84% in the near-infrared (NIR) region, decreasing the indoor-outdoor light-heat interaction and thereby reducing the building energy consumption. The self-powered DESCD demonstrated in this study has multiple functions of energy harvesting, energy storage, and energy saving, providing a promising strategy for the development of self-powered smart windows.

Viologens and extended viologen derivatives with mono- and di-hexyl substituents for highly stable all-in-one ECDs and solar cell powered large-area ECDs

Viologen-based electrochromic devices (ECDs) have attracted considerable attention due to their potential applications in smart windows. Herein, two viologen derivatives with N-substituted monohexyl (MHEV) and dihexyl (DHEV), and two extended viologen derivatives with a thiophene unit inserted between the bipyridine moieties and N-substituted monohexyl (m-MHEV) and dihexyl (m-DHEV) were synthesized. All-in-one ECDs were assembled using these materials. m-DHEV and m-MHEV-based ECDs exhibited red and dark orange colors, while DHEV and MHEV-based ECDs exhibited blue and magenta colors. The extended conjugation of the chromophore by the thiophene unit endowed the devices with visible-NIR absorption and excellent cyclic stability. After 10000 cycles, ECDs based on m-DHEV and m-MHEV retained 94.2% and 95.0% of their initial optical contrasts, respectively. A binary chromophore mixture of DHEV and m-DHEV was used to fabricate a uniform large-area ECD (8 cm × 8 cm) with strong sunlight absorption ability. The device maintained high optical contrast (80.2% of initial state) after 2000 cycles. Furthermore, a solar cell powered ECD (8 cm × 8 cm) with negligible loss of optical contrast after 100 cycles of coloring and bleaching under sunlight was developed, demonstrating the application potential of self-powered smart windows using these materials.

A near-infrared photoelectrochromic device with indoor thermal management for self-powered smart windows

A near-infrared photoelectrochromic device (NIR-PECD) is a combination of a dye-sensitized solar cell (DSSC) and an electrochromic device (ECD) that directly generates transmittance contrast in IR region from solar radiation without an additional power source.

Designing highly transparent electropolymerized PANI/rGO nanocomposite as a Pt-free electrocatalytic layer in photoelectrochromic device for self-powered green building

The multifunctional device combining electrochromic and photovoltaic performance is defined as a photoelectrochromic device (PECD), which is designed for self-powered smart window applications. Conventionally, Pt is used as an electrocatalyst to reduce the I3− in the electrolyte of PECD. However, the optical contrast of PECD with Pt-based counter electrode (CE) is restricted by an intrinsic opaque. In view of this problem, a polyaniline/reduced graphene oxide (PANI/rGO) nanocomposite electrocatalytic layer with highly optical transmittance and good electrocatalytic performance is designed to replace conventional Pt-based CE for further improving the optical performance of the corresponding PECD. Based on the advantages of low cost and promising electrocatalytic activity of PANI, highly transparent and remarkable conductive rGO is introduced to further boost up its electrical conductivity and electrochemical performance. To embed the rGO into the matrix of PANI uniformly, PANI/rGO nanocomposite is deposited on the conductive glass of ITO via electropolymerization. After systematically optimizing the film thickness and composition of PANI/rGO nanocomposite, the PECD with optimized PANI/rGO based CE possesses better optical contrast (ΔT = 26.8%) than that with Pt-based CE (ΔT = 9.4%), which clearly reveals that PANI/rGO nanocomposites with high optical transparency and electrocatalytic ability have the great potential to replace traditional Pt CE in PECDs.

Self-switching photoelectrochromic device with low cost, plasmonic and conducting Ag nanowires decorated V2O5 and PbS quantum dots

To build an affordable photoelectrochromic energy conversion unit for self-powered smart window applications, the attractive multi-color Ag/V2O5 electrochromic counter electrode (CE) is coupled with a co-sensitized photoanode TiO2/CdS/PbS. V2O5 based devices are well-known for providing smart solutions when a voltage is applied but in this kind of configuration, the quantum dot sensitized solar cell (QDSC) drives the chromatic switching, with sunlight as the natural stimulus. The key objective in coating silver nanowires (AgNW) over the V2O5 film is to enhance the electrochromic as well as electrochemical performance of the device. AgNW impart good electrical conductivity to the layered V2O5 structure making it a promising CE and the transparency of the hybrid film in the visible-light region together with the plasmonic effect contributes to a better optical contrast. The PECD with Ag/V2O5 CE shows a transmission modulation (ΔT) of 31.1% with 45.8 cm2 C-1 coloration efficiency, which is significantly improved than with just V2O5. As compared to the liquid junction photoelectrochromic assembly, the individual films have a much higher ΔT (45.1% at 655 nm). The 5.21% power conversion efficiency (PCE) of the TiO2/CdS/PbS−S2−−Ag/V2O5 QDSC based PECD is a marked rise over that without both AgNW in the CE and PbS near infrared light harvesting QDs at the anode. This work attempts a detailed analysis of the photoelectrochromic and photovoltaic outputs of this novel PECD design with the hybrid film.

Selectively absorbing small-molecule solar cells for self-powered electrochromic windows

Dynamic control of solar transmission by photovoltaic-powered electrochromic smart windows is an up-and-coming approach towards the reduction of energy consumption in buildings. Selectively-absorbing transparent organic solar cells are capable of exhibiting excellent visible-light transparency as well as respectable power conversion efficiencies. This work presents three different transparent small-molecule solar cells (TSCs) with an area of 2.52 cm2, two of which are UV-absorbing and one of which absorbs in the NIR, each in combination with an organic electrochromic device (EC). The NIR-absorbing TSC uses a BDP-OMe:C60 combination, and has a power conversion efficiency of 4% with an average visible light transmission (AVT) of 40%. The two UV-harvesting systems, α-6T/B4PYMPM and NPB:B4PYMPM, each have an AVT of 50–65%, as well as high open-circuit voltages of 1.5–2.0 V. We demonstrate that these photogenerated voltages are sufficient to power a fluoran dye-based organic EC, which has excellent optical properties: its color ranges from highly transparent to deep black, and its on/off contrast ratio is higher than 80% in the range between 390 nm and 640 nm. Self-powered smart windows made by the combination of TSCs and ECs provide a way to significantly reduce energy consumption from air conditioning and lighting, towards zero-energy buildings.

Designing a hybrid type photoelectrochromic device with dual coloring modes for realizing ultrafast response/high optical contrast self-powered smart windows

The self-powered smart window is a promising wire-free system to integrate on the energy-saving building due to its independent and sustainable operations without an external power source. Solar-driven photoelectrochromic devices (PECDs), which derived from the hybridization of dye-sensitized solar cells (DSSCs) and electrochromic devices (ECDs), are potential systems to realize the convenient self-powered smart window. To further boosting up the optical contrast and minimizing the response time, in this study, a brand new hybrid type photoelectrochromic device (H-PECD) composed with a new architecture of independently covered photoelectrode with electrochromic conducting polymeric layer and a novel counter electrode (CE) with bifunctional electrochemical layer is proposed in the first time. Compared to traditional combined-type PECDs (C-PECD), the electrochromic and the photoactive layers are independently integrated on the photoelectrode to overcome the limitation of electrochromic material selection. By taking this advantage, a conducting polymer of PEDOT-MeOH with high coloration efficiency can be introduced to serve as the electrochromic layer for further enhancing the optical performance of H-PECD. Furthermore, a highly transparent electrochemical layer serves as bifunctional CE for not only facilitating the I3- reduction reaction for accelerating the bleaching rate, but also contributes additional optical contrast of 3% under coloring process. By comparing with another classic configuration of separated type PECD (S-PECD), the coloring and bleaching time of H-PECD can be shortened within 5 s under maximum transmittance change at 600 nm for 31.7% since the photovoltaic performance and photo-coloration efficiency (PhCE) is improved by integrating with bifunctional CE. By taking advantage of H-PECD, duel-coloring modes of high optical contrast and ultrafast response can be achieved by controlling the operating processes. This research is a substantial advancement toward the practical application of PECDs and self-powered smart windows.

Triboelectric-optical responsive cholesteric liquid crystals for self-powered smart window, E-paper display and optical switch

Intelligent responsive devices are crucial for a variety of applications ranging from smart electronics to robotics. Electro-responsive cholesteric liquid crystals (CLC) have been widely applied in display panels, smart windows, and so on. In this work, we realize the mechanical stimuli-triggered optical responses of the CLC by integrating it with a triboelectric nanogenerator (TENG), which converts the mechanical motion into alternating current electricity and then tunes the different optical responses of the CLC. When the voltage applied on the CLC is relatively low (15–40 V), the TENG drives the switching between the bistable planar state and focal conic state of the CLC, which shows potential applications in self-powered smart windows or E-paper displays. When the voltage supplied by the TENG is larger than 60 V, a self-powered optical switch is demonstrated by utilizing the transformation between focal conic state and instantons homeotropic state of the CLC. This triboelectric-optical responsive device consumes no extra electric power and suggests a great potential for future smart electronics.

A fully self-powered, ultra-stable cholesteric smart window triggered by instantaneous mechanical stimuli

Smart windows (SWs), especially self-powered SWs, are desirable in a great variety of applications. Nowadays, nearly all SWs require continuous power supply enabled by batteries or energy harvesters such as solar cells, etc. However, batteries are usually with limited lifetime and potential environmental issues, while solar cells largely depend on the weather conditions. In this work, a fully self-powered, instantaneous-mechanical-stimuli-triggered, normally transparent smart window was developed based on an elaborately tailored cholesteric liquid crystal (LC) and a freestanding sliding triboelectric nanogenerator (FS-TENG). The transparency switching including transparency-to-haziness and haziness-to-transparency are facilely triggered by instantaneous TENG-charging and pressure-loading, respectively, with the high transparency contrast of 71.5% and the haze contrast of 61.8%. Both transparent and opaque modes can sustain for an extremely long time without continuous power supplies from energy harvesters. The smart window demonstrated in this work shows the capability of fully self-powered irradiation control for indoor temperature modulation and battery-free privacy information protection while the continuous power supply is no longer required, benefiting a wide variety of fields such as self-powered sunroofs, smart farming systems, motion-driven privacy protection systems, etc . A fully self-powered, mechanical-pulse-triggered, normally transparent smart window was developed based on a cholesteric liquid crystal (LC) and a freestanding sliding triboelectric nanogenerator (FS-TENG). Both transparent and hazy states can last for a long time without continuous power supplies from environments, thanks to the bi-stable characteristic of the cholesteric LC material. The mechanical switching from hazy-to-transparent and transparent-to-hazy states are based on the TENG-charging and pressure-loading, respectively. • It is the first-time ever that an instantaneously-mechanically-triggered cholesteric smart window was developed. • The transparency and opacity of the smart window can be switched back and forth by instantaneous mechanical triggering. • After triggering, both transparent and opaque states can sustain for a long time without continuous charge feeding. • This work correlates two important forms of energies in physics, mechanics and radiance, which is a totally new paradigm.

Normally Transparent Tribo-Induced Smart Window.

Self-powered smart windows are desirable with the expectations of their energy-saving, weather-independent, user-controllable, and miniature performance. Recently developed solar- or thermal-powered smart windows largely depend on the weather conditions and have an extremely slow response, and only a certain portion of thesaved energy can be utilized by the external circuit for mode conversion. In this work, a self-powered normally transparent smart window was developed by the conjunction of a rotary freestanding sliding triboelectric nanogenerator (RFS-TENG) and a polymer network liquid crystal (PNLC) cell. To fabricate the PNLC cell, the alignment layer with randomly distributed microdomains was constructed to encapsulate a mixture of LC polymers and nematic LCs. The opacity of the smart window exposed to an alternating electric field was considerably improved owing to the embedded microdomains and a dense web of LC polymers. The ultrahigh haziness greatly alleviates the charge density required for the LC actuation and thus enables the driving by the TENG where the charge amount is usually limited. The RFS-TENG was elaborately designed with six periodic bent triboelectric films and Ag electrodes, which presented an ultralow friction wear and met the frequency requirement to achieve the steady opacity. By harvesting the mechanical energies from ambient environments, the tribo-induced smart window can benefit a wide variety of fields, such as self-powered sunroofs, wind-driven smart farming systems etc.

Influence of TiO2 layer's nanostructure on its thermoelectric power factor

Rutile-phased TiO2 thin films consist of single layer of nanorod structure and bilayer of nanorod and nanoflower structure with thickness of 2–10 μm were synthesized on FTO glass substrate and its Seebeck coefficient and electrical conductivity were measured in order to clarify the influence of layer's structure on its thermoelectric power factor for self-powered smart window material application. The Seebeck coefficient and electrical conductivity of TiO2 thin films were found to be dependent on the type of layer's structure, and to be independent on the thickness of the layer, which is likely due to the elimination of phonon system contribution and its anisotropic dependency. The bilayer TiO2 thin film is found to possess the highest power factor of 79.7 μW/mK2 at 390 K, which is almost three times larger compared with a reported value for oxide material on glass substrate. These show a promising possibility to apply TiO2 thin film as thermoelectric harvester film fabricated on glass window.

Piezoelectrically and triboelectrically hybridized self-powered sensor with applications to smart window and human motion detection

In this paper, we demonstrate a hybrid generator, derived from the concurrent adoption of piezoelectric and triboelectric mechanisms in one press-and-release cycle, called a Hybridized Self-Powered sensor (HSPS). A new integration of print circuit board (PCB) technology-based piezoelectric generator (PG) concurrently adopted the direct-write, near-field electrospun polyvinylidene fluoride (PVDF) nano/micro-fibers as piezoelectric source materials. On the other hand, triboelectric nanogenerators have the advantages of a high output performance with a simple structure which is also concurrently combined with the PG. The working mechanism of the HSPS includes the PCB-based substrate mounted with parallel aligned piezoelectric PVDF fibers in planar configuration which first bended and generated the electric potential via the effect of piezoelectricity. In what follows, the deformation of a cylindrical rolled-up piezoelectric structure is exercised, and finally, the triboelectric contact of Cu and PTFE layers is physically rubbed against each other with a separation to induce the triboelectric potential. This hybridized generator with a double domed shape design simultaneously combines piezoelectric output and triboelectric output and offers a built-in spacer with automatically spring back capability, which produces a peak output voltage of 100 V, a current of 4 μA, and a maximum power output of 450 nW. A self-powered smart window system was experimentally driven through finger-induced strain of HSPS, showing the optical properties with reversibly tunable transmittances. This research is a substantial advancement in the field of piezoelectric PVDF fibers integration toward the practical application of the whole self-powered system.

Perovskite Photovoltachromic Supercapacitor with All-Transparent Electrodes.

Photovoltachromic cells (PVCCs) are of great interest for the self-powered smart windows of architectures and vehicles, which require widely tunable transmittance and automatic color change under photostimuli. Organolead halide perovskite possesses high light absorption coefficient and enables thin and semitransparent photovoltaic device. In this work, we demonstrate co-anode and co-cathode photovoltachromic supercapacitors (PVCSs) by vertically integrating a perovskite solar cell (PSC) with MoO3/Au/MoO3 transparent electrode and electrochromic supercapacitor. The PVCSs provide a seamless integration of energy harvesting/storage device, automatic and wide color tunability, and enhanced photostability of PSCs. Compared with conventional PVCC, the counter electrodes of our PVCSs provide sufficient balancing charge, eliminate the necessity of reverse bias voltage for bleaching the device, and realize reasonable in situ energy storage. The color states of PVCSs not only indicate the amount of energy stored and energy consumed in real time, but also enhance the photostability of photovoltaic component by preventing its long-time photoexposure under fully charged state of PVCSs. This work designs PVCS devices for multifunctional smart window applications commonly made of glass.

PV 일체형 차세대 스마트 윈도우 기술개발 동향

Among several types of energy saving smart window technologies, the leader, the dynamic EC (electrochromic) window one needs integrated PV (photovoltaics), to minimize expensive electrical wiring as well as to obviate the need for external energy. Self-powered smart windows were reviewed according to PV types used. DSSCs (dye sensitized solar cells) were found to be compatible with EC cells, to have several categories of next generation smart windows such as PECCs (photoelectrochromic cells), PVCCs (photovoltachromic cells), EC polymer PECCs. In addition silicon solar cells and third generation solar cells were investigated. They are summarized in a table showing their advantages and disadvantages respectively for a fast comparison. The strategy to expedite the commercialization of these next generation smart windows includes developing retrofit smart window coverings for use on flexible polymer substrates adhered to the inside surface of a window and easily replaced after use for upto 10 years.

Syntheses and Applications of Inorganic Electrochromic Materials and Devices

Tungsten oxide (WO3) nanorods were synthesized by a hydrothermal process. Transparent film was fabricated by an aggregation-deposition process of WO3 nanorods on transparent conductive glass. The as-synthesized WO3 nanorods exhibit good electrochromic properties. WO3 nanopaltes were directly grown on transparent conductive glasses by a crystal-assisted hydrothermal process, showing enhanced response and coloration efficiency. These properties of WO3 nanostructures endow their promising application in large-area smart windows. Prussian blue films were fabricated and used in color-changeable betteries. A bi-functional Prussian blue/Aluminium device has been demonstrated for self-powered electrochromic window and self-rechargeable transparent battery. Without applying any external bias, Prussian blue can be bleached to Prussian white by connecting the Prussian blue and Al electrodes. After bleaching, the blue colour of the device can be spontaneously recovered. In this regard, the designed device can be used as an energy-saving electrochromic smart window which requires no external power source. The as-prepared device can also be used as a battery with a high output voltage. Most importantly, after discharging, such a battery can automatically self-recharge. The as-prepared device exhibits promising applications in broad fields, for example, as a self-powered smart window to perform indoor light and heat management, and as a self-rechargeable transparent battery to power some delicate devices.

Self-Powered Electrochromic Smart Window Driven By Transparent Triboelectric Nanogenerators Via Harvesting Wind and Rain Energies

Self-powered system is one of promising electronic concepts in upcoming future due to its independent and sustainable operations without a battery. To realize this idea, triboelectric nanogenerator (TENG) was recently invented that could effectively convert the ambient mechanical energy into electricity to power up portable electronics. In this work, the concept of self-powered smart window system was realized through integrating an electrochromic device (ECD) with a transparent TENG driven by wind blowing and raindrops The ECD consisted of Prussian blue and zinc hexacyanoferrate as the electrochromic material and the ion storage layer, respectively. Driven by the sustainable output of the TENG, the optical properties, especially the transmittance of the ECD displays reversible variations due to electrochemical redox reactions. The maximum transmittance change can reach up to 32.4% at 695 nm which is comparable to that operated by conventional electrochemical potentialstation (32.5%). This research is a substantial advancement towards the practical application of nanogenerators and self-powered systems, and it paves the way for the development of fully independent smart windows or high-performance displays.

Motion-Driven Electrochromic Reactions for Self-Powered Smart Window System

The self-powered system is a promising concept for wireless networks due to its independent and sustainable operations without an external power source. To realize this idea, the triboelectric nanogenerator (TENG) was recently invented, which can effectively convert ambient mechanical energy into electricity to power up portable electronics. In this work, a self-powered smart window system was realized through integrating an electrochromic device (ECD) with a transparent TENG driven by blowing wind and raindrops. Driven by the sustainable output of the TENG, the optical properties, especially the transmittance of the ECD, display reversible variations due to electrochemical redox reactions. The maximum transmittance change at 695 nm can be reached up to 32.4%, which is comparable to that operated by a conventional electrochemical potentiostat (32.6%). This research is a substantial advancement toward the practical application of nanogenerators and self-powered systems.

Self-powered smart window controlled by a high open-circuit voltage InGaN/GaN multiple quantum well solar cell.

A self-powered complementary electrochromic device (CECD) driven by a high open-circuit voltage InGaN/GaN multiple quantum well (MQW) solar cell has been designed. The coloration and bleaching time of the system were 5 and 8 s, respectively.

A bi-functional device for self-powered electrochromic window and self-rechargeable transparent battery applications

Electrochromic smart windows are regarded as a good choice for green buildings. However, conventional devices need external biases to operate, which causes additional energy consumption. Here we report a self-powered electrochromic window, which can be used as a self-rechargeable battery. We use aluminium to reduce Prussian blue (PB, blue in colour) to Prussian white (PW, colourless) in potassium chloride electrolyte, realizing a device capable of self-bleaching. Interestingly, the device can be self-recovered (gaining blue appearance again) by simply disconnecting the aluminium and PB electrodes, which is due to the spontaneous oxidation of PW to PB by the dissolved oxygen in aqueous solution. The self-operated bleaching and colouration suggest another important function of the device: a self-rechargeable transparent battery. Thus the PB/aluminium device we report here is bifunctional, that is, it is a self-powered electrochromic window as well as a self-rechargeable transparent battery.