Smart photochromic glass films: the evolution in glass performance

Smart photochromic glass films: the evolution in glass performance | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Smart photochromic glass films: the evolution in glass performance Augustinus J.J. Kragt, Julia S. van der Burgt This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6221722/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 10 You are reading this latest preprint version Abstract By improving the insulation value of glazing, the glass industry contributes successfully to reduce global heating demand in the built environment. However, as temperatures are increasing and heat waves are more frequently occurring, increased insulation values of glazing also contribute to the vast growing cooling demand. Therefore, the glass industry is evolving further with smart glazing to reject solar heat entrance during summer seasons, while allowing it to heat up indoor spaces during winter seasons. This paper presents a photochromic window film with a unique combination of optical properties compared to other smart glass technologies. The film has a high visible light transmission in the transparent state (88%), showing a modulation of 48% accompanied with a change in solar heat gain coefficient from 0.87 to 0.54 upon irradiation with UV solar light. This way the film enhances both daylight- and thermal comfort as well as energy efficiency all by itself. The film is simply prepared from solution by a roll-to-roll scalable coating method. Simulation shows that the film, when integrated in a low-e coated double glazing, can save up to 35% on annual energy consumption compared to the same glazing without the film depending on the climate where it is applied. Upgrading all glazing in Europe with the smart film has the potential to save about 1200 TWh of energy use annually. Smart glass Photochromic Scalable Easy applicable Energy efficiency Figures Figure 1 Figure 2 Figure 3 1. Introduction Buildings account for 34% of the world-wide energy consumption, of which most originates from building operations. On average 40% of a building’s energy use is spent on heating and cooling of indoor spaces, which comes down to more than 14.000 TWh or 6.7 Gton CO 2 -eq emissions per year globally (Global Alliance for Buildings and Construction, 2024 ; IEA, 2021 ). Although heating demand takes up the largest part, space cooling is the fastest growing use of energy in buildings. Over the past 30 years the energy consumption for space cooling has more than tripled to about 2020 TWh/year globally, growing at an average rate of 4% per year, today taking up about 6% of the total energy consumption of buildings. Due to rising temperatures and a more frequent occurrence of heat waves together with rising economies in hot and humid climates and general increasing thermal comfort demand, this trend is expected to continue to 6200 TWh/year energy use for space cooling in 2050, then responsible for 30% of a building’s total electricity use (International Energy Agency (IEA), 2018 ). In 2022, residential cooling units in operation reached 1.5 billion, a threefold increase since 2000 (Global Alliance for Buildings and Construction, 2024 ). This trend is also observed in Europe. With about 3200 TWh/year spent on space heating and only 107 TWh/year on space cooling, space heating is still dominating the energy consumption in European buildings (Gevorgian et al., 2021 ). However, following the global trend the energy use for space cooling has tripled over the past 30 years. It is expected that 85% of the commercial buildings and 50% of the residential buildings are equipped with air-conditioning by 2050, coming from 50% and 15% today, respectively (Glass for Europe, 2019 ). This trend strains peak electricity demands, particularly during hot days, increasing the likelihood of power outages. To reduce this global electricity demand for cooling, there is a need for a fast shift towards adaptive building designs (Global Alliance for Buildings and Construction, 2024 ). Glazing, as a crucial element in the heat management of a building, plays a significant role in these energy demand trends. As heating demands are still dominating the energy use in the building sector, policies focussed on renovations that enhance the insulation values of building materials, with a special interest on glass (European Comission, 2020 ). The glass industry responded to that by innovations to increase the insulating properties by lowering the thermal transmittance (U-value) through glazing, including developments in low-e coatings, promoting triple glazing, and, more recently, developing vacuum glass, which can already reach U-values as low as 0.4 W/(m 2 .K) (AGC, 2022 ; Beng Glas, 2024 ). As still 81% of the European building stock is equipped with low-performance glazing (e.g. single or double clear glazing), there is still a huge job to be done in renovating this glass (Gevorgian et al., 2021 ). Upgrading all European buildings with high-performance glazing by 2030 would save 29% of energy equaling 878 TWh or 94.3 Mtons of CO 2 -eq emissions (Glass for Europe, 2019 , 2020 ). Although this potential is already huge, current high-performance glazing does not provide the ideal solution in terms of energy efficiency all-year through. The excellent insulation values greatly reduce the heating demand during winter times. However, during summer times they introduce problems of overheating in buildings, as the solar heat that comes in through glazing is captured indoors, further enhancing the trend of increasing cooling demand. Although solar heat rejection functionalities can be added to the glazing as well to keep heat out during summertime, this value is permanent and thus also rejects available solar heat during wintertime, pressing again demand for heating. Therefore, the next step in the evolution of glass is to make glazing smart. Smart glass has the ability to adapts its visible light transmission (T vis ) and its solar heat gain coefficient (SHGC) based on an external trigger, such as an electric field, sunlight intensity or temperature (Brzezicki, 2021 ; Casini, 2018 ; Dussault, Gosselin, & Galstian, 2012 ; Jelle et al., 2012 ; Kamalisarvestani, Saidur, Mekhilef, & Javadi, 2013 ; Ke et al., 2019 ; Rezaei, Shannigrahi, & Ramakrishna, 2017 ; Sibilio et al., 2016 ; Y. Wang, Runnerstrom, & Milliron, 2016 ). In this way, they can adapt the glazing characteristics to outdoor weather conditions providing additional daylight comfort and blocking more solar heat in summer, to save energy use on cooling, while letting more of it through during winter, to prevent additional heating energy demand. Introducing smart glass to the European building stock will increase the energy saving potential with an additional 20% compared to current high-performance glazing (Glass for Europe, 2019 , 2020 ). Therefore, the industry attention to develop smart glass products is increasing and smart glass products emerge (see discussion). Examples of smart glass triggered by electric fields (electrochromic) are abundant, showing high modulation of both T vis as well as SHGC, fast switching rates and appealing due to their manual control to various intermediate state by the wishes of the end-user (Converlight by Chomogenics, 2018 ; Halio, 2020 ; SageGlass Saint Gobain, n.d.). As a cheaper to install alternative with a higher feasibility of application in widespread building scenarios, self-regulating smart glass technologies triggered by sunlight intensity (photochromic) or temperature (thermochromic) are also attracting attention. These products typically show a large change in T vis between the transparent and tinted state, providing additional daylight comfort, but show a limited change in SHGC, and thus contribute less to enhanced energy efficiency (CoolVu, n.d.; SmartGlassNordics, n.d.; SwitchFoil International, n.d.). Furthermore, smart glass coatings are typically fabricated by expensive, energy consuming vapor deposition techniques (Kamalisarvestani et al., 2013 ; Ke et al., 2019 ; Rezaei et al., 2017 ; Y. Wang et al., 2016 ). Here, a photochromic coated film is presented, simply prepared from solution by a roll-to-roll scalable coating technique, with high transparency in the transparent state, large modulation of solar heat (ΔSHGC), whilst showing a large change in T vis . Through simulation studies on a model office the energy saving potential when applied across Europe is shown. In the discussion a comparison is made with existing smart glass products on the market and benefits and challenges are elaborated. 2. Methods 2.1. Film fabrication method The ink formulation is fabricated by mixing in WCl 6 , a precursor for the WO 3 nanopigments, together with PMMA in an appropriate solvent, suitable for large scale processing, as described in earlier work (Meng et al., 2024 ) Various dopants and additives are added to aid the bleaching process of the final film and enhance the processing of the ink formulation on large scale. On lab scale the films are fabricated by coating directly on an acrylic adhesive substrate using blade coating technique, followed by drying at elevated temperature to evaporate the solvent. For large scale prototypes this method is translated to an industrial roll-to-roll coating line using gravure coating at 40 cm wide. In both methods the dry coating thickness is controlled around 40 µm. 2.2. Application of the film to glass The film can be adhered to glass plates using methods commonly used in the application of retrofit window films. This includes removing the liner from the adhesive, applying retrofit film application liquid or water with a few drops of mild soap on both the adhesive and the glass plate, placing the film on the glass plate, squeezing out excess of liquid underneath the film and let it dry for at least 24 hours to let the adhesive properly adhere to the glass plate. 2.3. Tinting and bleaching The tinting is done by irradiating the film with UV-light, which can be provided by sunlight in outdoor conditions or by sunlight mimicking lamps typically used for reptiles containing UV-light (Lucky Reptile Bright Sun UV Jungle 70W) in laboratory conditions. The light intensity was varied by changing the height of the lamp and measured using a radiometer (Opsytec Radiometer RM12) operating in the UV-A range. Bleaching of the samples is carried out by storing them in a dark cabinet. 2.4. Transmission measurements Transmission spectra were measured using a UV-Vis-nIR spectrometer (PerkinElmer Lambda 750) over a range between 300 and 2500 nm with an interval of 5 nm. For full glass characterization also reflection spectra are measured from both sides of the glass plate to which the film is adhered. Visible light transmission values for time-related tinting and bleaching behaviour measurements are measured using a haze meter (Hangzhou Baiteng Electronic Technology, DH-10 Portable Haze Meter) having a measure aperture of 7mm, allowing to retrieve the visible light transmission by the press of a single button. 2.5. Calculation of glazing characteristics Glazing characteristics were calculated by implementing the transmission and reflection spectra of the film in the transparent and fully tinted state when adhered to a 4 mm single clear glass plate in the LBNL Software Optics6 and Window7.7. 2.6. Energy efficiency modelling The building energy efficiency simulations were carried out by the software DesignBuilder. A model office was used as designed and described in earlier work (Kragt, Ham, Sentjens, Schenning, & Klein, 2022; Meng et al., 2024 ). The glazing characteristics for the film in combination with different glazing types was calculated in the DesignBuilder software according to EN673. For the clear double glazing two 4mm Optifloat clear glass plates were chosen from the International Glazing Database with a 16mm argon cavity. For the low-e glass 1 the inner glass plate is replaced by 4mm Pilkington K Glass and for low-e glass 2 by 4 mm Pilkington Optitherm S1 Plus. To integrate the photochromic film the glazing characteristics are calculated using the LBNL software Optics6 and Window7.7 using the transmission and reflection spectra at various UV-light intensities mimicking various sunlight intensities. This was done by increasing the UV-light intensity to a certain level and maintain this for 30 minutes before going to the next UV-light intensity. In this way the UV-light intensity was increased and decreased to also account for hysteresis during the tinting and bleaching process. To introduce the photochromic effect in the calculation, the “window shading” feature was used. Here the optical properties of the outer glass pane at various sunlight intensities were defined based on the optical properties determined above, as if the photochromic film is applied on position 2 of the glass built-up. The window shading was controlled by “daylight only” and operated “24/7” to mimic the autonomous working principle of the photochromic film. For the model calculation each window was provided with a single light-intensity “sensor,” so the various windows of the building model operated individually. The most recent weather data files were downloaded from www.climate.onebuilding.org , which provided typical meteorological year datasets for the specific locations, which were then imported into the DesignBuilder model. 3. Results The roll-to-roll produced photochromic film tints under illumination of UV-light (Fig. 1 A). The film can be adhered to a glass plate and used as a retrofit film or subsequently assembled inside the cavity of a multi-layered glazing unit. When the film is irradiated by UV-light from the sun, the film turns into its tinted state, thereby reducing both visible light and infrared light transmission (Fig. 1 B and 2 A). The film is based on a coating containing photochromic tungsten oxide (WO 3 ) nano pigments in a polymer matrix. When UV-light hits these particles the tungsten atoms got excited and their valence state reduced (Bourdin et al., 2020 ; Kim et al., 2024 ; Li et al., 2019 ; S. Wang, Fan, Liu, Yu, & Jiang, 2018 ). This change of the material is accompanied by a change in the absorption spectrum giving rise to the observed optical change. Expressing this change in glazing characteristics when adhering the film to a 4 mm single clear glass plate, this results in a T vis change from 88 to 40% between the transparent and tinted state, accompanied by a change in SHGC from 0.87 to 0.54 (Fig. 2 B). The optical properties of the film are investigated in a controlled way by irradiating with a sunlight mimicking lamp at various intensities ranging from 5 to 50 W/m 2 of measured UV-A radiation (Fig. 2 C). At the maximum intensity the film tints in 20 minutes from a T vis of 87–39%, where it stabilizes. With 20 W/m 2 the films still obtain a significant tint, although T vis after 20 minutes equals 54% and reaches 39% after 120 minutes. At 10 W/m 2 irradiation the maximum tint suddenly becomes less and T vis reaches 60% after 120 minutes, which further increases to 73% upon further decreasing the intensity to 5 W/m 2 within this timeframe. When the film is fully tinted and left in the dark it bleaches to a T vis of 80% in 120 minutes and fully recovers in 240 minutes (Fig. 2 D). The energy saving potential of the smart photochromic glazing was explored by implementing these glass properties in a model of an office building using DesignBuilder. Various glazing types were implemented in the model: double clear glass, low-e coated glass with a high SHGC (low-e glass 1), and low-e coated glass with a low SHGC (low-e glass 2). The two types of low-e coated glass are simulated without and with the smart glass film (Table 1 ). These glazing types were chosen as they represent typical glass choices in the built environment. It is not expected that the smart film in practice would be used much with clear double glazing, as the primary aim of glass renovation usually is to upgrade insulation properties. In addition, the smart film is not very effective in keeping solar heat out when combined with low insulating glass, as the film absorbs the solar heat, which is then radiated to the room interior. Therefore, the best way to use the film is to apply the film on position 2 (the inner side of the outer pane) or position 1 (in case of retrofitting) of a low-e coated glazing unit with the low-e coating on position 3 (the inner side of the inner pane). Furthermore, within the simulations the intermediate states of the film are implemented as well, so that the tint level varies with the solar intensity variation within the used weather data files. Table 1 – Glazing characteristics used in the energy performance analysis Double clear glass Low-e glass 1 Low-e glass 2 No film No film With Smart film No film With Smart film Transparent Tinted Transparent Tinted SHGC 0.78 0.74 0.74 0.36 0.55 0.54 0.27 T vis [%] 82 75 75 34 75 75 34 U-value [W/m 2 K] 2.6 1.4 1.4 1.4 1.1 1.1 1.1 The energy use for lighting, heating, and cooling are simulated when placing the model building in various cities across Europe representing different climates (Fig. 3 and Table 2 ). Although in all climates, applying the smart film to glazing will provide additional daylight comfort compared to current high-performance glazing, in terms of energy performance the presented smart film has the biggest impact in southern European cities, such as Rome and Madrid. In these warmer climates the building energy use is dominated by cooling, and so the biggest impact can be made by taking solar heat rejection measures. Additional energy savings ranging between 27 and 35% are achieved in these cities when a building owner would choose low-e coated glass with the smart film compared to the same glass without the film. In mid-European cities, such as Paris and Amsterdam, this additional energy saving is 8 to 16%, whereas in Praha 2 to 6% can be achieved. As in these climates the energy use for space heating is more significant the impact of the smart film on the total energy use is less. Although the film still reduces cooling energy use during summertime, an increase in heating energy use can be observed. This originates from the fact that also during wintertime there are still moments that the film is in an (intermediate) tinted state and thus rejecting more solar heat compared to glazing without the film. This effect would, however, be enlarged when one would use a glazing or film with a permanent solar heat rejection level equal to that of the tinted state of the smart film as shown in previous simulation studies (Meng et al., 2024 ). In cities with more severe winters, such as Oslo and Stockholm, heating energy use is even more dominating and the effect of increasing heating energy use by addition of the smart film is balancing out with the reduced cooling energy use. In these climates, a building owner could still choose for smart glazing with the film because of the benefits on daylight comfort for the users. Table 2 – Potential annual energy savings according to the simulations of replacing clear double glazing by low-e glass 2 with smart film (1st column), and the additional energy savings of retrofitting the two types of low-e glass with our smart glass film (2nd and 3rd column), across various European cities. Replacing double clear glass with low-e glass 2 with smart film Retrofitting low-e glass 1 with smart film Retrofitting low-e glass 2 with smart film Rome 38% 35% 31% Madrid 39% 28% 27% Paris 42% 16% 13% Amsterdam 43% 12% 8% Praha 41% 6% 2% Oslo 45% -3% -5% Stockholm 40% 1% -1% Still 81% of the current European building stock is equipped with outdated glazing having low insulating values and solar heat rejection levels (Gevorgian et al., 2021 ). Therefore, renovation of glazing offers a high potential to reduce the energy consumption for space heating and cooling in buildings, which today takes up an energy consumption of 3307 TWh per year. Replacing current low-performance glazing (e.g. double clear glass) present in most buildings in Europe today with smart high-performance glass (e.g. low-e glass 2 with smart film) would save, according to the presented simulations, 38 to 45% on a building’s annual energy use across various European climates. Following these results and assuming an average energy saving of 41%, 1122 TWh could be saved when upgrading all European buildings that are still equipped with low-performance glazing with smart high-performance glazing including the presented film. When also retrofitting the buildings that are already equipped with high-performance glazing with the smart film, assuming an average energy saving of 12%, an additional 80 TWh could be saved, given a total of about 1200 TWh to be saved annually. To put this number in perspective, the energy saving potential when upgrading all European buildings with current high-performance glazing (e.g. low-e glass 2) following the simulation results with an average energy saving of 32%, would be 873 TWh. This number is fairly in line with the energy saving potential of 878 TWh reported by Glass for Europe when all glazing would be replaced with readily available high-performance glazing by 2030 (Glass for Europe, 2019 ). It should be realized that application of the smart glass film would only be beneficial in terms of energy performance in buildings that are equipped with an active cooling installation. However, also in buildings that are not yet equipped with air-conditioning, the smart film provides benefits on daylight comfort and preventing overheating issues. This might result in postponing or even cancelling the decision to install expensive air-conditioning and therefore indirectly saving energy. 4. Discussion As glass is evolving, smart glass products are emerging in the market (Table 3 ). Electrochromic glazing has attracted much interest due to its ability to be manually controlled by the user to their desires with fast switching speeds, usually in the order of minutes. The ΔT vis from the transparent to tinted state is large and tints as low as 1% can be achieved. Also, the ΔSHGC is significant giving them not only the ability to provide daylight comfort to the user, but also contribute to the energy efficiency of a building compared to glazing technologies with permanent SHGC levels. Nevertheless, in their transparent state the SHGC is typically already quite low (< 0.51), which makes it not the ideal solution during wintertime, and as the operations are controlled by the user the tinting level is not always synchronized with the energetically most favourable state. Although the operations can be overruled by sensors for outdoor temperature and/or sunlight irradiation, these add further costs and complexity to the installation, making this option less feasible for building owners. In these occasions, self-adaptive smart glass products, such as photochromic films, are an appealing alternative. They can simply be installed similar to the commonly used glass products of today and add only limited costs. Therefore, they have the potential to become a more mainstream smart glass product. In addition, and in contrast to electrochromic glass products, they can often be applied as retrofit film product, further enhancing their potential widespread application. Nevertheless, photochromic glass films currently on the market can show a large variation in T vis between the transparent and tinted state but have a limited ΔSHGC (0.09) at maximum. Therefore, they can enhance daylight comfort of buildings, but their impact on energy efficiency compared to regular glass products with a permanent tint is limited. The novelty of the photochromic smart glass technology presented in this work lies in the combination of a large ΔT vis and ΔSHGC (48% and 0.33, respectively, when adhered to a single 4 mm clear glass plate). In addition, the transparency level of the initial transparent state is supremely high. This provides the technology presented here all the benefits of current photochromic glass products, e.g. daylight comfort and a widespread applicability, together with a high potential to make impact on the energy efficiency of buildings. Table 3 – Overview of various electrochromic (EC) and photochromic (PC) smart glass technologies available on the market. For most products variants with different tint levels are available. For this table the most transparent version is noted. T vis [%] SHGC Mode Composition Transp. Tinted ΔT vis Transp. Tinted ΔSHGC Ref. Sage glass clear EC Low-e IGU 58 1 57 0.40 0.08 0.32 (SageGlass Saint Gobain, n.d.) Converlight EC Low-e IGU 59 15 44 0.43 0.13 0.30 (Converlight by Chomogenics, 2018 ) Halio glass EC Low-e IGU 65 2 63 0.51 0.09 0.42 (Halio, 2020 ) Dynaclime PC Single clear 73 22 51 0.35 0.26 0.09 (SmartGlassNordics, n.d.) CoolVu PC Single clear 54 35 19 0.43 0.41 0.02 (CoolVu, n.d.) ActiveFoil PC Single clear 49 34 15 0.43 0.41 0.02 (SwitchFoil International, n.d.) This work PC Single clear Low-e glass 1 Low-e glass 2 88 75 75 40 34 34 48 41 41 0.87 0.74 0.54 0.54 0.36 0.27 0.33 0.38 0.27 - - - 5. Conclusion This paper describes a highly transparent smart photochromic film with unique optical properties, that are unmet in current self-adaptive glass technologies. The film shows both a high modulation in T vis from 88 to 40% as well as a high modulation in SHGC from 0.87 to 0.54 in response to increasing sunlight intensity. Compared to state-of-the-art electrochromic window technologies this resembles a similar change in SHGC, but allowing more solar heat in its transparent state. Moreover, the active photochromic nano pigment-based coating material is simply produced from solution and processed through a scalable roll-to-roll coating technique. The installation of the film is simple and cost-effective making the widespread application in the built environment feasible. Simulations provide the additional energy savings of the film are 27 to 35% compared to the same low-e coated double glazing without the film in Southern European climates, like Madrid and Rome, respectively. In mid-European climates like Praha, Amsterdam and Paris, this benefit ranges from 2 to 16%. In Scandinavian climates the energy benefit vanished, limiting the benefit of the film to additional daylight comfort. Renovating all current European low-performance building glass with smart glazing containing this film and further upgrading already installed low-e coated glazing by retrofitting would have the potential to save about 1200 TWh on energy use annually, thereby outperforming the current predictions of 878 TWh potential energy saving when renovating with current high-performance glazing. Declarations Article Information (this info will be completed later by the editors) Published by GPD, on behalf of the author(s) Published as part of the peer-reviewed Glass Performance Days Conference Proceedings, June 2025 Editors: Jan Belis, Christian Louter & Marko Mökkönen This work is licensed under a Creative Commons Attribution 4.0 International (CC BY 4.0) license. Copyright © 2025 with the author(s) 6.1. Funding The research leading to these results is carried out within the SFEER project, which received funding from the Topsector Energy Subsidy of the Dutch Ministry of Economic Affairs and Climate Policy carried out by The Netherlands Enterprise Agency (RVO), in the framework of the MOOI-subsidy round 2023 (MOOI322002). 6.2. Competing interest The authors have no relevant financial or non-financial interests to disclose. 6.3. Other declarations An Ethics declaration is not applicable to the content of this research. Data is gathered by the authors and are not shared openly. They can be shared upon request. Author Contribution J.S. did the experimental work related to coated film preparation and characterization and reviewed the manuscript. A.K. did the simulation work and wrote the manuscript text. Acknowledgement The authors would like to acknowledge the funding for this research from SFEER project, which is carried out with the Topsector Energy Subsidy of the Dutch Ministry of Economic Affairs and Climate Policy carried out by The Netherlands Enterprise Agency (RVO), in the framework of the MOOI-subsidy round 2023. In addition, authors would like to thank Prof. A.P.H.J. Schenning from the research group Stimuli-responsive Functional Materials and Devices (SFD) of the department of Chemical Engineering and Chemistry at the Eindhoven University of Technology for support in discussions and hosting ClimAd Technology as a company in his research group. References AGC: Fineo by AGC. 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Retrieved from https://doi.org/10.1016/j.solmat.2011.08.010 Kamalisarvestani, M., Saidur, R., Mekhilef, S., Javadi, F.S.: Performance, materials and coating technologies of thermochromic thin films on smart windows. Renewable and Sustainable Energy Reviews , 26, 353–364. (2013). Retrieved from https://doi.org/10.1016/j.rser.2013.05.038 Ke, Y., Chen, J., Lin, G., Wang, S., Zhou, Y., Yin, J., Long, Y.: Smart Windows: Electro-, Thermo-, Mechano-, Photochromics, and Beyond. Advanced Energy Materials , 9(39), 1–38. (2019). Retrieved from https://doi.org/10.1002/aenm.201902066 Kim, M.S., Yoon, J.H., Kim, H.M., Lee, D.J., Hirose, T., Takeda, Y., Kim, J.P.: Amplifying Photochromic Response in Tungsten Oxide Films with Titanium Oxide and Polyvinylpyrrolidone. Nanomaterials , 14(13), 1–15. (2024). Retrieved from https://doi.org/10.3390/nano14131121 Kragt, A.J.J., Ham, E.R., Van Den, Sentjens, H., Schenning, A.P.H.J., Klein, T.: The Potential of Static and Thermochromic Window Films for Energy Efficient Building Renovations. Journal of Facade Design & Engineering , 10, 87–104. (2022). Retrieved from https://doi.org/https://doi.org/10.47982/jfde.2022.powerskin.6 Li, R., Zhou, Y., Shao, Z., Zhao, S., Chang, T., Huang, A., Jin, P.: Enhanced Coloration/Bleaching Photochromic Performance of WO3 Based on PVP/PU Composite Matrix. ChemistrySelect , 4(33), 9817–9821. (2019). Retrieved from https://doi.org/10.1002/slct.201902068 Meng, W., Kragt, A.J.J., Gao, Y., Brembilla, E., Hu, X., van der Burgt, J.S., Jiang, L.: Scalable Photochromic Film for Solar Heat and Daylight Management. Advanced Materials , 36(5), 1–12. (2024). Retrieved from https://doi.org/10.1002/adma.202304910 Rezaei, S.D., Shannigrahi, S., Ramakrishna, S.: A review of conventional, advanced, and smart glazing technologies and materials for improving indoor environment. Solar Energy Materials and Solar Cells , 159, 26–51. (2017). Retrieved from https://doi.org/10.1016/j.solmat.2016.08.026 SageGlass Saint Gobain: (n.d.). IGU Product Guide. Retrieved from https://www.sageglass.com/sites/default/files/2024-07/MKT-382_IGU_Product_Guide_US.pdf Sibilio, S., Rosato, A., Scorpio, M., Iuliano, G., Ciampi, G., Vanoli, G.P., De Rossi, F.: A review of electrochromic windows for residential applications. International Journal of Heat and Technology , 34(Special Issue 2), S481–S488. (2016). Retrieved from https://doi.org/10.18280/ijht.34S241 SmartGlassNordics: (n.d.). Dynaclime. Retrieved from https://smartglassnordic.com/images/faktablad/SGN_DYNACLIME_Solar_Film_Product_sheet.pdf SwitchFoil International: (n.d.). Technical specifications ActivFoil. Retrieved 27 February 2025, from https://switchfoil.com/activfoil-photochromic-window-film/technical-specifications-activfoil/ Wang, S., Fan, W., Liu, Z., Yu, A., Jiang, X.: Advances on tungsten oxide based photochromic materials: Strategies to improve their photochromic properties. Journal of Materials Chemistry C , 6(2), 191–212. (2018). Retrieved from https://doi.org/10.1039/c7tc04189f Wang, Y., Runnerstrom, E.L., Milliron, D.J.: Switchable Materials for Smart Windows. Annual Review of Chemical and Biomolecular Engineering , 7(1), 283–304. (2016). Retrieved from https://doi.org/10.1146/annurev-chembioeng-080615-034647 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 08 Jul, 2025 Reviews received at journal 04 Jul, 2025 Reviewers agreed at journal 28 Jun, 2025 Reviews received at journal 14 May, 2025 Reviewers agreed at journal 02 May, 2025 Reviewers agreed at journal 03 Apr, 2025 Reviewers invited by journal 02 Apr, 2025 Editor assigned by journal 22 Mar, 2025 Submission checks completed at journal 22 Mar, 2025 First submitted to journal 13 Mar, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6221722","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":439153084,"identity":"9e1a7672-6c37-4d08-b3d4-411ff1164eac","order_by":0,"name":"Augustinus J.J. Kragt","email":"data:image/png;base64,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","orcid":"","institution":"ClimAd Technology B.V","correspondingAuthor":true,"prefix":"","firstName":"Augustinus","middleName":"J.J.","lastName":"Kragt","suffix":""},{"id":439153086,"identity":"8b300b6a-27af-4570-ae56-6b468096bdd4","order_by":1,"name":"Julia S. van der Burgt","email":"","orcid":"","institution":"ClimAd Technology B.V","correspondingAuthor":false,"prefix":"","firstName":"Julia","middleName":"S. van der","lastName":"Burgt","suffix":""}],"badges":[],"createdAt":"2025-03-13 16:23:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6221722/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6221722/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":81296314,"identity":"40bb17f5-c3e1-409d-b823-5f00c48f9a7c","added_by":"auto","created_at":"2025-04-24 13:01:33","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":628147,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Roll-to-roll produced film tinted by UV-light present in the coating line. (B) A 30 x 30 cm piece of film is incorporated inside the cavity of a clear double glazing by application on position 2. Upon sunlight illumination the film gets to its tinted state. In cloudy conditions or during the evening it returns to its transparent state.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-6221722/v1/8a7537307d2de76513026c12.png"},{"id":81296313,"identity":"d0b29312-c66e-4203-942e-14673ddf030c","added_by":"auto","created_at":"2025-04-24 13:01:33","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":202706,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Transmission spectra of the film adhered to a 4 mm single clear glass plate in its transparent and fully tinted state. The background shows the AM1.5 solar irradiance spectrum (B) Table with glass properties according to NEN410. (C) Tinting behaviour of the film upon various intensities of UV-A radiation. (D) Bleaching behaviour of the film in dark conditions.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-6221722/v1/ce15e8091276bdb31f36a174.png"},{"id":81296318,"identity":"9bf8ca81-fb51-4440-ba33-846a2aa606c8","added_by":"auto","created_at":"2025-04-24 13:01:34","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":111772,"visible":true,"origin":"","legend":"\u003cp\u003eEnergy performance data for lighting, heating, and cooling of the model office in various cities across Europe representing various climates equipped with the various types of glazing.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6221722/v1/ebf89f9324021185519453c0.png"},{"id":81298576,"identity":"ddbeda54-343b-4d02-81fa-7f8f6d58b8e2","added_by":"auto","created_at":"2025-04-24 13:25:34","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1731165,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6221722/v1/1f9b2131-82bd-4464-9387-fc0848dfe715.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Smart photochromic glass films: the evolution in glass performance","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eBuildings account for 34% of the world-wide energy consumption, of which most originates from building operations. On average 40% of a building\u0026rsquo;s energy use is spent on heating and cooling of indoor spaces, which comes down to more than 14.000 TWh or 6.7 Gton CO\u003csub\u003e2\u003c/sub\u003e-eq emissions per year globally (Global Alliance for Buildings and Construction, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; IEA, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Although heating demand takes up the largest part, space cooling is the fastest growing use of energy in buildings. Over the past 30 years the energy consumption for space cooling has more than tripled to about 2020 TWh/year globally, growing at an average rate of 4% per year, today taking up about 6% of the total energy consumption of buildings. Due to rising temperatures and a more frequent occurrence of heat waves together with rising economies in hot and humid climates and general increasing thermal comfort demand, this trend is expected to continue to 6200 TWh/year energy use for space cooling in 2050, then responsible for 30% of a building\u0026rsquo;s total electricity use (International Energy Agency (IEA), \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). In 2022, residential cooling units in operation reached 1.5\u0026nbsp;billion, a threefold increase since 2000 (Global Alliance for Buildings and Construction, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). This trend is also observed in Europe. With about 3200 TWh/year spent on space heating and only 107 TWh/year on space cooling, space heating is still dominating the energy consumption in European buildings (Gevorgian et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). However, following the global trend the energy use for space cooling has tripled over the past 30 years. It is expected that 85% of the commercial buildings and 50% of the residential buildings are equipped with air-conditioning by 2050, coming from 50% and 15% today, respectively (Glass for Europe, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). This trend strains peak electricity demands, particularly during hot days, increasing the likelihood of power outages. To reduce this global electricity demand for cooling, there is a need for a fast shift towards adaptive building designs (Global Alliance for Buildings and Construction, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eGlazing, as a crucial element in the heat management of a building, plays a significant role in these energy demand trends. As heating demands are still dominating the energy use in the building sector, policies focussed on renovations that enhance the insulation values of building materials, with a special interest on glass (European Comission, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The glass industry responded to that by innovations to increase the insulating properties by lowering the thermal transmittance (U-value) through glazing, including developments in low-e coatings, promoting triple glazing, and, more recently, developing vacuum glass, which can already reach U-values as low as 0.4 W/(m\u003csup\u003e2\u003c/sup\u003e.K) (AGC, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Beng Glas, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). As still 81% of the European building stock is equipped with low-performance glazing (e.g. single or double clear glazing), there is still a huge job to be done in renovating this glass (Gevorgian et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Upgrading all European buildings with high-performance glazing by 2030 would save 29% of energy equaling 878 TWh or 94.3 Mtons of CO\u003csub\u003e2\u003c/sub\u003e-eq emissions (Glass for Europe, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2019\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Although this potential is already huge, current high-performance glazing does not provide the ideal solution in terms of energy efficiency all-year through. The excellent insulation values greatly reduce the heating demand during winter times. However, during summer times they introduce problems of overheating in buildings, as the solar heat that comes in through glazing is captured indoors, further enhancing the trend of increasing cooling demand. Although solar heat rejection functionalities can be added to the glazing as well to keep heat out during summertime, this value is permanent and thus also rejects available solar heat during wintertime, pressing again demand for heating. Therefore, the next step in the evolution of glass is to make glazing smart. Smart glass has the ability to adapts its visible light transmission (T\u003csub\u003evis\u003c/sub\u003e) and its solar heat gain coefficient (SHGC) based on an external trigger, such as an electric field, sunlight intensity or temperature (Brzezicki, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Casini, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Dussault, Gosselin, \u0026amp; Galstian, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Jelle et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Kamalisarvestani, Saidur, Mekhilef, \u0026amp; Javadi, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Ke et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Rezaei, Shannigrahi, \u0026amp; Ramakrishna, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Sibilio et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Y. Wang, Runnerstrom, \u0026amp; Milliron, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). In this way, they can adapt the glazing characteristics to outdoor weather conditions providing additional daylight comfort and blocking more solar heat in summer, to save energy use on cooling, while letting more of it through during winter, to prevent additional heating energy demand. Introducing smart glass to the European building stock will increase the energy saving potential with an additional 20% compared to current high-performance glazing (Glass for Europe, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2019\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTherefore, the industry attention to develop smart glass products is increasing and smart glass products emerge (see discussion). Examples of smart glass triggered by electric fields (electrochromic) are abundant, showing high modulation of both T\u003csub\u003evis\u003c/sub\u003e as well as SHGC, fast switching rates and appealing due to their manual control to various intermediate state by the wishes of the end-user (Converlight by Chomogenics, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Halio, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; SageGlass Saint Gobain, n.d.). As a cheaper to install alternative with a higher feasibility of application in widespread building scenarios, self-regulating smart glass technologies triggered by sunlight intensity (photochromic) or temperature (thermochromic) are also attracting attention. These products typically show a large change in T\u003csub\u003evis\u003c/sub\u003e between the transparent and tinted state, providing additional daylight comfort, but show a limited change in SHGC, and thus contribute less to enhanced energy efficiency (CoolVu, n.d.; SmartGlassNordics, n.d.; SwitchFoil International, n.d.). Furthermore, smart glass coatings are typically fabricated by expensive, energy consuming vapor deposition techniques (Kamalisarvestani et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Ke et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Rezaei et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Y. Wang et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Here, a photochromic coated film is presented, simply prepared from solution by a roll-to-roll scalable coating technique, with high transparency in the transparent state, large modulation of solar heat (ΔSHGC), whilst showing a large change in T\u003csub\u003evis\u003c/sub\u003e. Through simulation studies on a model office the energy saving potential when applied across Europe is shown. In the discussion a comparison is made with existing smart glass products on the market and benefits and challenges are elaborated.\u003c/p\u003e"},{"header":"2. Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Film fabrication method\u003c/h2\u003e \u003cp\u003eThe ink formulation is fabricated by mixing in WCl\u003csub\u003e6\u003c/sub\u003e, a precursor for the WO\u003csub\u003e3\u003c/sub\u003e nanopigments, together with PMMA in an appropriate solvent, suitable for large scale processing, as described in earlier work (Meng et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) Various dopants and additives are added to aid the bleaching process of the final film and enhance the processing of the ink formulation on large scale. On lab scale the films are fabricated by coating directly on an acrylic adhesive substrate using blade coating technique, followed by drying at elevated temperature to evaporate the solvent. For large scale prototypes this method is translated to an industrial roll-to-roll coating line using gravure coating at 40 cm wide. In both methods the dry coating thickness is controlled around 40 \u0026micro;m.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Application of the film to glass\u003c/h2\u003e \u003cp\u003eThe film can be adhered to glass plates using methods commonly used in the application of retrofit window films. This includes removing the liner from the adhesive, applying retrofit film application liquid or water with a few drops of mild soap on both the adhesive and the glass plate, placing the film on the glass plate, squeezing out excess of liquid underneath the film and let it dry for at least 24 hours to let the adhesive properly adhere to the glass plate.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Tinting and bleaching\u003c/h2\u003e \u003cp\u003eThe tinting is done by irradiating the film with UV-light, which can be provided by sunlight in outdoor conditions or by sunlight mimicking lamps typically used for reptiles containing UV-light (Lucky Reptile Bright Sun UV Jungle 70W) in laboratory conditions. The light intensity was varied by changing the height of the lamp and measured using a radiometer (Opsytec Radiometer RM12) operating in the UV-A range. Bleaching of the samples is carried out by storing them in a dark cabinet.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4. Transmission measurements\u003c/h2\u003e \u003cp\u003eTransmission spectra were measured using a UV-Vis-nIR spectrometer (PerkinElmer Lambda 750) over a range between 300 and 2500 nm with an interval of 5 nm. For full glass characterization also reflection spectra are measured from both sides of the glass plate to which the film is adhered. Visible light transmission values for time-related tinting and bleaching behaviour measurements are measured using a haze meter (Hangzhou Baiteng Electronic Technology, DH-10 Portable Haze Meter) having a measure aperture of 7mm, allowing to retrieve the visible light transmission by the press of a single button.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5. Calculation of glazing characteristics\u003c/h2\u003e \u003cp\u003eGlazing characteristics were calculated by implementing the transmission and reflection spectra of the film in the transparent and fully tinted state when adhered to a 4 mm single clear glass plate in the LBNL Software Optics6 and Window7.7.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.6. Energy efficiency modelling\u003c/h2\u003e \u003cp\u003eThe building energy efficiency simulations were carried out by the software DesignBuilder. A model office was used as designed and described in earlier work (Kragt, Ham, Sentjens, Schenning, \u0026amp; Klein, 2022; Meng et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). The glazing characteristics for the film in combination with different glazing types was calculated in the DesignBuilder software according to EN673. For the clear double glazing two 4mm Optifloat clear glass plates were chosen from the International Glazing Database with a 16mm argon cavity. For the low-e glass 1 the inner glass plate is replaced by 4mm Pilkington K Glass and for low-e glass 2 by 4 mm Pilkington Optitherm S1 Plus. To integrate the photochromic film the glazing characteristics are calculated using the LBNL software Optics6 and Window7.7 using the transmission and reflection spectra at various UV-light intensities mimicking various sunlight intensities. This was done by increasing the UV-light intensity to a certain level and maintain this for 30 minutes before going to the next UV-light intensity. In this way the UV-light intensity was increased and decreased to also account for hysteresis during the tinting and bleaching process. To introduce the photochromic effect in the calculation, the \u0026ldquo;window shading\u0026rdquo; feature was used. Here the optical properties of the outer glass pane at various sunlight intensities were defined based on the optical properties determined above, as if the photochromic film is applied on position 2 of the glass built-up. The window shading was controlled by \u0026ldquo;daylight only\u0026rdquo; and operated \u0026ldquo;24/7\u0026rdquo; to mimic the autonomous working principle of the photochromic film. For the model calculation each window was provided with a single light-intensity \u0026ldquo;sensor,\u0026rdquo; so the various windows of the building model operated individually. The most recent weather data files were downloaded from \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e\u003ca href=\"http://www.climate.onebuilding.org\" target=\"_blank\"\u003ewww.climate.onebuilding.org\u003c/a\u003e\u003c/span\u003e\u003cspan address=\"http://www.climate.onebuilding.org\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e, which provided typical meteorological year datasets for the specific locations, which were then imported into the DesignBuilder model.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cp\u003eThe roll-to-roll produced photochromic film tints under illumination of UV-light (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA). The film can be adhered to a glass plate and used as a retrofit film or subsequently assembled inside the cavity of a multi-layered glazing unit. When the film is irradiated by UV-light from the sun, the film turns into its tinted state, thereby reducing both visible light and infrared light transmission (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA). The film is based on a coating containing photochromic tungsten oxide (WO\u003csub\u003e3\u003c/sub\u003e) nano pigments in a polymer matrix. When UV-light hits these particles the tungsten atoms got excited and their valence state reduced (Bourdin et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Kim et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Li et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; S. Wang, Fan, Liu, Yu, \u0026amp; Jiang, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). This change of the material is accompanied by a change in the absorption spectrum giving rise to the observed optical change. Expressing this change in glazing characteristics when adhering the film to a 4 mm single clear glass plate, this results in a T\u003csub\u003evis\u003c/sub\u003e change from 88 to 40% between the transparent and tinted state, accompanied by a change in SHGC from 0.87 to 0.54 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe optical properties of the film are investigated in a controlled way by irradiating with a sunlight mimicking lamp at various intensities ranging from 5 to 50 W/m\u003csup\u003e2\u003c/sup\u003e of measured UV-A radiation (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eC). At the maximum intensity the film tints in 20 minutes from a T\u003csub\u003evis\u003c/sub\u003e of 87\u0026ndash;39%, where it stabilizes. With 20 W/m\u003csup\u003e2\u003c/sup\u003e the films still obtain a significant tint, although T\u003csub\u003evis\u003c/sub\u003e after 20 minutes equals 54% and reaches 39% after 120 minutes. At 10 W/m\u003csup\u003e2\u003c/sup\u003e irradiation the maximum tint suddenly becomes less and T\u003csub\u003evis\u003c/sub\u003e reaches 60% after 120 minutes, which further increases to 73% upon further decreasing the intensity to 5 W/m\u003csup\u003e2\u003c/sup\u003e within this timeframe. When the film is fully tinted and left in the dark it bleaches to a T\u003csub\u003evis\u003c/sub\u003e of 80% in 120 minutes and fully recovers in 240 minutes (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eD).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe energy saving potential of the smart photochromic glazing was explored by implementing these glass properties in a model of an office building using DesignBuilder. Various glazing types were implemented in the model: double clear glass, low-e coated glass with a high SHGC (low-e glass 1), and low-e coated glass with a low SHGC (low-e glass 2). The two types of low-e coated glass are simulated without and with the smart glass film (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). These glazing types were chosen as they represent typical glass choices in the built environment. It is not expected that the smart film in practice would be used much with clear double glazing, as the primary aim of glass renovation usually is to upgrade insulation properties. In addition, the smart film is not very effective in keeping solar heat out when combined with low insulating glass, as the film absorbs the solar heat, which is then radiated to the room interior. Therefore, the best way to use the film is to apply the film on position 2 (the inner side of the outer pane) or position 1 (in case of retrofitting) of a low-e coated glazing unit with the low-e coating on position 3 (the inner side of the inner pane). Furthermore, within the simulations the intermediate states of the film are implemented as well, so that the tint level varies with the solar intensity variation within the used weather data files.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003e\u0026ndash; Glazing characteristics used in the energy performance analysis\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDouble clear glass\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c5\" namest=\"c3\"\u003e \u003cp\u003eLow-e glass 1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c8\" namest=\"c6\"\u003e \u003cp\u003eLow-e glass 2\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNo film\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNo film\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003eWith Smart film\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNo film\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003eWith Smart film\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTransparent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTinted\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eTransparent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eTinted\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSHGC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.27\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eT\u003csub\u003evis\u003c/sub\u003e [%]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e82\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e34\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eU-value [W/m\u003csup\u003e2\u003c/sup\u003eK]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe energy use for lighting, heating, and cooling are simulated when placing the model building in various cities across Europe representing different climates (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and \u003cb\u003eTable\u0026nbsp;2\u003c/b\u003e). Although in all climates, applying the smart film to glazing will provide additional daylight comfort compared to current high-performance glazing, in terms of energy performance the presented smart film has the biggest impact in southern European cities, such as Rome and Madrid. In these warmer climates the building energy use is dominated by cooling, and so the biggest impact can be made by taking solar heat rejection measures. Additional energy savings ranging between 27 and 35% are achieved in these cities when a building owner would choose low-e coated glass with the smart film compared to the same glass without the film. In mid-European cities, such as Paris and Amsterdam, this additional energy saving is 8 to 16%, whereas in Praha 2 to 6% can be achieved. As in these climates the energy use for space heating is more significant the impact of the smart film on the total energy use is less. Although the film still reduces cooling energy use during summertime, an increase in heating energy use can be observed. This originates from the fact that also during wintertime there are still moments that the film is in an (intermediate) tinted state and thus rejecting more solar heat compared to glazing without the film. This effect would, however, be enlarged when one would use a glazing or film with a permanent solar heat rejection level equal to that of the tinted state of the smart film as shown in previous simulation studies (Meng et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). In cities with more severe winters, such as Oslo and Stockholm, heating energy use is even more dominating and the effect of increasing heating energy use by addition of the smart film is balancing out with the reduced cooling energy use. In these climates, a building owner could still choose for smart glazing with the film because of the benefits on daylight comfort for the users.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cem\u003eTable\u0026nbsp;2 \u0026ndash; Potential annual energy savings according to the simulations of replacing clear double glazing by low-e glass 2 with smart film (1st column), and the additional energy savings of retrofitting the two types of low-e glass with our smart glass film (2nd and 3rd column), across various European cities.\u003c/em\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eReplacing double clear glass with low-e glass 2 with smart film\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRetrofitting low-e glass 1 with smart film\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRetrofitting low-e glass 2 with smart film\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRome\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e38%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e35%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e31%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMadrid\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e39%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e28%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e27%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eParis\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e42%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e16%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAmsterdam\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e43%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e12%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePraha\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e41%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOslo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e45%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-3%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-5%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStockholm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e40%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eStill 81% of the current European building stock is equipped with outdated glazing having low insulating values and solar heat rejection levels (Gevorgian et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Therefore, renovation of glazing offers a high potential to reduce the energy consumption for space heating and cooling in buildings, which today takes up an energy consumption of 3307 TWh per year. Replacing current low-performance glazing (e.g. double clear glass) present in most buildings in Europe today with smart high-performance glass (e.g. low-e glass 2 with smart film) would save, according to the presented simulations, 38 to 45% on a building\u0026rsquo;s annual energy use across various European climates. Following these results and assuming an average energy saving of 41%, 1122 TWh could be saved when upgrading all European buildings that are still equipped with low-performance glazing with smart high-performance glazing including the presented film. When also retrofitting the buildings that are already equipped with high-performance glazing with the smart film, assuming an average energy saving of 12%, an additional 80 TWh could be saved, given a total of about 1200 TWh to be saved annually. To put this number in perspective, the energy saving potential when upgrading all European buildings with current high-performance glazing (e.g. low-e glass 2) following the simulation results with an average energy saving of 32%, would be 873 TWh. This number is fairly in line with the energy saving potential of 878 TWh reported by Glass for Europe when all glazing would be replaced with readily available high-performance glazing by 2030 (Glass for Europe, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). It should be realized that application of the smart glass film would only be beneficial in terms of energy performance in buildings that are equipped with an active cooling installation. However, also in buildings that are not yet equipped with air-conditioning, the smart film provides benefits on daylight comfort and preventing overheating issues. This might result in postponing or even cancelling the decision to install expensive air-conditioning and therefore indirectly saving energy.\u003c/p\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eAs glass is evolving, smart glass products are emerging in the market (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Electrochromic glazing has attracted much interest due to its ability to be manually controlled by the user to their desires with fast switching speeds, usually in the order of minutes. The ΔT\u003csub\u003evis\u003c/sub\u003e from the transparent to tinted state is large and tints as low as 1% can be achieved. Also, the ΔSHGC is significant giving them not only the ability to provide daylight comfort to the user, but also contribute to the energy efficiency of a building compared to glazing technologies with permanent SHGC levels. Nevertheless, in their transparent state the SHGC is typically already quite low (\u0026lt;\u0026thinsp;0.51), which makes it not the ideal solution during wintertime, and as the operations are controlled by the user the tinting level is not always synchronized with the energetically most favourable state. Although the operations can be overruled by sensors for outdoor temperature and/or sunlight irradiation, these add further costs and complexity to the installation, making this option less feasible for building owners. In these occasions, self-adaptive smart glass products, such as photochromic films, are an appealing alternative. They can simply be installed similar to the commonly used glass products of today and add only limited costs. Therefore, they have the potential to become a more mainstream smart glass product. In addition, and in contrast to electrochromic glass products, they can often be applied as retrofit film product, further enhancing their potential widespread application. Nevertheless, photochromic glass films currently on the market can show a large variation in T\u003csub\u003evis\u003c/sub\u003e between the transparent and tinted state but have a limited ΔSHGC (0.09) at maximum. Therefore, they can enhance daylight comfort of buildings, but their impact on energy efficiency compared to regular glass products with a permanent tint is limited. The novelty of the photochromic smart glass technology presented in this work lies in the combination of a large ΔT\u003csub\u003evis\u003c/sub\u003e and ΔSHGC (48% and 0.33, respectively, when adhered to a single 4 mm clear glass plate). In addition, the transparency level of the initial transparent state is supremely high. This provides the technology presented here all the benefits of current photochromic glass products, e.g. daylight comfort and a widespread applicability, together with a high potential to make impact on the energy efficiency of buildings.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003e\u0026ndash; Overview of various electrochromic (EC) and photochromic (PC) smart glass technologies available on the market. For most products variants with different tint levels are available. For this table the most transparent version is noted.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"10\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c6\" namest=\"c4\"\u003e \u003cp\u003eT\u003csub\u003evis\u003c/sub\u003e [%]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c9\" namest=\"c7\"\u003e \u003cp\u003eSHGC\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMode\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eComposition\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTransp.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTinted\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eΔT\u003csub\u003evis\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eTransp.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eTinted\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eΔSHGC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eRef.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSage glass clear\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLow-e IGU\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e58\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.08\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e(SageGlass Saint Gobain, n.d.)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eConverlight\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLow-e IGU\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e(Converlight by Chomogenics, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2018\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHalio glass\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLow-e IGU\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e(Halio, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2020\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDynaclime\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSingle clear\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e73\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e(SmartGlassNordics, n.d.)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCoolVu\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSingle clear\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e(CoolVu, n.d.)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eActiveFoil\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSingle clear\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e(SwitchFoil International, n.d.)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eThis work\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSingle clear\u003c/p\u003e \u003cp\u003eLow-e glass 1\u003c/p\u003e \u003cp\u003eLow-e glass 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e88\u003c/p\u003e \u003cp\u003e75\u003c/p\u003e \u003cp\u003e75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e40\u003c/p\u003e \u003cp\u003e34\u003c/p\u003e \u003cp\u003e34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e48\u003c/p\u003e \u003cp\u003e41\u003c/p\u003e \u003cp\u003e41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.87\u003c/p\u003e \u003cp\u003e0.74\u003c/p\u003e \u003cp\u003e0.54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.54\u003c/p\u003e \u003cp\u003e0.36\u003c/p\u003e \u003cp\u003e0.27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.33\u003c/p\u003e \u003cp\u003e0.38\u003c/p\u003e \u003cp\u003e0.27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e-\u003c/p\u003e \u003cp\u003e-\u003c/p\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eThis paper describes a highly transparent smart photochromic film with unique optical properties, that are unmet in current self-adaptive glass technologies. The film shows both a high modulation in T\u003csub\u003evis\u003c/sub\u003e from 88 to 40% as well as a high modulation in SHGC from 0.87 to 0.54 in response to increasing sunlight intensity. Compared to state-of-the-art electrochromic window technologies this resembles a similar change in SHGC, but allowing more solar heat in its transparent state. Moreover, the active photochromic nano pigment-based coating material is simply produced from solution and processed through a scalable roll-to-roll coating technique. The installation of the film is simple and cost-effective making the widespread application in the built environment feasible. Simulations provide the additional energy savings of the film are 27 to 35% compared to the same low-e coated double glazing without the film in Southern European climates, like Madrid and Rome, respectively. In mid-European climates like Praha, Amsterdam and Paris, this benefit ranges from 2 to 16%. In Scandinavian climates the energy benefit vanished, limiting the benefit of the film to additional daylight comfort. Renovating all current European low-performance building glass with smart glazing containing this film and further upgrading already installed low-e coated glazing by retrofitting would have the potential to save about 1200 TWh on energy use annually, thereby outperforming the current predictions of 878 TWh potential energy saving when renovating with current high-performance glazing.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eArticle Information (this info will be completed later by the editors)\u003c/p\u003e\n\u003cul\u003e\n \u003cli\u003ePublished by GPD, on behalf of the author(s)\u003c/li\u003e\n \u003cli\u003ePublished as part of the peer-reviewed Glass Performance Days Conference Proceedings, June 2025\u003c/li\u003e\n \u003cli\u003eEditors: Jan Belis, Christian Louter \u0026amp; Marko M\u0026ouml;kk\u0026ouml;nen\u003c/li\u003e\n \u003cli\u003eThis work is licensed under a Creative Commons Attribution 4.0 International (CC BY 4.0) license.\u003c/li\u003e\n \u003cli\u003eCopyright \u0026copy; 2025 with the author(s)\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003e6.1. Funding\u003c/p\u003e\n\u003cp\u003eThe research leading to these results is carried out within the SFEER project, which received funding from the Topsector Energy Subsidy of the Dutch Ministry of Economic Affairs and Climate Policy carried out by The Netherlands Enterprise Agency (RVO), in the framework of the MOOI-subsidy round 2023 (MOOI322002).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e6.2. Competing interest\u003c/p\u003e\n\u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e6.3. Other declarations\u003c/p\u003e\n\u003cp\u003eAn Ethics declaration is not applicable to the content of this research. Data is gathered by the authors and are not shared openly. They can be shared upon request.\u003c/p\u003e\n\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\n\u003cp\u003eJ.S. did the experimental work related to coated film preparation and characterization and reviewed the manuscript. A.K. did the simulation work and wrote the manuscript text.\u003c/p\u003e\n\u003ch2\u003eAcknowledgement\u003c/h2\u003e\n\u003cp\u003eThe authors would like to acknowledge the funding for this research from SFEER project, which is carried out with the Topsector Energy Subsidy of the Dutch Ministry of Economic Affairs and Climate Policy carried out by The Netherlands Enterprise Agency (RVO), in the framework of the MOOI-subsidy round 2023. In addition, authors would like to thank Prof. A.P.H.J. Schenning from the research group Stimuli-responsive Functional Materials and Devices (SFD) of the department of Chemical Engineering and Chemistry at the Eindhoven University of Technology for support in discussions and hosting ClimAd Technology as a company in his research group.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAGC: Fineo by AGC. 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Retrieved from \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1146/annurev-chembioeng-080615-034647\u003c/span\u003e\u003cspan address=\"10.1146/annurev-chembioeng-080615-034647\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"glass-structures-and-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"glas","sideBox":"Learn more about [Glass Structures \u0026 Engineering](http://link.springer.com/journal/40940)","snPcode":"40940","submissionUrl":"https://submission.springernature.com/new-submission/40940/3","title":"Glass Structures \u0026 Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Smart glass, Photochromic, Scalable, Easy applicable, Energy efficiency","lastPublishedDoi":"10.21203/rs.3.rs-6221722/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6221722/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eBy improving the insulation value of glazing, the glass industry contributes successfully to reduce global heating demand in the built environment. However, as temperatures are increasing and heat waves are more frequently occurring, increased insulation values of glazing also contribute to the vast growing cooling demand. Therefore, the glass industry is evolving further with smart glazing to reject solar heat entrance during summer seasons, while allowing it to heat up indoor spaces during winter seasons. This paper presents a photochromic window film with a unique combination of optical properties compared to other smart glass technologies. The film has a high visible light transmission in the transparent state (88%), showing a modulation of 48% accompanied with a change in solar heat gain coefficient from 0.87 to 0.54 upon irradiation with UV solar light. This way the film enhances both daylight- and thermal comfort as well as energy efficiency all by itself. The film is simply prepared from solution by a roll-to-roll scalable coating method. Simulation shows that the film, when integrated in a low-e coated double glazing, can save up to 35% on annual energy consumption compared to the same glazing without the film depending on the climate where it is applied. Upgrading all glazing in Europe with the smart film has the potential to save about 1200 TWh of energy use annually.\u003c/p\u003e","manuscriptTitle":"Smart photochromic glass films: the evolution in glass performance","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-24 13:01:29","doi":"10.21203/rs.3.rs-6221722/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-07-08T13:36:13+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-05T02:26:42+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"99079036340186042547958600439573293617","date":"2025-06-28T08:35:18+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-14T10:18:43+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"270995945499734029217858871445610496972","date":"2025-05-02T13:17:41+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"319372015880373307667342905409697907773","date":"2025-04-03T06:45:09+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-04-02T18:28:14+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-03-22T08:02:46+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-03-22T07:59:26+00:00","index":"","fulltext":""},{"type":"submitted","content":"Glass Structures \u0026 Engineering","date":"2025-03-13T16:11:31+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"glass-structures-and-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"glas","sideBox":"Learn more about [Glass Structures \u0026 Engineering](http://link.springer.com/journal/40940)","snPcode":"40940","submissionUrl":"https://submission.springernature.com/new-submission/40940/3","title":"Glass Structures \u0026 Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"b7f45be9-e6f6-414b-ad95-a460dc113da3","owner":[],"postedDate":"April 24th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-18T16:55:22+00:00","versionOfRecord":[],"versionCreatedAt":"2025-04-24 13:01:29","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6221722","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6221722","identity":"rs-6221722","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}