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  • Review Article
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Inorganic electrochromic smart windows for advancing building energy efficiency

Nature Reviews Clean Technology volume 1, pages 396–412 (2025)Cite this article

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Abstract

Indoor temperature control is responsible for half of the energy consumption in buildings. Electrochromic smart windows (ESWs) actively control the transfer of light and heat, which could increase the energy efficiency of buildings by helping to control indoor temperatures on demand. However, the implementation of ESW continues to encounter challenges in terms of colour neutrality, long-term durability, effective recyclability and integrability. Some commercial organic ESWs have been installed, but implementing superior inorganic ESWs to improve building energy efficiency deserves more investigation. In this Review, we discuss the working modes, assembly protocols and implementation of ESWs. Key aspects of ESW effectiveness and operation include material selection and electrochemical and optical processes. In addition, we argue for the use of dual-band regulation and reversible metal-deposition technology in inorganic ESWs. Alternative transparent conductors (such as carbon nanotubes, graphene and metal grids), additive manufacturing methods, high integration levels and retrofittable electrochromic thin films could enable more effective and widely applicable inorganic ESWs by overcoming the issues of cost-effectiveness, scalability and durability.

Key points

  • Electrochromic smart windows (ESWs) offer reversible, on-demand control over optical properties such as transmittance, reflectance and emittance.

  • ESWs play a crucial part in reducing building energy consumption by decreasing the need for heating, ventilation and air conditioning, thereby promoting energy-efficient and environmentally friendly practices in green building construction.

  • Integrating ESWs into buildings enables flexible window design and modulation of energy usage. These windows facilitate decarbonization efforts and support the transition towards low-emissions buildings.

  • ESWs can be retrofitted and scaled up in both new construction and retrofit projects, and they present a compelling solution for achieving energy savings and sustainability goals.

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Fig. 1: The light- and heat-regulation mechanism of electrochromic smart windows.
Fig. 2: Configuration of different electrochromic devices.
Fig. 3: Photograph of real electrochromic smart windows.
Fig. 4: Energy savings brought by electrochromic smart windows.

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Acknowledgements

This work was supported by the National Natural Science Foundation of China (grants 62105185, 62375157, 52202320 and 62374104), the Guangdong Basic and Applied Basic Research Foundation (grant 2022A1515011516), the Shandong Excellent Young Scientists Fund Program (Overseas, grants 2022HWYQ-021 and 2023HWYQ-060), the Fundamental Research Funds for the Central Universities (grants 202201013153 and 202312030), the Open Foundation of the State Key Laboratory of Featured Metal Materials and Life-Cycle Safety for Composite Structures, Guangxi University (grant 2022GXYSOF06), the Open Foundation of the State Key Laboratory of Vanadium and Titanium Resources Comprehensive Utilization, the Taishan Scholar Program of Shandong Province and the National Science Foundation (grant TI-2345804).

Author information

Author notes

  1. Deceased: Haizeng Li.

  2. These authors contributed equally: Feifei Zhao, Bin Wang, Bingkun Huang.

Authors and Affiliations

  1. School of Energy and Power Engineering, Shandong University, Jinan, China

    Feifei Zhao, Bin Wang, Bingkun Huang, Linhua Liu & Haizeng Li

  2. Institute of Frontier and Interdisciplinary Science, Shandong University, Qingdao, China

    Feifei Zhao, Bin Wang, Bingkun Huang & Haizeng Li

  3. School of Chemistry and Chemical Engineering, Shandong University, Jinan, China

    Feifei Zhao & William W. Yu

  4. Department of Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada

    Wu Zhang & Abdulhakem Y. Elezzabi

  5. McKetta Department of Chemical Engineering, The University of Texas at Austin, Austin, TX, USA

    Wu Zhang & Delia J. Milliron

  6. School of Materials Science and Engineering, Ocean University of China, Qingdao, China

    Jingwei Chen

  7. State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai, China

    Hongzhi Wang

  8. School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore

    Pooi See Lee

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  1. Feifei Zhao
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Contributions

All authors researched data for the article and wrote the article. H.L., J.C. and W.Z. reviewed and edited the manuscript before submission.

Corresponding authors

Correspondence to Wu Zhang, Jingwei Chen or Haizeng Li.

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Nature Reviews Clean Technology thanks the anonymous reviewers for their contribution to the peer review of this work.

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Dedication

This article is dedicated to the memory of author Haizeng Li, who passed away in August 2024. He was a warm friend, a nice colleague, an innovative researcher and an enthusiastic scholar. He devoted his efforts to the field of electrochromism for more than 10 years and contributed greatly to this community. He proved his excellence by creating and leading the development of Zn-anode-based electrochromic devices, and he strove to expedite the application of electrochromic devices for smart windows and displays. His departure is a huge loss, and he will be fondly remembered by the electrochromic community.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Glossary

Bi-stability

The ability of a system, such as an electrochromic device, to maintain two distinct states without continuous power input.

Colour neutrality

A property of optical materials ensuring minimal colour distortion across visible wavelengths, maintaining a natural appearance.

Dual-band modulation

The capability of a device to independently control optical or electrical properties in two separate wavelength ranges, often in visible and infrared spectra.

Electrochromic layer

A thin film in electrochromic devices that changes colour or transparency when voltage is applied, enabling dynamic light control.

Free carrier concentration

The density of charge carriers (electrons or holes) in a semiconductor, determining its electrical and optical properties.

Ion storage layer

A coating layer on the counter-electrode in electrochromic devices, helping to store and release ions during the switching process to ensure charge balance with the electrochromic layer.

Localized surface plasma resonance

(LSPR). A phenomenon in which conduction electrons in metal nanoparticles oscillate collectively when exposed to light.

n-PBDF

(N-doped poly(3,7-dihydrobenzo[1,2-b:4,5-b′]difuran-2,6-dione)). A transparent conducting polymer that can be used as both a transparent conductor and ion-storage material.

PEDOT:PSS

(Poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate)). A widely utilized organic conductive polymer offering a unique combination of high conductivity, excellent transparency, great chemical stability, remarkable flexibility and efficient solution processability.

Prussian blue

(Iron hexacyanoferrate, KFe4[Fe(CN)6]3). An important electrochromic material with advantages including cost-effectiveness, biosafety, chemical stability, suitable redox potential, rich colour states and fast colour-switching kinetics.

Reversible metal electrodeposition

(RME). An electrochemical process in which metal ions are deposited onto a surface and then dissolved back into the electrolyte, allowing dynamic control of optical and electrical properties.

Solar heat gain coefficient

(SHGC). Quantifies the percentage of solar heat entering the building through a window, door or skylight.

Structural colour

Created by the manipulation of light through microstructures and is produced by the interference, diffraction and scattering of light, which means that the colour changes depending on the angle of observation, resulting in an iridescent effect.

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Zhao, F., Wang, B., Huang, B. et al. Inorganic electrochromic smart windows for advancing building energy efficiency. Nat. Rev. Clean Technol. 1, 396–412 (2025). https://doi.org/10.1038/s44359-025-00065-x

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