Advanced Spectrum Modulation and Utilization for Next-Generation Energy-Efficient Smart Windows

Abstract

Windows play a pivotal role in building energy consumption, accounting for a significant portion of heating, cooling, and lighting demands. The pursuit of building energy efficiency and sustainability has driven the development of advanced window technologies capable of modulating and utilizing the solar spectrum for dynamic light and heat regulation, as well as energy harvesting. This thesis explores the design, fabrication, and application of innovative optical and energy-related materials and devices, encompassing thermochromic perovskites, transparent wood, and luminescent solar concentrators, accelerating the development of next-generation energy-efficient windows.

The research begins with a focus on light modulation through thermochromic smart windows. A fundamental and comprehensive investigation of dihydrated methylammonium lead halide hybrid perovskites (MA₄PbX₆·2H₂O) reveals the critical role of halide composition in tuning optical properties such as luminous transmittance and solar modulation ability. Optimal material composition—MA4PbI₅Br₁·2H₂O—is also identified and demonstrated in field tests, showcasing its ability to maintain stable thermochromic performance and regulate indoor temperatures for building energy saving. This work establishes a foundation for the device-level studies deploying perovskite-based smart windows in real-world building scenarios. To further enhance thermal performance and sustainability, the research extends to employing transparent wood as a sustainable and multifunctional substrate with synergetic optical, thermal and mechanical benefits. A novel perovskite-coated thermochromic transparent wood (PTTW) is developed, combining excellent light-modulation performance (78.0% luminous transmittance, 21.6% solar modulation ability) with excellent thermal insulation and mechanical robustness. Field tests in Hong Kong demonstrate its superior indoor thermal regulating performance (5.4 °C) and HVAC energy saving potential (12.9%), outperforming conventional glass-based perovskite smart windows. This integration of thermochromic perovskites with transparent wood represents a significant step toward energy-efficient and sustainable smart windows. Expanding the scope to light utilization, the thesis explores transparent wood as a host matrix for luminescent solar concentrators (LSCs). By leveraging its anisotropic scattering properties and embedding CdSe/ZnS quantum dots, a double-layer laminated wood structure is designed to achieve effective light management (high luminous transmittance (~75%), bi-directional light scattering) and enhanced light harvesting across the UV-VIS-NIR spectrum. The resulting LTW LSC devices exhibit a threefold improvement in power conversion efficiency compared to conventional polymer-based LSCs, underscoring their potential for building-integrated photovoltaics.

In summary, this thesis advances the field of energy-efficient window technologies by integrating spectrum modulation and solar energy utilization through holistic material innovation and device engineering. The findings provide both fundamental insights and practical solutions for developing multifunctional and sustainable smart window devices that combine dynamic optical regulation, thermal management, and energy harvesting. By bridging material innovation with real-world applications, this work contributes to the development of next-generation energy-efficient windows and the broader goal of building sustainability.

Date of Award	9 Jul 2025
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Chi Yan TSO (Supervisor)