Optical-Thermal Regulation Materials: A Product-Engineering Design Logic from Application Demands to Multifunctional Material Realization

Abstract

Conspectus Optical-thermal regulation materials (OTRMs) control wavelength-dependent reflection, transmission, absorption, and emission across the ultraviolet, visible, near-infrared, and mid-infrared regions to regulate heat transfer and optical functionality. Their importance is increasing as extreme and variable climates threaten human health, thermal comfort, and energy security, while conventional mechanical heating and cooling technologies impose growing electricity demand and greenhouse-gas emissions. Optical-thermal regulation can be broadly implemented through passive, active, or hybrid modes. Passive regulation relies on intrinsic material properties or structurally defined spectral responses without continuous external input, whereas active regulation dynamically adjusts spectral properties under external stimuli. Hybrid regulation integrates passive and active mechanisms within the same material, device, or system, allowing dynamic tunability to coexist with persistent optical-thermal functions in other spectral bands or functional channels. Radiative cooling and electrochromic modulation are representative implementations of passive and active regulation, respectively. Although OTRMs rely fundamentally on wavelength-dependent light–matter interactions, their spectral design and multifunctional strategies are strongly application-oriented. Therefore, in this Account, we extract a product-engineering design logic comprising four interconnected stages: application-demand analysis, optical-thermal regulation strategy definition, material, structural, and device realization, and multifunctional integration and validation. Application-demand analysis identifies the thermal boundary conditions, optical functions, service environments, user requirements, and manufacturing constraints of a target scenario. These requirements are then translated into appropriate passive, active, or hybrid regulation modes and corresponding wavelength-dependent target spectral responses. The resulting specifications guide material selection, structural construction, device configuration, and fabrication. The developed systems are subsequently evaluated not only for optical-thermal performance but also for application-relevant requirements such as durability, scalability, safety, manufacturability, and system compatibility. Importantly, the latter two stages are iterative rather than strictly sequential: validation results can feed back into material, structural, device, and fabrication optimization when the realized performance does not fully satisfy the predefined application-specific criteria. This framework therefore integrates these four stages within a unified design process. This Account uses our group’s recent work to illustrate how this product-engineering design logic can guide the design of OTRMs across four representative application classes: building energy savings, including spectrally engineered transparent and opaque envelope structures; vehicle energy savings, especially dynamically regulated intelligent sunroofs; personal wearable systems, including thermal management and intelligent optical function textiles; and security-related devices, including anti-counterfeiting and multispectral camouflage systems. Finally, we discuss future directions for translating real-world requirements into quantitative design criteria, establishing composition–structure–spectrum–function relationships, standardizing performance evaluation, and advancing OTRMs from laboratory-scale demonstrations toward scalable, durable, and multifunctional material systems. We hope that this product-engineering perspective can provide a useful reference for the application-oriented design and practical development of future OTRMs.