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Scalable colored sub-ambient radiative coolers based on a polymer-Tamm photonic structure

This paper introduces a scalable polymer-Tamm photonic structure that enables the production of colored daytime radiative coolers capable of achieving significant sub-ambient temperature drops through engineered solar absorption and high infrared emittance.

Original authors: Tianzhe Huang, Qixiang Chen, Jinhua Huang, Yuehui Lu, Hua Xu, Meng Zhao, Yao Xu, Weijie Song

Published 2026-02-10

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Tianzhe Huang, Qixiang Chen, Jinhua Huang, Yuehui Lu, Hua Xu, Meng Zhao, Yao Xu, Weijie Song

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The "Magic Color-Changing Sunglasses" for Buildings: A Simple Guide

Imagine you are standing outside on a scorching summer day. You’re sweating, the sun is beating down, and you desperately wish you could just "turn off" the heat. Usually, to stay cool, we turn on an air conditioner—but that uses electricity, which creates more heat and pollution elsewhere.

Scientists have discovered a way to cool things down using nothing but the "emptiness" of outer space. This paper describes a breakthrough in making this technology not just effective, but also beautiful and scalable.

1. The Concept: The "Heat Vacuum"

To understand this, imagine the universe is a giant, freezing-cold vacuum cleaner. There is a specific "window" in our atmosphere (between 8 and 13 micrometers) where heat can escape from Earth directly into space without getting blocked by clouds or gases.

Radiative Cooling is like opening a specialized window in your house that lets all your heat pour out into the cold void of space, while simultaneously acting like a high-tech shield that reflects the sun's burning rays.

2. The Problem: The "Silver Mirror" Dilemma

Until now, most of these "heat-escaping" materials had a major flaw: they were either bright white or shiny silver.

The Analogy: Imagine if every car on the road had to be silver, or every house had to be painted bright white to stay cool. It works, but it’s boring, it looks industrial, and it might even cause "glare" (light pollution) that hurts people's eyes.

Scientists wanted to create Colored Daytime Radiative Coolers (CDRCs)—materials that could be yellow, magenta, or cyan, looking like beautiful architectural features rather than just pieces of metal.

3. The Breakthrough: The "Photonic Filter"

The researchers created a "Polymer-Tamm photonic structure." That sounds complicated, but think of it as a highly sophisticated, microscopic musical instrument.

The "Tamm" Part (The Color): They built a microscopic "sandwich" of layers. This sandwich is designed to be incredibly picky about light. It reflects almost all sunlight (keeping the heat out) but has a tiny, precise "dip" where it absorbs just enough specific light to create a vivid color (like yellow or cyan). It’s like a pair of sunglasses that lets you see the world in a beautiful tint while blocking the blinding glare.
The "Polymer" Part (The Heat Exchanger): They coated this sandwich with a special plastic (polymer). This plastic acts like a one-way heat valve. It is invisible to the sun, but it is "loud" in the infrared spectrum, meaning it screams its heat out through that "atmospheric window" we mentioned earlier.

4. The Results: Cool, Colorful, and Massive

The team didn't just make a tiny speck in a lab; they proved this could work in the real world:

It actually works: They tested these colored films outside. Even under the hot sun, the yellow, magenta, and cyan materials stayed 2.6 to 8.8 °C cooler than the air around them. It’s like having a personal breeze that follows you around, powered by nothing.
It’s "Roll-to-Roll" ready: This is the most exciting part for the planet. They showed they could manufacture a piece of this material that was 60 cm wide and 5 meters long using a process similar to how newspapers are printed (roll-to-roll).

Why does this matter?

Imagine a future where:

Your car is a beautiful, deep magenta color but stays cool to the touch even in a desert.
Your house is painted a stylish cyan, saving you massive amounts of money on electricity.
Solar panels are coated in these materials so they don't overheat, making them more efficient.

In short: This paper provides the "recipe" for a future where our world is colorful and beautiful, but also naturally cool and energy-efficient.

Technical Summary: Scalable Colored Sub-Ambient Radiative Coolers Based on a Polymer-Tamm Photonic Structure

1. Problem Statement

Daytime radiative coolers (DRCs) are passive devices capable of cooling objects below ambient air temperature (sub-ambient cooling) by reflecting solar radiation and emitting thermal energy through the atmospheric transparency window (8–13 μm). However, existing DRC technologies face a significant "aesthetic-performance" dilemma:

Visual Limitation: Most high-performance DRCs are limited to silvery or white appearances to maximize solar reflectance, which is unsuitable for architectural integration (building envelopes) or automotive applications due to aesthetic concerns and potential light pollution.
Color-Cooling Trade-off: Implementing colors typically requires dyes or pigments that absorb near-infrared solar radiation, increasing the thermal load and preventing sub-ambient cooling.
Scalability Issues: Previous attempts to achieve colored DRCs via photoluminescence or complex nanostructures often suffer from limited color variety, poor durability, or manufacturing processes that are difficult to scale for industrial use.

2. Methodology

The researchers developed a novel polymer-Tamm photonic structure to decouple color control from thermal management. The approach involves two primary components:

Inorganic Tamm Unit (Color & Solar Reflection): Instead of using pigments, the team utilized Tamm Plasmon Resonances (TPRs). By designing an aperiodic multilayer structure (alternating $\text{Nb}_2\text{O}_5$ and $\text{SiO}_2$ layers atop a metal layer), they engineered high-quality factor ( $Q$ -factor) reflectance dips in the visible spectrum. This allows for specific subtractive primary colors (Cyan, Magenta, Yellow) while maintaining high solar reflectance elsewhere.
Organic Polymer Unit (Thermal Emission): To achieve high infrared emittance, the Tamm unit was integrated with transparent organic polymers. Polyvinyl alcohol (PVA) was used for broadband thermal emission (5–20 μm), while PMMA was used for selective emission within the atmospheric window.
Theoretical Modeling: The team established a mathematical framework to determine the critical $Q$ -factor thresholds required to maintain sub-ambient cooling for specific colors. They modeled the net cooling power ( $P_{\text{cool}}$ ) by balancing solar absorption, atmospheric thermal radiation, and convective/conductive heat exchange.

3. Key Contributions

Theoretical Thresholds: The study provides the first explicit guidelines for the $Q$ -factor required for sub-ambient cooling in colored structures (e.g., $Q > 9.06$ for yellow, $10.07$ for magenta, and $10.86$ for cyan).
Decoupled Design: The use of a polymer-Tamm structure allows the color (governed by the TPR $Q$ -factor) and the thermal emission (governed by polymer functional groups) to be engineered independently.
Scalable Manufacturing: The researchers demonstrated that the entire structure can be produced using industrial-standard Roll-to-Roll (R2R) magnetron sputtering and blade coating techniques.

4. Results

Optical Performance: The fabricated CDRCs exhibited vivid subtractive primary colors (CMY). The measured $Q$ -factors (ranging from 20.7 to 34.3) significantly exceeded the theoretical thresholds required for cooling.
Cooling Efficiency:
- Daytime: Observed temperature drops of 2.6–8.8 °C below ambient.
- Nighttime: Observed temperature drops of 4.0–4.4 °C below ambient.
- The yellow CDRC showed the most efficient cooling due to its higher $Q$ -factor and lower solar absorption.
Large-Scale Demonstration: A large-area magenta CDRC was successfully manufactured with dimensions of 60 cm (width) × 500 cm (length).
Mechanical Durability: The device showed excellent stability, passing high-level adhesion tests (5B), resisting abrasion after 2,000 cycles, and demonstrating high tensile strength (withstanding 152% strain).

5. Significance

This work represents a breakthrough in passive thermal management by solving the long-standing conflict between aesthetic color requirements and sub-ambient cooling performance. By providing a scalable, durable, and theoretically grounded method for creating colored DRCs, this research opens unprecedented opportunities for:

Energy-efficient architecture: Colorable building envelopes that reduce air conditioning loads.
Automotive industry: Aesthetic vehicle coatings that assist in temperature regulation.
Sustainable urban design: Integration of cooling technologies into the visual fabric of smart cities without compromising visual comfort or light safety.