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Real-time control over infrared (IR) radiation of objects is highly desired in a variety of areas such as personal thermal regulation and IR camouflage. This requires the dynamic modulation of IR emissivity in a stepless manner over a wide range (>50%), which remains a daunting challenge. Here, an emissivity modulation phenomenon is reported in stacked 2D Ti3C2Tx MXene nanosheets, from 12% to 68% as the intercalation/discharging of water molecules within the interlayers. The intercalation of water molecules dynamically changes the electronic properties and the complex permittivity in IR frequencies of Ti3C2Tx. This emissivity modulation is a stepless and reversible process without the assistance of any external energy input. Further, intercalating cellulose nanofibers into the Ti3C2Tx interlayers makes this dynamic process highly repeatable. Last, a sweat-responsive adaptive textile that can improve thermal comfort of human body under changes in metabolic rates and environmental conditions is demonstrated, showing great potential of this mechanism in passive on-demand radiation modulation.

Radiative cooling may serve as a promising option to reduce energy consumption for space cooling. Radiative cooling paints provide a cost-effective and scalable solution for diverse applications and attract great attention, but the state-of-art cooling paints generally use non-eco-friendly organic solvents and need large thicknesses (>400 mu m) to realize high performance, which leads to high cost and environmental issues in implementation. This work aims to address these challenges by developing eco-friendly aqueous paints with low thickness (below 150 mu m) by adopting a double-layer design based on a complementary spectrum strategy. The structure consists of a wide bandgap top layer to scatter short-wavelength light and a bottom layer with high reflectance to visible and near-infrared (NIR) irradiation. Effects of different design factors are studied using numerical simulation and experiments to attain the optimal design. The resulting Y2O3-ZnO paints show a strong reflectance of 95.4 % and a high atmospheric window emissivity of 0.93 at a low thickness of 150 mu m. Field tests in the subtropic humid climate of Hong Kong demonstrated sub-ambient cooling of 2 degrees C at noon and 4 degrees C at night without shielding convection. The paints also show high robustness and excellent resistance to water and UV light attacks, rendering them promising for large-scale applications.

High-quality organic field-effect transistors (1L-OFETs) based on monolayers have made significant progress and are expected to be key components in the development of next-generation flexible electronics. However, a flexible, low-cost, damage-free, and metallic conductance electrode that can accurately demonstrate the exceptional electrical properties of 1L-OFETs is still in high demand. In this study, the vacuum-filtrated MXene (Ti3C2Tx) is demonstrated to serve as electrodes without causing chemical or thermal damage to the delicate active layer via a dry-lithography method. By integrating monolayer 2,9-didecyldinaphtho[2,3-b:2,3 '-f]thieno[3,2-b]thiophene (C10-DNTT) with MXene, the 1L-OFETs exhibit a low subthreshold swing of 60.7 mV per decade and high field-effect mobility of 9.5 cm2 V-1 s-1 on a high-kappa dielectric hafnium oxide. The use of MXene electrodes enables the production of solution-processed conductors that can achieve uncompromised performance compared to metal contacts. Furthermore, owing to the well-matched work functions, the contact resistance can be reduced to 165 omega cm by this printing technique. The 1L-OFETs fabricated on an ultra-thin conformal parylene substrate also exhibit uniform electrical properties. It is believed that this processing approach of vacuum-filtrated MXene conductors is a crucial step toward the application of non-metal contacts for high-performance flexible electronics. A large-area vacuum-filtrated MXene electrode deposition and patterning strategy for organic field-effect transistors is demonstrated in this study. By eliminating the harsh integration process, the unique combination of MXene contact with a monolayer organic semiconductor exhibits a smooth contact interface and uncompromised electrical performance. The findings expand the application range of solution-processed conductors for organic electronics.image

A photo- and electro-thermal film can convert sunlight and electricity into heat to solve icing problems. Combination of them provides an efficient strategy for all-day anti-/de-icing. However, only opaque surfaces have been reported, due to the mutual exclusiveness between photon absorption and transmission. Herein, a highly transparent and scalable solution-processed photo-electro-thermal film is reported, which exhibits an ultra-broadband selective spectrum to separate the visible light from sunlight and a countertrend suppress of emission in longer wavelength. It absorbs ≈ 85% of invisible sunlight (ultraviolet and near-infrared) for light-heat conversion, meanwhile maintains luminous transmittance > 70%. The reflection of mid-infrared leads to low emissivity (0.41), which further preserves heat on the surface for anti-/de-icing purpose. This ultra-broadband selectivity enables temperature elevation > 40 °C under 1-sun illumination and the mutual support between photo-thermal and electro-thermal effects contributes to > 50% saving of electrical consumption under weak solar exposure (0.4-sun) for maintaining unfrozen surfaces at −35 °C environment. The reverberation from photo-electro-thermal and super-hydrophobic effects illustrates a lubricating removal of grown ice in short time (< 120 s). The self-cleaning ability and the durability under mechanical, electrical, optical, and thermal stresses render the film stable for long-term usage in all-day anti-/de-icing applications.

Radiative cooling shows great promise in eco-friendly space cooling due to its zero-energy consumption. For subambient cooling in hot humid subtropical/tropical climates, achieving ultrahigh solar reflectance (>= 96%), durable ultraviolet (UV) resistance, and surface superhydrophobicity simultaneously is critical, which, however, is challenging for most state-of-the-art scalable polymer-based coolers. Here an organic-inorganic tandem structure is reported to address this challenge, which comprises a bottom high-refractive-index polyethersulfone (PES) cooling layer with bimodal honeycomb pores, an alumina (Al2O3) nanoparticle UV reflecting layer with superhydrophobicity, and a middle UV absorption layer of titanium dioxide (TiO2) nanoparticles, thus providing thorough protection from UV and self-cleaning capability together with outstanding cooling performance. The PES-TiO2-Al2O3 cooler demonstrates a record-high solar reflectance of over 0.97 and high mid-infrared emissivity of 0.92, which can maintain their optical properties intact even after equivalent 280-day UV exposure despite the UV-sensitivity of PES. This cooler achieves a subambient cooling temperature up to 3 degrees C at summer noontime and 5 degrees C at autumn noontime without solar shading or convection cover in a subtropical coastal city, Hong Kong. This tandem structure can be extended to other polymer-based designs, offering a UV-resist but reliable radiative cooling solution in hot humid climates.

Textiles with radiative cooling/warming capabilities provide a green and effective solution to personal thermal comfort in different climate scenarios. However, developing multiple-mode textiles for wearing in changing climates with large temperature variation remains a challenge. Here a Janus textile is reported, comprising a polyethersulfone (PES)-Al2O3 cooling layer optically coupled with a Ti3C2Tx warming layer, which can realize sub-ambient radiative cooling, solar warming, and active Joule heating. Owing to the intrinsically high refractive index of PES and the rational design of the fiber topology, the nanocomposite PES textile features a record high solar reflectance of 0.97. Accompanied by an infrared (IR) emittance of 0.91 in the atmospheric window, sub-ambient cooling of 0.5–2.5 °C is achieved near noontime in humid summer under ≈1000 W m−2 solar irradiation in Hong Kong. The simulated skin covered with the textile is ≈10 °C cooler than that with white cotton. The Ti3C2Tx layer provides a high solar-thermal efficiency of ≈80% and a Joule heating flux of 66 W m−2 at 2 V and 15 °C due to its excellent spectral selectivity and electrical conductivity. The switchable multiple working modes enable effective and adaptive personal thermal management in changing environments. © 2023 Wiley-VCH GmbH.

Most broadband metamaterial absorbers are realized by patterning periodic arrays of plasmonic nanoparticles (>100 nm) on dielectric/metallic substrates to enable both electric and magnetic resonances. These metamaterials, however, require costly nanolithographic top-down techniques for fabrication. Here, we demonstrate new-concept nanoparticle-on-mirror (NoM) metamaterial absorbers by densely packing plasmonic nano-particles of much smaller size (similar to 30 nm) on metal films directly. Such a simple but rational design enables the use of all-solution-based bottom-up processes. Because of the decoupling of electric and magnetic polarizations in these ultrasmall nanoparticles, excellent impedance match and near-perfect light absorption can be achieved in a broad band over the solar spectrum with weak thermal emission. Proof-of-concept large-area NoM metamaterial absorbers that offer a solar absorptance of 94% but a low IR emittance of 2% are experimentally demonstrated. The outstanding performance, bottom-up process, and great compatibility render the design promising for efficient and large-scale solar energy harvesting.