Passive radiative cooling using nanophotonic structures is limited by its high cost and poor compatibility with existing end uses, whereas polymeric photonic alternatives lack weather resistance and effective solar reflection. We developed a cellular ceramic that can achieve highly efficient light scattering and a near-perfect solar reflectivity of 99.6%. These qualities, coupled with high thermal emissivity, allow the ceramic to provide continuous subambient cooling in an outdoor setting with a cooling power of >130 watts per square meter at noon, demonstrating energy-saving potential on a worldwide scale. The color, weather resistance, mechanical robustness, and ability to depress the Leidenfrost effect are key features ensuring the durable and versatile nature of the cooling ceramic, thereby facilitating its commercialization in various applications, particularly building construction.

Tin selenide (SnSe) and tin sulfide (SnS) have recently attracted particular interest due to their great potential for large-scale thermoelectric applications. A complete prediction of the thermoelectric performance and the understanding of underlying heat and charge transport details are the key to further improvement of their thermoelectric efficiency. We conduct comprehensive investigations of both thermal and electrical transport properties of SnSe and SnS using first-principles calculations combined with the Boltzmann transport theory. Due to the distinct layered lattice structure, SnSe and SnS exhibit similarly anisotropic thermal and electrical behaviors. The cross-plane lattice thermal conductivity ${\kappa }_L$ is $40–60\%$ lower than the in-plane values. Extremely low ${\kappa }_L$ is found for both materials because of high anharmonicity, while the average ${\kappa }_L$ of SnS is $\sim 8\%$ higher than that of SnSe from 300 to 750 K. It is suggested that nanostructuring would be difficult to further decrease ${\kappa }_L$ because of the short mean free paths of dominant phonon modes (1–30 nm at 300 K), while alloying would be efficient in reducing ${\kappa }_L$ considering that the relative ${\kappa }_L$ contribution $(\sim 65\%)$ of optical phonons is remarkably large. On the electrical side, the anisotropic electrical conductivities are mainly due to the different effective masses of holes and electrons along the $a, b$, and $c$ axes. This leads to the highest optimal $\mathit{ZT}$ values along the $b$ axis and lowest ones along the $a$ axis in both $p$-type materials. However, the $n$-type ones exhibit the highest $\mathit{ZT}\mathrm{s}$ along the $a$ axis due to the enhancement of power factor when the chemical potential gradually approaches the secondary conduction band valley that causes significant increase in electron mobility and density of states. Owing to the larger mobility and smaller ${\kappa }_L$ along the given direction, SnSe exhibits larger optimal ZTs compared with SnS in both $p$- and $n$-type materials. For both materials, the peak $\mathit{ZT}\mathrm{s}$ of $n$-type materials are much higher than those of $p$-type ones along the same direction. The predicted highest $\mathit{ZT}$ values at 750 K are 1.0 in SnSe and 0.6 in SnS along the $b$ axis for the $p$-type doping, while those for the $n$-type doping reach 2.7 in SnSe and 1.5 in SnS along the $a$ axis, rendering them among the best bulk thermoelectric materials for large-scale applications. Our calculations show reasonable agreements with the experimental results and quantitatively predict the great potential in further enhancing the thermoelectric performance of SnSe and SnS, especially for the $n$-type materials.

Phonon and electron transport in ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ has been investigated using a multiscale approach, combining the first-principles calculations, molecular dynamics (MD) simulations, and Boltzmann transport equations (BTEs). Good agreements are found with the available experimental results. The MD simulations along with the Green-Kubo autocorrelation decay method are used to calculate the lattice thermal conductivity in both the in-plane and cross-plane directions, where the required classical interatomic potentials for ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ are developed on the basis of first-principles calculations and experimental results. In the decomposition of the lattice thermal conductivity, the contributions from the short-range acoustic and optical phonons are found to be temperature independent and direction independent, while the long-range acoustic phonons dominate the phonon transport with a strong temperature and direction dependence (represented by a modified Slack relation). The sum of the short-range acoustic and optical phonon contribution is about $0.2\mathrm{W}∕\mathrm{m}\mathrm{K}$ and signifies the limit when the long-range transport is suppressed by nanostructure engineering. The electrical transport is calculated using the full-band structure from the linearized augmented plane-wave method, BTE, and the energy-dependent relaxation-time models with the nonparabolic Kane energy dispersion. Temperature dependence of the energy gap is found to be important for the prediction of electrical transport in the intrinsic regime. Appropriate modeling of relaxation times is also essential for the calculation of electric and thermal transport, especially in the intrinsic regime. The maximum of the Seebeck coefficient appears when the chemical potential approaches the band edge and can be estimated by a simple expression containing the band gap. The scatterings by the acoustic, optical, and polar-optical phonons dominate the electrical conductivity and electric thermal conductivity.

Adaptive control of solar and thermal radiation through windows is of pivotal importance for building energy saving. However, such synchronous passive regulations are challenging to be integrated into one thermochromic window. Here, we develop a solar and thermal regulatory (STR) window by integrating poly( N -isopropylacrylamide) (pNIPAm) and silver nanowires (AgNWs) into pNIPAm/AgNW composites. A hitherto unexplored mechanism, originating from the temperature-triggered water capture and release due to pNIPAm phase transition, is exploited to achieve simultaneous regulations of solar transmission and thermal emission. The STR window shows excellent solar modulation (58.4%) and thermal modulation (57.1%) and demonstrates effective regulation of indoor temperatures during both daytime and nighttime. Compared to other thermochromic technologies, the STR window reduces heat loss in cold environment while promotes heat dissipation in hot conditions, achieving efficient energy saving in all weathers. This dual solar and thermal regulation mechanism may provide unidentified insights into the advancement of smart window technology.