Thermoelectric materials have attracted great attention due to their important applications in power generation, energy saving, and electric refrigeration. In this article, we designed three two-dimensional materials SnX (X = O, S, Se), which exhibit high stability. All three monolayers are direct band gap semiconductors with a "multivalley" characteristic in band structures, showing bandgaps of 2.87, 1.83, and 1.27 eV for SnO, SnS, and SnSe, respectively. In addition, the SnX monolayers with the optimum power factor values can be up to 0.91−0.97 W m −1 K −2 at room temperature. The small group velocities and strong anharmonic phonon behavior led to an intrinsic lattice thermal conductivity as low as ∼0.92−2.27 W m −1 K −1 . As results, SnX exhibit excellent thermoelectric properties, with the figure of merit (ZT) up to ∼0.07−0.52, ∼0.13−0.89, and ∼0.25−1.41 for SnO, SnS, and SnSe at temperatures of 300−700 K, respectively.
In order to enhance the visible-light transmittance while reducing the insulator–metal transition (IMT) temperature, Hf–W co-doping is designed for modification of VO2. We grow high-quality HfxWyV1−x−yO2 (HfWVO2) alloy films on c-plane sapphire substrates by pulsed laser deposition, and test structural, electrical, and optical properties of the films by various techniques. The Hf–W co-doped VO2 films exhibit outstanding thermochromic performances with a high luminous transmittance up to 41.1%, a fairly good near-infrared modulation capacity of 13.1%, and a low phase transition temperature of 38.9 °C. The enhanced luminous transmittance along with reduced IMT temperature in HfWVO2 is attributed to the co-doping synergetic effect of Hf and W, which effectively improves the optical bandgap and donates extra electrons into the system, respectively, while largely retaining the near-infrared modulation capacity of VO2. Our work provides an effective strategy in tailoring VO2 toward practical smart-coating applications by Hf–W co-doping.
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