Jian Yu

Narrow-bandgap full-Heusler Fe₂VAl-based alloys have received increasing attention for thermoelectric applications due to their favorable electrical transport behavior, high mechanical strength, and Earth-abundant constituent elements. However, the significant enhancement of the figure of merit is severely hindered by the low Seebeck coefficient due to the near-linear band structure and intrinsically high lattice thermal conductivity caused by the strong bonding. Here, employing first-principles calculations, we find that substituting 1/16 Fe atoms with Cu atoms can induce a strong localization of the 3d e_g orbital electrons of Fe and V atoms around the impurity atoms. This leads to the coexistence of dispersive bands and flat bands near the Fermi level, significantly boosting the Seebeck coefficient while maintaining high electrical conductivity, yielding a power factor of 5.8 mW m⁻¹ K⁻² at room temperature. Meanwhile, the Cu atoms with large atomic displacement form weak bonds with surrounding V atoms, strengthening low-frequency phonon scattering. Furthermore, the introduction of Cu atoms enhances the crystal anharmonicity, triggering a further decrease in the lattice thermal conductivity to 4.57 W m⁻¹ K⁻¹ at 300 K. Consequently, promising zT values of 0.36 and 2.3 are achieved at 300 K and 700 K, respectively. Our work demonstrates that Cu substitution in Fe sites may successfully decouple electrical and thermal transport of Fe₂VAl, offering an effective and scalable strategy for designing high-performance Fe₂VAl-based thermoelectric materials.

Bi₂Te₃-based alloys are representatively commercialized thermoelectric materials for refrigeration and power generation. Refrigeration mainly utilizes thermoelectric properties near room temperature, while the power generation temperature is relatively high. However, it is difficult for bismuth telluride to maintain good thermoelectric properties throughout the entire temperature range of 300–500 K. Herein, a series of Bi_xSb_2−xTe₃ alloys with different Bi contents were prepared by a simple preparation method and systematically investigated, and their best application temperature range was found. The Bi content can modulate carrier concentration and band gap, and the maximum dimensionless figure of merit (ZT) value of Bi_xSb_2−xTe₃ can be achieved in the corresponding application temperature range. The maximum ZT of Bi_0.3Sb_1.7Te₃ with a Bi content equal to 0.3 reaches 1.14 at 400 K, and the average ZT is 1.06 in the range of 300–500 K, which is suitable for both power generation and refrigeration. Therefore, power generation technologies with higher application temperatures should be selected from Bi_xSb_2−xTe₃ materials with Bi content less than 0.3, and refrigeration technologies with lower application temperatures should be selected with Bi content greater than 0.3. This work provides experimental guidance for finding the composition of Bi₂Te₃-based alloys in scientific research and practical applications.

Nanostructured transition metal dichalcogenide MnSe₂ has attracted much attention due to its fascinating magnetic properties. In this article, a series of MnSe₂ nanoparticles with different particle sizes are successfully prepared by a facile top‐down method of solid‐state reaction combined with ball milling, and the effects of ball milling on the phase composition, microstructure and magnetic properties of the MnSe₂ are systematically studied. The results show that pure MnSe₂ microparticles are obtained by the solid‐state reaction, however, partial MnSe₂ is decomposed after ball milling for 16 h. The average particle size of the MnSe₂ gradually decreases with the increase of milling time. MnSe₂ nanoparticles with average particle size approximately 65 nm are obtained after milling for 40 h. After milling, the antiferromagnetic MnSe₂ nanoparticles exhibit weak ferromagnetic characteristics due to the surface effect and the microstrain induced by ball milling. The residual magnetization (M_r) and coercivity (H_c) of the sample gradually increase as the particle size decreases. The M_r and H_c of the sample milled for 40 h reach 70.13 × 10⁻⁴ emu g⁻¹ and 67.47 Oe, respectively.

Full-Heusler alloys with earth-abundant elements exhibit high mechanical strength and favorable electrical transport behavior, but their high intrinsic lattice thermal conductivity limits potential thermoelectric application. Here, the thermoelectric transport properties of Fe-based Full-Heusler Fe₂MAl (M = V, Nb, Ta) alloys are comprehensively investigated utilizing density functional theory. The results suggest that Fe₂NbAl exhibits exceptionally low lattice thermal conductivity due to the strong anharmonic scattering induced by weakly bound Fe atoms and the low phonon velocities caused by heavy Nb atoms. Meanwhile, the high band degeneracy and large electrical conductivity lead to a maximum p-type power factor of 255.6 μW·K^-2·cm^-1 at 900 K. The combination of low lattice thermal conductivity and favorable electrical transport properties results in a maximum p-type dimensionless figure of merit of 1.7. Our work indicates Fe₂NbAl, as a low-cost, environmentally friendly compound, is a potential high-performance p-type thermoelectric material.

In this study, we aim to minimize light loss and achieve high power conversion efficiencies (PCE) in perovskite solar cells (PSCs) by employing a spectral conversion film component with antireflection properties. In our scheme, NaYF₄:Tm, Yb, and Gd luminescent nanorod/silica nanosphere-based thin films are applied on CH₃NH₃PbI₃ PSCs to improve the device efficiency. The film was fabricated by spin coating an aged silica sol containing NaYF₄:Tm, Yb, and Gd luminescent nanorods. The size and the spectral conversion properties of the NaYF₄:Tm, Yb, and Gd luminescent nanorods were controlled by tuning the Gd³⁺ ion concentration. The microstructure and the transmittance properties of the thin film were controlled by changing the concentration of NaYF₄:Tm, Yb, and Gd luminescent nanorod in silica sol. The thin films have excellent spectral conversion properties while exhibiting a maximum transmittance. The photovoltaic performance of PSCs with NaYF₄:Tm, Yb, and Gd luminescent nanorod/silica nanosphere-based thin films was systematically investigated. The light transmittance was optimized to 95.1% on a cleaned glass substrate, which resulted in an average increase of about 3.0% across the broadband range of 400–800 nm. The optimized films widen the spectrum of light absorbed by conventional PSC cells and reduce reflections across a broad range, enhancing the photovoltaic performance of PSCs. As a result, the PCE of the PSC increased from 14.51% for the reference device without a thin film to 15.67% for the PSC device with an optimized thin film. This study presents a comprehensive solution to the problem of Fresnel reflection and spectral response mismatch of the PSCs, which provides new ideas for the light management of PSCs.