RESUMO
Thermoelectric power can convert heat and electricity directly and reversibly. Low-dimensional thermoelectric materials, particularly thin films, have been considered a breakthrough for separating electronic and thermal transport relationships. In this study, a series of Bi0.5Sb1.5Te3 thin films with thicknesses of 0.125, 0.25, 0.5, and 1 µm have been fabricated by RF sputtering for the study of thickness effects on thermoelectric properties. We demonstrated that microstructure (texture) changes highly correlate with the growth thickness in the films, and equilibrium annealing significantly improves the thermoelectric performance, resulting in a remarkable enhancement in the thermoelectric performance. Consequently, the 0.5 µm thin films achieve an exceptional power factor of 18.1 µWcm-1K-2 at 400 K. Furthermore, we utilize a novel method that involves exfoliating a nanosized film and cutting with a focused ion beam, enabling precise in-plane thermal conductivity measurements through the 3ω method. We obtain the in-plane thermal conductivity as low as 0.3 Wm-1K-1, leading to a maximum ZT of 1.86, nearing room temperature. Our results provide significant insights into advanced thin-film thermoelectric design and fabrication, boosting high-performance systems.
RESUMO
Mg-Sn alloy thin films have garnered significant attention for their outstanding thermoelectric (TE) properties and cost-effective elemental composition, making them potential candidates for wearable energy harvesting devices. While previous studies have explored the properties of these thin films, limited research has been conducted to identify physical factors that can further enhance their performance. In this study, we present a novel approach utilizing a convenient electron beam coevaporation technique to fabricate Mg-Sn alloy thin films. Experimental results revealed that controlling the tin content in the Mg-Sn thin films at 38.9% led to the formation of a mixed-phase structure, comprising Mg2Sn and Mg9Sn5. This dual-phase structure exhibited a notable advantage in enhancing the TE performance. The presence of the Mg9Sn5 phase significantly increased the carrier concentration, while maintaining the original Seebeck coefficient and mobility, thereby improving the conductivity of Mg2Sn. Theoretical calculations indicated that the Mg9Sn5 phase displayed 1D-like characteristics, leading to a highly effective valley degeneracy and consequently a high power factor. Overall, this work introduces a promising approach to fabricate high-performance Mg-Sn alloy thin films through electron beam coevaporation, opening up possibilities for their application in wearable energy harvesting devices.
RESUMO
Bismuth telluride-based thermoelectric (TE) materials are historically recognized as the best p-type (ZT = 1.8) TE materials at room temperature. However, the poor performance of n-type (ZT≈1.0) counterparts seriously reduces the efficiency of the device. Such performance imbalance severely impedes its TE applications either in electrical generation or refrigeration. Here, a strategy to boost n-type Bi2 Te2.7 Se0.3 crystals up to ZT = 1.42 near room temperature by a two-stage process is reported, that is, step 1: stabilizing Seebeck coefficient by CuI doping; step 2: boosting power factor (PF) by synergistically optimizing phonon and carrier transport via thermal-driven Cu intercalation in the van der Waals (vdW) gaps. Theoretical ab initio calculations disclose that these intercalated Cu atoms act as modulation doping and contribute conduction electrons of wavefunction spatially separated from the Cu atoms themselves, which simultaneously lead to large carrier concentration and high mobility. As a result, an ultra-high PF ≈63.5 µW cm-1 K-2 at 300 K and a highest average ZT = 1.36 at 300-450 K are realized, which outperform all n-type bismuth telluride materials ever reported. The work offers a new approach to improving n-type layered TE materials.
