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Film thickness is very important in the preparation of film thermoelectric (TE) devices. To define the effect of the film thickness on the power factor and output power, the ZnO:Al films with thicknesses in the range of 100 nm–900 nm were prepared by thermal evaporation method assisted by radio frequency atomic source. The results show that the film thickness has no effect on the phase composition and the (002) preferred orientation of the wurtzite phase in the films. However, the grain size, surface particle size, and surface roughness increase with increasing film thickness. Transmittance significantly reduced for the 900 nm film. Meanwhile, the film thickness affects the carrier concentration and mobility through the defects and growth modes, so that the TE parameters of the films change with the film thickness. The 700 nm film has the highest power factor, and the maximum power factor is 627 μW m−1 K−2 at 560 K. The output power of the films increases as the increase of the temperature on the hot side and higher power factor results in higher output power. The maximum output power of the 700 nm film is 116.01 pW at temperature difference of 1 K. This indicates that film thickness, temperature difference, and power factor are the key factors affecting the film output power. [ABSTRACT FROM AUTHOR]

In this study, we explored the role of the intrinsic defects on the tuning thermoelectric (TE) performance of Al-doped ZnO (ZnO:Al) films. The intrinsic defects of the Zn interstitial (Zn i) and the oxygen vacancy (V O) were controlled by varying the Zn content by using the radio frequency atomic source vacuum evaporation method. In the Zn-rich case, the excessive Zn formed Zn i to provide most of the carriers. V O became the main origin of the carriers with a decreasing Zn content. When the Zn content was 55.2% and 52.5%, the segregation of Zn i decreased the carrier concentration and subsequently, enhanced the resistivity and the Seebeck coefficient. The ZnO:Al film with a Zn content of 52.5% had the highest power factor of 274.03 μW·m−1·K−2 at 819 K. In addition, the higher Zn i concentration had a more prominent effect on thermal conductivity. The thermal conductivity increased to 1.756 W·m−1·K−1 from 0.608 W·m−1·K−1 with the Zn content decreasing from 55.2% to 50.6%. The ZT value reached the highest of 0.121 when the film had the optimum Zn concentration of 51.5%. This study concluded that the tuning of the intrinsic defects was an effective method to enhance the TE performance. [ABSTRACT FROM AUTHOR]

Unstable nanosheet morphology of polycrystalline SnSe film becomes a limitation for its application in the field of waste heat recovery. This study dopes Co into the evaporated SnSe film to smooth the surface and to improve power factor. The results show that Co dopant makes the rough nanosheet change to surface densely packed structure. The dopant Co forms Co particles distributing around SnSe grain boundary, which suppress SnSe (011) plane growth and subsequent reduce nanosheet formation. In addition, Co dopant increases electric conductivity through increasing the carrier concentration, but the magnetism of Co particles decreases carrier mobility due to spin-charge coupling and also affects the Seebeck coefficient. The power factor thus is improved after doped Co. This study presents a method to fabricate polycrystalline SnSe film with smooth surface morphology and high power factor. [ABSTRACT FROM AUTHOR]

Improving the thermoelectric (TE) properties of typical p-type Bi 0.5 Sb 1.5 Te 3 film is crucial for power generation in film-based thermoelectric devices. The shape of the hexagonal structure in the Bi 0.5 Sb 1.5 Te 3 film can be controlled by adjusting the magnetron sputtering parameters. The results indicate that a high nucleation rate under high sputtering power promotes island growth with a preferred orientation of (015). Thermal energy influences the growth in the in-plane direction along the (00 l) orientation and induces the c-axis orientation in the out-of-plane direction. Consequently, a dense layered hexagonal structure with a high grain boundary density is formed, leading to increased defect density, carrier concentration, and phonon scattering. In this case, the power factor reaches 3149.01 μW·m-1·K-2 at 480 K and the ZT value is 1.14 at 480 K. These results indicate that the film with a dense layered hexagonal structure enhances the TE properties. [ABSTRACT FROM AUTHOR]

• Angle of grain boundaries converts to low from high by electrostatic force. • Low energy of low-angle grain boundary scatters carrier but not phonon. • Pulse current treatment provides a method to get high power factor and power density. Current applications of thermoelectric (TE) materials are limited by their low conversion efficiency. Interfacial engineering is a common way to improve TE properties. This study employed a pulsed electric field to tune the grain interfacial structure of Bi 2 Te 3 films and thereby improve their power factor. The high-angle grain boundaries of the as-deposited films were transformed into low-angle grain boundaries (LAGBs) by the electrostatic force of a high pulse current density. The low interfacial energy of LAGBs maintains high carrier mobility while their reduced defects result in a low carrier concentration. These effects improve the Seebeck coefficient and conductivity simultaneously, with the power factor reaching 5394.77 μW·m−1·K−2 at 513 K. In addition, the compression stress generated by LAGBs enhances phonon scattering, creating a film with the highest power density yet reported (1.31 W·m−2). This provides a method for using PEF to improve the performance of TE materials. [ABSTRACT FROM AUTHOR]

Zn 4 Sb 3 has brought into sharp focus by its low cost and excellent thermoelectric (TE) properties in the medium temperature range. Zn atoms can diffuse in the Zn 4 Sb 3 matrix under the treatment of temperature or current. This provides a way to control its TE performance. In this study, the TE properties of the Zn 4 Sb 3 films were improved by the Zn atomic diffusion under the treatment of periodic pulsed electric field. The Zn atomic diffusion is caused by the electrostatic interaction of the pulsed electric field and the diffusion mode is related to the pulse period. When the pulse period is smaller than 10 s, the interstitial Zn atom diffuses first. The Zn vacancy increases, leading to the increase of the carrier concentration and the decrease of the resistivity. When the pulse period increases to 100 s, more Zn(1) atoms diffuse through the interstitial position, resulting in a small amount of ZnSb phase. Thereby in the Zn 4 Sb 3 films, the carrier concentration decreases and the Seebeck coefficient increases. This kind of the synergistic effect decreases the resistivity and increases the Seebeck coefficient. The power factor of the Zn 4 Sb 3 films treated with a pulse period of 100 s is more than 4500 μW m−1 K−2 in the range of 373 K–573 K. This study presents a new method to control atomic diffusion by periodic pulsed electric field, and the TE properties of the Zn 4 Sb 3 films are improved. • Pulsed electric field can control the diffusion of Zn atoms in Zn–Sb films. • The diffusion of interstitial Zn i atoms increased the carrier concentration in films. • The diffusion of Zn(1) atoms increased with the increase of pulse period. • The diffusion of Zn(1) atoms caused a small amount of the ZnSb phase. • The power factor of the film treated with the pulse period is 4901.31 μW m−1 K−2. [ABSTRACT FROM AUTHOR]

Cu 2 Se is one kind of popular thermoelectric materials due to its performance of the phonon glass-electron crystal. However, the poor thermal stability limits its application. Regulating the distribution of the Cu+ by elemental dopant is a general method to solve the stability and to improve the thermoelectric performance. In this study, the Ag-doped β-Cu 2−x Se films were prepared by vacuum thermal evaporation method. The Cu+ distribution on the octahedral 32(f) sites in the Cu 2 Se crystal is tuned by the Ag content. It found that when the Ag content is 1.0%, the Cu+ and Ag+ contents in the 32(f) sites reach the maximum. In this case, the power factor of the film is 1750 μW·m−1·K−2 at 530 K. As the Ag content rises, the second phase of CuAgSe appears. This results in the decrease of the power factor. It shows that controlling the distribution of the Cu+ by the Ag dopant is conducive to improve the thermoelectric properties of the β-Cu 2−x Se films. • Occupancy increase of Cu+ and Ag+ in 32(f) sites decreases resistivity. • CuAgSe second phase increases carrier concentration and effective mass. • Power factor of Ag-1.0% film is maximum and 300% higher than that of Ag-0.0% film. [ABSTRACT FROM AUTHOR]

• Different dimensions of carbon have different effects on thermoelectric performance. • The lower the dimension of carbon, the higher the carrier concentration of the film. • The CNT composite makes ZnO: Al films have the best performance. The low-dimensional carbon composite is expected to improve electrical conductivity and reduce the thermal conductivity of thermoelectric (TE) materials, which is considered an effective method to improve the TE properties of materials. However, the different dimensions of carbon have various effects on the properties of TE film composite. This study investigated the effects of zero-dimensional fullerene, one-dimensional carbon nanotubes (CNT), and two-dimensional graphene on the TE properties of vacuum evaporated ZnO: Al films. The results demonstrated that these three types of composites influenced the carrier concentration and mobility of the films, which in turn affected the TE properties and output power. The lower the dimension of carbon, the higher the carrier concentration of the film. The CNT composite did not affect the microstructure and preferred orientation. However, it increased the particle size and surface roughness. The interface between CNT and ZnO: Al provided more carriers and improved effective mass, thereby increasing the Seebeck coefficient. In addition, the CNT can be used as a carrier transport channel to improve carrier mobility because of its unique tubular structure. Therefore, the CNT composited ZnO: Al films demonstrated the best TE performance and output power. Its power factor reached 136.5 μWm−1K−2 at room temperature. [ABSTRACT FROM AUTHOR]