Al–Si Alloy as a Diffusion Barrier for GeTe-Based Thermoelectric Legs with High Interfacial Reliability and Mechanical Strength

Abstract

To build high-performance thermoelectric (TE) devices for power generation, a suitable diffusion-barrier layer between the electrodes and the TE materials in a TE device is generally required for achieving good interfacial connection with high reliability, high mechanical strength but low electrical and thermal contact resistivities. GeTe-based materials have attracted great attention recently due to their high TE performance in the mid-temperature range, but studies on their TE devices are still limited. Here, we selected the Al66Si34 alloy as a diffusion barrier for GeTe-based TE legs based on the matching test of the coefficient of thermal expansion. The good connection between Al66Si34 and Ge0.9Sb0.1TeB0.01 is realized by the interfacial reaction, where the randomly distributed Al2Te3 and Ge precipitates are formed at the interface of the joint. The as-prepared interfacial electrical contact resistivity can be as low as 20.7 μΩ·cm2 and only slightly increases to 26.1 μΩ·cm2 after 16 days of aging at 500 °C. Moreover, the shear strength of the joints can be as high as 26.6 MPa and unexpectedly increases to 41.7 MPa after 16 days of aging. The thickness of the reaction layer tends to be stabilized after 8 days of aging and nearly does not change after further aging to 16 days, which may be ascribed to the drag effect from Si and the secondary Ge phases. These results demonstrate the great potential of the Al–Si alloy as a diffusion barrier for GeTe-based TE devices with high performance.

Boron Strengthened GeTe‐Based Alloys for Robust Thermoelectric Devices with High Output Power Density

“…[ 16,25 ] This problem can be alleviated by introducing appropriate diffusion barriers between electrodes and TE legs. [ 25–29 ]…”

Realizing a 14% single-leg thermoelectric efficiency in GeTe alloys

“…This corresponds to an interfacial contact resistivity (ρ c ) of only ~8 microhm·cm 2 , which is one of the lowest among reported thermoelectric devices (fig. S11) ( 26 , 29 , 31 ). Note that the total resistance of contacts at both cold and hot sides is limited to be within 4% of the internal resistance ( R in ) of the device, ensuring the high power output and conversion efficiency ( 27 ).…”

“…One further step that has to be taken for realizing an efficient thermoelectric application of GeTe is the fabrication of high-efficiency devices. Both electrically and thermally conductive but chemically inert contacts between thermoelectric materials and electrodes are essential to ensure the high device efficiency offered by the high-performance materials ( 26 , 27 ). Usually, a stack of multiple layers can be applied for a prevention of atomic diffusion, a release of thermal expansion mismatch, and a reduction of contact resistance ( 28 , 29 ).…”

“…For GeTe-based devices, Fe and Ni were considered as electrodes, yet a direct bond to GeTe results in a notable atomic diffusion thus a notable decrease in conduction and efficiency ( 29 , 30 ). Existing work indicates that alloys ( 26 ), compounds ( 29 ), and metals ( 31 ) can be used as a medium between thermoelectric materials and electrodes for inhibiting atomic diffusion.…”

Realizing zT Values of 2.0 in Cubic GeTe

“…For instance, while it is generally desirable to have a high power factor (S 2 σ) and low thermal conductivity (κ L +κ e ), improving the electrical conductivity (σ) leads to higher electronic thermal conductivity (κ e ). In addition to optimizing thermoelectric properties, the mechanical properties such as hardness, stiffness, and thermal expansion coefficient cannot be overlooked to ensure practical applications [7–13] . With respect to its application temperature, thermoelectrics can be classified into low (300–500 K), medium (500–800 K), and high temperature (>800 K) materials.…”