Inorganic plastic-deformable thermoelectric compounds can break the limitations of traditional inorganic brittle thermoelectric materials and organic flexible counterparts, offering promise for use in the fields of flexible electronics and power generation. 

The scientists from Shanghai Institute of Ceramics (SICCAS) have found the abnormal plastic-deformability at room temperature in inorganic semiconductors Ag₂S (Nature Materials, 2018) and Van der Waals single crystal InSe (Science, 2020). They also developed n-type high-performance inorganic flexible/plastic-deformable thermoelectric materials and devices (Energy & Environmental Science, 2019), opening up a new research direction of inorganic plastic-deformable thermoelectrics. 

However, the members of inorganic plastic-deformable materials are still scarce. Especially, the p-type inorganic plastic-deformable materials are still absent. 

Recently, the scientists from SICCAS and Shanghai Jiao Tong University have developed n-type Ag₂₀S₇Te₃ and p-type (Ag_0.2Cu_0.8)₂S_0.7Se_0.3 high-performance inorganic plastic-deformable thermoelectric compounds. By utilizing their extraordinary shape-conformability at room temperature, the researchers fabricated a ring-shaped thermoelectric device which was conformable with curved heat source surface. 

Ag₂₀S₇Te₃ crystalizes in a body-centered cubic structure, which is analogous with that of middle-temperature phase of Ag₂S. At ambient temperature, Ag₂₀S₇Te₃ exhibits even better shape-conformability than Ag₂S and could be easily bent into different shapes. The first-principle calculations reveal that cubic-Ag₂₀S₇Te₃ has a lower generalized stacking fault energy (GSFE) and a higher cleavage energy (CE) than monoclinic-Ag₂S, which is responsible for the better shape-conformability of Ag₂₀S₇Te₃ than Ag₂S at room temperature. 

At 600 K, the zT of Ag₂₀S₇Te₃ is 0.8, which is comparable to that of Bi₂Te₃-based alloys prepared by zone melting method. The researchers connected the bent n-type Ag₂₀S₇Te₃ stripes and p-type Pt-Rh wires to fabricate a ring-shaped thermoelectric device. Under a temperature difference of 70 K, the maximum output power was 17.1 μW. The related results were published on Advanced Materials (2021, DOI: 10.1002/adma.202007681), with the title of “Ductile Ag₂₀S₇Te₃ with Excellent Shape-Conformability and High Thermoelectric Performance”. 

The researchers further selected the n-type Ag₂S_0.7Se_0.3 as the starting material to prepare p-type inorganic plastic-deformable thermoelectric compounds. By alloying Cu atoms in Ag site, they successfully converted its n-type conduction behavior into p-type. When the composition of Cu is in the range of 0.7-0.8, the material shows both plastic shape-conformability and p-type conduction behavior. The first-principle calculations show that (Ag_0.2Cu_0.8)₂S_0.7Se_0.3 has a high ratio of cleavage energy to slip energy, which is comparable to that of Ag₂S_0.7Se_0.3. 

This explains the observed large deformation ability at room temperature. By further introducing Cu vacancy to improve the electrical conductivity, the zT of p-type (Ag0.2Cu0.8)₂S_0.7Se_0.3 can be enhanced to 0.95 at 800 K. The related results were published on Advanced Energy Materials (2021, DOI:10.1002/aenm.202100883), with the title of “p-Type Plastic Inorganic Thermoelectric Materials”. 

The related works are supported by the National Key Research and Development Program of China, the National Natural Science Foundation of China, Chinese Academy of Sciences, and Shanghai Rising-Star Program. 

References: 

https://doi.org/10.1002/adma.202007681  

https://doi.org/10.1002/aenm.202100883  

Fig. 1 a) Optical images of n-type inorganic plastic-deformable thermoelectric compound Ag₂₀S₇Te₃ and its thermoelectric performance. b) Ag₂₀S₇Te₃-based ring-shaped thermoelectric device and its output performance.

Fig. 2 a) Seebeck coefficients and mechanical properties for (Ag_1-xCu_x)₂S_0.7Se_0.3 compounds. b) Optical images of p-type inorganic plastic-deformable thermoelectric compound (Ag_0.2Cu_0.8)₂S_0.7Se_0.3 with different shapes.

Contact:

Prof. SHI Xun

Shanghai Institute of Ceramics

Email: xunshi@mail.sic.ac.cn