Manjusha Battabyal

The Mg₃Sb₂-based layered compounds exhibit exceptional thermoelectric properties over a wide temperature range and possess the potential to supplant traditional Bi₂Te₃ modules with reliable and economical Mg₃Sb₂-based thermoelectric devices, contingent upon the availability of a complementary p-type Mg₃Sb₂ material with high thermoelectric efficiency comparable to that of n-type Mg₃Sb₂. We provide a simpler method involving the codoping of monovalent atoms (K and Na) at the Mg site of the Mg₃Sb₂ lattice to improve the thermoelectric performance of p-type Mg₃Sb₂. K-Na codoping results in a peak power factor of around 0.85 mW/mK² at 675 K in Mg_2.97K_0.02Na_0.01Sb₂ by enhancing the carrier concentration at the Fermi level. Furthermore, the temperature-dependent development of the Raman modes substantiates the existence of significant lattice anharmonicity in Mg_2.97K_0.02Na_0.01Sb₂, ascribed to volumetric quasi-anharmonicity and three- and four-phonon interactions. As a result, decay of optical phonon happens at higher temperatures, yielding an exceptionally low lattice thermal conductivity of 0.38 W/mK at 675 K in Mg_2.97K_0.02Na_0.01Sb₂, the lowest recorded in p-type Mg₃Sb₂ materials. The thermoelectric figure of merit for Mg_2.97K_0.02Na_0.01Sb₂ attains 0.9 at 675 K, representing the highest documented value for double-doped p-type Mg₃Sb₂ materials thus far. Our extensive findings validate the optical phonon decay and improvement in thermoelectric efficiency of p-type Mg₃Sb₂ via codoping with monovalent atoms for midtemperature thermoelectric applications.

Flexible thermoelectric devices offer huge potential for wearable electronics due to their ability to generate green energy by using low-grade heat. However, achieving both high thermoelectric performance and flexibility simultaneously remains a challenge for these devices. Here, we present a simple and cost-effective method for fabricating a high-performance flexible inorganic-organic thermoelectric film by depositing Ag₂Se on a porous nylon membrane. The resulting Ag₂Se/nylon film exhibits an ultrahigh power factor of approximately 3.4 mW/mK² at 300 K, the highest value reported for flexible thermoelectric films to date. The Ag₂Se/nylon film also demonstrates remarkable flexibility, confirming its potential application in wearable electronics. A thermoelectric module constructed using eight strips of the processed Ag₂Se/nylon film generates an impressive output voltage of 65 mV and an output power of 30 μW at a 30 K temperature difference. Additionally, the fabricated module maintains strong flexibility, producing more than 2 mV when wrapped around a human arm with a temperature difference of 1.6 K. This work highlights the significant potential of inorganic-organic films for flexible thermoelectric applications in wearable and implantable devices.

We report the magnificent thermoelectric properties of the n-type Ag₂Se film printed onto a flexible polyimide (PI) substrate. The orthorhombic β-Ag₂Se phase of the processed Ag₂Se film is confirmed from the X-ray diffractogram. Remarkably, the resulting Ag₂Se/PI film exhibits outstanding thermoelectric properties, boasting maximum power factors of 1.4 and 2.1 mW/mK² at 300 and 405 K, respectively. Furthermore, the flexibility of the Ag₂Se/PI film remains intact even after undergoing 1500 bending cycles with no degradation observed in its thermoelectric performance. To demonstrate the practical application of our findings, a flexible thermoelectric prototype is constructed using the fabricated Ag₂Se/PI films, which can harvest an impressive output voltage of 52 mV across a temperature difference of 53 K. Additionally, the prototype generates a maximum power output of 7.2 μW with a 40 K temperature difference and can produce 13 mV output voltage when subjected to around a 10 K temperature gradient when the cold side temperature is maintained at 308 K. Moreover, leveraging body heat with just a 1 K temperature variance between the body and the surrounding environment, the prototype could yield an impressive voltage output of 1.6 mV, marking the highest reported voltage output from human body heat to date. Our study not only introduces a cost-effective method for producing high-performance flexible thermoelectric films but also highlights their potential applications in wearable and implantable electronics.

Al doped CuI exhibit the increase in carrier density, decrease in optical bandgap and phonon life time thus improves the power factor and figure of merit. The maximum PF and ZT obtained at 400 K are 79 μW m⁻¹ K⁻² and 0.08 for 0.1 mol% Al-doped CuI.