Simultaneous control of the stoichiometry, microstructure, and compositional homogeneity is a prerequisite for understanding the properties of Ag₂Se. These are difficult to attain because of the highly mobile Ag⁺ ions above the superionic phase transition at 407 K. Here we report on a novel synthesis of well crystallized orthorhombic Ag₂Se carried out at room temperature, which requires no expensive instrumentation, and yields a single-phase material in a very short time. Our facile reaction process is a self-sustaining room temperature synthesis driven by the dissociative adsorption of Se by Ag and promoted by stirring and intermittent grinding under ambient conditions. Systematic experimental and theoretical studies of chemical reactions between Ag and Q (Te, Se, and S) revealed that the reaction mechanism between Ag and Q is in line with the Hard Soft Acid Base (HSAB) scheme (rate order Ag₂Te > Ag₂Se > Ag₂S). The low carrier concentration achieved ∼10¹⁸ cm⁻³ and the optimized weighted majority-to-minority carrier mobility ratio observed in the samples as corroborated by the state-of-the-art thermoelectric performance of ZT ∼1.2 at 390 K attest to the superiority of the synthesis route in yielding highly stoichiometric Ag₂Se samples.

The development of wearable thermoelectric generators (w-TEGs) toward lightweight, economical and high-power-generation performance can provide more opportunities for their application in self-powered wearable electronics. For existing w-TEGs, insight into the physical parameter coupling between the substrate and TE legs is lacking, which leads to inefficient utilization of the temperature difference and deterioration of the power generation performance. In this work, comprehensive thermal management of the heat collector, TE legs and heat radiator is carried out using finite element simulation. It is found that increasing the thermal conductivity of the substrates for heat collection and dissipation is conducive to reducing the optimal fill factor and substrate thickness and improving the power density, thus facilitating comfortable-to-wear, economical, and functional w-TEGs. Specifically, a laminated film with good flexibility prepared from polyimide (PI) film and graphene assembly film (GAF) acts as the substrate of w-TEG. The PI film compensates and enhances the mechanical strength of the laminated substrate. The GAF has high thermal conductivity, which reduces the in-plane and out-of-plane thermal resistance of the laminated substrate, thus contributing to the heat collection of the bottom substrate. The GAF also has high emissivity, which enhances the radiative heat transfer and facilitates the heat dissipation of the top substrate, which is cut into blocks without affecting the electrical path to ensure the overall flexibility of the w-TEG. When the w-TEG with the laminated substrate and a fill factor of 10% (four w-TEG units connected in series, 20 × 145 mm² in plane) is worn on the wrist for running (contact pressure: 0 kPa, wind speed: 3 m s⁻¹), the optimal output voltage and power density reach 281.6 mV and 45.6 μW cm⁻², respectively, which is one of the best results among recently reported heatsink-less w-TEGs. This work provides guidance for optimizing the output performance of w-TEG and accelerating the development of self-powered electronics.

Wearable thermoelectric generators (w-TEGs) convert thermal energy into electrical energy to realize self-powering of intelligent electronic devices, thus reducing the burden of battery replacement and charging, and improving the usage time and efficiency of electronic devices. Through finite element simulation, this study successfully designed high-performance thermoelectric generator and made it into wearable thermoelectric module by adopting “rigid device—flexible connection” method. It was found that higher convective heat transfer coefficient (h) on cold-end leads to larger effective temperature difference (ΔT_eff) and better power generation performance of device in typical wearable scenario. Meanwhile, at same h on the cold-end, longer TE leg length leads to larger ΔT_eff established at both ends of device, larger device output power (P_out) and open-circuit voltage (U_oc). However, when the h increases to a certain level, optimization effect of increasing TE leg length on device power generation performance will gradually diminish. For devices with fixed temperature difference between two ends, longer TE leg length leads to higher resistance of TEGs, resulting in lower device P_out but slight increase in U_oc. Finally, sixteen 16 × 4 × 2 mm² TEGs (L = 1.38 mm, W = 0.6 mm) and two modules were fabricated and tested. At hot end temperature T_h = 33 °C and cold end temperature T_c = 30 °C, the actual maximum P_out of the TEG was about 0.2 mW, and the actual maximum P_out of the TEG module was about 1.602 mW, which is highly consistent with the simulated value. This work brings great convenience to research and development of wearable thermoelectric modules and provides new, environmentally friendly and efficient power solution for wearable devices.

For the optimized TEG, heat collection with a copper film at the skin end and a copper foam heat sink at the air end were installed to improve the power generation performance of the TEG. When the wearer is running outdoors, the power density is 138.46 μW cm⁻².

This study proposes a constrained hot compression-molding (CHCM) technique for preparing Bi₂Te₃-based alloys. This method overcomes the problem of easy cleavage and destruction for the zone-melted Bi₂Te₃-based alloy, which is beneficial to improve the material utilization rate and thermoelectric devices yield in the commercial manufacturing process. The stress field distribution inside the CHCM specimen is explored via finite element analysis. The compressive strength of the CHCM sample is above 44 MPa, which is about 38% higher than that of the zone melting (ZM) material. Meanwhile, the CHCM sample shows a much lower electrical conductivity and thermal conductivity, but a higher Seebeck coefficient than that of the ZM sample, which is mainly due to the increase of the line defect concentration induced by the CHCM process. Finally, a maximum thermoelectric figure of merit (ZT) value of 0.6 was achieved for CHCM sample.