Fig. 1 Timelines underscoring the improvement in (a) zT value of typical thermoelectric materials[6,7] and (b) conversion efficiency of typical thermoelectric power generation devices[10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40]

Fig. 2 Schematic diagram of the full-chain development of thermoelectric conversion technology

Fig. 3 Diagram of key scientific and technical issues in the design and integration of TE devices

Fig. 4 Schematic diagram of energy conversion process for thermoelectric power generation devices[45]

Fig. 5 (a) Conversion efficiency as a function of thermoelectricelement height for different thermal contact parameter,r,and (b) power output ratio Pc/Pmax as a function of the electrical contact parameter,n, for different thermoelectric element height[46]

Fig. 6 Schematic diagram of various thermal losses in thermoelectric devices

Fig. 7 Analogical scheme of the thermoelectric phenomena with the thermal capacitances $C_{n}=\rho ·n·C_{p_{n}}·\frac{H}{N}·A$ and thermal conductances $K_{n}=\frac{k_{n}·A}{H/N}$ [55]

Fig. 8 Logical framework for the full-parameter optimization of a thermoelectric power generation module[40]

Fig. 9 Diagram of main failure modes of thermoelectric devices

Fig. 10 Scanning electron microscope images of CoSb3/Ti/Mo-Cu interface after thermal aging at 550 ℃ for different periods[115](a) 0; (b) 8 d; (c) 20 d; (d) 30 d

Fig. 11 (a) Schematic diagram of the formation of Ti(100-x)Alx-Yb0.6Co4Sb12 interface, (b) the diffusion layer thickness and (c) specificcontact resistivity of the Ti(100-x)Alx-Yb0.6Co4Sb12 interface as a function of the thermal aging time under 600 ℃ and vacuum condition[79]