###### Abstract  
Thermoelectric power generation using human body heat can be applied to wearable sensors, and various applications are possible. Because the thermoelectric generator (TEG) is highly dependent on the thermoelectric material, research on improving the performance of the thermoelectric material has been conducted. Thus far, in developing thermoelectric materials, the researchers have focused on improving the figure of merit, ZT. For a TEG placed on the human body, however, the power density does not always increase as the material ZT increases. In this study, the material properties and ZT of P-type BiSbTe\({}_{3}\) were simulated for carrier concentration ranging from \(3\times 10^{17}\) to \(3\times 10^{20}\) cm\({}^{-3}\), and the power density of a TEG fabricated from the material dataset was calculated using a thermoelectric resistance model for human body application. The results revealed that the maximum ZT and the maximum power density were formed at different carrier concentrations. The material with maximum ZT showed 28.8% lower power density compared to the maximum obtainable power density. Further analysis confirmed that the mismatch in the optimum carrier concentration for the maximum ZT and maximum power density can be minimized when a material with lower thermal conductivity is used in a TEG. This study shows that the ZT enhancement of materials is not the highest priority in the production of a TEG for human body application, and material engineering to lower the thermal conductivity is required to reduce the optimum point mismatch problem. thermoelectric generator; human body heat; device simulation; first-principles calculation; material engineering 1  
[PERSON], [PERSON], [PERSON], H.  
perspective of device engineering, it is important to increase the output power. The maximum efficiency of power generation is one of the most frequently used indicators for device performance because it represents generated power per unit of heat flux. The equation of power generation efficiency is shown below [14; 15]. \[\eta=\frac{P}{Q_{in}}=\frac{T_{h}-T_{c}}{T_{h}}\cdot\frac{\sqrt{1+Z_{dev}T}-1}{ \sqrt{1+Z_{dev}T}+\frac{T_{c}}{T_{h}}}, \tag{1}\]  
where \(T_{h}\) and \(T_{c}\) are the temperatures at the hot and cold side of the device, respectively, and \(Z_{dev}T\) is the ZT of the device. As shown in the Equation (1), generated power from the device is increased with \(Z_{dev}T\) for constant input heat flux. In the practical situation, the \(Z_{dev}T\) changes depending on the contact resistance in the device [16], the thermal parasitic resistance [17], etc. All of these factors, however, are negligible in the ideal case and the material ZT is a more dominant factor that affects \(Z_{dev}T.\) If the condition is ideal and the N and P type of thermoelectric leg (TE leg) have the same properties, \(Z_{dev}T\) is exactly the same as material ZT [14]. Therefore, improving the performance of the thermoelectric material is the best way to improve the performance of the thermoelectric device. This is consistent with existing research on thermoelectric materials that focus on increasing material ZT. For the TEG placed on the human body, however, heat flux passing through the thermoelectric (TE) material is not constant. Thus, the output power of the device placed on the human body is not proportional to the power generation efficiency and ZT is no longer the only factor that increases the output power. [PERSON] et al. suggested a thermal resistance model of thermoelectric generation on the human body [18]. In the model, the thermal resistance outside of the device is large enough, thus the thermal resistance of the device is negligible and heat flux through the device changes as the material or the structure of the device changes. Various studies have confirmed that output power can be changed by structural variation even though the devices are made of the same thermoelectric material. The optimum conditions regarding device structure have been studied to generate maximum power density on the human body.