Structural Design And Performance Optimization Of Bismuth Telluride Based Thermoelectric Devices

To date,the increasing energy consumption of chemical fuels around the world results in energy crisis and environmental pollution.Thus,the alternative utilization of eco-friendly and renewable clean energy resources has become a critical solution for sustainable development of society and economic growth.The thermoelectric conversion technology can directly convert the waste heat dissipated from human activities into electricity through the Seebeck effect of thermoelectric materials.Reversely,the Peltier effect can also transfer input electricity into heat absorption and release.Currently,the market diversification has put forward urgent demands for clean energy,durable and stable power supplies,high power electronic devices,and flexible electronics.Flexible electronics and thermoelectric devices can be integrated by conforming onto the surface morphology of the environmental heat source.The waste heat from the heat source can be directly harvested into electricity by flexible thermoelectrics.Consequently,the flexible thermoelectrics attracted tremendous attention in recent years.Owing to the performance matching at room-temperature,Bi2Te3-based thermoelectric materials have been widely used for power generation and refrigeration near room temperature in academy and industry.From a view of materials engineering,the p-type material Bi Sb Te and the n-type material Bi Te Se were fabricated by hot-pressing and crystal-pulling,respectively.The maximum thermoelectric figure of merit ZT is around 1.1 and 0.9,respectively.Ceramic substrates are used to fabricate the flat thermoelectric devices with 24 pairs of p-and n-type Bi2Te3-based thermoelectric legs.The dimension of the device is 25 mm × 19 mm × 2.38 mm and the maximum output power of 0.46 W,as well as energy conversion efficiency of 5.56% are achieved under 130 K temperature difference.In terms of flexible thermoelectrics,conventional approaches are mainly focused inorganic thermoelectric materials,and the devices are fabricated with flat-plate ceramic substrates to maintain the high mechanical performance and stability.However,there is an increasing demand for flexible and wearable electronic devices in daily life and industrial applications,which also promotes continuous research and development of flexible thermoelectrics.Compared with inorganic bulk thermoelectric materials,the thermoelectric performance of typical flexible thermoelecric materials are relatively poorer than that of inorganic bulk materials.In this work,the mathematical geometry algorithm is rationally introduced into flat-to-flexible device design and optimization of flexible thermoelectrics with inorganic thermoelectric materials.This flexible thermolectric devices(f-TED)have both high thermoelectric performance and high flexibility.Inspired by the cyclotomic rule,artificial cracks and selected substrate cutting methods are utilized,a fully flexible inorganic thermoelectric device with bending angle from 0 to 360 degrees isachieved.In addition,the interfacial metal-semiconductorcontact behavior is design and fabrication method of the flexible inorganic thermoelectric device introduces low contact resistance.Based uponexperimental measurement,numerical simulation and contact resistance model analysis in this work,the energy conversion efficiency and output power under various temperature differences and artificial cracks are investigated.Noticeably,the bismuth telluride-based f-TED with a 360-degree full flexible bending can generate normalized maximum power density of 19.6 m W/cm2 and the power conversion efficiency of 3% under 53 K temperature difference(near room temperature).These results provide the feasibility of using f-TED for energy generation and thermal management of heat sources or heat sinks with different surface curvatures,especially in self-powered wearable mechatronic devices and flexible chip cooling in the Internet of Things(IoT).