Novel Nano-Structured High-Performance Thermoelectric Materials and Devices

Abstract

Recent developments of high-performance nano-structured thermoelectric (TE) materials show that these materials have much higher conversion efficiencies than the state-of-the-art (SOTA) thermoelectrics. In these new quantum well (QW) materials, the carrier and barrier materials (in this case SiGe and Si) are confined in alternating layers less than 10 nm thick, and this confinement has been shown to result in greatly improved TE properties (Seebeck coefficient, electrical resistivity and thermal conductivity) leading to higher TE Figure of Merit, ZT, conversion efficiencies and Coefficient of Performance (COP) for cooling applications than for SOTA bulk thermoelectrics. From the most recent QW test data, ZTs greater than 3 at room temperature have been obtained which constitutes a significant improvement over the SOTA bulk thermoelectrics which have ZTs less than 1. The QW TE materials with ZTs greater than 3 lead to conversion efficiencies greater than 20 percent and higher COPs than for the SOTA vapor-compression cooling systems, which allow for much wider commercial applications, particularly in the applications such as the waste-heat recovery from truck engines and power plants, refrigeration and air conditioning, where the SOTA bulk TE modules were shown to be technically feasible but economically unjustified due to low conversion efficiencies. With higher efficiency QW materials, these applications become economically attractive. In a recent QW test, a conversion efficiency corresponding to 60 percent of the Carnot efficiency was measured and this is believed to be the highest such value ever measured for a TE material. For power generation applications, QW TE generators can be designed for capacities ranging from milliwatts to kilowatts and for cooling applications with capacities ranging from watts to several tons of refrigeration. This involves the transition from the nano scale QW thin films to macro scale TE devices. This paper discusses the status of the prototype QW TE generators and coolers being designed and fabricated, and the latest test results.