Key issues in development of thermoelectric power generators: High figure-of-merit materials and their highly conducting interfaces with metallic interconnects

Thermoelectric generators (TEGs) are devices that convert temperature differences into electrical energy, which work on the thermoelectric phenomena known as Seebeck effect. The thermoelectric phenomena have widely been used for heating and cooling applications, however electric power generation has only been limited to niche applications e.g. thermoelectric power generators for space missions. TEG provides one of cleanest energy conversion method, which is noise-free, virtually maintenance free and can continuously produces power for several years under ambient conditions. In recent years, energy generation through thermoelectric harvesting has witnessed an increased interest for various applications, including tapping waste heat from the exhaust of vehicles, from industries, etc. The development of an efficient TEG requires the fulfillment of several factors, which includes availability of n- and p-type thermoelectric materials with high figure-of-merit (ZT), preparation of ohmic contacts between thermoelements and metallic interconnects and management of maximum heat transfer though the device. In this review, we present an overview on the various aspects of device development i.e. from synthesis of high ZT thermoelectric materials to issues & design aspects of the TEG. A discussion on the various strategies employed to improve ZT is described. It is shown that a ZT of >2 has widely been reported in literature, which has been achieved either by enhancing the power factor and/or reducing the thermal conductivity of the materials. A discussion on the status on the development of TEGs suitable for operation at different temperature ranges i.e. <250 degrees C, 250-650 degrees C and >650 degrees C is presented. Finally, the cost of fabrication of TEGs and their potential applications in different areas have been highlighted. (C) 2016 Elsevier Ltd. All rights reserved.