Tailoring the thermoelelctric properties of polycrystaline tin selenide

Abstract

Thermoelectric (TE) conversion is one of the globally focused research topic in the recent decades as being a solution for two major universal problems: energy demand, and environmental issue. The globally growing population and industries have been facing massive demand for energy and could reach about 30-40% in upcoming 20 years. As shown in Figure 1.1 almost 90% of the world’s energy depends on fossil fuel [1] and 70% of fuel is wasted in the form of waste heat. Search for cleaner and sustainable alternative energy source is highly motivated with the concerns of economy, demand of source and greenhouse gas emission. TE power generation uses waste heat as source. This source could be from a human body, cooking stove, automotive exhaust, industries, sunlight, CPUs etc, which can be properly channelized to reduce global warming and greenhouse gas emission. Al though viable technologies like solar energy, wind energy, bioenergy, and geothermal energy exist, thermoelectric conversion attracts attention as a solution for both power generation as well as environmental friendly nature due to its advantages like noise free, vibration free, lifetime maintenance free, and lack of moving part or chemical reactions during operations. Need less to say, there has been a monotonously increasing publications in the field of thermoelectrics with each passing year [2]. Thermoelectric effect can be defined as a direct conversion of heat to electricity. The operating principle is based on Seebeck effect, Peltier effect and Thomson effects. The first TE device was invented after a century from the discovery of Seebeck effect in 1826 [3]. Since then, it has found application as an implantable medical device, wearable device, automotive TE generators (TEGs), solar TE generators, radio isotope TE generators (RTGs), and TE coolers. It is also used as CPU micro thermo-siphon cooler, air coolers, refrigerators. TE conversion efficiency strongly depends on TE materials and can be quantified by a dimensionless quantity called figure of merit, ZT. The average ZT of TE materials currently in use is around 1, and this efficiency is too low to be competitor with conventional energy technology for commercial applications. The projected benchmark value for ZT is set to 3 [4], and to achieve this value, present research is being persued in two major directions, increasing the efficiency of existing materials and finding the new TE materials.