Moving to low dimensional structures for thermoelectric harvesting

Dr Jeremy Watling from the University of Glasgow recently presented at the "Intelligent Harvesting Workshop" in London, covering their progress with Thermoelectric Energy Harvesters.

 

Thermoelectric energy harvesters consist of two materials - a n and p type semiconductor, arranged between a temperature gradient. Provided there is a temperature gradient power is generated. However, when the two materials are used in their 3 dimensional bulk form there is a limit to the performance of the thermoelectric energy harvester - known as the Wiedemann-Franz limit. The performance is typically shown as ZT - "the figure of merit", and up to about 1 is the theoretical limit in a 3D bulk material. Double it to 2 would see the efficiency of the energy harvester more than double.

 

To break the limit, 2D structures have been proposed and a ZT of 2.4 has now been demonstrated, with up to 10 theoretically possible. This equates to a much more efficient energy harvester, resulting in more power produced in the same area and therefore opening it to more markets. Bi₂Te₃ and Sb₂Te₃ are used in superlattices which show a ZT of over 2. In a 3D arrangement bulk Bi₂Te₃ has a fundamental limit of about ZT=1.

 

Now the university are looking to improve this by exploring structures that move to being closer to one dimension such as quantum wires and quantum dots. These offer higher performance because in each case phonon transport and propogation is reduced.

 

 

The university is working under a EU project with partners in Italy, Austria and Switzerland to explore using silicon in thermoelectrics. Si/SiGe lattices demonstrate ZT 1.1, where bulk Si is just 0.00031. Si nanowires show improvement of more than 600 times that of bulk silicon. Silicon has been chosen because it is an abundant material, and its fabrication, processing and integration are well known. Indeed, the university see mass production possible by using flip chip attachment.

 

The university of Glasgow have a 750m² cleanroom in which they are progressing this work. For more information see www.zero-power.eu .

 

 

For more read : Energy Harvesting and Storage for Electronic Devices 2010-2020

 

and attend Energy Harvesting & Storage and Wireless Networks & RTLS Europe 2011