Hot Lattice or Thermoelectric Cells
A spin-off of theoretical work in 2003 has included
the application of the concept of energy-selective electron transport,
used in hot carrier solar cells, to thermoelectrics and thermionics.
This has led to the discovery of two types of equivalence that
simplify the description of this class of devices. Firstly, it
has been found that a thermoelectric or thermionic cell with electronic
transport restricted to a narrow energy range is equivalent to
the Hot Lattice cell concept reported previously.[see Annual
Report 2002] In the latter, the carriers in a Hot Carrier cell
are allowed to interact with the lattice resulting in a hot lattice.
Minibands limit electron flow through a quantum dot
superlattice (QDSL) to the energy where the effects of the opposing
thermal and electrochemical gradients cancel out. At this energy
electron transport is reversible and the thermoelectric power generator
would operate with Carnot efficiency if phonon heat leaks could
be avoided.
Carriers are extracted from the hot lattice over
a narrow selected energy range whilst maintaining insulation of
the hot lattice from the cold contacts. Secondly, it has also been
realised that the distinction between the diffusive transport of
a thermoelectric cell and the ballistic transport in a thermionic
cell becomes blurred when the carrier energies are restricted to
a narrow range, such that the two descriptions are equivalent.
A schematic of a QDSL based thermoelectric
power generator equivalent to a Hot Lattice cell.
Work in the Centre has shown that properly designed thermoelectric
nanomaterials such as quantum dot superlattices (QDSL) with narrow
peaks in their electronic density of states operate with an efficiency
approaching the theoretical (Carnot) limit in the absence of phonon
heat leaks. Expressions have been derived for the theoretical limiting
power and efficiency of thermionic power generators and refrigerators,
demonstrating that, in principle, increases in both power and efficiency
can be gained via energy filtering of electrons in these devices. |
