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Photonic Crystals for Thermophotovoltaic
Applications
LEES
Ivan Celanovic, Francis OSullivan, Natalija
Jovanovic, Prof. J. Kassakian, Dr. T. Keim and
Prof. D. Perreault Massachusetts Institute of
Technology, Laboratory for Electromagnetic and
Electronic Systems
Fig. 5 a) Top view and b) cross sectional
view of 2D PhC selective emitter. A metal-coated
array of low-permittivity holes can be modeled as
an array of parallel-plate wave guides. The
propagating modes are determined by the
dimensions of the wave guide. By controlling the
lateral dimensions of the wave guide array it is
possible to define the emitters selectivity,
while increasing the depth of each feature
enhances the selective properties of the
structure. The 2D selective emitter structures
are fabricated using advanced lithographic and
reactive ion etch techniques. Testing and
characterization In order to test the
selectivity of the 2D emitter structures a high
temperatures apparatus has been designed (Fig.
6). The 2D PhC structures are heated to operating
temperature in vacuum and the emitted spectrum is
measured using a Fourier transform infrared
spectrometer. Fig. 6 High temperature
emittance testing apparatus used for emitted
spectral characterization of 2D PhC structures.
Introduction Thermophotovoltaic (TPV) devices
statically convert heat into electricity using
photovoltaic (PV) diodes. The system consists of
an emitter, a spectral control component and a PV
diode (as in Fig. 1). Project Goals Improve
performance of TPV systems using photonic
crystals (PhC) as spectral control components
(filters and selective emitters). Develop models
for, and an understanding of the radiation and
filtering phenomena occurring in
thermophotovoltaic (TPV) and micro-thermophotovolt
aic (MTPV) systems using photonic crystals (In
MTPV systems the separation between the emitter
and PV diode is less than the radiation
wavelength). Experimentally verify the PhC
component performance in a TPV system. Modeling
A fuel, e.g. gasoline, is used to heat an
emitting surface (BB in Fig. 1) to approximately
1500K, and the emitter in turn radiates
high-energy photons. Fig. 1 TPV
system with a front side dielectric stack filter
(layers 1 to n), where the thickness of the gap
(layer 0) between the emitter (BB) and the
dielectric stack is Lo. The PV diode extends to
?. The amount of power generated by a TPV system
with an emitter temperature of TBB can be
calculated using the ideal thermodynamic model
1,2 where ?g denotes the electronic
bandgap of the photodiode, TPV the diode
temperature, nBB the refractive index of the
blackbody and nPV the refractive index of the
diode, V is the photodiode voltage, and e is the
electron charge. T13 and T31 are the sum of the
TE and TM mode transmittances from the emitter to
the photodiode and are functions of frequency ?,
the angle of incidence ? and the distance between
the emitter and photodiode Lo . 1D photonic
crystals Two types of 1D photonic crystals have
been designed, - a modified quarter wave stack
filter, and genetic algorithm optimized
dielectric stack filter. The normal
transmittance of these filters is shown in Fig. 2.
(a)
(b) Fig. 2
Transmittance at normal incidence for a)
modified quarter wave stack and b) genetic
algorithm optimized dielectric stack
filters. Fig. 3 a) TPV efficiency with
different filter configurations as a function of
emitter temperature and b) MTPV efficiency for
different gap widths with and without a filter
for fixed emitter temperature (1500
K). Fig. 4 SEM and transmittance of
Si/SiO2 TPV dielectric stack filter fabricated
using low pressure chemical vapor deposition
(LPCVD) techniques. 2D photonic crystals 2D
photonic crystal structures which act as
selective thermal emitters are being developed.
The introduction of a pattern onto the surface of
an emitter modifies its emission properties. For
the purposes of this project a circular hole
hexagonal pattern has been chosen. (commonly
referred to as honeycomb), because of its
selective properties for both transverse electric
(TE) and transverse magnetic (TM) modes.
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Transmittance
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Transmittance
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References 1 I. Celanovic, F. OSullivan, M.
Ilak, J. Kassakian, D. Perreault, Design and
Optimization of One-Dimensional Photonic
Crystals for Thermophotovoltaic Applications,
Optics Letters, Accepted for publication January
2004. 2 M. Zenker et. al., Efficiency and
Power Density Potential of Combustion-Driven
Thermophotovoltaic Systems Using GaSb
Photovoltaic Cells," IEEE Transactions on
Electron Devices, Vol. 48, No.2, February
2001. Acknowledgements Robert DiMatteo and Dr.
Marc Weinberg, Charles Stark Draper
Laboratories. Shoji Akiyama and David Danielson,
Department of Material Science. This work is
sponsored by the MIT/Industry Consortium on
Advanced Automotive Electrical/Electronic
Components and Systems