Shanhui Fan Ginzton Laboratory and Department of ... · Ginzton Laboratory and Department of...
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Control of thermal radiation for energy applications
Shanhui Fan Ginzton Laboratory and Department of Electrical Engineering
Stanford University
Thermal radiation: an ubiquitous aspect of nature Sun (6000K)
Outer Space (3K)
Human Body (~ 310K)
Tungsten light bulb (~3000K)
Conventional view of a blackbody
(Well, it is black.)
2000K
• Typically strongly absorbing/emitting in both the solar and the thermal wavelength range
• Broad-band, broad-angle absorption.
Narrow-band thermal radiation from gold antenna
X. Liu et al, PRL 107, 045901 (2011)
w=0.4µm, l = 1.7µm
Gold
L. Zhu et al, APL 102, 103104 (2013)
Daytime radiative cooling
emissivity
1
0
Wavelength (micron)
8 13
• A mirror in the solar wavelength range. • “black” in the 8-13 micron window.
E. Rephaeli, A. Raman and S. Fan, Nano Letters 13, 1451 (2013).
Radiative access to the universe
http://www.astronomy.ohio-state.edu/~pogge/Ast161/Unit5/atmos.html
300K Blackbody Spectrum
Stanford daytime radiative cooling experiment
A. Raman, M. Anoma, L. Zhu, E. Rephaeli, and S. Fan, Nature 515, 540 (2014).
Sample: 8 inch wafer
Daytime Cooling Experiment: Results
A. Raman, M. Anoma, L. Zhu, E. Rephaeli, and S. Fan, Nature 515. 540 (2014).
Towards Fundamental Limit of Radiative Cooling
Z. Chen, L. Zhu, A. Raman, and S. Fan, Nature Communications (2016, in press)
(Supported by a GCEP project)
Ultra-High Performance Continuous Radiative Cooling Over Day and Night
Z. Chen, L. Zhu, A. Raman, and S. Fan, Nature Communications (2016, in press)
Indoor cooling
• In a typical office environment, 40-60% of heat dissipation of human body is through thermal radiation.
• Controlling thermal radiation is therefore important for indoor cooling.
Design textile for indoor cooling application
Normal textile (such as cotton)
Visible Thermal IR
Blocks both IR and visible
Cooling textile
Visible Thermal IR
Blocks visible, but allow IR to go through
Nanoporous polyethylene (PE)
P. Hsu et al, Science 353, 1019 (2016). collaboration with Prof. Y. Cui’s group at Stanford
Visible and thermal spectra
Wavelength (micron) Tr
ansm
issi
on
Tran
smis
sion
Wavelength (nm)
Visible spectrum Thermal infrared spectrum
P. Hsu et al, Science 353, 1019 (2016). collaboration with Prof. Y. Cui’s group at Stanford
Shockley-Queisser Limit
P
N V
Sun Semiconductor PN junction
Photons with energy below band gap are not absorbed by the semiconductor Photons above the band gap are absorbed, but each photon only contributes part of its energy.
30-40% efficiency limit depending on concentration
Solar thermophotovolatics
P
N
Broadband absorber Selective emitter
Compress the spectral bandwidth of light that is incident on the PV cell
R. M. Swanson, Proc. IEEE 67, 446-447 (1979) S. Fan, Nature Nanotechnology 9, 92 (2014).
Solar Thermo-Photovoltaics (STPV)
Sun (Ts = 6000K)
P
N
Intermediate Absorber and Emitter (Ti = 2544K)
Solar Cell (Te = 300K)
The sun to the intermediate
The intermediate to the cell
P. Harder and P. Wurfel, Semicond. Sci. Technol. 18, S151 (2003);
Solar to electric energy conversion of 6.8%
D. M. Bierman, Nature Energy 1, 16068 (2016)
The record today in solar thermophotovoltaics
Our GCEP Project
6000K
P
N
2544K 300K
To develop structures and materials for emitters that are stable at high temperature. To achieve high efficiency cell specifically tailored for TPV applications.
PIs: Shanhui Fan, Mark Brongersma, and James Harris
Enhancing stability of thermal emitter under high temperature
Tungsten inverted opal
No thermal treatment 1000oC
1200oC 1400oC
1 micron
K. Arpin, S. Fan and P. Braun et al, Nature Communications 4, 2630 (2013).
~3000oC
W
SiC
Y. Guo and S. Fan, Optics Express (2016, in press).
Flat Tungsten Thermal Emitter With Spectral Tailoring
Previous work: world-record multi-junction cell
Harris group
Vapp
Jout
top bottom Combined
Voc,tandem=Voc,top+Voc,mid+Voc,bottom
Jsc,tandem= min{Jsc,top, Jsc,mid, Jsc,bot}
middle
GaInNAsSb
GaAs
InGaP
Solar Junction record efficiency 44%
In0.2Ga0.8As0.18Sb0.82 emitter
GaSb BSF
GaSb window n+
n
p
p+ In0.2Ga0.8As0.18Sb0.82 base
In0.53Ga0.47As emitter
In0.53Ga0.47As base
InP BSF
InP window n+
n
p
p+
High-efficiency low band gap cell for TPV applications
Harris group