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.

Strong angular emission from SiC grating

Greffet et al, Nature 416, 61 (2002)

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

Emissivity of the photonic cooler

Strong solar reflection Strong and selective thermal emission

Rooftop Setup

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

Thermal Metasurfaces for Full Control of Thermal Radiation

Brongersma group

Phase-gradient thermal metasurface for the focusing of the thermal radiation

Brongersma group

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

Summary Sun (6000K)

Outer Space (3K)

Human Body (~ 310K)

Tungsten light bulb (3000K)

Control of thermal radiation offers tremendous opportunity for energy applications.