Doing the Work: Farzaneh Afshinmanesh, Ed Barnard, Linyou Cao, Pengyu Fan,
Kevin Huang, Ragip Pala, Jon Schuller, Min-Kyo Seo, Isabel
Thomann, David Schoen, Alok Vasudev,.
Speaking: Mark Brongersma @ Stanford University
Thank you: McGehee Group
Yi Cui Group
Bruce Clemens group
Funding: GCEP, KAUST, DOE, AFOSR
Plasmonics and Mie Scattering
for Solar Energy Harvesting
Electronics
1st transistor and IC
Current technology
Linyou Cao et al., Nano Lett., 2649, 10 (2010)
Semiconductor nanostructures
Semiconductor wafers
Optical Properties Semiconductors
30 nm 185 nm
Optical Properties Metals
Halas Group @ Rice
Metallic nanostructures
Metal wire
E
New Optical Properties Naturally Emerge at the Nanoscale
Solar
?
Measurement of the light absorption in a germanium nanowire
Optical Properties of a High Index Semiconductor Nanowires
The measurement
Challenge: Wires are small compared to the diffraction limit……
L. Cao, J.S. White, J-S Park, J.A. Schuller, B.M. Clemens, and M.L. Brongersma, Nature Mat. 8, 643-647 (2009).
Solution: Light absorption in designed semiconductor nanostructures is naturally enhanced
(With Bruce Clemens Group)
P
ho
tocu
rrent (
a.u
.)
Wavelength (nm)
Photocurrent shows strong enhancement peaks in the photocurrent
Spectral Photocurrent Response of Ge nanowires
Spectral photocurrent measurements on Ge nanowires of different radius
L. Cao, J.S. White, J-S Park, J.A. Schuller, B.M. Clemens, and M.L. Brongersma, Nature Mat. 8, 643-647 (2009).
R=10 nm R=25 nm R=110 nm
Optical resonances give rise to absorption enhancements
Spectral Photocurrent Response of Ge Nanowires
Mie theory can quantify the absorption efficiency
10 nm radius
25 nm radius
110 nm radius
Simulated
Experiment
L. Cao et al., Nature Mat. 8, 643-647 (2009).
Qabs = σabs/σgeom = optical size/physical size
Intuitive resonance condition:
mλeff = 2πr
Simple optimization procedure
Engineering Better NW Photodetectors and Solar Cells
10 nm radius
25 nm radius
110 nm radius
Simulated
Experiment
1
2
3
4
1
2
3
4
Tunable Optical Properties of Si Nanostructure Arrays
Si nanowire arrays can be used to produce structural colors
1µm
170 nm width
200 nm width
240 nm width
300 nm width
Linyou Cao et al., Nano Lett., 2649–2654, 10, 2010.
Every High-index Semiconductor Nanostructure Exhibits Optical Resonances
L. Cao et al., Nano Lett., 10, 439–445 (2010).
Resonant enhancements in light absorption occur in a wide variety of sub- shapes
Example: one-wavelength or dipolar resonances in Si nanowires of different cross sectional shape
Similar behavior was observed for CIGS, Ge, CdTe, aSi, and GaAs.
130 nm
t=130nm
Patterned a-Si with 130 nm beams
Unpatterned a-Si film
• Simple patterning step can improve efficiency by 25%..after removing 50% of the material !
Application to Solar Cells
A simple thought experiment….
t=130nm
Performance of a “cell”
Linyou Cao et al., Nano Lett., 10, 439–445 (2010)
s
Patterning Transparent Conductive Oxides (TCOs)
Alok Vasudev et al, Optics Express 20, A385 (2012)
TCO electrodes are present on many types of solar cells
ZnO Nanobeam Array Outperforms Optimized Planar ZnO layer
300 nm aSi solar cell with either a 240 nm ZnO thick film or a 240nm x 240 nm beams
ZnO
Transparent Electrodes: A Great Use of Metallic Nanostructures
Lee, Peumans et al. Nano Letters 8, 689 (2008)
Wu et al. Nano Letters 10, 4242 (2010)
Plasmonic Nanowelding of a Ag Nanowire Mesh (Led by Erik Garnett in McGehee, Cui, and Brongersma Groups)
Ag nanowires synthesized
by polyol, chemical process
Regular furnace anneal
New approach: plasmonic nanowelding
500 nm
200 nm
Tungsten halogen lamp
I = 30W/cm2
Erik Garnett et al., Nature Materials (2012 )
500 nm
TEM Before and After Plasmonic Nanowelding
50 nm
Conclusion: Bottom nanowire always recrystalizes onto top nanowire at the junction
After welding: Twinning defects continue through the junction only for top nanowire
50 nm
Before welding After welding
As synthesized: Ag nanowires feature a pentagonally twinned crystal structure
Erik Garnett et al., Nature Materials (2012 )
Before melting : 2 nm gap
After melting: – 2 nm overlap
Self-limited Plasmonic Nanowelding Simulations
10
0 n
m
Erik Garnett et al., Nature Materials (2012) and consistent w work by Nordlander, Aizpurua, Garcia de Abajo,…
Heat generation focused in bottom wire near junction
+
+ + - - -
E
Heat generation is self-limited !
gap
k
+ + - - + - - - + - -
Junction resistance is similar to the single wire resistance
Resistance of Welded Wires
Erik Garnett et al., Nature Materials (2012 )
Determining the resistance of two welded Ag nanowires
We can measure single on resistance is similar to the wire resistance
2 µm
Electrical and Optical Properties of Welded Wires
IV curves demonstrate cell survives
welding and improves upon welding
Nanowire meshes can be welded onto
low thermal budget organic solar cells
Erik Garnett et al., Nature Materials (2012)
Ag nanowire mesh on organic cell IV Characteristics semitransparent
Electrical and Optical Properties of Welded Wires
NW meshes with reasonable sheet-conductivities can be welded on heat sensitive saran wrap
Erik Garnett et al., Nature Materials (2012 )
RS = 580 /
Welding nanowire meshes on flexible substrates
Summary and Conclusions
New plasmon science facilitates self-limited welding of Ag NW transparent electrodes
From fundamental process to single NW conduction measurements to first solar cells
50 nm 2 µm
High index semiconductor nanostructures exhibit strong light matter inteaction
From fundamental process to single NW photocurrent measurements to new solar cells
Optical Nanowelding: A Plasmonic Effect
Heating is most effective when E-field is polarized to enable surface plasmon excitation
Heating occurs near the surface plasmon resonance frequency of an individual Ag nanowire
Can Metallic Structures be Used as Transparent Electrodes ?
Lee, Peumans et al. Nano Letters 8, 689 (2008)
Wu et al. Nano Letters 10, 4242 (2010)
Plasmonic Nanowelding of a Ag Nanowire Mesh (Erik Garnett in McGehee, Cui, and Brongersma Groups)
Ag nanowires synthesized
by polyol, chemical process
Regular furnace anneal
New approach: plasmonic nanowelding
500 nm
200 nm
Tungsten halogen lamp
I = 30W/cm2
Erik Garnett et al., Nature Materials (2012 )
500 nm
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