Light management in
nanostructured solar cells
Albert Polman
Center for Nanophotonics
FOM-Institute AMOLF
Amsterdam, The Netherlands
Collaborators
Piero Spinelli
Jorik van de Groep
Claire van Lare
Vivian Ferry
Frank Lenzmann
Wim Soppe
ECN
AMOLF
UU
Ruud Schropp
Philips
Marc Verschuuren
CALTECH
Vivian Ferry
Harry Atwater
Outline
4. Solving Voc < Eg
1. Light coupling
2. Light trapping
3. Current collection
5. Towards 70% efficiency
The scattering solar cell
• Integrate nanoscatterers in
the solar cell
• Couple incident light to
in-plane waveguide modes or
localized modes
Nature Mater. 9, 205 (2010)
Light scattering from nanoparticles
Large scattering
cross section
Strong forward
scattering
4%
air (n=1.0)
Si (n=3.5)
96%
Light scattering from nanoparticles
Large scattering
cross section
All light captured
Ag nanoparticles; scattering vs. Ohmic losses
Albedo → 1 for D > 150 nm
Albedo
Ag particle in air
50 nm
Absorption ~ r3
Scattering ~ r6
Ag
For Ag particles
>150 nm
nearly all light is
scattered
For 50 nm particles
50% of the light is
absorbed
in the metal
Substrate Conformal Imprint Lithography
PDMS Stamp
Thin glass
PDMS stamp (6”) on 200 µm AF-45
glass
1
µm
Full-wafer soft nano-imprint
• Flexible rubber on thin glass
• Conform to substrate bow and roughness
• No stamp damage due to particles
Marc Verschuuren
PhD thesis, Utrecht University (2010)
Total reflectivity (specular+diffuse)
Experimental data
Piero Spinelli
Nano Lett. 11, 1760 (2011)
Ag nanoparticle coated thin-film a-Si cells
10% enhanced photocurrent
350 nm i-a-Si:H
120 nm ZnO, 80 nm ITO
Cell area: 0.13 cm2
Ag particles:
pitch 500 nm
height 120 nm
diameter 240 nm
Claire van Lare, Wim Soppe
Transparent resonant conductive plasmonic networks
2 µm
Ag wire network fabricated with
e-beam lithography
width: 45-110 nm
height: 60 nm
Jorik van de Groep, Piero Spinelli
Optical transmission measurements
Metal-insulator-metal
plasmons
Localized
plasmons
Surface
plasmons
Jorik van de Groep, Piero Spinelli
Optical transmission measurements
ITO:
Pitch:
w=45 nm
Thin wire networks
are better than
80 nm ITO
Jorik van de Groep, Piero Spinelli
Electrical resistance measurements
w=45 nm
• Four-Point-Probe
• Ohmic behavior
Jorik van de Groep, Piero Spinelli
Tradeoff between transmission and resistance
• Dilute network better than ITO
• Optimum for smallest w and small pitch
Jorik van de Groep, Piero Spinelli
Combining light trapping and current collection
Jorik van de Groep, Piero Spinelli
Metallic vs. dielectric scatterers
1
1
E2
2
E2
2
Qscat
Cscat
=
C geom
ε − εm
• Metal NP: plasmonic resonance α = 4πε 0 R
ε + 2ε m
• Dielectric NP: Mie (geometrical) resonance
3
Piero Spinelli
Si surface Mie scatterers
sphere
cylinder
In cylindrical particles light leaks into
the substrate and resonance broadens
Nature Comm. 3, 692 (2010)
Si
nm
300
Light incoupling using Si nanoparticle array
Weakly coupled
Mie scatterers
Near-perfect anti-reflection coating!
5
4
200
3
100
2
0
1
-200-100 0 100 200 nm
0
Si3N4
Si
Si
radius = 125 nm
height = 150 nm
pitch = 450 nm
Si3N4 thickness = 45 nm
Piero Spinelli
Nature Comm. 3, 692 (2012)
Black silicon using leaky Mie resonances
Average reflectivity: 1.3%
Si3N4
Si
Si
Piero Spinelli
Nature Comm. 3, 692 (2012)
The scattering solar cell
• Integrate nanoscatterers in
the solar cell
• Couple incident light to
in-plane waveguide modes or
localized modes
Nature Mater. 9, 205 (2010)
Back contact nanopatterns on ultrathin a-Si:H solar cells
ITO
a-Si:H
ZnO:Al
500 nm
Ag
sol-gel
90-160 nm thick
a-Si:H cells
Vivian Ferry, Claire van Lare
Nano Lett. 11, 4239 (2011)
Ultra-thin Si solar cell: 90 nm i–layer light
enhanced red and blue response
blue Simulation
Experiment
400 nm
pitch
Asahi
500 nm
500 nm
pitch
pitch
400 nm
400 nm
pitch
pitch
flat
flat
flat
random
red
Vivian Ferry, Claire van Lare
Nano Lett. 11, 4239 (2011)
Outline
4. Solving Voc < Eg
1. Light coupling
2. Light trapping
3. Current collection
5. Towards 70% efficiency
Thermodynamic energy losses in PV energy conversion
Nature Mater. 11, 174 (2012)
Light management structures for
reaching ultra-high efficiency
Nature Mater. 11, 174 (2012)
Multi-junction solar cell
Nature Mater. 11, 174 (2012)
Triple-junction tandem solar cell layer geometry
Record efficiency: 43.5 %
From: Richard King (Spectrolab)
Integrated parallel multi-junction solar cell
Light
management
Nature Mater. 11, 174 (2012)
Scalable inexpensive large-area layer transfer and
nanofabrication techniques
Nature Mater. 11, 174 (2012)
Outline
4. Solving Voc < Eg
1. Light coupling
2. Light trapping
3. Current collection
5. Towards 70% efficiency
www.erbium.nl
Nature Mater. 11, 174 (2012)