Light management for photovoltaics using surface nanostructures
Roberta De Angelis
Department of Industrial Engineering and INSTM, University of Rome ‘Tor Vergata’
New Materials For Optoelectronics webnemo.uniroma2.it
Credits:
M. Casalboni, R. Francini, P. Prosposito, F. De Matteis, L. D’Amico (Industrial Engineering Dept., Univ. of Rome ‘Tor Vergata’).
A. Di Carlo, D. Barettin, D. Colonna (Electronic Engineering Dept., Univ. of Rome ‘Tor Vergata’), E. Placidi (Physics Dept., Univ.
of Rome ‘Tor Vergata’), P. Steglich (TH Wildau).
NeMO Lab
New Materials for Optoelectronic
Development, fabrication and
characterization
of MATERIALS for applications in
1. Optics
2. Integrated optics
3. Optoelectronics
4. Energy
5. Sensors
Sol-gel materials
SiO2
TMOS + 4 H2O
Si(OH)4 + 4 CH3OH
Sol-gel materials
SiO2
TMOS + 4 H2O
Si(OH)4 + 4 CH3OH
Sol-gel materials
SiO2
TMOS + 4 H2O
Si(OH)4 + 4 CH3OH
il processo sol-gel: materiali ibridi
Hybrid sol-gel materials
methanol
GLYMO
SiO2
Film deposition
Spin coating
Dip coating
Cast coating
Samples: hybrid films
Chemical laboratory: synthesis of sol-gel materials by liquid precursors
Clean room: class 5000
Deposition: under laminar flow cabin class 100
Substrates: Corning glasses/silicon wafers/fused silica
Post-deposition treatment: densification in oven
Film thickness: 1  100 m
Film deposition by spin coating
H2O + acid
hydrolysis
Dip/spin
deposition
Heat
treatment
film
substrate
Metallic
alkoxides
in alcohol
solvents
Viscous
gel
Laser interference lithography (LIL)
• Photopatternable film exposed to UV laser light in
Lloyd-mirror configuration.
• Grating pitch P determined by laser wavelength λ and
angle of incidence θ in the range 300 nm - 2 μm.
• Grating depth D depends on material (sol-gel ≈ 300 nm,
commercial photoresist ≈ 1 μm).
sample
P

2  sin 
Diffraction gratings
pitch
P  sin i  sin  m   m
angle of incidence
diffraction angle
Soft Lithography and UV-nanoimprinting
Mold Fabrication steps by Soft lithography (SL)
1. Poly-Dimethyl-Siloxane (PDMS) silicone rubber is prepared using
Sylgard 184 from Dow Corning mixed in 10:1 ratio with its
initiator
2. It is poured on the AZ5214 master and held under vacuum to
remove air bubbles
3. It is cured, peeled off from the master and cut
14
UV Nanoimprinting
PDMS mold allows the realization of high-fidelity replicas of the master grating.
Film
Substrate
Replica
Substrate
Substrate
Substrate
PDMS mold can be reused up to 50 times
Light management
Dye Solar Cell - DSC
SQ2
I3 -
II3-
I-
Dye-sensitized TiO2
FTO-Fluorine doped Tin Oxide
Soda-lime float glass
Light management
Dye Solar Cell - DSC
1.75
Absorption (o.d.)
1.50
SQ2
1.25
1.00
0.75
0.50
0.25
0.00
500
550
600
Wavelength (nm)
650
700
1D Bragg grating nanostructuring
• Wavelength scale 1D periodic grating on dye sensitized solar cell (DSC).
• Grating parameters optimization by computational simulations (COMSOLTM).
• Novel solar cell design with 1D rectangular grating between the TiO2 layer and the electrolyte.
1D Bragg grating nanostructuring
without grating
700 nm TE polarized light
D. Barettin, A. Di Carlo, R. De Angelis, M. Casalboni and P. Prosposito. Opt. Express 20 (S6) A888-A897 (2012).
with grating
1D Bragg grating nanostructuring
+23.4% light absorption - grating depth 300 nm - pitch 500 nm
Soft Lithography and UV-nanoimprinting
Master AZ5214E obtained with
Laser Interference Lithography
Nanograting of Titania on
ITO substrate
Replica in PDMS
L. D’Amico, D. Colonna, R. De Angelis, M. Casalboni, F. De Matteis, A. Di Carlo, P. Prosposito. RSC Advances 4 (2014) 43828-43833.
SEM image
(ACK Dr. I. Cacciotti)
UV-nanoimprinting on DSC
2,0
Reflectance (%)
40
30
20
10
550
600
650
700
1,5
1,0
+15% JSC - +6% VOC - +31% η
0,5
500
750
550
Wavelength (nm)
650
700
750
with grating
Wavelength (nm)
Semi-transparent
3 μm thick TiO2 layer
Illumination conditions:
100 mW/cm2, AM 1.5G
600
2,5
25
2,0
20
IPCE (%)
0
500
J (mA/cm2)
Transmittance (%)
50
1,5
1,0
0,5
15
10
5
(a)
0,0
0,0
0,1
0,2
0,3
0,4
Voltage (V)
0,5
0,6
without grating
0
500
(b)
550
600
650
Wavelength (nm)
700
750
Light loss by reflection
n=1.0
n=1.5
BK7 glass
500 nm light
Moth-eye antireflection layers
Credit: Rick Cowen
D.G Stavenga, S Foletti, G Palasantzas, K Arikawa
Proc. R. Soc. B 2006
Crossed laser interference lithography
(c-LIL)
2.0µm
1.0µm
We obtained 2D
structures with pitch in
the range 500 nm -2 μm
and 100-200 nm in
height
Optical characterization of coatings
- Refractive index
- Thin film Tickness
- Transmittance & Reflectance
Variable angle spectroscopic ellipsometer (WVASE32 –
Woollam) - Spectral range 300 -1700 nm
Total transmittance & reflectance
measurement set-up
Nanocoating Transmission
grating depth 100 nm - pitch 1 μm
Total transmittance
0,06
0,97
Reflectance (s-pol, i=20°)
without coating
with coating
Transmittance
0,96
0,95
0,94
0,93
0,05
0,04
0,03
without coating
with coating
0,92
520
560
600
640
680
wavelength (nm)
720
760
800
0,02
400
500
600
700
Wavelength (nm)
800
900
Permanent staff:
Prof. Mauro Casalboni
Prof. Roberto Francini
Dr. Paolo Prosposito
Dr. Fabio De Matteis
Post-doc:
Dr. Roberta De Angelis
Ph.D student:
Dr. Liliana D’Amico
Thank you for your
attention.
DSC modeling
DSC modeling
Grating size optimization
Grating structural characterization
AZ 4521E - grating depth 200 nm - pitch 500 nm
TiO2- grating depth 130 nm - pitch 500 nm
ACK Dr. E. Placidi, Dr. I. Cacciotti