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ECE 695Numerical Simulations
Lecture 30: Finite-Difference Time Domain in MEEPPV
Prof. Peter Bermel
March 31, 2017
Si thin film
2 μm
PhC thin film
2 μm
silicon
aluminum
Wafer cell
200 μm
silicon
glass
Example: Simulating Si PV Absorption
Absorbed
Lost energy
Absorbed
3/31/2017ECE 695, Prof. Bermel 2
Different Geometric Light Trapping Approaches for Commercial mc-Si Cells
M.J. Keevers et al., “10% Efficient CSG Minimodules,”
Treatment #1 Sand blast Abrasion etch Bead coat
Treatment #2 HF etch HF etch (used in our samples)
Feature
depth
10-100 mm 500 nm 500 nm
Feature width 10 mm 1-5 mm 500 nm
3/31/2017ECE 695, Prof. Bermel 3
Correlated Randomness
Combine periodicity with texturing in systematic fashion
A.N. Bloch & P. Sheng, US Patent 4,683,160 (1987)
X. Sheng et al., Opt. Express 19, A841 (2011)
Combine gratings for each wavelength
inhomogeneous homogeneous
ECE 695, Prof. Bermel3/31/2017 4
Correlated Randomness in 2D
For n=3.46 and 33% bandwidth (e.g., 500-700 nm)
ECE 695, Prof. Bermel3/31/2017 5
Angle-Sensitive Solar Absorbers
X. Sheng et al., Opt. Express 19, A841 (2011)
X. Wang et al., "Approaching the Shockley-Queisser Limit in GaAsSolar Cells", IEEE J. Photovolt. (2013).
ECE 695, Prof. Bermel3/31/2017 6
-
From flat to totally random structures via correlated random textures
Keevers, M. J., et al. “10% efficiency CSG minimodules.” Proceedings of the 22nd European Photovoltaic Solar Energy Conference. (2007).
Higher correlation Lower correlation
Experimental absorption versus simulated absorption
L. T. Varghese, Y. Xuan, B. Niu, L. Fan, P.
Bermel, and M. Qi, “Enhanced photon
management of thin-film silicon solar cells using
inverse opal photonic crystals with 3d photonic
bandgaps,” Advanced Optical Materials 1, 692–
698 (2013).
Experiment Simulation (3D QCRF-FDTD) SiO2
Silver
c-Si
ITO
H. Chung, K-Y. Jung, X. T. Tee, and P. Bermel,
"Time domain simulation of tandem silicon solar
cells with optimal textured light trapping enabled
by the quadratic complex rational function," Opt.
Express 22, A818-A832 (2014).
MEEPPV: https://nanohub.org/tools/meeppv
MEEPPV: https://nanohub.org/tools/meeppv
Computational Set-up
• Thickness of film = our experimental samples (1.47 mm)
• Four geometries tested
• Random texturing:
– Uniform height distribution over 500 nm
– Distance between features varies
• Photonic crystal:
– Reflection captured by metal
– Diffraction captured by grating (optimized for this thickness)
texturing silicon metal
grating
3/31/2017ECE 695, Prof. Bermel13
Varying spacing between features
5 periods
10 periods
20 periods3/31/2017ECE 695, Prof. Bermel
14
Propagation of Light in Planar Geometry
Light In
Silicon
Metal
backing
3/31/2017ECE 695, Prof. Bermel 15
Propagation of Light in Textured Geometry (no backing)
Light In
Silicon
Texturing
3/31/2017 16ECE 695, Prof. Bermel
Propagation of Light in Textured Geometry + Metal Grating
Light In
Silicon
Texturing
3/31/2017 17ECE 695, Prof. Bermel
Calculated Absorption Spectrum for 2 mm mc-Si
Aluminum: 12.08% efficiency
3D PhC: 16.32% efficiency
DBR + 2D grating: 14.97% efficiency
P. Bermel et al., Opt. Express 15, 16986 (2007)3/31/2017 18ECE 695, Prof. Bermel
Efficiency Enhancement of Period Structures
For optimized parameters, 2D grating efficiency enhance-
ment ranges from 7% at 128 mm up to 35% at 2 mm
ECE 695, Prof. Bermel3/31/2017 19
Thin c-Si Solar Cell Designs Incorporating Plasmonics
EM monitor
scattered light
diffractedlight
transmitted light (parasitic)
SPP (parasitic)
Active Si material
Air
Flat Ag back reflector
ZnO Ag NPTextured Ag back reflector
Active Si material
Air
EM monitor
scattered light
diffractedlight
transmitted light (parasitic)
SPP (parasitic)
EM monitor
scattered light
diffractedlight
transmitted light (parasitic)
SPP (parasitic)
Random texturing on the front and back surfaces, deposited conformally
Periodic (grating-like) texturing on the front and back surfaces, deposited conformally
Random texturing on the front surface combined with a back plasmonicnanoparticle
Plasmonics can double path length from ideal light trappingK. Catchpole & A. Polman, Appl. Phys. Lett. 2008, 93, 191113.
ECE 695, Prof. Bermel4/14/2015
Simulation Methodology
t = t + ∆𝒕
Update E, D, H field
over volume
Start
t > t_max EndYesNo
t = 0
Calculate 𝑼𝒍𝒐𝒔𝒔 over
frequency over
volume
𝑶(𝑵𝟑)
𝑶(𝑵𝟒)
t = t + ∆𝒕
Update E, D, H field
over volume
Start
t > t_max EndYesNo
t = 0
Calculate 𝑼𝒍𝒐𝒔𝒔 over
frequency over
surface
𝑶(𝑵𝟑)
𝑶(𝑵𝟑)
> ≈
Volume-Integrated Finite-Difference Time Domain Method
Flexible Flux Plane Finite-Difference Time Domain Method
Haejun Chung, K.Y. Jung, and Peter Bermel, “Understanding light trapping in nano-textured
silicon thin-film solar cells by a novel simulation approach” Opt. Express (2015, submitted)
ECE 695, Prof. Bermel4/14/2015
Simulation Methodology
𝒏𝒂,𝟏,𝟏
x y
z
Yee’s
unit cell
𝒏𝒃,𝟏,𝟏
𝑺𝒂,𝟏,𝟏
𝑺𝒃,𝟏,𝟏
Flexible flux planes offer rapid frequency-sensitive integration of parasitic losses.
ECE 695, Prof. Bermel4/14/2015
Periodically Textured Cells: Theory and Experiment
200nm𝜆 = 800nm
ZnOp/c-Si
i/c-Si
Ag
𝐥𝐨𝐠𝟏𝟎 𝑬𝟐
𝟎
𝟏
𝟐
𝟑
𝟒
𝟓
𝟔
𝟕
𝟖
Detailed comparison of experimental and simulated total absorption, and the parasitic
component
Electric field energy distribution, with enhancement observed near the Ag/ZnO
interface
Haejun Chung, K.Y. Jung, and Peter Bermel, “Understanding light trapping in nano-textured
silicon thin-film solar cells by a novel simulation approach” Opt. Express (2015, submitted)
ECE 695, Prof. Bermel4/14/2015
150nm𝜆 = 800nm
ZnOp/c-Si
i/c-Si
Ag
𝐥𝐨𝐠𝟏𝟎 𝑬𝟐
𝟎
𝟏
𝟐
𝟑
𝟒
𝟓
𝟔
𝟕
𝟖
Randomly Textured Cells: Theory and Experiment
Comparison of experimental and simulated total absorption, and the parasitic
component
Electric field energy distribution, with enhancement observed near the Ag/ZnO
and c-Si/ZnO interfaces
Haejun Chung, K.Y. Jung, and Peter Bermel, “Understanding light trapping in nano-textured
silicon thin-film solar cells by a novel simulation approach” Opt. Express (2015, submitted)
ECE 695, Prof. Bermel4/14/2015
150nm𝜆 = 800nm
ZnO
p/c-Si
i/c-Si
Ag
Ag NP
(b)
𝐥𝐨𝐠𝟏𝟎 𝑬𝟐
𝟎
𝟏
𝟐
𝟑
𝟒
𝟓
𝟔
𝟕
𝟖
Ag Nanoparticle Cells: Theory and Experiment
Comparison of experimental and simulated total absorption, and the parasitic
component
Electric field energy distribution, with enhancement observed throughout the
structure, except Ag
Haejun Chung, K.Y. Jung, and Peter Bermel, “Understanding light trapping in nano-textured
silicon thin-film solar cells by a novel simulation approach” Opt. Express (2015, submitted)
ECE 695, Prof. Bermel4/14/2015
𝜆 = 1058 nm
Ag NP
150nm𝜆 = 1058 nm
150nm
65 %
10 %
Ag Nanoparticle Cell Absorption Enhancement
ECE 695, Prof. Bermel4/14/2015
w/ NP, 65 % absorption w/o NP, 10 % absorption
𝜆 = 1058 nm
Ag NP
150nm 𝜆 = 1058 nm150nm
Ag Nanoparticle Cell Absorption Enhancement
Haejun Chung, K.Y. Jung, and Peter Bermel, “Understanding light trapping in nano-textured
silicon thin-film solar cells by a novel simulation approach” Opt. Express (2015, submitted)
ECE 695, Prof. Bermel4/14/2015
Ag NP Cell Absorption
Enhancement
4/14/2015 ECE 695, Prof. Bermel 28
Again, the Ag nanoparticle increases field power throughout most of the structure, except the Ag itself; removing NPs cancels out most of this effect
Haejun Chung, K.Y. Jung, and
Peter Bermel, “Understanding
light trapping in nano-textured
silicon thin-film solar cells by a
novel simulation approach” Opt.
Express (2015, submitted)
Ag Nanoparticle Cell Absorption Enhancement
Haejun Chung, K.Y. Jung, and Peter Bermel, “Understanding light trapping in nano-textured
silicon thin-film solar cells by a novel simulation approach” Opt. Express (2015, submitted)
ECE 695, Prof. Bermel4/14/2015
Optimizing Ag Nanoparticle Cell Absorption
Jsc = 36. 6 mA/cm2
Jrefl= 5.0 mA/cm2
Jsc = 26.1 mA/cm2
Max Jsc = 43.8 mA/cm2
Jpar=3.7 mA/cm2
Haejun Chung, K.Y. Jung,
and Peter Bermel,
“Understanding light
trapping in nano-textured
silicon thin-film solar cells
by a novel simulation
approach” Opt. Express
(2015, submitted)
Effective path length: 700x enhancement
ECE 695, Prof. Bermel4/14/2015
4/14/2015 ECE 695, Prof. Bermel 31
Optimizing Ag NP Cell Front Texture
Optimal correlated random front surface texture
Completely random front surface texture
Haejun Chung, K.Y. Jung, and Peter Bermel, “Understanding light trapping in nano-textured
silicon thin-film solar cells by a novel simulation approach” Opt. Express (2015, submitted)
Next Class
• Next time: we will continue finite-difference time domain techniques
• Suggested reference: S. Obayya’sbook, Chapter 5, Sections 4-6
3/31/2017 ECE 695, Prof. Bermel 32