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Passivation
of Si and CIGS surfaces
• Part I: Al2O3 passivation for Si PERx
• Part II: PERC meets CIGS - PercIGS
Bart Vermang et al.
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Part I: Al2O3 passivation for Si PERx
• p-type PERL ≥ 20.5 %
• n-type PERT ≥ 21.5 %
• Rear passivation stack = ALD Al2O3 (+ capping)
L. Tous et al., Prog. Photovolt: Res. Appl. (2014) DOI: 10.1002/pip.2478
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Part II: PERC meets CIGS - PercIGS
(i-)ZnO(:Al)
n-CdS
p-CIGS
Al2O3 pass. layer
Soda lime glass
Mo
Local point
contact
Local point
contact
500 nm
B. Vermang et al., IEEE J. Photovoltaics (2014) in press
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Leuven, Belgium
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Interuniversity Micro-Electronics
Centre (imec), Leuven, Belgium
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24,400 m² of office space,
laboratories, training facilities,
and technical support rooms
• 200 mm clean room
• 300 mm clean room (450 mm ready)
• silicon PV pilot line
• state-of-the-art laboratories for solar cell research,
research on wireless communication, biomedical
research and long-term brain research
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Imec’s research structure
• Si PV, OPV, TF PV (CZTS, a-Si), Perovskites, multi-junctions ...
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Part I - outline
• Why Al2O3?
• Spatial atomic layer deposition (ALD) of Al2O3
• Thermal stability
• p-type PERL
• Illumination independency
• n-type PERT and Al2O3 contact passivation / doping
J. Vac. Sci. Technol. A (2012) DOI: 10.1116/1.4728205
Prog. Photovolt: Res. Appl. (2011) DOI: 10.1002/pip.1092
38th IEEE PVSC (2012) DOI: 10.1109/PVSC.2012.6317802
Sol. Energy Mater. Sol. Cells (2012) DOI: 10.1016/j.solmat.2012.01.032
Prog. Photovolt: Res. Appl. (2012) DOI: 10.1002/pip.2196
Phys. Status Solidi RRL (2012) DOI: 10.1002/pssr.201206154
Prog. Photovolt: Res. Appl. (2014) DOI: 10.1002/pip.2478
Energy Procedia (2014) DOI: 10.1016/j.egypro.2014.08.041
Phys. Status Solidi (a) (2013) DOI: 10.1002/pssa.201329058
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Why Al2O3?
• Chemical passivation - Low Dit
• Field effect passivation - Qf < 0
G. Dingemans et al., J. Vac. Sci. Technol. A (2012) DOI: 10.1116/1.4728205
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Spatial ALD Al2O3
• Atmospheric pressure
• Increased throughput and TMA efficiency compared to standard
“temporal” ALD
B. Vermang et al., Prog. Photovolt: Res. Appl. (2011) DOI: 10.1002/pip.1092
In-line
1-side depo
> 1 nm/s
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Thermal stability (blistering)
• Thick or capped (ALD) Al2O3 films blister upon annealing
• Blisters lead to additional point contacts
B. Vermang et al., 38th IEEE PVSC (2012) DOI: 10.1109/PVSC.2012.6317802
B. Vermang et al., Sol. Energy Mater. Sol. Cells (2012) DOI: 10.1016/j.solmat.2012.01.032
+ capping
+ Al metal
+ firing
EP 2 482 328, TW 2012 50839, US 2012 192943, JP 2012 160732
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Thermal stability (blistering)
• Combination of (tensile) stress and outgassing (effusion of H2, H2O)
• Solution: thin ALD films and annealing before capping
B. Vermang et al., 38th IEEE PVSC (2012) DOI: 10.1109/PVSC.2012.6317802
B. Vermang et al., Sol. Energy Mater. Sol. Cells (2012) DOI: 10.1016/j.solmat.2012.01.032
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p-type PERL
• Rear pass. stack = spatial ALD Al2O3 (≤ 10 nm) + annealing + SiNx
• Best cell 20.5 %
– VOC = 665 mV; JSC = 38.6 mA/cm2; FF = 79.9 %
• Imec’s Si PV focus moved to n-type
B. Vermang et al., Prog. Photovolt: Res. Appl. (2012) DOI: 10.1002/pip.2196
L. Tous et al., Prog. Photovolt: Res. Appl. (2014) DOI: 10.1002/pip.2478
Similar technologies:
Trina Solar
Suntech
Canadian Solar
Ja Solar
Hanwha Solar
...
EP 2 398 044, TW 2012 06857, US 2011 0308603, JP 2012 039088
EP 2 533 305, TW 2013 20188, US 2012 0306058, JP 2012 253356
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Illumination independency
• VOC → pos./neg. charged surf. pass. (Seff, S.R.H.)
• JSC → parasitic shunting
– Rear passivation of p-type Si PERC =
• Pos. charged dielectric → inversion = floating junction, constant loss of
photo-generated e- from the inverted region via the shunt
• Neg. charged dielectric → accumulation
B. Vermang et al., Phys. Status Solidi RRL (2012) DOI: 10.1002/pssr.201206154
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Illumination independency
B. Vermang et al., Phys. Status Solidi RRL (2012) DOI: 10.1002/pssr.201206154
• SiO2 compared to Al2O3 rear passivated p-type Si PERC
• Filters are used to reduce the light intensity < 100 %
• SiO2 rear pass. p-Si PERC
• Average efficiency up to 0.5 % (abs.) lower in low solar irradiation regions
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n-type PERT
and contact pass. + doping
• Rear pass. stack = spatial ALD Al2O3 (≤ 10 nm) (+ ann.) + SiNx
• Best cell 21.5 %
– VOC = 677 mV; JSC = 39.1 mA/cm2; FF = 81.3 %
• Contact pass. of n+-Si & p+-doping by laser ablation of Al2O3/SiNx
L. Tous et al., Prog. Photovolt: Res. Appl. (2014) DOI: 10.1002/pip.2478
J. Deckers et al., Energy Procedia (2014) DOI: 10.1016/j.egypro.2014.08.041
N.-P. Harder, Phys. Status Solidi (a) (2013) DOI: 10.1002/pssa.201329058
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All of this is teamwork!
My promoter Jef Poortmans and all imec colleagues
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Uppsala, Sweden
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Ångström Solar Center,
University of Uppsala
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Ångström laboratiet / laboratory
• Group
– Tunnfilmssolceller / Thin Film Solar Cells
• Department
– Fasta Tillståndets Elektronik / Solid State Electronics
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1 Ångström = 1 Å = 0.1 nm
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Ångström Solar Center - Lab
Mo sputtering
CIGS co-evaporation
• Inline
• 2 x Batch (+ MS control)
CIGS sputtering
CZTS sputtering
(i-)ZnO(:Al) sputtering
CBD CdS
ALD (Cd-free)
NaF evaporation
ARC MgF2
EG evaporation Al/Ni/Al
Scribing / lamination
Soda lime glass
Mo back contact
Absorber layer (CIGS)
i-ZnO + ZnO:Al
Buffer layer (CdS)
Cell and module fabrication
Electrical and material characterization
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Ångström Solar Center - Goals
• CIGS solar cell ≥ 22 % efficiency (1-stage!)
– Cd-free alternative buffers ≥ 20 %
• CZTS solar cell ≥ 12 % efficiency
• Back contact passivation
• Electrical modeling
• Absorber layer formation
• Module energy yield modeling
– Focus: northern climate
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Part II - outline
• Standard CIGS solar cells
• PercIGS = PERC meets CIGS
• Al2O3 as CIGS surface passivation
• Al2O3 rear passivated CIGS solar cells
• Contacting approaches (3)
• Na optimization in rear passivated CIGS solar cells
Appl. Phys. Lett. (2012) DOI: 10.1063/1.3675849
Sol. Energy Mater. Sol. Cells (2013) DOI: 10.1016/j.solmat.2013.07.025
IEEE J. Photovoltaics (2013) DOI: 10.1109/JPHOTOV.2013.2287769
Prog. Photovolt: Res. Appl. (2014) DOI: 10.1002/pip.2527
Uppsala University MSc. Thesis (2014) ISSN: 1650-8300, UPTEC ES14 030
Phys. Status Solidi RRL (2014) DOI: 10.1002/pssr.201409387
IEEE J. Photovoltaics (2014) in press
Thin Solid Films (2014) under review
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Standard CIGS solar cells
• Back surface field (BSF) to passivate Mo/CIGS rear interface
– Highly recombinative (1x104 cm/s ≤ Sb ≤ 1x106 cm/s)
and lowly reflective (Rb < 60 %)
– Very comparable to Al BSF in standard Si solar cells
Aluminum
Si
p-type CIGS
Mo BSF
Thick
absorber
layer
B. Vermang et al., Sol. Energy Mater. Sol. Cells (2013) DOI: 10.1016/j.solmat.2013.07.025
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PercIGS = PERC meets CIGS
• Rear of Si PERC = a combination of an adequate rear surface
passivation layer and micron-sized local point contacts
B. Vermang et al., Sol. Energy Mater. Sol. Cells (2013) DOI: 10.1016/j.solmat.2013.07.025
Passivation layer
Micron-sized
local point
contact
Ever thinner
wafer thickness
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PercIGS = PERC meets CIGS
• PercIGS = a combination of an adequate rear surface passivation
layer and nano-sized local point contacts
B. Vermang et al., Sol. Energy Mater. Sol. Cells (2013) DOI: 10.1016/j.solmat.2013.07.025
(i-)ZnO(:Al)
n-CdS
p-CIGS
Al2O3 pass. layer
Soda lime glass
Mo
Local point
contact
Local point
contact
500 nm
Ever thinner
absorber
layer
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PercIGS
• European project
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Al2O3 as CIGS surface passivation
• Chemical passivation - Low Dit
– First principle calculations: 35 % reduction in Dit as compared to
unpassivated CIGS surface
W.-W. Hsu, Appl. Phys. Lett. (2012) DOI: 10.1063/1.3675849
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Al2O3 as CIGS surface passivation
• Field effect passivation - Qf < 0
– Qf < 0 – positive shift in flat-band voltage (VFB) a.f.o. Al2O3 thickness
– ∆Qf < 0 – positive shift in VFB after annealing
– Reduction in Dit – steeper CV slope after annealing
J. Joel, Uppsala University MSc. Thesis (2014) ISSN: 1650-8300, UPTEC ES14 030
300 K
50 kHz 300 K
50 kHz
as-dep
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Al2O3 rear passivated
CIGS solar cells
• Always increase in VOC compared to unpassivated standard cells
• More obvious for ever thinner tCIGS
• Rear surf. pass. - very comparable as “PERC ↔ std. Si solar cell”
B. Vermang et al., Prog. Photovolt: Res. Appl. (2014) DOI: 10.1002/pip.2527
Rear pass. CIGS solar cell
Standard CIGS solar cell
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Al2O3 rear passivated
CIGS solar cells
• Only increase in JSC for ever thinner tCIGS
• Still a loss in JSC compared to thick standard CIGS solar cells
• Rear int. refl. & surf. pass. - comparable as “PERC ↔ std. Si cell”
B. Vermang et al., Prog. Photovolt: Res. Appl. (2014) DOI: 10.1002/pip.2527
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Contacting approach 1:
CdS nano-particles + removal
1. Deposit (chemical bath deposition = CBD) a particle-rich CdS layer
on the Mo back contact
2. Deposit the surface passivation layer
• DC-sputt. Al2O3 or evap. MgF2/ALD-Al2O3
3. Remove the CdS nano-particles
Soda Lime Glass (SLG)
Mo
CdS
Pass.
layer
B. Vermang et al., Sol. Energy Mater. Sol. Cells (2013) DOI: 10.1016/j.solmat.2013.07.025
B. Vermang et al., IEEE J. Photovoltaics (2013) DOI: 10.1109/JPHOTOV.2013.2287769
B. Vermang et al., Prog. Photovolt: Res. Appl. (2014) DOI: 10.1002/pip.2527
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Contacting approach 1:
CdS nano-particles + removal
• Particle diameter = 285 ± 30 nm
• Point opening diameter = 220 ± 25 nm
• High RS, as the point contacting grids are only sub-optimized
B. Vermang et al., Sol. Energy Mater. Sol. Cells (2013) DOI: 10.1016/j.solmat.2013.07.025
B. Vermang et al., IEEE J. Photovoltaics (2013) DOI: 10.1109/JPHOTOV.2013.2287769
B. Vermang et al., Prog. Photovolt: Res. Appl. (2014) DOI: 10.1002/pip.2527
Da 1 = 273 nm
Da 2 = 270 nm
Da 1 = 216 nm
Da 2 = 194 nm
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Contacting approach 2:
Mo nano-particles
1. Deposit Mo NP (formed by a plasma process) on the Mo back
contact
2. Deposit the surface passivation layer
• DC-sputt. Al2O3 (< 25 nm)
SLG
Mo
Mo NP
Pass.
layer
B. Vermang et al., Thin Solid Films (2014) under review
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Contacting approach 2:
Mo nano-particles
B. Vermang et al., Thin Solid Films (2014) under review
(i-)ZnO(:Al)
n-CdS
p-CIGS
Soda lime glass
Mo
Thin pass. layer Mo NP Mo NP
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Contacting approach 2:
Mo nano-particles
• STEM-EDX picture of a finished solar cell
B. Vermang et al., Thin Solid Films (2014) under review
Cu
Al
Mo
![Page 38: Passivation of Si and CIGS surfaces - University of New ... · PDF filePassivation of Si and CIGS surfaces • Part I: Al 2 O 3 ... f < 0 G. Dingemans et al., ... a.f.o. Al 2 O 3 thickness](https://reader031.vdocument.in/reader031/viewer/2022030506/5ab54b2d7f8b9ab7638c92bc/html5/thumbnails/38.jpg)
Contacting approach 3:
Electron beam lithography
1. Deposit the surface passivation layer
• Sputt. Al2O3 or ALD-Al2O3 (thick layers!)
2. Deposit the resist
3. Open the resist by e-beam litho
4. Etch the passivation layer
5. Remove the resist
SLG
Mo
Pass.
layer
Resist
B. Vermang et al., IEEE J. Photovoltaics (2014) in press
![Page 39: Passivation of Si and CIGS surfaces - University of New ... · PDF filePassivation of Si and CIGS surfaces • Part I: Al 2 O 3 ... f < 0 G. Dingemans et al., ... a.f.o. Al 2 O 3 thickness](https://reader031.vdocument.in/reader031/viewer/2022030506/5ab54b2d7f8b9ab7638c92bc/html5/thumbnails/39.jpg)
Contacting approach 3:
Electron beam lithography
• Optical microscopy top-view picture of an opened passivation layer
– Well-structured grid
B. Vermang et al., IEEE J. Photovoltaics (2014) in press
![Page 40: Passivation of Si and CIGS surfaces - University of New ... · PDF filePassivation of Si and CIGS surfaces • Part I: Al 2 O 3 ... f < 0 G. Dingemans et al., ... a.f.o. Al 2 O 3 thickness](https://reader031.vdocument.in/reader031/viewer/2022030506/5ab54b2d7f8b9ab7638c92bc/html5/thumbnails/40.jpg)
Contacting approach 3:
Electron beam lithography
• SEM-EDX top-view picture of an opened passivation layer
– Al2O3 etching is satisfactory
• High FF and VOC
– Low RS
B. Vermang et al., IEEE J. Photovoltaics (2014) in press
![Page 41: Passivation of Si and CIGS surfaces - University of New ... · PDF filePassivation of Si and CIGS surfaces • Part I: Al 2 O 3 ... f < 0 G. Dingemans et al., ... a.f.o. Al 2 O 3 thickness](https://reader031.vdocument.in/reader031/viewer/2022030506/5ab54b2d7f8b9ab7638c92bc/html5/thumbnails/41.jpg)
Optimization of Na
in rear passivated CIGS solar cells
• “Curing” Na-deficient cells by applying electrical fields
B. Vermang et al., Phys. Status Solidi RRL (2014) DOI: 10.1002/pssr.201409387
-100 -50 0 50 100 150 200 250 300 350 400 450 500
Before PID
After PID
After recovery
Na in
tensity (
a.u
.)
CIGS depth (nm)
CdS Al2O3
(a)
![Page 42: Passivation of Si and CIGS surfaces - University of New ... · PDF filePassivation of Si and CIGS surfaces • Part I: Al 2 O 3 ... f < 0 G. Dingemans et al., ... a.f.o. Al 2 O 3 thickness](https://reader031.vdocument.in/reader031/viewer/2022030506/5ab54b2d7f8b9ab7638c92bc/html5/thumbnails/42.jpg)
p-CIGS
n-CdS
(i-)ZnO(:Al)
Mo
Soda lime glass
(i-)ZnO(:Al)
n-CdS
p-CIGS
Mo
Soda lime glass
(i-)ZnO(:Al)
n-CdS
p-CIGS
Mo
Soda lime glass
Pass. layer
Pass. layer
Pass. layer Local
contact
Local
contact Local
contact
Approach 1
Approach 2 Approach 3
PERC meets CIGS: PercIGS
Introduction of a rear surface passivation layer
and nano-sized local contacts
Increase in VOC, JSC and FF for rear surface
passivated ultra-thin CIGS solar cells
compared to (unpassivated) standard ultra-
thin CIGS solar cells
![Page 43: Passivation of Si and CIGS surfaces - University of New ... · PDF filePassivation of Si and CIGS surfaces • Part I: Al 2 O 3 ... f < 0 G. Dingemans et al., ... a.f.o. Al 2 O 3 thickness](https://reader031.vdocument.in/reader031/viewer/2022030506/5ab54b2d7f8b9ab7638c92bc/html5/thumbnails/43.jpg)
Thank you for your
attention!
M. Edoff
V. Fjällström
C. Frisk
C. Hägglund
J. Joel
J. Keller
J. Larsen
D. Ledinek
J. Olsson
F. Rostvall
P. Szaniawski
J.T. Wätjen
U. Zimmermann
Former:
A. Hultqvist
J. Pettersson
G. Xindong
D. Flandre
F. Henry
R. Kotipalli
R. Gunnarsson
U. Helmersson
I. Pilch
J. Borme
S. Sadewasser
P. Salomé
A. Uruena