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Progress of IBC Si solar cells(ACAP PP1.2a)
ANU: Kean Chern Fong, Teng Choon Kho(PhD), WenSheng Liang, Pheng
Phang, Marco Ernst, Daniel Walter, Matthew Stocks, and Andrew Blakers.
PVLighthouse: Keith McIntosh
Contact: kean.fong@anu.edu.au
ANU 25% IBC Solar Cell
In 2018, ANU received certification
for a 24.95 ± 0.61% single-junction
Si solar cell.
– VOC 717 mV
– JSC 42.9 mA cm-2,
– FF 81.1
Key features of the cell:
– Oxide-Nitride-Oxide passivation
– High bulk lifetime >50ms
– Excellent light trapping
2
ANU 25% IBC Solar Cell
3
Front surface:• Textured
• Phosphorus diffusion
• Oxide-Nitride-Oxide
TLM
Finger resistance
test structures
Dielectric
test structures
IBC Cells
-
+
Rear surface:• Non-textured
• Phosphorus diffusion
• Oxide-Nitride-Oxide
ANU 25% IBC Solar Cell
4
N-type BSF
+ metal finger- metal finger
Light Phosphorus
- metal finger
P-type emitter
Cross section
Bottom-up
View
Light Phosphorus
(ONO)
(ONO)
(100 Ω cm)
5
Key design improvements
Franklin E., Fong K.C., et al, Progress in Photovoltaics: Research and Applications, 2014
Need high lifetimeTR, Gettering, Cz → FZ,
1.5 →100 Ω-cm
Need better optics,
Thinner wafer or edge
treatment
Front Surface: ONO
Reduce Boron regions
Thinner wafer
Loss analysis of (2014) 24.4% IBC cell:
Oxide-Nitride-Oxide
6
Si wafer
Thermal oxide
PECVD SiNx
PECVD SiOx
Si wafer
Origin:
The idea of ONO passivation is derived from SONOS
memory cells, which has properties of being chargeable
with good charge retention capacity.
It turns out, that an ONO performs excellently as a
passivation layer, and surface charges can be tuned from
+ve to –ve.
Oxide-Nitride-Oxide
7
O-N-O on undiffused Si
T.C. Kho, K.C. Fong, et al., “Exceptional silicon surface passivation by
an ONO dielectric stack”, Solar Energy Materials and Solar Cells, 2018.
Si waferThermal oxide
PECVD SiNx
PECVD SiOx
Planar:
• < 0 fAcm-2, exceeding (Richter)
Auger lifetime limits.
Random Textured:
• ~ 1-5 fAcm-2
Phos diffused ONO
8
Si wafer
O-N-O
O-N-O
Phos diffusion
Phos diffusionSi wafer
O-N-O
O-N-O
Phos diffusion
Phos diffusion
T.C Kho, PhD thesis , in preparation. (est. 2019)
Boron diffused- ONO
• Uncharged 25 fAcm-2
• Negatively charged J0 at 9 fAcm-2
9
Si wafer
O-N-O
O-N-O
Boron diffusion
Boron diffusion
T.C Kho, PhD thesis , in preparation. (est. 2019)
Optics of ONO
10
43.6543.20
43.60
43.30
43.55
43.50
43.40
43.300 5 10 15 20 25 30
36
40
44
48
52
56
60
64
68(a) ONO OPAL2 Simulation
Thic
kness o
f S
iNx (
nm
)
Thickness of thermal SiO2 (nm)
42.70
42.90
43.10
43.30
43.50
43.70
JGen
(mA/cm2)
0.0
0.5
1.0
1.5
2.0
Spectr
al in
t. (
W/m
2/n
m)
400 600 800 1000
0
5
10
15
20
25
30
35
40(b) Reflectance Measurement
Simulated SiNx
Simulated NO
Simulated ONO
Measured ONO Cell
Wavelength (nm)
Reflecta
nce (
%)
25% cell
T.C Kho, PhD thesis , in preparation. (est. 2019)
Optimal Optics is achieved when SiO2 is thinnest.
• Trade-off between optics & passivation
Application of ONO to IBC cells
11
7 fAcm-2
(~500 Ω∕)
2 fAcm-2
(~500 Ω∕)
16 fAcm-2
(~170 Ω∕)210 fAcm-2
(~15 Ω∕)
Area Weighted J0 indicates the surfaces and contacts
contribute approximately 16 fAcm-2 to the entire cell.
Improvement to Texturing
• ANU adopted the use of monoTEX additive for the formation
of random pyramid structures.
– Physical : Uniform, repeatable, smaller pyramids (~3um), consumes less silicon
(~10um)
– Electrical : Slightly higher bulk lifetimes achieved in controlled test versus TMAH-
IPA texturing.
12
W.S.Liang, K.C. Fong, et al, “TMAH etchant and monoTEX agent induced highly reproducible and non-metal contamination
c-Si texturing“, ASPRC 2018
TMAH + MonoTEX
(presented improvement)TMAH + IPA
Quantum Efficiency
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+0.5 mA cm-2-0.04 mA cm-2
300-400 nm
+0.4 mA cm-2
400-950 nm 950-1200 nm
IV measurements
14
• High VOC of 717 mV..
• Bulk lifetime >50ms
before metallisation.
• High JSC of
42.9mAcm-2.
• But weak knee, low
FF of 81.1.
Future Improvements
• Low FF, identifying
source of non-ideality
• Application of
passivated contacts in
combination with ONO
15
T.C Kho, in preparation for presentation at SiliconPV 2019.
ANU IBC Cell progression
16
+ metal finger
(shaded)- metal finger
(shaded)
Light phosphorus
Metal contact
(black dots)
- metal finger
(shaded)
Heavy Boron
Boron diffusionundiffused
Heavy Phos
diffusion
2013: 24.4% (independently confirmed)
• 703mV, 42.0 mAcm-2, FF 82.7%
• 1.5 Ohm-cm n-type
• PECVD SiN/SiO front, LPCVD SiO/SiN rear.
2016: 24.7% (in-house)
• 714mV, 42.0 mAcm-2, FF 82.3%
• High resistivity (100 Ohm-cm)
• ONO passivation
• Phosphorus gettering
2018: 25.0% (independently confirmed)
• 717mV, 42.9 mAcm-2, FF 81.1%
• Phos + BRL gettering
• Improved texturing (MonoTex)
undiffused
Conclusion
• 25% efficient IBC cells fabricated at ANU.
• Key features: ONO, TMA-MonoTEX, Bulk lifetime (TR,
BRL & Phos gettering.)
• Publications:– T. K. Choon, K.C. Fong, et al., SOLMAT, 2018.
– W. S. Liang, K.C. Fong, et al., ASPVC, 2018.
– E. Franklin, K.C. Fong, et al., PIPV, 2016.
– K.C Fong, et,al, JPV, 2016.
– K.C Fong, et,al, JPV, 2015.
– A.Fell, K.C. Fong, JPV, 2014
– K.R. McIntosh, PVSC 2014, ... many more...
• Open to collaboration.
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