insight into metal induced recombination losses and...
TRANSCRIPT
![Page 1: Insight into Metal Induced Recombination Losses and ...isc-konstanz.de/fileadmin/doc/WCPEC_7_2018/... · V.D. Mihailetchi et al., 7 thWCPEC, Waikoloa, June 13 , 2018 Introduction](https://reader034.vdocuments.site/reader034/viewer/2022052104/603f82ff6c9ba727e9631c38/html5/thumbnails/1.jpg)
Insight into Metal Induced Recombination Losses
and Contact Resistance in Industrial Silicon Solar
Cells
Valentin D. Mihailetchi, Haifeng Chu, Radovan Kopecek
International Solar Energy Research Center e.V., Konstanz, Germany
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V.D. Mihailetchi et al., 7th WCPEC, Waikoloa, June 13th, 2018
Motivation
2
Metallization technologies in PV industry
World market share [%]
Data from: International Technology Roadmap for PV, 2018
screen printing
plating
PVD (evaporation/sputtering)
Challenges:
reduce contact recombination:
J0,met J0,pas
achieve low contact resistance (C)
Screen printing and firing-through of a
Ag paste
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V.D. Mihailetchi et al., 7th WCPEC, Waikoloa, June 13th, 2018
Introduction
3
Screen printing and firing-through metallization technology
Question: what causes the high J0,met?
- etching of passivation layer and Si emitter [1,2]
- spiking and/or Ag-crystallites formation [3-5]
Outline:
- Photoluminescence (PL) method to extract
J0,met: PL2J0met
- Experimental details
- Results for J0,met & C
- Validation on solar cells
[1] Koduvelikulathu et al., IEEE J. Photovoltaics, 5 (2015)
[2] Edler et al., Prog. Photovoltaics Res. App., 23 (2015)
[3] Ballif et al., Appl. Phys. Lett. vol. 82 (2003)
[4] Hoerteis et al., Adv. Funct. Mater., vol. 20 (2010)
[5] Kiefer et al., IEEE J. Photovoltaics, 6 (2016)
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V.D. Mihailetchi et al., 7th WCPEC, Waikoloa, June 13th, 2018
PL to J0,met analysis (PL2J0met)
4
Layout:
• five levels of metallization fractions
• QSSPC measurements for MF1:
implied VOC and J0,pas
Method:
1. Convert PL image to VOC[1-4]
2. Calculate J01 from VOC image
(1-diode model) [2]
3. Linear fit to obtain J0,met
MF1:
0%MF4:
7.6%
MF3:
5.3%
MF3:
5.3%
MF2:
2.6%
MF5:
10.2%
MF5:
10.2%
MF1:
0%
MF2:
2.6%
VOC image (PL2Voc)
[1] Glatthaar et al., J.Appl.Phys., 108 (2010);
[2] Shanmugam et al., Sol. Energy, 118 (2015);
[3] Trupke et al., Appl.Phys.Lett., 89 (2006);
[4] Shen et al., Sol. Energy Mater. Sol.Cells,109 (2013)
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V.D. Mihailetchi et al., 7th WCPEC, Waikoloa, June 13th, 2018
MF1:
0%MF4:
7.6%
MF3:
5.3%
MF3:
5.3%
MF2:
2.6%
MF5:
10.2%
MF5:
10.2%
MF1:
0%
MF2:
2.6%
VOC image (PL2Voc)
PL to J0,met analysis (PL2J0met)
5
0 2 4 6 8 10 12
80
120
160
200
240
280 Exp. data
linear fit
J0
1 (f
A/c
m2)
Metal fraction, MF (%)
Example fit:
J0,met = 1720 fA/cm2
R2 = 98.7%
slope = J0,met - J0,pas
[1] Glatthaar et al., J.Appl.Phys., 108 (2010);
[2] Shanmugam et al., Sol. Energy, 118 (2015);
[3] Trupke et al., Appl.Phys.Lett., 89 (2006);
[4] Shen et al., Sol. Energy Mater. Sol.Cells,109 (2013)
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V.D. Mihailetchi et al., 7th WCPEC, Waikoloa, June 13th, 2018
Experimental details
6
Sample structure and diffusion profiles
- symmetrically diffused planar or texture wafers
- SiO2/SiNx passivation stack [1]
- commercial firing-through Ag paste for both, n+ and p+
- different firing temperature profiles
- different SiNx thicknesses (on metal side)[1] Mihailetchi et al., IEEE J. Photovoltaics, 8 (2018)
0.0 0.1 0.2 0.3 0.4 0.5 0.61016
1017
1018
1019
1020
boron (140 sq)
phos. (150 sq)
Ca
rrie
r d
en
sity (
cm
-3)
depth (µm)
Ns ≈ 2×1019 cm-3
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V.D. Mihailetchi et al., 7th WCPEC, Waikoloa, June 13th, 2018
Experimental details
7
Contact formation [1-3] and firing profiles
[1] Fields et al., DOI: 10.1038/ncomms11143 (2016)
[2] Schubert G., PhD thesis Univ. of Konstanz, Germany (2006)
[3] Ballif et al., Appl. Phys. Lett. vol. 82 (2003)
1. T < 550 °C
- burning of organics
2. 550 °C <T < 700 °C
- SiNx etching
3. T > 700 °C
- Ag crystallites/nanocolloids
- Ohmic contact
0 10 20 30 40 50 60 70 80
300
400
500
600
700
800Profile (T
peak):
F1 (480 °C)
F2 (650 °C)
F3 (740 °C)
F4 (790 °C)
F5 (825 °C)
Tem
pe
ratu
re, T
(°C
)
Time, t (s)
Experimental firing profiles:
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V.D. Mihailetchi et al., 7th WCPEC, Waikoloa, June 13th, 2018
Results: C and J0,met
8
n+ (phosphorus) doped surface:
Results:
Simulation (Quokka3)
upper J0,met limit
(for Smet 107 cm/s)
Phase 1:
J0,met = J0,pas , C = n/a
1
10
100
1000
480 600 650 700 750 800 850
1020
500
1000
1500
2000
480 600 650 700 750 800 850
c=n/a
c=n/a
SiNx thickness:
38 nm
65 nm
91 nm
126 nm
c (
m
cm
2)
SiNx thickness:
40 nm
100 nm
150 nm
textureplanar
J0
,me
t(n
+) (
fA/c
m2)
Peak firing temperature, Tpeak
(°C)
Simulation Simulation
Phase 1 Phase 1
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V.D. Mihailetchi et al., 7th WCPEC, Waikoloa, June 13th, 2018
Results: C and J0,met
9
n+ (phosphorus) doped surface:
Results:
Simulation (Quokka3)
upper J0,met limit
(for Smet 107 cm/s)
Phase 1:
J0,met = J0,pas , C = n/a
Phase 2:
J0,met J0,met (max.)
C 100 mcm2
1
10
100
1000
480 600 650 700 750 800 850
1020
500
1000
1500
2000
480 600 650 700 750 800 850
c=n/a
c=n/a
SiNx thickness:
38 nm
65 nm
91 nm
126 nm
c (
m
cm
2)
SiNx thickness:
40 nm
100 nm
150 nm
textureplanar
J0
,me
t(n
+) (
fA/c
m2)
Peak firing temperature, Tpeak
(°C)
Simulation Simulation
Phase 1 Phase 2 Phase 1 Phase 2
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V.D. Mihailetchi et al., 7th WCPEC, Waikoloa, June 13th, 2018
Results: C and J0,met
10
n+ (phosphorus) doped surface:
1
10
100
1000
480 600 650 700 750 800 850
1020
500
1000
1500
2000
480 600 650 700 750 800 850
c=n/a
c=n/a
SiNx thickness:
38 nm
65 nm
91 nm
126 nm
c (
m
cm
2)
SiNx thickness:
40 nm
100 nm
150 nm
textureplanar
J0
,me
t(n
+) (
fA/c
m2)
Peak firing temperature, Tpeak
(°C)
Simulation Simulation
Phase 1 Phase 2 Phase 3 Phase 1 Phase 2 Phase 3 Results:
Simulation (Quokka3)
upper J0,met limit
(for Smet 107 cm/s)
Phase 1:
J0,met = J0,pas , C = n/a
Phase 2:
J0,met J0,met (max.)
C 100 mcm2
Phase 3:
J0,met J0,met (max.)
C ohmic contact
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V.D. Mihailetchi et al., 7th WCPEC, Waikoloa, June 13th, 2018
Results: C and J0,met
11
p+ (boron) doped surface:
Phase 1 Phase 2 Phase 3 Phase 1 Phase 2 Phase 3
1
10
100
1000
480 600 650 700 750 800 850
10
1000
2000
300040005000
480 600 650 700 750 800 850
c=n/a
c=n/a
SiNx thickness:
38 nm
65 nm
91 nm
126 nm
c (
m
cm
2)
SiNx thickness:
40 nm
100 nm
150 nm
textureplanar
J0
,me
t(p
+) (
fA/c
m2)
Peak firing temperature, Tpeak
(°C)
Simulation Simulation
Results:
Simulation (Quokka3)
upper J0,met limit
(for Smet 107 cm/s)
Phase 1:
J0,met = J0,pas , C = n/a
Phase 2:
J0,met J0,met (max.)
C 100 mcm2
Phase 3:
J0,met J0,met (max.)
C ohmic contact
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V.D. Mihailetchi et al., 7th WCPEC, Waikoloa, June 13th, 2018
Results: C and J0,met
12
At optimum firing temperature, Tpeak = 790 °C:
Results:
1
10
100
20 40 60 80 100 120 140 160
400
800
1200
1600
2000
2400
2800
3200
3600
4000
Boron (planar)
Boron (texture)
Phosphorus (planar)
Phosphorus (texture)
c (
m
cm
2)
J0
,me
t (fA
/cm
2)
SiNx thickness, d
SiNx (nm)
Tpeak
= 790 °C
SiNx J0,met
SiNx C constant (texture)
J0,met (p+) > J0,met (n+)
Thicker SiNx improves Voc (and)
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V.D. Mihailetchi et al., 7th WCPEC, Waikoloa, June 13th, 2018
Results: C and J0,met
13
At optimum firing temperature, Tpeak = 790 °C:
SiNx = 38 nm SiNx = 126 nm
1
10
100
20 40 60 80 100 120 140 160
400
800
1200
1600
2000
2400
2800
3200
3600
4000
Boron (planar)
Boron (texture)
Phosphorus (planar)
Phosphorus (texture)
c (
m
cm
2)
J0
,me
t (fA
/cm
2)
SiNx thickness, d
SiNx (nm)
Tpeak
= 790 °C
SiNxSiNx
contact
area
40 60 80 100 120 140
10
20
30
40
50
60 Boron
Phosphorus
co
nta
ct S
iNx c
ove
rag
e (
%)
SiNx thickness, d
SiNx (nm)
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V.D. Mihailetchi et al., 7th WCPEC, Waikoloa, June 13th, 2018
Validation on solar cells
14
ZEBRA IBC: cell structure and characteristics [1]
• BBr3 and POCl3 diffusions
• SiO2/SiNx passivation stack [2]
• firing through Ag paste for both p+ and n+
[1] Galbiati et al., 7th WCPEC, Waikoloa (2018)
[2] Mihailetchi et al., IEEE J. Photovoltaics, 8 (2018)
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V.D. Mihailetchi et al., 7th WCPEC, Waikoloa, June 13th, 2018
-40 -20 0 20 40
674
676
678
680
682
684
686
Exp. data
Quokka3 simulation [1]
Vo
c (m
V)
relative SiNx thickness (nm)
Ref.
Validation on solar cells
15
VOC improvement and best cell results
SiNx VOC
FF constant
JSC
[mA/cm2]
VOC
[mV]
FF
[%]
Efficiency
[%]
41.7 684 81.4 23.2
Best IBC (ZEBRA) cell [2]:
[1] A. Fell, IEEE Trans. Electron Devices, 60 (2013)
[2] Galbiati et al., 7th WCPEC, Waikoloa (2018)
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V.D. Mihailetchi et al., 7th WCPEC, Waikoloa, June 13th, 2018
Conclusion
Causes for high J0,met on p+ & n+ Si:
16
Main: etching of SiNx & Si
Minor: Ag crystallites (contact formation)
SiNx J0,met , C constant
C and J0,met: not necessarily correlated
Thank you for your attention!