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Effect of Aluminum in Metallization Paste on the Electrical Losses in Bifacial N-type Crystalline Silicon Solar Cells

Takayuki Aoyama1, 2, Mari Aoki3, Isao Sumita3, Yasushi Yoshino1, Yoshio Ohshita3, Atsushi Ogura2

1Noritake Co., Limited 2Meiji University 3Toyota technological Institute

6th Metallization Workshop, Konstanz, Germany, 2016

Corresponding author: [email protected]

6th Metallization Workshop, Konstanz, Germany, 2016 /16

Motivation Evaluation method Test pastes Aluminum effects on n-type solar cells

Conclusion

- Problems in metallization with paste - In the case of Ag/Al metallization for n-type solar cells - Conventional evaluation for pastes

- Electrical losses … Voc, Rsh, J02

- Interface morphology between contact and Si wafer

- Homemade three test pastes

Outline

- “Floating contact method”

2


recombination shunting

emitter

…Loss in Voc ⇒ Severe limit of cell efficiency !

c-Si

glass

Ag Metallization with paste

・Ag ・glass frit

Significant effect

Problems in metallization with paste

Screen-printing with conductive paste -simple process and cheaper cost

3


Ag/Al paste

p+-emitter

n-Si large spike - Shunting ? - Recombination ?

? glass

Ag

Al

? Al

glass

Al

Problems in Ag/Al metallization

To elucidate the specific effects of Al The purpose of our study…

4

Ag/Al paste : Al addition ⇒ “Good” contact to p+-emitter

⇒ Complex composition

It’s still a big question how glass frit and aluminum affect ?


Conventional evaluation for pastes

How can we elucidate “specific” effects of Al ?

- Ag - Glass frit - Aluminum

Cell parameters

= Complex system

glass

Ag

Al

to evaluate respective effects of materials in paste

The conventional method cannot divide effects of glass frit and Al on cell parameters, accurately.

Changing paste composition…

Indirect method

5


Standard H-pattern grid-contact

emitter

detected

“Floating contact method”

R. Hoenig, Ph. D. dissertation, 2014.

Floating contacts electrically and geometrically isolated

from grid-contact

Floating contact “fraction”…

0% 5% 11% 16%

- Shunting - Carrier recombination

effects on an emitter

Advantages - Conductive ✓ - Nonconductive ✓ - Non-contact ✓ …Al less Ag past to p+-emitter

busbar

6


SiNx/SiO2

Floating contacts： Three test pastes H-pattern grid contact:

Ag/Al paste

Standard Ag paste

156mmx156mm n-type c-Si

Boron doped p+ emitter 70Ω/sq.

Phosphorus doped n+ BSF 40Ω/sq.

Ag

glass

Ag

glass

Ag

Al

Only-Ag

Ag/glass

Ag/glass/Al

Effect of glass frit

Effect of Al

Glass frit: PbO-SiO2-B2O3-ZnO

Test pastes - To elucidate specific effects of aluminum on p+-emitter

7


0 0.200 0.400 0.600

10.0

20.0

30.0

40.0

Cur

rent

den

sity

(mA

/cm

2 )

Voltage

Voc (V)

Jsc (mA/cm2)

FF (%)

Eff. (%)

0.641 37.84 77.62 18.77

Cell properties without floating contact

The cell parameters are good enough to evaluate the effects of floating contacts.

No floating contacts

8


0 5 10 15 20 250.628

0.632

0.636

0.640

0.644

Floating contact fraction (%)

Ope

n ci

rcui

t vol

tage

Voc

(V)

Same tendency

Open circuit voltage, Voc

Conductive paste causes loss in Voc in n-type solar cells even if the paste does not contain aluminum

9


Al mitigates generation of Ag-crystallites and their growth Adding Al causes forming the large spike

SiNx /SiO2

fewer shallower

Imprints of Ag-crystallites

Imprints of Ag/Al spike

p-Si mirror

contact

Interface morphology underneath contact HNO3/HCl HF HNO3/HCl

Shunting? , Recombination? Shunting? 1µm

10


0 0.200 0.400 0.60010-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

102

Voltage (V)

Cur

rent

den

sity

(mA

/cm

2 )

Al mitigates the current increase at low voltage range. Numerical fitting with the two-diode model ⇒ Rsh, J02

Dark IV curves

Fraction:16%

hump

11


0 5 10 15 20 25103

104

105

106

107


Shu

nt re

sist

ance

Rsh

(Ωcm

2 )

Al in Ag/Al paste does not induce significant shunting

Shunt resistance, Rsh

12

mitigated


0 5 10 15 20 250

1.0

2.0

3.0

4.0

5.0

6.0


Rec

ombi

natio

n cu

rrent

den

sity

J 02 (

10-9

A/c

m2 )

Al mitigates the increase of recombination current

Recombination current, J02

13

mitigated


Al effects on p+-emitter

Al glass

Ag-crystallite fewer

shallower

Rsh, J02

mitigated

Rsh, J02

degraded

The Al effects on Ag-crystallite mitigates the decrease of Rsh and the increase of J02 The large spikes do not induce the significant electrical losses

14

2.0µm


Conclusion

Conductive paste causes loss in Voc in n-type solar cells even if the paste does not contain Al

Al in Ag/Al paste mitigates shunting of pn junction and carrier recombination on p+-emitter by mitigating generation of Ag-crystallite and their growth

The big metallic spikes underneath Ag/Al paste do not induce significant shunting of pn junction and carrier recombination

“Specific” effects of Al on p+-emitter can be elucidated by using the “floating contact method”

with the homemade test pastes.

The “floating contact method” have big advantages for elucidating respective effects of paste component on cell parameters.

15

6th Metallization Workshop, Konstanz, Germany, 2016

“Effect of Glass Frit in Metallization Paste on the Electrical Losses in Bifacial N-type Crystalline Silicon Solar Cells” Takayuki Aoyama, Mari Aoki, Isao Sumita, Yasushi Yoshino, Yoshio Ohshita, Atsushi Ogura “A Study on the Evaluation Method of Glass Frit Paste for Crystalline Silicon Solar Cells” Mari Aoki, Takayuki Aoyama, Isao Sumita, Yasushi Yoshino, Atsushi Ogura, Yoshio Ohshita

Thank you for your attention!

effect of aluminum in metallization paste on the ... · 6th metallization workshop, konstanz,...

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