abasifreke ebong, nirupama bezawada, veysel unsur, … · university of north carolina at charlotte...

Energy Production and Infrastructure Center (EPIC) [email protected] Metallization & Interconnection Workshop 2017

7th Workshop on Metallization & Interconnection for Crystalline Silicon Solar Cells Energy Production and Infrastructure Center (EPIC)

Abasifreke Ebong, Nirupama Bezawada, Veysel Unsur, Ren Keming and Ahrar Chowdhury

Department of Electrical and Computer Engineering University of North Carolina at Charlotte

9201 University City Blvd, Charlotte NC 28223-0001, USA



2

(i) R1 – metal-semiconductor back contact (ii) R2 – bulk semiconductor (iii) R3 – emitter between two gridlines (iv) R4 – metal – semiconductor – contact on gridline (v) R5 – gridline (vi) R6 - busbar


7th Workshop on Metallization & Interconnection for Crystalline Silicon Solar Cells

1970; 20 1980; 25

1990; 35 1995; 40

2000; 45 2005; 50

2008; 55 2011; 60

2012; 65 2013; 70

2014; 75 2015; 80

2016; 90

2017; 100

2019; 110

2021; 120

2024; 130 2027; 130

20

40

60

80

100

120

140

1970 1980 1990 2000 2010 2020 2030

Shee

t Res

ista

nce

(ohm

/sq.

)

Year

ITRPV 2017 Expected trend for sheet resistance



1970; 200

1980; 180

1990; 160

2000; 140

2005; 120

2010; 100

2015; 70

2016; 48 2017; 45

2019; 38 2021; 30 2024; 30

2027; 25 20

40

60

80

100

120

140

160

180

200

1970 1980 1990 2000 2010 2020 2030

Grid

line

wid

th (u

m)

Year

ITRPV 2017 Expected trend for gridline width



2-5%

85-90% 5-10%

[1] R. Prunchak, US patent 7,736,546B2, 2010. [2] Carroll et al, US Patent, 8,889,980 B2 [3] R. G. Rajendran, US 2013/0099177 A1



p.7

(i) 𝑆𝑆(𝑤𝑤𝑤𝑤𝑤) + 2𝑃𝑃𝑂(𝑔𝑔𝑤𝑔𝑔) → 𝑆𝑆𝑂2(𝑔𝑔𝑤𝑔𝑔) + 2𝑃𝑃 (ii) 𝑆𝑆(𝑤𝑤𝑤𝑤𝑤) + 2𝐴𝐴2𝑂(𝑔𝑔𝑤𝑔𝑔) → 𝑆𝑆𝑂2 (𝑔𝑔𝑤𝑔𝑔) + 4𝐴𝐴 (iii)𝑆𝑆3𝑁4(𝑑𝑑𝑤𝑔𝑤𝑑𝑑𝑤𝑑𝑑 𝑜𝑜 𝑤𝑤𝑤𝑤𝑤) + 6𝐴𝐴2𝑂(𝑔𝑔𝑤𝑔𝑔) → 3𝑆𝑆𝑂2 (𝑔𝑔𝑤𝑔𝑔) +

12𝐴𝐴 + 2𝑁2 ↑

[1] C. Ballif, et al, App. Phys. Lett., 82 (12), 1878-1880, 2003.

[2] Schubert et al, Solar Energy Materials and Solar Cells, 90, 33399-3406, 2006.

[3] Hilali et al, J. Electrochem. Soc. 153, A5, 2006.

[4] Li et al, J. Appl. Phys. 105, 066102, 2009

[5] Eberstein et al, Energy Proceedia 27, 522-530, 2012.

[6] Tai et al, RSC Advances, 5, 92515-92521, 2015



p.8

TEM micrograph: overfired Ag/Si contact. The intermediate SiNx

layer has been dissolved in the firing process.

Ballif et al : Appl. Phys. Lett., Vol. 82, No. 12, 24 March 2003



p.9

SEM-picture of the interface of a silver thick film-finger on [1 0 0] orientated silicon. Silver crystallites grown into the silicon are clearly visible.

Schubert et al., Solar Energy Materials & Solar Cells 90 (2006) 3399–3406



SEM micrographs of: contact layer, finger layer, full layer and elemental analysis

Si

Ag Crystallites

Contact and Finger layers

Ag Crystallites

Contact layers Top view of contact and finger layers after sintering



p.11

Paste particle size Series Resistance (Ω-cm2)

Contact Resistance (Ω-cm2)

Fill factor

(%) Paste ID D10 D50 D90

A 1.273 2.102 3.466 13.813 0.825 43.4 B 1.125 2.031 3.657 0.812 0.442 78.4 C 1.194 2.145 3.784 0.737 0.390 78.8 D 1.205 2.085 3.568 0.638 0.312 79.4 E 1.208 2.029 3.506 1.737 0.774 73.8 F 1.238 2.056 3.366 1.829 0.552 73.5 G 1.182 2.032 3.437 1.983 1.099 73.1 H 1.159 2.062 3.628 1.107 0.334 76.9 I 1.159 1.914 3.100 2.321 0.929 71.1 J 1.140 2.066 3.761 0.874 0.222 78.2 K 1.171 2.060 3.579 4.263 0.906 63.6 L 1.150 2.028 3.518 6.703 1.018 56.1

CP 1.545 3.456 4.965 5.876 0.967 60.3



Contact characterization

SEM/EDX for Ag paste D and J after drying at 200oC for 2-mins

Paste D 34/66 PbO/TeO2

Paste J 50/50 Pbo/TeO2



EDX analyses of Contact

Paste J Paste D

Element Wt% At% CK 43.92 77.82 OK 06.10 08.12 MgK 03.62 03.17 AlK 02.81 02.22 SiK 03.86 02.92 PbM 13.51 01.39 TeL 26.19 04.37 Matrix Correction ZAF

Element Wt% At% CK 53.34 82.10 OK 07.53 08.70 MgK 03.39 02.58 SiK 04.52 02.97 PbM 15.72 01.40 TeL 15.50 02.25 Matrix Correction ZAF

After 2-min drying at 200oC



Si

Ag + Pb + Te

K_C

ou

nt


Paste J

K_C

ou

nt

Ag + Te + Pb

Si

SEM/EDX for Ag paste D and J after contact co-firing at 815oC peak firing temperature in IR belt furnace.

Paste D



EDX analyses of Contact Paste J

After contact co-firing at 815oC peak firing temperature in IR belt furnace.

Paste D




0

50

100

150

200

250

300

350

30 40 50 60 70 80 90 100

Co

un

t p

er S

ec

2θ (degree)

Paste D after 200oC dry

Paste D after 815oC sinteringSi peak

(111)

(200)(220)

(311)

(222)0

50

100

150

200

250

300

350

20 30 40 50 60 70 80 90 100

Coun

ts p

er s

ec

2Ѳ (degree)

Paste J after 200oC dry

Paste J after 815oC firing

(111)

(200)

(220)

Si Peak(311)

(222)

XRD pattern for Ag paste D and J after drying at 200oC for 2-mins and after contact co-firing at 815oC peak firing temperature in IR belt furnace. Before: All Ag phases are similar After: (111) phase in D doubles due to PbO/TeO2 ratio difference

Paste D Paste J



Raman Spectra of contact

100 200 300 400 500 600 700 800 900 1000

100020003000400050006000700080009000

100001100012000130001400015000

124-

D-H

NO

3-1

Wavenumber

124-D-HNO3-1 124-D-HNO3-2 124-D-HF-1 124-D-HF-2

Paste D

Inte

nsity

Ag2Te

TeO2

Si



p.18

1. Nano-sized metallic Zn additives - uniformly etch the non-conductive SiNx:H layer

2. TeO2 additive - uniform etching of siNx:H layer - Decreases viscosity of molten glass and causes uniform wetting of SiNx:H - No Te after glass removal with HF (i) Ag, Te and Si form Ag-Te, Ag-Si and Ag-Te-Si alloys.

(ii) Formation of Ag2Te – a semimetal increases conductivity of glass – low contact resistance and gridline resistance.

3. Both 66PbO-34TeO2 and the 50PbO-50TeO2 glasses enable higher isothermal conductivity. The resulting low melting nature of the glass facilitate diffusion process introducing ionic conductivity leading to high isothermal conductivity.

1. Li et al., J. Appl. Phys. 110, 074304 (2011) 2. Ionkin et al, ACS Appl. Mater. Interfaces 3, 606 (2011) 3. Ebong et al, JJAP, 56, 08MB07 (2017) 4. ] R. Prunchak, US patent 7,736,546B2, 2010 5. Vithal et al., J. Appl. Phys. 81 (12), 7922-7926, (1997)



Abasifreke Ebong, Nirupama Bezawada, Veysel Unsur, Ren Keming and Ahrar Chowdhury

Department of Electrical and Computer Engineering University of North Carolina at Charlotte

9201 University City Blvd, Charlotte NC 28223-0001, USA



• Belt speed: 230 pm • Peak Temp: 815oC

abasifreke ebong, nirupama bezawada, veysel unsur, … · university of north carolina at charlotte...

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