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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

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  • 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

  • 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)

    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

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

    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

  • 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) [email protected] Metallization & Interconnection Workshop 2017

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

    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

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

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

    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

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

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

    p.7

    (i) () + 2() 2() + 2 (ii) () + 22() 2 () + 4 (iii)34( ) + 62() 32 () +

    12 + 22

    [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

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

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

    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

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

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

    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) 33993406

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

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

    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

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

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

    p.11

    Paste particle size Series Resistance (-cm2)

    Contact Resistance (-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

  • 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)

    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

  • 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)

    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

  • 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)

    Si

    Ag + Pb + Te

    K_C

    ou

    nt

    Contact characterization

    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

  • 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)

    EDX analyses of Contact Paste J

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

    Paste D

  • 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)

    Contact characterization

    0

    50

    100

    150

    200

    250

    300

    350

    30 40 50 60 70 80 90 100

    Co

    un

    t p

    er S

    ec

    2 (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

    2 (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

  • 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)

    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

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

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

    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)

  • 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

  • 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)

    Belt speed: 230 pm Peak Temp: 815oC

    Investigation of tellurite based ag pastes for fire through dielectric contacts (FTdc) solar cells with lightly doped emitterFoliennummer 2Homogeneous Emitter sheet resistance for p-doping (p-type cells)Effect of surface concentration and Schottky Barrier Height (eV) on FFFront gridline widths (m)Foliennummer 6Screen-printed contacts formation - reactionsScreen-printed contacts microstructureScreen-printed contacts microstructureSEM micrographs of: contact layer, finger layer, full layer and elemental analysisScreen-printed pastes with varying PbO/TeO2 ratioContact characterizationEDX analyses of ContactContact characterizationEDX analyses of ContactContact characterizationRaman Spectra of contactAdditives to Ag paste to improve contact resistanceInvestigation of tellurite based ag pastes for fire through dielectric contacts (FTdc) solar cells with lightly doped emitterRTP firing: Temperature Profile