Evolution of Cell Technology and its Impact on ... Celltech 17/PV... · DuPont Photovoltaic and Advanced Materials PV CellTech 14 & 15 March 2017 ... step change in efficiency Solamet®

Evolution of Cell Technology and its Impact on Metallization Paste Development

Dr. Mike F. Barker R&D Manager, Asia Pacific DuPont Photovoltaic and Advanced Materials

PV CellTech 14 & 15 March 2017 Penang, Malaysia

For over 40 years

our material innovations have led the photovoltaics industry

forward, and helped our clients transform the power of the Sun

into power for us all. Today we offer a portfolio of solutions that

deliver proven power and lasting value over the long term.

Whatever your material needs, you can count on quality DuPont

Photovoltaic Solutions to deliver the performance, efficiency and

value you require, day after day after day…

Copyright © 2017. All rights reserved. 2 2

Solar Cell Efficiency Evolution

High Efficiency LDE Solamet® PV17x, 18x, 19x

High Efficiency PERC Solamet® PV36x, 56x, 76x

PV20x Excellent fine line and contact capability for

LDE and PERC

Ncell Solamet® PV3Nx

HJT Solamet® PV4xx

Back Contact Solamet® PV93x

• LDE & PERC is still the majority with PERC gaining share.

• Adoption of N type, IBC, HJT is still uncertain due to the high technology content and investment threshold.


2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022

DuPont™ Solamet® Product Generation Roadmap

PV17x for LDE

Metallization for advanced screens

PV18x for Enhanced LDE

PV3N1, PV3N2 for P-contact

PV19x for Extreme LDE

Back Contact Metallization Pastes (p and n contacts)

PV3Nx Improved fine line, conductivity and P-contact capability

PV51x , PV52x Low cost tabbing interconnects

PV36x Al for PERC (Laser Contact Openings)

Fro

nt S

ide

Silv

er

PV56x non-fire through tabbing interconnect for PERC

PV20x

HJT Metallization Pastes (Finger with excellent conductivity and Solderable Busbar)

PV18J with improved fine line and high adhesion

Pioneer in LDE

PV76x for PERC Maximizing contact capabilities on PERC architectures

PV19B market benchmark with superior aspect ratio and fine line printability

PV19L, PV19H with superior adhesion

Superior contact, Voc and fine line

Improving cell performance for LDE and PERC

Driving fine line and enabling new technologies (including

more aggressive emitters and advanced texturing)

PVM1x with excellent fine line printability and aspect ratio on MCF screens

Sin

gle

Print

A

l

Rea

r S

ide

Ta

b

P-t

yp

e

N-t

yp

e

PVD2A, PVD2B Pioneer in floating busbars

PVD1x / PVD2x for Double Print driving higher aspect ratios

Multi P

rint

Ncell

IBC

HJT

Copyright © 2017. All rights reserved. 4

DuPont™ Solamet® Next Gen Front Side Silver Achieving Higher Cell Performance for P-Type Solar Cells


DuPont™ Solamet® Enabled Significant Improvement in P-Type Cell Efficiency

First to introduce LDE with Solamet® PV17x achieving a

step change in efficiency

Solamet® Next Gen. FS silver enabling

adoption of fine line screen with excellent aspect ratio

Standard p-type PV16x

High efficiency LDE, PV17x

High efficiency enhanced LDE, PV18x

Next Generation Metallization

High efficiency improved fine line, PV19x

Integrated PERC Solution PV76x, PV56x, PV36x

First to offer an integrated solution for PERC unlocking

further efficiency entitlements for p-type cells


Metallization Paste Development for Fine Line Printing

• Excellent paste transfer property enables moving to finer line screens

Next Gen FS Solamet®

PV19B

23um 26um 29um 32um 23um 26um 29um 32um

Note: Screen opening is narrow side.


Enabling Finer Line Contact Wafer : 6” M2 Mono 90 ohm/sq

Significant contact resistance improvement to further boost efficiency

through diffusion optimization


Enabling Fine Line Screen

360.16-31um 380.14-27um

PV19x

Next Gen FS

[VALUE]

[VALUE]

[VALUE]

[VALUE] [VALUE]

0%

[VALUE]

0% 0%

20%

40%

60%

80%

100%

120%

PV19x Next Gen FS

360.16-31um 380.14-27um

EL Defect Count

0 1 2 >=3

EL defect count

(50pcs/group inspection)


Efficiency Optimization by Finer Line Screen

Wafer : 6” M2 Mono 90 ohm/sq

Paste Screen Eff Voc Isc FF Rs

Next Gen 380.14.27um-110F +0.12 0.639 9.311 80.50 1.59

Next Gen 380.14.29um-105F +0.06 0.640 9.299 80.25 1.72

Next Gen 360.16.31um-105F +0.04 0.639 9.290 80.43 1.62

Next Gen 360.16.31um-105F Ref 0.639 9.299 80.16 1.75

Note: Screen opening is narrow side.

Paste

opening

screen

PV19BNext Gen FS

31312927

360.16360.16380.14380.14

19.80%

19.60%

19.40%

NCell

19.50%

19.54%

19.56%

19.62% >0.1% Efficiency gain

demonstrated. Higher Isc without FF drop while moving to

finer line


Maintain Good Adhesion Performance

Comparable Adhesion Performance as Solamet® PV19L


DuPont™ Solamet® Next Generation Front Side Silver – Enabling Fine Line Screen

• Excellent gridline resistance and printability, which enables < 27μm opening screen printing with 0.1% efficiency gain

• Wide screen selection allows fine line printing performance without high cost

• Quality and consistent materials are critical to ensure long term printability for stable mass production


DuPont™ Solamet® Front Side Silver Development Direction


Efficiency Entitlements from FS silver

• 0.1% by 10μm narrower lines

• 0.3% by reduced recombination

• 0.1% by better contact

Enable extreme Lightly Doped Emitter (LDE) by reducing contact resistance and optimizing overall cell performance through fill factor (FF) and open circuits voltage (Voc) improvement.

Focus on PERC

FS Recombination

(Emitter) 0.3%

FS Recombination

(Metal) 0.1%

Bulk Lifetime 0.5%

BSF Recombination 0.3%

Rear Passivation 0.1%

Rear Contact 0.3%

Front Contact 0.1%

Metal Shading 0.1%


Metallization Paste Development for “Mesh Cross Free” Screens

Incumbent on std. mesh

• With 25μm design > 0.1% Efficiency improvement demonstrated over incumbent 38μm screen. • Adoption of this novel screen technology is still at early stage Front side

A B

Concept Standard mesh with low mesh count

Special mesh (2~3 wires removed at finger location)

Requirement Precise alignment in screen MFG process

Work with upstream mesh supplier

Solamet® PVM1A


Metallization Paste Considerations for Black Si

Process (multi) STD acidic etching Reactive ion etching (RIE)

Metal catalysis chemical etching (MCCE)

Etch rate Slow Fast

Cost High Relative Low

SEM photo

• The current challenge of Black silicon is lower adhesion than on

standard texture.

• Need to continue to monitor contact and printability performance.


DuPont™ Solamet® Metallization Paste Development for N-cell


n-Si (base)

p+ (B-doped) emitter

n+(P-doped) BSF

Need to reduce Jo

under metal (Jo,m) ~2x ~+60%

Ag/Al contact still has much higher rho-c and

rho-gl compared to P-type standard

Voc improvement

ref ref

Opportunities for Further Improvement on N-cell

• Screen printing paste improvement

• Reduce contact resistivity and gridline resistivity

• Improve recombination parameter (Jo) for higher Voc

• Floating busbar (PVD2x, PV61B) to reduce Jo,m under busbars

• Improve PV3Nx to further reduce Jo,m under fingers

• <40µm fine-line printing

Bi-facial Design


• Double Print process enables a Decoupling of the functions of each layer to maximize overall performance.

• 1st layer paste can focus more on improving the contact resistance on the B-doped emitter.

• 2nd layer paste focusing on conductivity and soldered adhesion. Also, the “Non-contacting” nature of PVD2A (floating busbar) provides an additional benefit in improving Voc of the cell (less recombination under the busbar).

Double Print Package for N-cell: Solamet® PV3N2+PVD2A

2nd print: Finger lines & busbar: PVD2A

1st print: Finger lines only: PV3N2


Sample

Process

C7878PV3N2

FireDryWetFireDryWet

65

60

55

50

45

Wid

th

C7878PV3N2

20

15

10

5

Sample

Hp

k

48.2

7

47.1

133

47.4

117

54.7

983

58.9

067

57.7

067

15.1

117

10.2

521

Boxplot of Width Boxplot of Hpk

Improved Fine Line Performance

Width Height

• Better aspect ratio with 10% laydown saving • 0.05% efficiency increase demonstrated


Next Gen Paste Development Progress for N-cell

Next genC7878

0.2

0.1

0.0

-0.1

-0.2

Sample

∆N

Cel

l(%

)

Next genC7878

0.0002

0.0000

-0.0002

-0.0004

Sample

∆ρ

c(o

hm

*cm

2)

Next genC7878

5.0

2.5

0.0

Sample

∆U

oc(

mV

)

Next genC7878

0.2

0.0

-0.2

-0.4

Sample

∆R

s(m

oh

m)

Boxplot of ∆NCell(%) Boxplot of ∆ρc(ohm*cm2)

Boxplot of ∆Uoc(mV) Boxplot of ∆Rs(mohm)

• Significant contact resistance improvement to further boost efficiency through

diffusion optimization

• Candidate pastes identified with improved conductivity, contact resistance, & Voc.


DuPont™ Solamet® Metallization Pastes for HJT Finger Line and Busbar


Properties

Line width (um) <100

Thickness (um) >25

Cross section (um2) >1500

Not recommend

190-230

83.0-86.0

Printing properties (#325 W:80um Emuls ion:25um)

Table.1 Typical physical properties

Viscosity (Pa.s)

@ 10rpm

Solid content (wt%)

@ 750degC

Test

Resistivity (uohm cm)

@ 200degC-30min13

Solderable

Table.2 Composition properties

L9281: Polymer thick film paste for fine line electrode

【Features】

• Process temperature 150 - 200degC • Air curable

• Screen printable • Low resistivity

• Store in room temperature (Thermoplastic)

L9180: Solderable PTF paste

【Features】 • Process temperature 150 - 250degC

• Air curable • Screen printable

• Good solder-abilty and adhesion (>3N) • OK with Pb-free solder

• Store in room temperature (Thermoplastic)

Recommended Process Conditions Dry: 180deg.C for 60mins

Thickness: 30μm (A) Ribbon: Sn/Pb solder coated Cu

Flux: Kester 955 (B) Pre-heat Temp: 90deg.C Iron Temp: 230 deg.C

(A) >25um electrode thickness required for

good adhesion (B) Only apply flux on Ribbon. Not on PTF.


DuPont™ Solamet® Metallization Paste Options for IBC


Metallization Options for IBC Two Pastes System One Paste System

Print/Dry 2 times 1 time

Contact via openingNo need

(Fire-through)

Need

(Laser, Etching)

Firing temperature 700-800℃ 550-600℃

Electrode width As narrow as possible< 600µm

less than p-n pitch

Electrode thickness As thick as possible < 10µm

Passivation area loss

by metallization

(electrode width)

(p-n pitch)

No limitation

with electrode width

p+ n+ p+ n+

p-n pitch Electrode width

Before metallization Two pastes system One paste system

Contact via

Further progress on IBC paste development will require

close collaboration with cell / module customers


DuPont™ Solamet® Interconnect Paste for Advanced Cell Assembly


• In parallel to innovation on new cells structures (PERC, n-PERT), there is a move towards advanced module structures, for example shingled cell modules.

• DuPont has developed innovative interconnect paste to replace materials like SnPb Alloy used for advanced cell assembly

Introduction

Interconnect Ag

Laser cutting

Si

Shingled cells assembly in DuPont facility DuPont Interconnect Paste

Stable at room temperature


• Innovative paste chemistry enables performance differentiation from alternatives

• Module reliability

– Low elastic modulus helps modules release stress

– High temperature durability from new binder matrix

• Processing flexibility

– Equipment and application developers enjoy flexibility with DuPont offerings as they are stable at room temperature

Technical Features

Key Features of DuPont Value Delivered Comparison with other interconnect materials

DuPont pastes Epoxy ECA Silicone ECA Solder (Sn/Pb) Elastic modulus1 (MPa) Lower mechanical stress 20 2000 50 20000

Resistivity (ohm cm) Effective electrical connection 0.5-3 x 10-4 1-25 x 10-4 2-30 x 10-4 1.5 x 10-5

High adhesion to multiple substrates Meeting process standard

High temperature durability Use in high temperature applications @ 250oC

bleeding out control Avoids shading, waste and short-circuit N/A

Product stability at room temperature Lower cost of shipping and storage; Flexibility for processing;

N/A

Intermediate state available for processing, inspection and re-working

Flexibility for processing; New application like coated ribbons

Environment-friendly Lead free

1. Measured value for binder materials w/o metallic fillers


Dispensing

Module Maker

“Attachment”

Screen Printing

“Easy-to-Use” for Both Dispensing and Screen Printing


• Shingled cell design

• Floating electrode design – Less recombination

• passivation layer preserved at busbar area bringing significant Uoc contribution.

– More light absorption • combined together with textured ribbons

• Other applications (IBC, HJT etc.) where a flexible & low process temperature cell interconnection solution is required

Potential Applications

Ag

Si

Cu

Sn/Pb

SiNx finger Busbar Ag

Si

Cu

SiNx finger

New paste

Traditional cell busbar / ribbon Floating electrode / new interconnect / ribbon

Uoc boost

Sn/Pb

Isc boost


Solamet® Metallization Technology Lower Cost of Ownership and Greater Profitability

• Moving to finer lines with excellent contact performance is the key for P-type metallization development to further boost cell efficiencies

• Next generation Solamet® front side silver maximizes cell efficiency on P-type solar cell (LDE & PERC) more than 0.1%

• DuPont continues to set the pace of innovation in the solar industry by introducing leading performance pastes that work to deliver greater solar panel efficiency and power.


Copyright © 2017 DuPont or its affiliates. All rights reserved. The DuPont Oval Logo, DuPont™, The miracles of science™ and all products denoted with ™ or ® are registered trademarks or trademarks of E. I. du Pont de Nemours and Company or its affiliates.

Images reproduced by E. I. du Pont de Nemours and Company under license from the National Geographic Society.

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Evolution of Cell Technology and its Impact on ... Celltech 17/PV... · DuPont Photovoltaic and Advanced Materials PV CellTech 14 & 15 March 2017 ... step change in efficiency Solamet®