Update on metallization technologies from silver to copper based solutions Highlights of the 3 rd Workshop on Metallization Gunnar Schubert (Sunways AG), Jaap Hoornstra (ECN Solar Energy), Guy Beaucarne (Dow Corning) Sponsors Supporters
2008 1 st Workshop on Metallization Utrecht, October, 2008 135 participants 2010 2 nd Workshop on Metallization Konstanz, April, 2010 190 participants peer reviewed proceedings 2011 3 rd Workshop on Metallization Charleroi, Belgium, October, 2011 2 day workshop with podium discussion Over 200 participants 29 contributions peer reviewed proceedings
Dominating metal contacts Contacts to highly doped n typ silicon (Phosphorous Emitter / BSF): Market dominating: Silver based thick film Contacts to highly doped p typ silicon (e.g. Boron Emitter / BSF): Often used: Silver based thick film Contacts to lowly doped p typ silicon (e.g. local / full area BSF): Market dominating: Aluminum based thick film
Cost drivers of dominant metal contacts Material (most important: Ag) Efficiency limitations From: J. Bartsch (ISE), Met. Workshop 2011, Charleroi
Topics at workshop Fundamentals of contact formation New developments in metallization technology Interaction of cell metallization and module interconnection 25 share contributions Contributions contacts to highly doped Si 20 20 full plating; 5 15 10 thick film; 11 7 5 hybrid; 4 2 0 contacts to highly doped Si contacts to lowly doped Si module interconnection
Contacts to highly doped Silicon From Silver to Copper printed printed Ag seed + printed Ag seed + Plated Ni seed + Ag Ag plating Ni/Cu plating Ni/Cu plating From: E. Cabrera (ISC), Met. Workshop 2011, Charleroi From: S, Binder (ISE), Met. Workshop 2011, Charleroi From: J. Bartsch (ISE), Met. Workshop 2011, Charleroi
Contacts to highly doped Silicon From Silver to Copper printed printed Ag seed + printed Ag seed + Plated Ni seed + Ag Ag plating Ni/Cu plating Ni/Cu plating From: E. Cabrera (ISC), Met. Workshop 2011, Charleroi From: S, Binder (ISE), Met. Workshop 2011, Charleroi From: J. Bartsch (ISE), Met. Workshop 2011, Charleroi
Understanding silver thick film contacts Contact formation Nucleation centers key for Ag crystal growth on p or n type Si Main parameter: crystal defects induced by e.g. Surface concentration Surface topography Paste composition doping species S. Riegel (UKON) Crystal imprints on highly doped n Si Crystal imprints on bulk p Si Ag crystals of Al free Ag paste on B emitter From: E. Cabrera (ISC), Met. Workshop 2011, Charleroi From: A. Kalio (ISE), Met. Workshop 2011, Charleroi
Understanding silver thick film contacts Current transport Still under investigation: Dominating current transport path: Via direct interconnections from crystal to silver e.g K. Butler (UOS) Via tunneling process through glass G. Laudisio (Dupont) Current Current From: E. Cabrera (ISC), Met. Workshop 2011, Charleroi Discussion among participants pointed out: More investigations are necessary
Application of silver thick film contacts Contacting low surface concentrations possible! (Hybrid approach) B Emitter: N A = 2x10 19 cm 3 Contact Resistivity : ρ C = 5 mohmcm 2 A. Kalio (ISE) From: A. Kalio (ISE), Met. Workshop 2011, Charleroi P Emitter: N D = 8x10 18 cm 3 Contact Resistivity: ρ C = 7 mohmcm 2 S. Binder (ISE) From: S. Binder (ISE), Met. Workshop 2011, Charleroi
Application of silver thick film contacts High efficiency silver pastes (screen printing) Enormous progress in pastes for P Emitters G. Laudisio (Dupont) R. Hoenig (ISE) Heinz (BASF) Efforts to reduce silver deposition From:G. Laudisio (Dupont), Met. Workshop 2011, Charleroi From: R. Hoenig (ISE), Met. Workshop 2011, Charleroi
Progress in Printing Technology Goal: high aspect ratio and low silver consumption Dispensing Aspect ratio in lab: up to 0.5 R. Hoenig (ISE) Screens From: R. Hoenig (ISE), Met. Workshop 2011, Charleroi Single print: ultrafine mesh: Line width < 50μm T. Falcon (DEK) Double print: Δη abs = +0.08% (large scale test) Tomasi (X Group) Stencils Double print approach with single layer stencil most favorable Bettinelli (INES), Falcon (DEK), Tomasi (X Group) From: A. Bettinelli (INES), Met. Workshop 2011, Charleroi
Contacts to highly doped Silicon From Silver to Copper printed printed Ag seed + printed Ag seed + Plated Ni seed + Ag Ag plating Ni/Cu plating Ni/Cu plating From: E. Cabrera (ISC), Met. Workshop 2011, Charleroi From: S, Binder (ISE), Met. Workshop 2011, Charleroi From: J. Bartsch (ISE), Met. Workshop 2011, Charleroi
Progress in Hybrid approach: printed seed + plating Lab Scale Short Ag plating step decreases contact resistance R. Hoenig (ISE) PERC + hybrid front side: Ag + Ni/Cu plating: 20.7% S. Binder (ISE) N typ solar cell with boron emitter: 19.6% A. Kalio(ISE)
Progress in Hybrid approach: printed seed + plating Pilot Line (standard industrial solar cell) Standard industrial solar cell: 18.8% after degradation A. Mette (Q Cells) From: A. Mette (Q Cells), Met. Workshop 2011, Charleroi
Contacts to highly doped Silicon From Silver to Copper printed printed Ag seed + printed Ag seed + Plated Ni seed + Ag Ag plating Ni/Cu plating Ni/Cu plating From: E. Cabrera (ISC), Met. Workshop 2011, Charleroi From: S, Binder (ISE), Met. Workshop 2011, Charleroi From: J. Bartsch (ISE), Met. Workshop 2011, Charleroi
Full Plating Typical process sequence for fully plated contacts ARC Opening Ni seed layer deposition NiSi x formation Ni / Cu / Sn plating Module integration e.g. Russel (IMEC)
Full Plating process sequence Challenges This Workshop ARC Opening Ni seed layer deposition NiSi x formation Ni / Cu / Sn plating Emitter / surface damage, opening width, CoO Uniformity, thickness control, CoO Spiking, shunting, contact resistance, emitter Adhesion, background plating Bartsch (ISE) Russel (IMEC) Tous (IMEC) Wehkamp (ISE) Tous (IMEC) Notarp (NBT) Braun (UKON) Module integration Adhesion, long term stability Bartsch (ISE) Russel (IMEC) e.g. Russel (IMEC)
Full Plating Cell Results PERC 2x2, Mask & Etch opening of ARC: 21.4% Bartsch (ISE) PERC 125x125, Laser ablation of ARC : 19.6% Russel (IMEC) Ni s Si Si interface Long Term Stability of Ni / Cu Contacts Adhesion > 1N/mm achieved From: L. Tous (IMEC), Met. Workshop 2011, Charleroi From: J. Bartsch (ISE), Met. Workshop 2011, Charleroi From: R. Russel (IMEC), Met. Workshop 2011, Charleroi
Contacts to lowly doped p type silicon Main topic: Metallization of a passivated rear side Concept 1: Thermally alloyed contacts Concept 2: Laser fired contacts Concept 3: Fire through Al pastes From: E. Urrejola (ISC), Met. Workshop 2011, Charleroi
Understanding thermally alloyed contacts Amount of Al in relation to exposed Si plays critical role in contact depth and local BSF formation Mueller (ISFH), Ruehle (ISE), Urrejola (ISC) Simple model to predict observed phenomena developed Mueller (ISFH), Ruehle (ISE) Improved understanding of process control Urrejola (ISC) Local BSF of line contacts and typical failure (void) From: E. Urrejola (ISC), Met. Workshop 2011, Charleroi Local BSF of point contacts From: C. Ruehle (ISE), Met. Workshop 2011, Charleroi
Paste development Paste development for LFC contacts: Paste and passivation have to be matched Schwab (ISE) Paste development for firing through Al: BSF is formed, dependent on paste composition, temperature and dielectric Shaikh (Ferro) From: A. Shaikh (Ferro), Met. Workshop 2011, Charleroi
Will plating be the next dominant metallization technology? Improvements in materials for silver contacts have pushed efficiencies with printing methods Material costs increased drastically in the last years Increasing effort to overcome challenges of fully plated contacts Which approach will make its way into production? Let s ask the experts of the workshop
What is the share of metallization techniques in the next years? 90.00% 80.00% 70.00% 60.00% 50.00% 40.00% 30.00% in 3 Years in 5 years in 10 years 20.00% 10.00% 0.00% Screen print Plating Hybrid Ink Jet New concepts
What is the share of metallization techniques in the next years? 90.00% 80.00% 70.00% 60.00% 50.00% 40.00% 30.00% 2013 Survey 2008 5 years 2013 Survey 2010 3Years 2014 Survey 2011 3Years 20.00% 10.00% 0.00% Screen print Plating Hybrid Ink Jet New concepts Screen printing is seen to dominate longer than expected! Importance of hybrid approach has decreased!
Summary Printing technology has again pushed the limits! Physical understanding of contact formation mechanism improved Transfer into paste products led to efficiency increase Improvements in printing technology Importance of fully plated contacts has increased Progress in understanding of process stability for copper plating Efficiency potential shown However: Complex process with several challenges Local aluminum contacts on back side Progress in understanding contact formation with printed aluminum Specific paste development for PERC concepts According to the experts of the workshop printing technology dominates longer than expected two years ago
The authors would like to thank: Sponsors 3 rd Workshop on Acknowledgment participants of the 3 rd metallization workshop in Charleroi, 2011 contributors for their high level presentations scientific committee sponsors and supporters Supporters
For latest information please check our website http://www.metallizationworkshop.eu/ Sponsors Supporters