METALLIZATION OF PASSIVATING AND CARRIER SELECTIVE CONTACTS: STATUS AND PERSPECTIVES AT FRAUNHOFER ISE

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1 METALLIZATION OF PASSIVATING AND CARRIER SELECTIVE CONTACTS: STATUS AND PERSPECTIVES AT FRAUNHOFER ISE M. Bivour, J. Bartsch, F. Clement, G. Cimiotti, D. Erath, F. Feldmann, T. Fellmeth, M. Glatthaar, M. Hermle, M. Jahn, S. Kluska, R. Keding, A. Lorenz, I. Lacmago-Lontchi, S. Mack, A. Moldovan, J. Nekarda, M. Pospischil, A. Rodofili, J. Rentsch, B. Steinhauser, J. Schube, L. Tutsch, W. Wolke and R. Preu, S. W. Glunz Fraunhofer Institute for Solar Energy Systems ISE 7 th Metallization Workshop Konstanz, 24 th October 2017

2 Passivating Contacts Overcoming Recombination at Metallized Regions Homojunction + fire-through contacts Main stream technology Intrinsic efficiency limitation by J 0,met >> J 0,pass Passivating contacts J 0,met = J 0,pass Current challenge: Establishing industrial cell process including metallization and module integration 2 Graph adapted from M. Bivour, PhD thesis, University of Freiburg (2015)

3 Passivating Contacts Amorphous Silicon Heterojunction (SHJ) Champion efficiencies for c-si solar cells 1,2 Back-end process temp. only ~220 C Not compatible with main stream c-si technology Adapted metal electrodes and cells interconnection Lower line conductivity TCO a-si(n) a-si(i) a-si(p) Si-absorber TCO 3 1 K. Yoshikawa et al., Nature Energy, 2:17032 (2017) 2 D. Adachi et al., APL, 107, (2015)

4 Screen Printing* Low Temperature Ag Paste SHJ Various low-t Ag pastes and drying/curing conditions evaluated Baseline process: single print Aspect ratio up to 0.3 Advanced process: double print Aspect ratio up to 0.6 Finger resistivity ρ finger ~ 6 µωcm Contact resistivity ρ c < 5 mωcm 2 w f, = 56 μm / h f,max = 13 μm Single print: 50 µm screen w f, = 34 μm / h f,max = 20 μm Double print: 30 µm screen 4 *D. Erath et al., Energy Procedia, 124, (2017)

5 Screen Printing* Cell Results SHJ Industrial solar cell precursors w f, = 56 μm / h f,max = 13 μm 5-busbar layout Bifacial Efficiency up to 21.9% Single print: 50 µm screen Metallization Area V OC J SC FF η [cm²] [mv] [ma/cm²] [%] [%] Single print (50 µm) best cell, 5-busbar, monofacial measurement, black chuck 5 *D. Erath et al., Energy Procedia, 124, (2017)

6 Ink Jet Printing* Towards Lower Ag Consumption SHJ Substrate heating for in-situ drying and ink wetting Width down to 32 μm for nano-silver-ink To be tested on cell level Multi-busbar layout Seed layer for selective plating using self passivating metal as plating mask 1 6 *D. Erath et al., Energy Procedia, 124, (2017) 1 M. Glatthaar et al., IEEE J-PV, 99, 1-5 (2017)

7 Laser Transfer and Firing of Seed Layer (LTF) + Plating* Overcoming the Need for Plating Resist SHJ plated Ag plated Cu dielectric TCO a-si(i/n) c-si(n) 7 *A. Rodofili et al., Sol. RRL 1 (2017)

8 Laser Transfer and Firing of Seed Layer (LTF) + Plating* Overcoming the Need for Plating Resist SHJ TCO a-si(i/n) c-si(n) 8 *A. Rodofili et al., Sol. RRL 1 (2017)

9 Laser Transfer and Firing of Seed Layer (LTF) + Plating* Overcoming the Need for Plating Resist SHJ Dielectric layer on TCO as plating mask dielectric TCO a-si(i/n) c-si(n) 9 *A. Rodofili et al., Sol. RRL 1 (2017)

10 Laser Transfer and Firing of Seed Layer (LTF) + Plating* Overcoming the Need for Plating Resist SHJ Dielectric layer on TCO as plating mask Laser induced forward transfer 1 of seed layer Transparent plastic foil with NiV layer No laser damage Foil NiV laser transfer dielectric TCO a-si(i/n) c-si(n) 10 *A. Rodofili et al., Sol. RRL 1 (2017) 1 J. Bohandy et al., Journal of Applied Physics 60, 1538 (1986).

11 Laser Transfer and Firing of Seed Layer (LTF) + Plating* Overcoming the Need for Plating Resist SHJ Dielectric layer on TCO as plating mask Laser induced forward transfer 1 of seed layer Transparent plastic foil with NiV layer No laser damage Laser firing of seed layer through dielectric Formation of contact to TCO No laser damage dielectric TCO a-si(i/n) c-si(n) laser firing 11 *A. Rodofili et al., Sol. RRL 1 (2017) 1 J. Bohandy et al., Journal of Applied Physics 60, 1538 (1986).

12 Laser Transfer and Firing of Seed Layer (LTF) + Plating* Overcoming the Need for Plating Resist SHJ Dielectric layer on TCO as plating mask Laser induced forward transfer 1 of seed layer Transparent plastic foil with NiV layer No laser damage Laser firing of seed layer through dielectric Formation of contact to TCO No laser damage Pulse plating to reduce parasitic plating 2 dielectric TCO a-si(i/n) c-si(n) plated Ag plated Cu 12 *A. Rodofili et al., Sol. RRL 1 (2017) 1 J. Bohandy et al., Journal of Applied Physics 60, 1538 (1986) 2 M. Glatthaar et al., IEEE J-PV, 99, 1-5 (2017)

13 Laser Transfer and Firing of Seed Layer (LTF) + Plating* Overcoming the Need for Plating Resist SHJ Industrial precursors 5-busbar layout Monofacial 30 µm Encouraging result for first cell batch No laser damage Optics and electrics improved compared to screen printing reference Metallization Area V OC J SC FF η [cm²] [mv] [ma/cm²] [%] [%] Screen printing LTF + Cu plating best cells, 5 busbar, monofacial, industrial precursors 13 *A. Rodofili et al., Sol. RRL 1 (2017)

14 Passivating Contacts* Poly-Si and TOPCon Back-end process temp. > 220 C Potentially, more compatible with main stream technology Currently, evaluation of suitable back-end processes Passivation / ARC doped c-si emitter Homojunction front Si-absorber thin SiO x doped Si-film??????????????? Poly-Si or TOPCon rear 14 *Y. Kwark PhD thesis, Stanford Univ. (1985) *F. Feldmann et al., SOLMAT, 120, (2014) *U. Römer et al., SOLMAT, 131, (2014)

15 40nm n-type TOPCon 800 C Firing of Commercial Ag Screen Printing FT Pastes thin SiO x c-si(n) n-type Si-film 80nm SiN x 1000 SiN x capping Poor contact ρ c (mωcm 2 ) nm SiN x 1 P1 P2 P3 P4 15

16 40nm n-type TOPCon 800 C Firing of Commercial Ag Screen Printing FT Pastes thin SiO x c-si(n) n-type Si-film 80nm SiN x 1000 SiN x capping Poor contact ρ c (mωcm 2 ) nm SiN x 1 P1 P2 P3 P4 16

17 40nm n-type TOPCon 800 C Firing of Commercial Ag Screen Printing FT Pastes thin SiO x c-si(n) n-type Si-film 80nm SiN x 1000 SiN x capping Poor contact ρ c (mωcm 2 ) Likely, contact to lowly doped absorber nm SiN x 1 P1 P2 P3 P4 17

18 40nm n-type TOPCon 800 C Firing of Commercial Ag Screen Printing FT Pastes thin SiO x c-si(n) n-type Si-film 150nm ITO 20nm SiN x 1000 SiN x capping Poor contact Likely, contact to lowly doped absorber ITO / SiN x capping Very good contact Likely, contact to highly doped ITO or Si-film ρ c (mωcm 2 ) nm SiN x 150nm ITO / 20nm SiN x P1 P2 P3 P4 18

19 300nm p-type Poly-Si* Firing of Commercial Ag Screen Printing FT Pastes thin SiO x p-type Si-film c-si(p) SDE surface, SiN x Low J 0,pass 80nm SiN x J 0,pass (fa/cm 2 ) before firing 780 C 810 C 840 C 870 C 900 C 19 *S. Mack et al., EUPVSEC, (2017)

20 300nm p-type Poly-Si* Firing of Commercial Ag Screen Printing FT Pastes thin SiO x p-type Si-film c-si(p) 1000 Ag 1 Ag 2 Ag 3 80nm SiN x Low J 0,pass J 0,met increases with T firing J 0,met >> J 0,pass J 0,met (fa/cm 2 ) Firing set temperature ( C) 20 *S. Mack et al., EUPVSEC, (2017)

21 300nm p-type Poly-Si* Firing of Commercial Ag Screen Printing FT Pastes thin SiO x p-type Si-film c-si(p) 80nm SiN x 900 C Low J 0,pass J 0,met increases with T firing J 0,met >> J 0,pass Local penetration / damage of poly-si*,1 21 *S. Mack et al., EUPVSEC, (2017) 1 H.E. Çiftpinar et al., Energy Procedia, 124, (2017)

22 300nm p-type Poly-Si* Firing of Commercial Ag Screen Printing FT Pastes thin SiO x p-type Si-film c-si(p) 1000 SDE surface, SiN x Low J 0,pass J 0,met increases with T firing J 0,met >> J 0,pass Local penetration / damage of poly-si*,1 Low ρ c for Ag2 80nm SiN x ρ c (mωcm 2 ) Ag1 Ag2 Ag Firing set temperature ( C) 22 *S. Mack et al., EUPVSEC, (2017) 1 H.E. Çiftpinar et al., Energy Procedia, 124, (2017)

23 300nm p-type Poly-Si Firing of Commercial Ag Screen Printing FT Pastes thin SiO x c-si(p) p-type Si-film 80nm SiN x 840 C J 0,pass 5fA/cm 2 J 0,met 250fA/cm 2 ρ c = 2mΩcm 2 23 *S. Mack et al., EUPVSEC, (2017)

24 Non-Firing Approach: Evaporated Ag High Efficiency Front Side Required High efficiency homojunction front essential to benefit from passivating contact at rear TOPCon + evaporated Ag J 0,met = J 0,pass 25.8% 1 lab-type cells thin SiO x n-type Si-film p + busbar DARC: SiN x + MgF 2 finger Al 2 O 3 p ++ selective boron emitter c-si(n) evaporated Ag Metallization Area V OC J SC FF η Front / Rear [cm²] [mv] [ma/cm²] [%] [%] Photolithography / evaporated Ag 4 (da) Certified by Fraunhofer ISE CalLab, da: designated area 24 1 A. Richter et al., EUPVSEC, (2017)

25 Non-Firing Approach: Evaporated Ag First Cell Batch Practicale Size Homogeneous boron emitter LCO + Cu-plating front side TOPCon + evaporated Ag 22.9% 1 SiN x /AlO x ARC thin SiO x n-type Si-film homogeneous boron emitter c-si(n) evaporated Ag Metallization Area V OC J SC FF η Front / Rear [cm²] [mv] [ma/cm²] [%] [%] LCO + Cu-plating / evaporated Ag 100 (ap) In-house measurement, ap: aperture area 25 1 F. Feldmann et al., EUPVSEC, (2017)

26 Non-Firing Approach Current Work homogeneous boron emitter c-si(n) TCO / metal stacks Similar to SHJ but >> 200 C evaporated Ag TCO metal TCO metal 26

27 Summary Amorphous Silicon Heterojunction (T back-end < 220 C) Baseline screen printing process (η = 21.9%) Ink jet printing of nano-silver ink promising for multi-busbar / plating Novel laser transfer of seed layer + Cu plating (η = 22.2%) TOPCon and poly-si (T back-end > 220 C) So far, J 0,met >> J 0,pass for firing-through metallization Only commercial Ag pastes investigated Hence, lots of room for improvement for paste optimization Non-firing approach under evaluation LCO + Cu-plating for high performance diffused front side TCO + metal optimized for > 220 C 27

28 Acknowledgments The authors would like to thank all colleagues at Fraunhofer ISE Part of this work was funded by German Federal Ministry for Economic Affairs and Energy under contract number D (PEPPER) A (HIPPO) (Folmet) B (HERA) (PV BAT 400) and by the EU s HORIZON 2020 programme for research, technological development and demonstration under grant agreement no (PROJECT DISC) Thank You Very Much for Your Attention! 28

29 Approach 2: Selective plating using conductive mask Precursor: Al ITO a-si(i/n) c-si(n) a-si(i/p) ITO Al 29 M. Glatthaar et al., IEEE J-PV, 99, 1-5 (2017)

30 Approach 2: Selective plating using conductive mask Step 1: seed layer print on both sides Inkjet particle-free Ag-ink 30 M. Glatthaar et al., IEEE J-PV, 99, 1-5 (2017)

31 Approach 2: Selective plating using conductive mask Step 2: simultaneous plating on both sides plated Ag plated Cu 31 M. Glatthaar et al., IEEE J-PV, 99, 1-5 (2017)

32 Approach 2: Selective plating using conductive mask Step 3: etching of Al layers plated Ag plated Cu 32 M. Glatthaar et al., IEEE J-PV, 99, 1-5 (2017)

33 TOPCon TCO Sputterdamage thin SiO x doped Si-film Si-absorber TCO > 200 C needed to cure damage iv oc (mv) before ITO after ITO 200 C 300 C 350 C 33

34 TOPCon TCO Sputterdamage thin SiO x doped Si-film Si-absorber TCO > 200 C needed to cure damage > 200 C poor mobility Trade-off passivation and TCO Mobility (cm²/vs) x x x x x10 20 Carrier density (cm -3 ) Annealing temperature ( C) 5.0x