Front grid metallization and module interconnections of industrial heterojunction solar cells

Transcription

1 Front grid metallization and module interconnections of industrial heterojunction solar cells P. Papet, T. Söderström, J. Ufheil, S. Beyer, J. Hausmann, J. Meixenberger, B. Legradic, W. Frammelsberger, D. Bätzner, D. Lachenal, G. Wahli, B. Strahm, J. Zhao, T. Hoes, M. Blanchet, E. Vetter, A. Richter, S. Leu Roth & Rau Research, Meyer Burger Metallization Workshop 2013

2 May 2013, Meyer Burger MB System Offering From ingot to solar module to complete BIPV energy system Cropping Bricking Squaring Texturing Coating Printing Testing Process Control Wafering Cleaning Separating Inspection Stringing Laminating Encapsulation

3 Heterojunction technology (HJT) x 3 HJT cells High Cell efficiency > 21% High Voltage >730 mv Low Temp. Coefficient Short process flow Front grid metallization challenge Curing temperature <250C Some paste suppliers Improvement on paste performances 3

4 How to reduce power losses in the cell front grid The ohmic power dissipation in solar cell front side fingers, P f, is given by : P f J 2 ρ. L. 12n lf 2 f n t J : current density of the cell L : cell size (width) ρ lf : finger line resistance n f : number of fingers n t : number of busbars 4

5 How to reduce power losses in metallisation The ohmic power dissipation in solar cell front side fingers, P f, is given by : P f J J : current density of the cell L : cell size (width) ρ lf : finger line resistance n f : number of fingers n t : number of busbars 2 ρ. L. 12n lf 2 f n t Should be maximum Efficiency Given Small variation, mainly driven by emitter or ITO sheet resistance 5

6 How to reduce power losses in metallisation The ohmic power dissipation in solar cell front side fingers, P f, is given by : P f J 2 ρ. L. 12n lf 2 f n t J : current density of the cell L : cell size (width) ρ lf : finger line resistance n f : number of fingers n t : number of busbars Paste resistivity is given Finger size & aspect ratio : limited Double print addition paste consumption & CAPEX Large impact on P f No impact on CoO No impact on CAPEX Need adaped cell interconnection 6

7 The multibusbars approaches The 5 busbars approches 7

8 From three to five busbars Full chuck Ribbon position HJT solar cell Metal chuck Pogo pins HJT solar cell Increase the number of Busbars : Large increase of cell FF and Efficiency Reduction of ohmic power losses in front & back side No impact on cell consumable cost (Ag paste) & CAPEX Need an adapted cell interconnection system 8

9 Somont Certus 2 stringer (5 busbars) 5 BB Stringer is ready and available 300W p HJT module Compatible with HJT & conventionnal solar cells Increase cell power without additionnal CAPEX & cell production cost 3 x time less sensitive to finger resistance than 3 BB pattern 9

10 The multibusbars approaches The 5 busbars approches The Smart Wire Connection technology 10

11 Smart Wire Connection Technology (SWCT) Cu wires coated with InSn alloy embedded in an electrode foil Compatible with various metals (Ag, Al, Ni, Cu, Al-BSF and ) Low Tm of In => interconnection during lamination process Reduced Ag paste consumption : Busbars are useless Little impact of finger resistance 11

12 SWCT front wires nb optimization Experiments conducted with Ø200µm wires Optimum nb of front wires for HJT : Finger length of 2-4mm Little sensibility to finger resistance (3BB : 25mm) Effective wire shading of 150µm (shading gain of 25%) 12

13 Fine line printing & metallisation cost saving Front grid Ag paste, ribbons, wires, electrodes Only 40mg of Ag paste needed to print full 6 front side Higher finger resistance didn t affect module performances Ag : Ag paste consumption for 6 front grid Fr : Finger line resistance Fw : optical finger width Thanks to SWCT technology, the HJT metallization & interconnection is more cost competive compare to the standard high temperature Ag paste with 3BB design & ribbons The drawback of low temperature front grid metallization of HJT cells becomes an advantage SWCT need about 3 g of indium for wires coating per 60 cells/module => 0.5 $cts/wp Goal : substitute In in the future Target : reduce metallization cost below 3$cts/Wp 13

14 Low cost Ag/Ni pastes Finger resistance up to 7Ω/cm Low cost Ag/Ni paste can be use to reduce metallization cost with limited impact on module performances FF drop is linked to contact resistance issues between AgNi paste & ITO Ni/Cu electrodeposited front grid is compatible with SWC Opportunity to alternative cell metallization technologies Ag : Ag consumption for 6 front grid Fr : Finger line resistance Fw : optical finger width 14

15 Conclusions Increase the number of busbars on HJT solar cells: Opportunity to balance higher bulk resistivity of low temp. Ag paste without additional metallization cost Increase cell performances Meyer Burger offers two adapted solutions to reach this goal : Somont Certus 2 stringer : Regular soldering adapted to 5 busbars cells : HJT or conventional >21% 5BB-HJT cells with finger resistance of 0.8Ω/cm (fired paste : ~0.3Ω/cm) HJT-5BB modules in the 300Wp range Smart Wire Contact technology Only 40mg of Ag paste consumption for 6 inches HJT cells front grid SWCT-HJT has no loss up to 800 TC & 8000H DH SWCT-HJT modules in the 300Wp range SWCT contacts various metals (Cu, Ni, Ag, Al PVD and BSF) Thanks to very short fingers, little sensibility to finger resistance Opportunity to alternative metallization techniques 15

16 Reliability for SWCT-HJT modules SWCT-HJT has no loss up to 800 TC SWCT-HJT has no loss up to 8000 h of DH 16

17 Impact of cell breakage Connected with ribbon Connected with SWCT Impact of cell breakage are reduced with SWCT 17