Conductive Adhesives as Interconnection Technology for Busbar- and Pad-free Solar Cells

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Conductive Adhesives as Interconnection Technology for Busbar- and Pad-free Solar Cells Andreas Schneider, Andreas Halm, Severin Aulehla, Rudolf Harney, Pavel Motyka 2, Simon Koch 3, Martin Wegner 4

1 Conductive Adhesives as Interconnection Technology for Busbar- and Pad-free Solar Cells Andreas Schneider, Andreas Halm, Severin Aulehla, Rudolf Harney, Pavel Motyka 2, Simon Koch 3, Martin Wegner 4 International Solar Energy Research Center (ISC), Konstanz, Germany 2 Hitachi Chemical Europe GmbH, Düsseldorf, Germany 3 PI Photovoltaik-Institut Berlin AG, Berlin, Germany 4 Conergy SolarModule GmbH & Co. KG, Frankfurt/Oder, Germany

2 Outline - Motivation for Conductive Adhesives - Challenges to overcome - CF Application Technique - Optimization - Mechanical and Electrical Results - 60 Cells Modules - Cell to Module Losses - Climatic Testing Results - Outlook and Summary 2

3 Motivation for CF Thinner cell HIT cell IBC cell Low temp. bonding No soldering Busbar less Pb free tab ribbon Narrow and thick tab ribbon Light capturing ribbon Bond to conductive BS Cost down Flux free Busbar less (Ag) High yield Less cleaning (down time) of stringer No out gas No flux residue Easy handling due to its film form

4 Challenges to Overcome - Modification of existing stringers Least financial impact requires modification of existing equipment rather than purchasing new equipment - Quality procedures in mass production string repair, peel test and electrical specifications, lamination recipes - Proof of concept Reliability (IEC, UL), long term stability, advantages 4

5 CF Application Tab ribbon Busbar Solar cell Solder connection Tab ribbon Busbar CF connection CF Lamp, Hot-air, etc. >210 (Pb solder) >250 (Pb free solder) Heating. Pressure <180 Higher temperature connection Higher stress bonding Lower temperature connection Lower stress bonding 5

Optimization - Mechanical Typical requirement for peel

Ref. 3-6 - 1-6 - - Lower peel forces for CF compared to

6 Optimization - Mechanical Typical requirement for peel strength in industry is 1-1.5N Average peel strength in Newton for Front BB Front No BB Rear Pads Rear Al gaps Conductive Film <1 Solder Ref Lower peel forces for CF compared to soldering - Homogenous peeling results on busbars and fingers - High peel forces on Si no adhesion to Al (SP) 6

7 Optimization - Electrical Mainly FF is impacted by different interconnection technique: Cell FF [%] Tabbing FF [%] Module FF [%] G1 Soldered G1 CF G2 CF G3 CF G4 CF G5 CF On mini-module level - Cells connected by CF show better FF on BB and pads - Less FF losses after encapsulation for cells without rear pads - Minor losses for cells without front BB - Losses for cells without front BB and rear pads 7

8 Optimization - Electrical Climatic testing was performed on mini-modules: TC200 Pmpp [%] DH1000 Pmpp [%] HF10 Pmpp [%] G G G G G On mini-module level - No losses after TC test - Losses >1% for cells without rear pads after DH test 8

60 Cells Modules - Overview CF application versus soldering on 60 cells module level Group 1 Cells without BB/Pads CF Application Group 2 Cells with BB/Pads

going to TC200 and one module going to DH1000 (according to IEC) - Solar cells (6, Cz) were processed at ISC Konstanz - Cells of group 1 and 2 were

9 60 Cells Modules - Overview CF application versus soldering on 60 cells module level Group 1 Cells without BB/Pads CF Application Group 2 Cells with BB/Pads CF Application Group 3 Cells with BB/Pads Soldering Climatic Testing Initial and intermediate EL and IV testing Light soaking (according to IEC) 1 module going to TC200 and one module going to DH1000 (according to IEC) - Solar cells (6, Cz) were processed at ISC Konstanz - Cells of group 1 and 2 were interconnected (CF) and stringed at Hitachi/Japan - Cells of group G3 were soldered and stringed at Conergy - Modules were measured and tested (DH and TC) at PI Berlin

10 60 Cells Modules - CTM CF application versus soldering on 60 cells module level CTM Pmpp Voc Isc FF [%] [W] [V] [A] [%] G1-6.50± ± ± ± ±0.21 G2-6.19± ± ± ± ±0.23 G3-5.56± ± ± ± ± Voc for busbar- and pad-free cells show an increase of approx. 4mV/cell - CF versus soldering on BB and pads show an increased CTM of 0.6% - 1% larger CTM losses for modules with BB and pad-free cells

11 60 Cells Modules Climatic Testing Climatic testing results for all 6 modules Group/ Module Test Sequence ΔPmpp [%] G2_1 DH % G2_1 DH % G2_2 DH % G2_2 TC % Group/ Module Test Sequence ΔPmpp [%] G3_1 DH % G3_1 DH % G3_2 TC % G3_2 TC % - CF and soldering on cells with BB and pads comparable - Larger losses for cells without BB and pads Group/ Module Test Sequence ΔPmpp [%] G1_1 TC % G1_2 TC % G1_2 TC % G1_2 DH %

12 60 Cells modules Climatic Testing How to explain the larger losses for group G1 - Transportation of strings from Japan to Europe G1_1 Before After - Strong dis-coloration after climatic testing

13 Outlook Latest results on cells without BB but rear pads Group P mpp [%] TC200 P mpp [%] TC400 P mpp [%] TC600 P mpp [%] DH1000 P mpp [%] DH2000 Sold. G1-1.55± ± ± ± ±0.74 CG G1 0.12± ± ± ± ±0.00 CG G2-0.29± ± ± ± ±0.65 CG G3-0.34± ± ± ± ± Very promising results for cells without BB and with pads - Even after TC600 and DH2000 no significant losses 13

14 Summary - Mechanical results showed promising results for CF - Larger cell to module losses for CF (pastes, ribbon) - Excellent results after climatic testing for CF (BB & pads) - Failure for cells without BB and pads in climatic testing - Excellent results for cells without BB but with pads 14

15 ISC Konstanz research for a sunny future THANK YOU! Special Thanks to Conergy, Hitachi and PI Berlin This work was supported by the German Ministry for Environment (BMBF) under contract no. FKZ 13N11447 (FutureFab)

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