Cost reduction n-pasha by improved metallization

Transcription

1 Cost reduction n-pasha by improved metallization Eric Kossen, Ingrid Romijn, Kees Tool Metallization workshop May 2013 Konstanz

2 Outline ECN n-pasha cell process Improved front-side metallization Is stencil ready for industry? Cost savings by silver reduction Conclusions 2

3 ECN s n-pasha cell process Proven industrial process, Panda cells in production at Yingli Solar p + emitter n + BSF Incident light n-type Cz Albedo light Emitter & BSF co-diffusion Both sides SiN x passivation and ARC H-patterned front and rear metallization (2x silver paste) Bifacial solar cell, suitable for very thin wafers no bowing Enables bifacial modules 3

4 ECN s n-pasha cell process Proven industrial process, Panda cells in production at Yingli Solar Silver p + emitter n + BSF Incident light n-type Cz Emitter & BSF co-diffusion Both sides SiN x passivation and ARC H-patterned front and rear metallization (2x silver paste) Albedo light Silver Bifacial solar cell, suitable for very thin wafers no bowing Enables bifacial modules 4

5 Front-side metallization Reduced metal area: Isc increase due to less shading Voc increase due to less contact recombination. Challenge: Maintain low resistivity losses and thus a high FF 5

6 Front-side metallisation: Step 1 Step 1: Reduction screen printed fingers from 125 µm to 100 µm Reduction of front-side metal coverage with 1% 3 mv gain in Voc due to decreased contact recombination 0.2 A gain in Isc due to reduced shading losses 6

7 Front-side metallisation: Step 2 Step 2: Printed fingers width reduced to 58 µm using stencil instead of screen printing. Line width reduced to 58 µm Better aspect ratio Less fingers possible 1.5 % reduction metal coverage Width [µm] Max Height [µm] Min Height [µm] Rline [mohm/cm] Stencil Screen

8 Front-side metallisation: Step 2 Reduction of the front-side metal coverage: 1,5 % 6 mv gain in Voc due to decreased contact recombination 0,3 A gain in Isc due to reduced shading losses 8

9 Front-side metallisation: Step 3 Step 3: Applying non-contacting busbar Busbar area ~ 2.5% cell area Reduce effective contact area to 3% Less contact recombination 6 mv Voc gain Same metallization area no Isc gain 9

10 Summary front-side metallisation Front side metal coverage reduced from 8 % to 5.5 % Voc improvement 6 mv Isc improvement 0.3 A Non-contacting busbar Effective coverage for Voc 3% Effective coverage for Isc 5.5 % Total efficiency gain 0.5 % absolute 10

11 Outline ECN n-pasha cell concept Efficiency gain on the front-side metallization Stencil ready for industry? Cost savings by silver reduction Conclusions 11

12 Stencil printing Stencil is a two step printing method: Busbar is printed first Fingers are printed on the bus-bar Screen printing Busbar only Drying Stencil printing fingers only Drying & Firing 55 12

13 Stencilled fingers: 58 µm (min height 24 µm) Almost no bleeding from the fingers Homogenous line (no valley s) Straight lines Straight connection to the bus-bar No resistance losses 13

14 Stencil lab results: 30 micron opening in the stencil Width(um) Max Height(um) Min Height(um) Height stdev(um) Cross section(um2) Before firing 39,71 29,79 23,27 1,60 737,77 After firing 33,54 24,10 19,64 1,12 551,43 Before firing After firing 14

15 Stencil test on an industrial line Reference double screen print Printed > 2500 wafers No cell and stencil breakage during the prints Stable print quality Normal process parameters can be used (print settings, firing) 25 % less silver consumption Possibility to use dedicated busbar paste (efficiency or cost) 0.1 % efficiency gain obtained 15

16 Is stencil ready for the industry? Yes 16

17 Outline ECN n-pasha cell concept Efficiency gain on the front-side metallization Stencil ready for industry? Cost savings by silver reduction Conclusions 17

18 Cost saving by silver reduction Front side: 20 % silver reduction after stencil print optimization Smaller line width / height without FF losses 18

19 Cost saving by silver reduction Front side: 20 % silver reduction after stencil print optimization Smaller line width / height without FF losses 20 % silver reduction after busbar optimization Introducing a non contacting busbar Low laydown paste 19

20 Cost saving by silver reduction Front side: 20 % silver reduction after stencil print optimization Smaller line width / height without FF losses 20 % silver reduction after busbar optimization Introducing a non contacting busbar Low laydown paste 40% silver reduction Below the Ag consumption p-type 20

21 Outlook front side metallisation Front side: Silver reduction after stencil print optimization Goal smaller line width < 58 micron without FF losses Decrease the silver consumption to 50 % of the original consumption. Front side becomes even more cost effective compared to p-type 21

22 Cost reduction back side Reduction of the silver paste usage on the rear side. Reducing line width. 22

23 Cost reduction back side Reduction of the silver paste usage on the rear side. Reducing line width Paste optimization. Lower lay down paste opt 1 Paste contains less silver opt 2 23

24 Cost reduction back side Reduction of the silver paste usage on the rear side. Reducing line width Paste optimization. Lower lay down paste opt 1 Paste contains less silver opt 2 Goal % less than original silver consumption by optimizing the back side grid. 24

25 Summary silver cost reduction 60% of total silver consumption reduced by implementing new pastes and reducing line width. Low lay down paste Reducing line width with no efficiency loss. The silver consumption per wafer higher compared to p-type and this will probably remain But the silver consumption per watt-peak for n-pasha is comparable to p-type 25

26 Conclusions: 0.5 % absolute efficiency gain while reducing front-side Ag by 40% 65 % Ag reduction rear side achieved with no losses n-pasha Ag consumption per watt peak comparable with p-type This makes n-pasha process high efficient and also very cost effective 26

27 Thanks to: John Anker, Teun Burgers, Astrid Gutjahr, Martien Koppes, Ingrid Romijn Machteld Lamers, Desislava Saynova, Kees Tool, Ye Zhang Markus König, Lindsey Karpowich, Nicole Georg, Arno Stassen 27