The Multi-Busbar Design: an Overview

Transcription

1 The Multi-Busbar Design: an Overview Stefan Braun 1, Giso Hahn 1 Robin Nissler 2, Christoph Pönisch 2, Dirk Habermann 2 Universität Konstanz 1 Gebr. Schmid GmbH 2 4 th Metallization Workshop, May 8 th 2013, Konstanz

2 Motivation Optimized Solar Cell Design for Module Integration* Ag consumption Solar cell optimization Module + = Multi-Busbar Solar Cell * et al., Solar Cell Improvement by Using a Multi-Busbar Design as Front Electrode, Energy Procedia 21, (2012) 4 th Metallization Workshop, May 8 th 2013, Konstanz 1

3 Outline Motivation Cell Concepts - Differences between 3-busbar and multi-busbar solar cell Simulation - Advantages of multi-busbar design on cell- and module-level Results of Experiment - Solar cells & one cell modules Summary 4 th Metallization Workshop, May 8 th 2013, Konstanz 2

4 Cell Concepts SE Solar Cell (6 inch Cz) Alkaline textured SiN x :H layer Screen printed fingers Full area Al BSF 4 th Metallization Workshop, May 8 th 2013, Konstanz 3

5 Cell Concepts SE Solar Cell (6 inch Cz) 3-Busbar Alkaline textured SiN x :H layer Screen printed fingers Full area Al BSF Multi-Busbar 3 Busbars Round Sn coated Cu wires 4 th Metallization Workshop, May 8 th 2013, Konstanz 3

6 Extraction IV Parameters Starting Point 2-diode model simulation 4 th Metallization Workshop, May 8 th 2013, Konstanz 4

7 Extraction IV Parameters Starting Point 2-diode model simulation Selective Emitter reference cell* j sc [ma/cm 2 ] V oc [mv] FF [%] η [%] Extracted parameters j 01 [fa/cm 2 ] j 02 [na/cm 2 ] r p [ cm 2 ] r s [ cm 2 ] j ph [ma/cm 2 ] ** ** without shading *B. Tjahjono et al., Optimizing selective emitter technology in one year of full scale production, Proc. 26 th EUPVSEC Hamburg, p th Metallization Workshop, May 8 th 2013, Konstanz 4

8 Simulation How many busbars do we need? Adding busbars to cell structure Busbar width 1.4 mm IV setup [%] IV setup Cell Stringed Stringed opt Busbars Shading dominates drop 4 th Metallization Workshop, May 8 th 2013, Konstanz 5

9 Simulation How many busbars do we need? Busbar width 1.4 mm Height of rectangular tabbing 200 µm drop due to stringing Additional R s by tabbing [%] IV measurement does not represent module..performance Stringed front side Cell Stringed Stringed opt Busbars Shading dominates drop 4 th Metallization Workshop, May 8 th 2013, Konstanz 6

10 Simulation How many busbars do we need? Busbar width variable Height of rectangular tabbing 200 µm [%] Stringed front side Cell Stringed Stringed opt Busbars R s reduction dominates η gain 4 th Metallization Workshop, May 8 th 2013, Konstanz 7

11 Busbar width [mm] Simulation How many busbars do we need? Busbar width variable Height of rectangular tabbing 200 µm [%] Stringed front side Cell Stringed Stringed opt Busbars R s reduction dominates η gain 4 th Metallization Workshop, May 8 th 2013, Konstanz 8

12 String Geometry Tabbing Wire Reflection on string Effectively shaded area: ~100% Reflection on wire Effectively shaded area: ~70% 4 th Metallization Workshop, May 8 th 2013, Konstanz 9

13 String Geometry Tabbing Wire Reflection on string Effectively shaded area: ~100% Total reflection on glass Effectively shaded area: ~36% 4 th Metallization Workshop, May 8 th 2013, Konstanz 10

14 String Geometry Tabbing Wire Reflection on string Effectively shaded area: ~100% Partial reflection on glass Effectively shaded area: 30% * * A.W. Blakers, "Shading losses of solar-cell metal grids, Journal of Applied Physics, vol. 71, p. 5237, th Metallization Workshop, May 8 th 2013, Konstanz 11

15 Finger Design 3-Busbar, 6 inch Multi-Busbar (15 wires), 6 inch L = 25 mm L = 5 mm Series resistance r s of finger grid: r s ~ L 2 r s 3BB 25 times higher with same grid structure 4 th Metallization Workshop, May 8 th 2013, Konstanz 12

16 r s [ cm 2 ] Finger Design 3-Busbar, 6 inch Multi-Busbar (15 wires), 6 inch L = 25 mm L = 5 mm Finger spacing constant (2 mm) Aspect ratio height/width = 0.5 Gaussian shaped fingers IV setup 3 Busbars 15 Wires Finger width [µm] 4 th Metallization Workshop, May 8 th 2013, Konstanz 13

17 r s [ cm 2 ] Finger spacing [mm] Finger Design 3-Busbar, 6 inch Multi-Busbar (15 wires), 6 inch L = 25 mm L = 5 mm Finger spacing variable Aspect ratio height/width = 0.5 Gaussian shaped fingers IV setup 3 Busbars 15 Wires Finger width [µm] 4 th Metallization Workshop, May 8 th 2013, Konstanz 14

18 r s [ cm 2 ] [%] Ag Consumption & Efficiency IV setup 3 Busbars 15 Wires Finger width [µm] Finger width η 3 Busbars 50 µm 19.3% 15 Wires 17 µm 19.7% 4 th Metallization Workshop, May 8 th 2013, Konstanz 15

19 r s [ cm 2 ] [%] r s [ cm 2 ] Ag paste [mg] Ag Consumption & Efficiency IV setup 3 Busbars 15 Wires IV setup 3 Busbars 15 Wires Finger width [µm] Finger width [µm] Finger width η Ag consumption 3 Busbars 50 µm 19.3% 108 mg 15 Wires 17 µm 19.7% 6.7 mg 4 th Metallization Workshop, May 8 th 2013, Konstanz 15

20 Aluminium Rear Side How many Ag Pads on Al Rear Side? Pad size 4 mm x 0.5 mm 15 round Cu wires R sheet Al = 10 m /sq. ~ 18 µm continuous Pads on unit cell Al rear side? 4 th Metallization Workshop, May 8 th 2013, Konstanz 16

21 r s [ cm 2 ] Aluminium Rear Side How many Ag Pads on Al Rear Side? Pad size 4 mm x 0.5 mm 15 round Cu wires R sheet Al = 10 m /sq. ~ 18 µm r s <0.3 cm 2 is sufficient Number of pads depends on wire diameter Stringed rear side 2 Pads 3 Pads 4 Pads 5 Pads 6 Pads Continuous Wire diameter [µm] 4 th Metallization Workshop, May 8 th 2013, Konstanz 17

22 r s [ cm 2 ] Aluminium Rear Side How many Ag Pads on Al Rear Side? TinPad* Sn pads instead of Ag pads Full area Al BSF Stringed rear side 2 Pads 3 Pads 4 Pads 5 Pads 6 Pads Continuous Wire diameter [µm] * TinPad by Schmid Group 4 th Metallization Workshop, May 8 th 2013, Konstanz 17

23 r s [ cm 2 ] Aluminium Rear Side How many Ag Pads on Al Rear Side? TinPad* Sn pads instead of Ag pads Full area Al BSF Stringed rear side 2 Pads 3 Pads 4 Pads 5 Pads 6 Pads Continuous Wire diameter [µm] * TinPad by Schmid Group 4 th Metallization Workshop, May 8 th 2013, Konstanz 17

24 Experiment Process Flow Solar Cell Level Cz-Si, 6 inch, 2 Ohmcm Alkaline texture POCl 3 emitter diffusion 55 Ohm/sq. 3 busbars + fingers Inkjet masking Front pads + fingers Emitter etch back 110 Ohm/sq. Chemical edge isolation SiN x :H deposition Screen printing full area Al BSF 3 busbars + fingers Screen printing front side Front pads + fingers Finger width 70 µm Spacing 2.1 mm Co-firing IV measurement Finger width 50 µm Spacing 1.8 mm Pads 500 x 700 µm 2 4 th Metallization Workshop, May 8 th 2013, Konstanz 18

25 Experiment Process Flow Module Level TinPad 3 ribbons Stringing front- / rear side Collector ribbons Lamination process 15 wires IV measurement 4 th Metallization Workshop, May 8 th 2013, Konstanz 19

26 Experiment V,I Process Flow Module Level TinPad 3 ribbons Stringing front- / rear side 15 wires Collector ribbons Lamination process Aperture area - IV measurement V,I Independently V,I European Solar Test Installation in Ispra, Italy V,I 4 th Metallization Workshop, May 8 th 2013, Konstanz 19

27 Experiment: IV Results Average IV Parameters of 3x Solar Cells Design Ag [mg] V oc [mv] j sc [ma/cm²] FF [%] r s [Ωcm 2 ] η [%] 3BB MBB Delta Ag paste reduction >50% for multi-busbar cells (72 mg) j sc loss -0.4 ma/cm² Efficiency loss -0.11% Similar η on cell level 4 th Metallization Workshop, May 8 th 2013, Konstanz 20

28 Experiment: IV Results Average IV Parameters of 3x Solar Cells and 3x 1-Cell Modules Design Ag [mg] V oc [mv] j sc [ma/cm²] FF [%] r s [Ωcm 2 ] η [%] 3BB MBB Delta Design Ag [mg] V oc [mv] j sc [ma/cm²] FF [%] r s [Ωcm 2 ] η [%] 3BB * MBB * Delta High module efficiencies with multi-busbar design *aperture area 4 th Metallization Workshop, May 8 th 2013, Konstanz 20

29 Conclusion Advantages of Multi-Busbar Solar Cell Design Multiple busbars can boost module efficiency Technology has high potential for metal reduction Ag reduction via fine line printing 72 mg 50% abs Module efficiencies 18.16% 3BB 18.49% MBB Best multi-busbar module efficiency 18.57% Outlook: - Optimized front pad design increased j sc η 18.7% possible (Simulation) 4 th Metallization Workshop, May 8 th 2013, Konstanz 21

30 Thank you for your attention! Special thanks to: Schmid Group for funding Harald Müllejans, Diego Pavanello, Elena Salis, Roberto Galleano for IV measurements 4 th Metallization Workshop, May 8 th 2013, Konstanz