Pattern Transfer Printing (PTP ) for solar cell metallization. Head Line: Verdana bold size 30, black

Transcription

1 Pattern Transfer Printing (PTP ) for solar cell metallization Head Line: Verdana bold size 30, black J. Lossen c), M. Matusovsky a), A. Noy a), Ch. Maier b), M. Bähr b) a) Utilight Ltd., Yavne, Israel b) CiS Foschungsinstitut für Mikrosensorik und Photovoltaik GmbH, Erfurt, D c) International Solar Energy Research Center Konstanz e.v., Konstanz, D 5th Workshop on Metallization of Crystalline Silicon Solar Cells 21st of October 2014 in Constance Utilight Ltd. Octobre 2014

2 Outline 1. Introduction: Challenges for new techniques 2. Pattern Transfer Printing (PTP TM ) 3. Capabilities 4. Experimental Details on Solar Cell Experiment 5. Results Finger geometries Paste lay down IV-Data 6. Conclusion and Outlook 5 th Metallization Workshop, Constance

3 Introduction Challenge for new techniques The hare and the hedgehog New metallization techniques have a tough rival! When they finally reach their goal, ing is already there! The need for a particular material is a secure stumbling block 5 th Metallization Workshop, Constance

4 The goal A new technique for the deposition of standard Ag screen printing paste, but: No limitations on features size No meshmarks Contactless Screen printing without Mesh (or stencil) SEM picture of 100 µm line on screen, from D. Buzby, A. Dobie, White Paper Heraeus, online 5 th Metallization Workshop, Constance

5 Pattern Transfer Printing (PTP TM, patented) Working principle 1. Creation of a negative image of the desired pattern into a polymer substrate (e.g. deep trenches) 2. Filling of the trenches with standard Ag paste Pitch 100µm Top width > 20µm Bottom width >5µm Drawing of polymer substrate Height < 50µm 3. Transfer of pattern by laser irradiation (in one piece/shot) Drawing of paste being filled into the substrate by blades (squeegees) 5 th Metallization Workshop, Constance

6 Transfer of Pattern Substrate is positioned in proximity ( µm) to the wafer Irradiation of laser light through the transparent substrate Evaporation of solvent at interface Overpressure accelerates paste towards wafer Laser overlapping the trench Filled trench Paste Wafer As a laser with a very high scanning speed of 200 m/s is used, a complete finger is deposited in one piece 5 th Metallization Workshop, Constance

7 Capabilities of Pattern Transfer Printing (PTP TM ) Very fine lines Uniform cross section 19µm High aspect ratio 30 µm - Ultra fine lines ( 20 µm) - High aspect ratio - Uniform thickness along the line - (Even lines < 20µm seem possible) 5 th Metallization Workshop, Constance

8 Details on solar cell experiment Precursors: p-type mono and multi crystalline wafers from industrial production homogeneous phosphorus emitter with 70 Ω/sq Al-paste metalized rear side (for BSF) Paste: Heraeus SOL9610A for all prints (PTP and SP reference) Front side layouts: PTP single: 160 fingers, 28µm width + 3 BB made of 60 PTP lines each PTP double: 110 fingers, 28µm, two layers + 3 BB made of 60 PTP lin. SP Ref. Mono: 78 fingers, 60µm opening + 3 BB, 1.45 mm opening SP Ref. Multi: 68 fingers, 70µm opening + 3 BB, 1.45 mm opening 5 th Metallization Workshop, Constance

9 Finger geometry and shaded area Typ width [µm] height [µm] line count shaded area 28,1 µm SP Ref % PTP double % PTP single % 23,0 µm 12,0 µm 76,6 µm 27,7 µm SEM pictures of cross sections on multi wafer; all pictures are scaled identically 27 µm 5 th Metallization Workshop, Constance

10 Paste Lay Down SP Ref Technique Paste apply/ wafer* [mg] Finger cross section area [µm 2 ] Finger volume [mm 3 ] Total vol. [mm 3 ] Pseudo density paste* [mg/ mm 3 ] Cal. weight* fingers [mg] PTP double SP Ref PTP double PTP single PTP single *all values refer to dried paste Paste consumption for finger grid reduced to 41 mg* for PTP single print (- 52%) 52 mg* for PTP double print (- 40%) 5 th Metallization Workshop, Constance

11 J SC [ma/cm²] V OC [V] Cell results Current and Voltage 38,0 37,5 multi-wafer mono-wafer 0,628 multi-wafer mono-wafer 37,0 36,5 0,626 36,0 35,5 0,624 35,0 34,5 0,622 34,0 33,5 0,620 33,0 0,618 Increased J sc and V oc due to reduced metal coverage 6.4 % (reference) -> 4.8% (double print) -> 5.5 % (single print) 5 th Metallization Workshop, Constance

12 R SER [m /cm²] FF [%] R Bus-Bus [m ] Cell results Resistance losses and Fill Factor multi-wafer mono-wafer R ser = R grid + R emitter + R contact + R grid increased due to reduced Ag apply R emitter ~ d 2 with d= finger pitch cut into half/quarter for PTP double/single 0,9 0,8 0,7 multi-wafer mono-wafer 79,5 79,0 78,5 multi-wafer mono-wafer FF for most of the cells increased! 0,6 78,0 0,5 77,5 0,4 77,0 5 th Metallization Workshop, Constance

13 [%] SP Ref PTP double PTP single SP Ref PTP double PTP single Cell results Efficiency 18,6 18,4 18,2 18,0 17,8 17,6 17,4 17,2 17,0 16,8 16,6 16,4 multi-wafer mono-wafer η [%abs] Multi SP Ref 16.8 Δη [%abs] PTP double PTP single Mono SP Ref 17.8 PTP double PTP single Up to 0.4% abs efficiency increase at drastically reduced paste consumption 5 th Metallization Workshop, Constance

14 Conclusion and Outlook Pattern Transfer Printing (PTP TM ) is capable of depositing contactless very fine, uniform lines from standard ing paste First cells showed up to 0,4% abs efficieny increase at drastically reduced paste consumption (~50%). Higher sheet resistance (>70 Ω/sq) emitters increased the potential further High accuracy demonstrated by double prints Production system will be introduced to the market soon by Utilight Ltd. Photo of beta production system for 1600 wafers /h (140 fingers) currently being tested by Utilight at a costumers site 5 th Metallization Workshop, Constance

15 Thank you for your attention! 20 µm PS: To show the full potential of PTP we are currently looking out for a partner that could supply cell precursors with homogeneous emitters > 100 Ohm/sq on > 20.5% PERC-Cells 5 th Metallization Workshop, Constance