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LOW COST SEMI AUTOMATED ASSEMBLY UNIT FOR SMALL SIZE BACK CONTACT MODULES AND LOW COST INTERCONNECTION APPROACH

Summary

- low cost assembly unit developed and successfully implemented for one and fourcell prototype back contact modules based on CBS

- low CTM FF losses achieved for LTSP CBS minimodules (2 % relative)- reliability tests (TC 400 and HF 10) successfully passed proving the

durability of the LTSP bond against mechanical stress and moisture ingress- degradation of ARC coating quality after reliability tests suspected

Tobias Meßmer, Fatih Demiralp, Andreas Halm

International Solar Energy Research Center - ISC Konstanz, Rudolf-Diesel Str.15 , 78467 Konstanz, Germanye-mail: tobias.messmer@isc-konstanz.de, phone: +49-7531-36 18 3-6626, fax: +497531-3618311

1) Back contact solar cell on vacuum chuck

2) Control software3) Tool (dispenser or cell

grabber)4) CBS on removable

vacuum chuck5) Commercial CNC

system6) Dispensing unit

Acknowledgements

The author wants to thank the European Union and the BmWi for funding the projects “moderNtype”(Eurostar E! 7232) and “InGrid” (SolarEraNet grant Nr. 0325821) and EppsteinTechnologies GmbH forproviding free samples of their Contacfoil®-connect. Moreover, a special thank you to Burkhard Lewetz Hard-und Software for supporting this work by providing his CNC control software “WinPC-NC” at no charge.

References[1] M. Späth et al. “A novel module assembly line using back contact solar cells”, proceedings of the 33rd IEEE PVSC 2008, San Diego, USA

I. Module assembly unit

III. LTSP as alternative to ECA

II. Module assembly process

IV. LTSP as alternative to ECA: proof of concept and reliability study

Module integration of back contact solar cells is currently investigated at differentR&D facilities using various approaches. The conductive backsheet (CBS) approach[1] is the most industrially relevant solution apart from classical stringing. Moduleassembly with CBS is mostly realized with costly, specialized productionequipment.We present here our self developed low cost solution to assemble prototypemodules containing up to four 6 inch back contact solar cells which is perfectly

suited for R&D experiments. Our assembly unit is a retrofit of a commerciallyavailable CNC system combined with a manual dispensing system from Nordson. Itis able to dispense electrically conductive adhesive (ECA) or similar materials likelow temperature solder paste (LTSP) onto a substrate as a means for cell-cellinterconnection as well as pick and place solar cells precisely. This automation isnecessary since manual positioning of back contact solar cells with the busbarsfacing down is not feasible. Cell misplacement though would lead to module failure.

Introduction

CTM (cell-to-module) losses Temperature cycle tests Humidity freeze tests

IEC restriction for HF10 (rel. power drop < 5%) met but not for HF20 due to high Isc losses attributed to degradation of ARC coating and glass corrosion observed by eye.

low FF losses indicate good mechanical strength and moisture resistance of the LTS contact

relative CTM drop vs. lamination condition

CTM losses are comparable or even lower than for ECA contacting in identical configuration

Why low temperature solder paste ?

+ low price compared to ECA+ storage at 5°C+ dispensable or screen printable

-/+ no polymeric component

preparation of contact layout

• transform any CAD drawing intomachine code to->dispense arbitrary 2-d patterns->place cell everywehere within the operation space

dispensing of conductive material onto conductive backsheet

Cell placing

module lamination

•remove module sandwich on vacuum chuck from assembly unit• module flipping• lamination

• place CBS onto vacuum chuck using alignment pins

• dispense contact layout-> choose needle diameter, set

pressure, z-height and speed to control paste laydown

• place cell on vacuum chuck withstoppers for alignment

•remove dispensing syringe from CNC unit• start cell grabber to place cell

anywhere on the operating space• place front encapsulation• place module glass

Features :-operating space: 400x600mm- modules with up to four

6 inch cells-dispense arbitrary lines and points

- repetitive positioning accuracy: 50µm

- costs ~4000€(exclusive dispensing unit)

- controlled paste laydown

IEC restriction for TC200 (rel. power drop < 5%) met even for TC 400 !High Isc losses attributed to optical degradation of ARC coating and glass corrosion observed by eye.

low FF losses indicate good mechanical strength of the LTSP contact