New concepts for front side metallization of industrial silicon solar cells [Elektronische Ressource] / vorgelegt von Ansgar Mette

Amette

Informations

• Publié par: albert-ludwigs-universitat_freiburg
• Publié le: 01 janvier 2007
• Nombre de lectures: 16
• Langue: English
• Poids de l'ouvrage: 8 Mo

Extrait

New Concepts for
Front Side Metallization of
Industrial Silicon Solar Cells


Dissertation zur Erlangung des Doktorgrades

der Fakultät für Angewandte Wissenschaften

der Albert-Ludwigs-Universität Freiburg im Breisgau



vorgelegt von

Ansgar Mette



Fraunhofer-Institut für Solare Energiesysteme
Freiburg im Breisgau

2007












Dekan: Prof. Dr. Bernhard Nebel
Hauptreferent: PD Dr. Volker Wittwer
Koreferent: Prof. Dr. Jürgen Wilde
Datum der Prüfung: 26. November 2007


























To my parents, with love and gratitude.
























Table of contents

INTRODUCTION..........................................................................................1
Thesis motivation ...................................................................................................... 1
Thesis outline ............................................................................................................ 3
1 CRYSTALLINE SILICON SOLAR CELLS ............................................5
1.1 Structure and operation principle.................................................................... 5
1.1.1 Current-Voltage curve.............................................................................. 6
1.1.2 Physical and technological efficiency limitations ................................... 9
1.2 Loss mechanisms due to front side metallization pattern............................. 13
1.2.1 Optical losses ......................................................................................... 14
1.2.2 Electrical losses...................................................................................... 15
1.2.3 Grid optimization for maximum power point........................................ 19
1.3 Metal-semiconductor contact........................................................................ 20
2 CELL PROCESSING AND METALLIZATION TECHNOLOGIES ......26
2.1 Processing of silicon solar cells .................................................................... 26
2.1.1 Screen-printed solar cell......................................................................... 26
2.1.2 PERL and LFC solar cell ....................................................................... 28
2.1.3 Comparison of an evaporated with a screen-printed front..................... 29
2.2 Metallization technologies............................................................................ 30
2.2.1 Thick- and thin-film metallization technologies.................................... 30
2.2.2 Screen-printing....................................................................................... 32
2.2.3 Stencil-printing....................................................................................... 36
2.2.4 Pad-printing............................................................................................ 37
2.2.5 Ink-jet printing ....................................................................................... 39
2.2.6 Dispensing.............................................................................................. 41
2.2.7 Photolithographical definition and evaporation..................................... 42
2.2.8 Laser micro-sintering ............................................................................. 43 ii Table of contents
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2.2.9 Nickel plating ......................................................................................... 43
2.2.10 Thickening of metal contacts by means of plating ................................ 45
2.3 Two-layer concept......................................................................................... 45
3 GRID DESIGN OF THE TWO-LAYER CONTACT STRUCTURE.......47
3.1 Calculation parameters and assumptions...................................................... 47
3.2 Solar cell with two busbars ........................................................................... 50
3.2.1 Assuming a cell with a sheet resistance of 55 Ω/sq............................... 50
3.2.2 Variation of the emitter sheet resistance................................................ 51
3.2.3 Influence of the contact resistivity ......................................................... 52
3.2.4 Considering irradiation reflection from the contact............................... 54
3.3 Solar cell with alternative busbar geometries ............................................... 55
3.3.1 Three busbars ......................................................................................... 56
3.3.2 Mesh of wires......................................................................................... 57
3.4 Losses caused by busbar and tab resistance.................................................. 59
3.4.1 Busbar losses.......................................................................................... 59
3.4.2 Tab losses ............................................................................................... 59
3.5 Chapter summary .......................................................................................... 60
4 SERIES RESISTANCE DETERMINATION FROM IV-CURVES.........62
4.1 Series resistance determination methods ...................................................... 62
4.1.1 Fitting of the two-diode equation to a dark IV-curve............................. 62
4.1.2 Comparison of the dark with the one-sun IV-curve............................... 63
4.1.3 Comparison of the Suns-V with the one-sun IV-curve ........................ 64 oc
4.1.4 Comparison of at least two IV-curves measured at different irradiation
intensities ............................................................................................... 64
4.1.5 Comparison of j and V values with the one-sun IV-curve................. 66 sc oc
4.1.6 Integration of the area under an IV-curve .............................................. 66
4.2 Correlation between fill factor and series resistance .................................... 67 Table of contents iii
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4.3 Experimental comparison of determination methods................................... 68
4.4 Influence of non-ideal IV-curves on r determination .................................. 71 s
4.5 Detailed discussion of presented methods.................................................... 72
5 EVAPORATION OF DIFFERENT CONTACT METALS .....................74
5.1 Solar cell processing ..................................................................................... 74
5.2 IV-Parameters of processed solar cells ......................................................... 75
5.2.1 Different metals evaporated on inverted pyramid front......................... 75
5.2.2 Different metals evaporated on a random pyramid front....................... 76
5.3 Discussion of the different metals ................................................................ 77
5.3.1 Aluminum .............................................................................................. 78
5.3.2 Palladium................................................................................................ 79
5.3.3 Silver ...................................................................................................... 80
5.3.4 Titanium-Palladium ............................................................................... 80
5.3.5 Titanium ................................................................................................. 82
5.3.6 Nickel ..................................................................................................... 82
5.3.7 Chromium .............................................................................................. 83
5.4 Chapter summary .......................................................................................... 84
6 SCREEN-PRINTING OF HOTMELT SILVER PASTE.........................85
6.1 Comparison of hotmelt and conventional paste............................................ 85
6.1.1 Composition ........................................................................................... 85
6.1.2 Rheology ................................................................................................ 87
6.1.3 Thermogravimetrical analysis................................................................ 89
6.2 Characterization of hotmelt printe