This work presents a novel and low-cost printing technique to construct a three-layer (Pd/Ni/Cu) structure as front-side conductor of textured mono-crystalline silicon solar cells. The technique involves microcontact printing and electrochemical deposition. Electrochemical deposition including electroless Ni and electroplated Cu offers an inexpensive method in contrast to the conventional silver-paste. The first step of this technique was activation by Pd nanoparticles. The Pd nanoparticles with average particle size about 2.65 nm were then mixed with organic solvent to prepare Pd ink. Then we imprinted Pd ink on the front side of solar cell by microcontact printing, which could print fine-lines of less than 60 μm width. The second layer is electroless nickel providing low contact resistance and good mechanical adhesion. The third layer is electrodeposited Cu to increase the line conductivity. X-ray Diffraction (XRD) technique, Secondary Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS) were employed to detect the presence of nickel-silicides phase and the thickness of nickel-silicides phase after annealing. Moreover, the depth profile of metal contact was determined by Secondary Ion Mass Spectrometry (SIMS) and Electron probe X-ray Microanalyzer (EPMA). Finally, the line conductivity of three layer structure is lower than silver paste, and this new scheme has proven to be workable and may become an alternative approach for surface metallization on solar cell.

Table of Contents
Abstract
Table of Contents……………………………………………………….Ⅰ
List of Figures…………………………………………………………..Ⅴ
List of Tables……………………………………………………………Ⅶ
Chapter 1 Introduction ..................................... 1
Chapter 2 Literature Review ........................... 4
2-1 Photovoltaic effect by solar cell ........................................................................ 4
2-2 Physical and technological efficiency limitation ........................................ 6
2-2.1 optical losses ............................................................................................................ 6
2-2.2 Recombination losses ............................................................................................... 9
Radiative recombination ........................................................................ 9
Auger recombination ............................................................................. 9
Recombination through impurity centers and crystal defects in the bulk.............................................................................................................. 10
Recombination at the surface ............................................................... 10
2-2.3 Electrical losses ..................................................................................................... 10
2-3 Metallization on front-side silicon-based solar cell ................................ 14
2-3.1 Screen printing ....................................................................................................... 15
The metallization process by screen printing....................................... 15
Metal contact formation process by screen-printed silver paste .......... 17
All possible current paths for plated contacts ...................................... 24
2-3.2 Photolithographical with evaporation or immersion ............................................. 26
2-3.3 Laser irradiation .................................................................................................... 27
2-3.4 Ink-jet printing ....................................................................................................... 30
VI
Nanoparticles ink ................................................................................. 31
Stabilization of nanoparticle inks ......................................................... 32
The PVP protective mechanism for nanoparticles ............................... 34
Synthesis Palladium Particles via PVP ................................................ 35
Synthesis Ag/Pd nanoparticles via PVP ............................................... 36
2-2.5 Microcontact print ................................................................................................. 38
Stamp mold formation via different material ....................................... 39
Different imprint methods .................................................................... 42
The transfer mechanisms of hydrophilic stamp and hydrophobic stamp.............................................................................................................. 44
2-4 Ni/Cu metallization .............................................................................................. 46
2-4.1 NiP thin film ........................................................................................................... 47
2-4.2 Efficiency improvement .......................................................................................... 48
2-5 Nickel silicide ......................................................................................................... 49
2-6 Copper electroplating........................................................................................... 54
Chapter 3 Experimental Sections ................ 58
3-1 Materials ................................................................................................................... 58
3-2 Experimental Instruments .................................................................................. 59
3-3 Principle and measurement of analytical methods .................................. 61
3-3.1 Ultraviolet-Visible Absorption Spectrometry (UV-vis) .......................................... 61
3-3.2 Scanning Electron Micorscope (SEM) ................................................................... 62
3-3.3 Transmission Electron Microscopy (TEM) ............................................................ 63
3-4 Stamp mold fabrication ....................................................................................... 64
3-5 Metallization process ........................................................................................... 66
3.4 Preparation of nanopartilces .............................................................................. 69
Chapter 4 Results and Discussion ............. 73
4-1 The essential properties of Pd, Ag/Pd and Cu/Pd nanoparticles ........ 73
4-1.1 Catalytic activity analysis ...................................................................................... 73
VII
ICP-MS quantitative analysis .............................................................. 73
Quartz Crystal Microbalance (QCM) analysis .................................... 74
4-1.2 Nanoparticles identification ~~ X-ray diffraction (XRD) ...................................... 77
4-1.3Particles size of nanoparticles ~~ TEM analysis .................................................... 79
4-2 The nanostructure of ink after annealing on silicon substrate ............. 81
4-2.1 The adsorption mechanism of ink on substrate ~ Contact angle analysis ............. 81
4-2.2 The thermal property study of PVP ........................................................................ 82
The trend of carbon residue ................................................................. 83
PVP thermal properties ~~ TGA analysis ............................................ 84
4-2.3 Morphology of particles on silicon substrate ~~ SEM and AFM analysis ............ 87
4-2.4 GIXRD and XPS analysis ....................................................................................... 93
4-3 Microcontact print ................................................................................................. 95
4-3.1 Mold ....................................................................................................................... 96
4-3.2 Thickness of ink-film on mold ................................................................................ 97
4-3.3 Diffusion problem................................................................................................... 99
4-4 The microstructure of NiP film on silicon substrate ............................. 100
4-4.1 The growing process of NiP film .......................................................................... 100
4-4.2 The topography and cross section of NiP film ..................................................... 103
Cross-section of NiP film ................................................................... 103
Topography of NiP film ..................................................................... 103
4-4.3 Sheet resistance v.s. different annealing temperatures ........................................ 107
4-5 Structure analysis of nickel silicide thin film .......................................... 108
4-5.1 The XRD ananlysis ............................................................................................... 108
4-5.2 XPS analysis ......................................................................................................... 113
4-5.3 FE-SEM and EDX analysis .................................................................................. 114
The study of nickel silicide ................................................................ 114
Nickel silicide observation for optimal annealing condition ............. 119
4-5.4 EPMA analysis ~ Depth profile ........................................................................... 121
Line scan ............................................................................................ 122
Mapping ............................................................................................. 125
VIII
4-5.5 Depth profile ~ SIMS analysis ............................................................................. 126
4-6 Cu film covered on full substrate by electroplating .............................. 128
4-6.1 Crystal orientation of copper deposit ~~ XRD analysis ...................................... 128
4-6.2 Sheet resistance of copper film ~~ Four point probe measurement .................... 131
4-6.3 Topography and cross section of copper film covered on full substrate ~~ SEM analysis .......................................................................................................................... 132
4.7 Finished product ................................................................................................... 134
4-7.1 Topography and Cross section of metal grids ~~ SEM analysis ......................... 134
4-7.2 I-V analysis ~ performance .................................................................................. 139
4-8 The mechanism of silicide formation ~ XPS analysis ......................... 143
4-8.1 Pd and Pd/Ag nanoparticles ................................................................................ 143
4-8.2 Depth profile of metal contact .............................................................................. 147
Chapter 5 Conclusions and Future Work 151
5.1 Conclusions ............................................................................................................ 151
Microcontact print .............................................................................. 151
Nanoparticles ..................................................................................... 151
NiP film and nickel silicide ................................................................ 152
Cu film and finished product ............................................................. 153
5.2 Future work ............................................................................................................ 154

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