Crystal Growth of Si Ingots for Solar Cells Using Cast Furnaces

1. Basic growth and crystallographic quality of Si crystals for solar cells 1

1.1 Si single and multi-crystals 1

1.2 Basic growth of Si crystals 2

1.3 Crystallographic structure and defects of Si crystals 14

1.4 Impurities and their activities in defects 39

1.5 Strain and stress 52

1.6 Appendixes 53

References 55

2. Basic characterization and electrical properties of Si crystals 63

2.1 Methods to measure electrical properties 63

2.2 Electrical properties 65

2.3 Optical measurement method and optical properties of Si crystals 77

2.4 Processes to control electrical and optical properties of Si crystals 78

2.5 Si crystal solar cells 88

2.6 Theoretical estimation for the characterization of crystals 94

References 95

3. Growth of Si multicrystalline ingots using the conventional cast method 101

3.1 Unidirectional growth of Si multicrystalline ingots 101

3.2 Growth behavior of Si multicrystalline ingots 110

3.3 Crystal defects and impurities in Si multicrystalline ingots 118

3.4 Si3N4 coating materials 133

3.5 Electrical properties and solar cells of Si multicrystalline ingots 143

3.6 Growth of large-scale ingots in industry 145

3.7 Key points for improvement 147

References 148

4. Dendritic cast method 155

4.1 Motivation to develop the dendritic cast method 155

4.2 Growth and behavior of dendrite crystals using the in-situ

observation system 156

4.3 Ingot growth controlled by dendrite crystals grown along the

bottom of a crucible 165

4.4 Arrangement of dendrite crystals 169

4.5 Generation of dislocations 175

4.6 Quality and solar-cell performance of Si ingots using the dendritic

cast method 179

4.7 Pilot furnace for manufacturing industrial scale ingots 184

4.8 Key points for improvement and impact 187

References 190

5. High performance (HP) cast method 195

5.1 Concept of the HP cast method 195

5.2 Control of grain size, grain orientation and grain boundaries using

assisted seeds 196

5.3 Behavior and control of dislocations and dislocation clusters in ingots 204

5.4 Structure and defects in Si ingots using the HP method 207

5.5 Electrical properties and solar cells 216

5.6 Key points for improvement 219

References 221

6. Mono-like cast method 225

6.1 Concept and feature of the mono-like cast method 225

6.2 How to control to obtain a large single grain 226

6.3 Growth and control of small grains appeared from crucible wall 230

6.4 Behavior of dislocations and precipitates in mono-like ingots 236

6.5 Quality of Si ingots using the mono-like cast method 249

6.6 Key points for improvement 254

References 255

7. Growth of Si ingots using cast furnaces by the NOC method 259

7.1 Development of the NOC method 259

7.2 Establishment of the low-temperature region in a Si melt 266

7.3 Growth of Si ingots using Si3N4 coated crucibles by the NOC method 278

7.4 Growth of Si single ingots using the NOC method 281

7.5 Electrical properties and solar cells of Si single ingots 299

7.6 Key points for improvement of the NOC method 308

References 312

8. Future technologies of Si ingots for solar cells 317

8.1 Proper grain size and stress in Si multicrystalline ingots 317

8.2 Novel technologies for dislocation-free single ingots with large

diameter and volume 318

8.3 Growth of square-shaped ingots using the NOC method 326

8.4 Ga-doped Si multicrystalline ingots 334

8.5 Si-Ge multicrystalline ingots 337

References 345

Index 349