Emerging Photovoltaic Materials

Silicon & Beyond
Standards Information Network (Verlag)
  • 1. Auflage
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  • erschienen am 3. Dezember 2018
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  • 828 Seiten
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978-1-119-40768-3 (ISBN)
This book covers the recent advances in photovoltaics materials and their innovative applications. Many materials science problems are encountered in understanding existing solar cells and the development of more efficient, less costly, and more stable cells. This important and timely book provides a historical overview, but concentrates primarily on the exciting developments in the last decade. It includes organic and perovskite solar cells, photovoltaics in ferroelectric materials, organic-inorganic hybrid perovskite, materials with improved photovoltaic efficiencies as well as the full range of semiconductor materials for solar-to-electricity conversion, from crystalline silicon and amorphous silicon to cadmium telluride, copper indium gallium sulfide selenides, dye sensitized solar cells, organic solar cells, and environmentally-friendly copper zinc tin sulfide selenides.
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978-1-119-40768-3 (9781119407683)

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Santosh K. Kurinec is a Professor of Electrical & Microelectronic Engineering at Rochester Institute of Technology (RIT), NY, USA. She received her PhD degree in Physics from the University of Delhi, India. She worked as postdoc at University of Florida and later faculty at Florida A&M/Florida State University College of Engineering prior to joining RIT. She is a Fellow of IEEE, received the 2012 IEEE Technical Field Award and was inducted in the International Women in Technology (WiTi) Hall of Fame in 2018. Her current research activities include photovoltaics, advanced integrated circuit materials, devices and processes.
Preface xxi

Part 1 Silicon Photovoltaics 1

1 Emergence of Continuous Czochralski (CCZ) Growth for Monocrystalline Silicon Photovoltaics 3
Santosh K. Kurinec, Charles Bopp and Han Xu

1.1 Introduction 4

1.1.1 The Czochralski (CZ) Process 5

1.1.2 Continuous Czochralski Process (CCZ) 11

1.2 Continuous Czochralski Process Implementations 13

1.3 Solar Cells Fabricated Using CCZ Ingots 15

1.3.1 n-Type Mono-Si High-Efficiency Cells 15

1.3.2 Gallium-Doped p-Type Silicon Solar Cells 17

1.4 Conclusions 19

References 19

2 Materials Chemistry and Physics for Low-Cost Silicon Photovoltaics 23
Tingting Jiang and George Z. Chen

2.1 Introduction 24

2.2 Crystalline Silicon in Traditional/Classic Solar Cells 26

2.2.1 Manufacturing of Silicon Solar Cell 26

2.2.2 Efficiency Loss in Silicon Solar Cell 29

2.2.3 New Strategies for the Silicon Solar Cell 32

2.3 Low-Cost Crystalline Silicon 33

2.3.1 Metallurgical Silicon 33

2.3.2 Upgraded Metallurgical-Grade Silicon 33 Properties of Upgraded Metallurgical-Grade Silicon 34 Production of Upgraded Metallurgical-Grade Silicon 35 Development of Upgraded Metallurgical-Grade Silicon Solar Cells 36

2.3.3 High-Performance Multicrystalline Silicon 37 Crystal Growth 37 Material Properties of High-Performance Multicrystalline Silicon 39 Solar Cell Based on High-Performance Multicrystalline Silicon 40

2.4 Advanced p-Type Silicon-in Passivated Emitter and Rear Cell (PERC) 41

2.4.1 Passivated Emitter Solar Cells 41 Passivated Emitter Solar Cell (PESC) 41 Passivated Emitter and Rear Cell 42 Passivated Emitter, Rear Locally Diffused Solar Cells 43 Passivated Emitter, Rear Totally Diffused Solar Cells 44

2.4.2 Surface Passivation 45

2.5 Advanced n-Type Silicon 46

2.5.1 Interdigitated Back Contact (IBC) Solar Cell 47

2.5.2 Silicon Heterojunction (SHJ) Solar Cells 50 The Device Structure and the Advantages of HIT Solar Cells 51 Strategies of Achieving High-Efficiency HIT Solar Cell 52

2.6 Conclusion 53

References 54

3 Recycling Crystalline Silicon Photovoltaic Modules 61
Pablo Dias and Hugo Veit

3.1 Waste Electrical and Electronic Equipment 62

3.2 Photovoltaic Modules 65

3.2.1 First-Generation Photovoltaic Modules 66

3.3 Recyclability of Waste Photovoltaic Modules 69

3.3.1 Frame 70

3.3.2 Superstrate (Front Glass) 71

3.3.3 Metallic Filaments (Busbars) 72

3.3.4 Photovoltaic Cell 73

3.3.5 Polymers 74

3.3.6 Recyclability Summary 75

3.4 Separation and Recovery of Materials The Recycling Process 76

3.4.1 Mechanical and Physical Processes 76 Shredding 77 Sieving 77 Density Separation 79 Manual Separation 82 Electrostatic Separation 82

3.4.2 Thermal Processes-Polymers 84

3.4.3 Separation Using Organic Solvents 86

3.4.4 Pyrometallurgy 90

3.4.5 Hydrometallurgy 90

3.4.6 Electrometallurgy 93

3.5 New Trends in the Recycling Processes 94

References 98

Part 2 Emerging Photovoltaic Materials 103

4 Photovoltaics in Ferroelectric Materials Origin, Challenges and Opportunities 105
Charles Paillard, Gregory Geneste, Laurent Bellaiche, Jens Kreisel, Marvin Alexe and Brahim Dkhil

4.1 Physics of the Photovoltaic Effect in Ferroelectrics 106

4.1.1 Conventional Photovoltaic Technologies 106 The p-n Junction 106 The Shockley-Queisser Limit 109

4.1.2 Mechanisms of the Photovoltaic Effect in Ferroelectric Materials 110 The Bulk Photovoltaic Effect 110 Barrier Effects 118

4.2 Opportunities and Challenges of Photoferroelectrics 123

4.2.1 To Switch or not to Switch 124 Switchability 124 Influence of Defects 125

4.2.2 The Bandgap Problem 127

4.2.3 Application of Light-Induced Effects in Ferroelectrics Beyond Solar Cells 129 Photovoltaics and ICTs 130 Photo-Induced Strain Toward Optically Controlled Actuators 130 Photochemistry for Clean Energy and Environment 131

4.3 Conclusions 133

Acknowledgements 134

References 134

5 Tin-Based Novel Cubic Chalcogenides A New Paradigm for Photovoltaic Research 141
Sajid Ur Rehman, Faheem K. Butt, Zeeshan Tariq and Chuanbo Li

5.1 Introduction 142

5.2 Cubic Tin Sulfide ( -SnS) 145

5.2.1 Application -SnS in Solar Cells 145

5.2.2 Application of -SnS in Optical Devices 147

5.3 Cubic Tin Selenide ( -SnSe) 153

5.3.1 Application of -SnSe in Solar Cells 153

5.3.2 Application of -SnSe in Optical Devices 154

5.4 Cubic Tin Telluride ( -SnTe) 157

5.4.1 Application of -SnTe in Optical Devices 158

5.5 Conclusion 160

Acknowledgement 160

References 161

6 Insights into the Photovoltaic and Photocatalytic Activity of Cu-, Al-, and Tm-Doped TiO2 165
Antonio Sanchez-Coronilla, Javier Navas, Elisa I. Martin, Teresa Aguilar, Juan Jesus Gallardo, Desiree de los Santos, Rodrigo Alcantara and Concha Fernandez-Lorenzo

6.1 Introduction 166

6.2 Materials and Methods 167

6.2.1 Experimental 167

6.2.2 Computational Framework 169

6.3 Cu-TiO2 Doping 170

6.3.1 Photovoltaics of the DSSCs 175

6.4 Al-TiO2 Doping 177

6.5 Tm-TiO2 Doping 181

6.5.1 Photovoltaic Characterization 184

6.5.2 Photocatalytic Activity 186

6.6 Conclusions 187

References 189

7 Theory of the Photovoltaic and Light-Induced Effects in Multiferroics 195
Bruno Mettout and Pierre Toledano

7.1 Insufficiency of the Traditional Approach to the Bulk Photovoltaic Effect 196

7.2 Theoretical Approach to the Photovoltaic and Light-Induced Effects 197

7.3 Response Functions under Linearly Polarized Light 199

7.3.1 Mean Symmetry of the Light Beam 199

7.3.2 Response Functions 202 Achiral and Nonmagnetic Materials 202 Chiral and Magnetic Materials 205

7.4 Selection Procedures 206

7.4.1 External Selection 206

7.4.2 Internal Selection 208

7.5 Application of the Theory to the Photovoltaic and Photo-Induced Effects in LiNbO3 210

7.5.1 Second-Order Photovoltaic Effect 210

7.5.2 Photovoltaic Effects in LiNbO3 212

7.5.3 Optical Rectification, Photomagnetic, and Photo-Toroidal First-Order Effects 215

7.5.4 First-Order Photoelastic and Photo-Magnetoelectric Effects 216

7.6 Magnetoelectric, Photovoltaic, and Magneto-Photovoltaic Effects in KBiFe2O5 218

7.6.1 Magnetoelectric Effects in KBiFe2O5 in Absence of Illumination 218

7.6.2 Photovoltaic and Magneto-Photovoltaic Effects in KBiFe2O5 220

7.7 Photo-Magnetoelectric and Magneto-Photovoltaic Effects in BiFeO3 224

7.7.1 Photo-Magnetoelectric Effects 224

7.7.2 Photovoltaic Effects in BiFeO3 226

7.7.3 Magneto-Photovoltaic Effects in BiFeO3 227

7.8 Photorefractive and Photo-Hall Effects in Tungsten Bronzes 229

7.8.1 The Photorefractive Effect 230

7.8.2 The Photo-Hall Effect 231

7.9 Summary and Conclusion 234

Acknowledgement 235

References 235

8 Multication Transparent Conducting Oxides: Tunable Materials for Photovoltaic Applications 239
Peediyekkal Jayaram

8.1 Introduction 239

8.2 Multication Film Growth and Analysis 243

8.3 Structural Analysis 244

8.4 Raman Spectra 247

8.5 Surface Morphology (AFM) 248

8.6 Optical Properties UV-Vis Transmittance Spectra 248

8.7 Electrical Properties 253

8.8 Conclusion 257

References 258

Part 3 Perovskite Solar Cells 261

9 Perovskite Solar Cells Promises and Challenges 263
Qiong Wang and Antonio Abate

9.1 The Scientific and Technological Background 264

9.1.1 The Share of Silicon Solar Cells and Thin Film Solar Cells in Photovoltaic Market 264

9.1.2 The Bottleneck of Dye-Sensitized Solar Cells and Organic Solar Cells 266

9.1.3 From a Cost-Effective Alternative to the Highly Efficient Solution 269

9.2 The Fast Development of PSCs 270

9.2.1 The Fundamental Optoelectronic Properties of Hybrid Organic-Inorganic Lead Halide Perovskite Materials 271 Optical Properties 272 Electronic Properties 276

9.2.2 Composition Adjustment of Perovskite 288 Mixed Halides 288 Multi-Cations 292 Phase Segregation 297

9.2.3 Versatile Deposition Methods of Perovskite Film 297 Solution-Processed Methods 298 Vapor Deposition Methods 306

9.2.4 Charge Selective Contacts in PSCs 308 Electron Selective Contacts 309 Hole Selective Contacts 311

9.2.5 Evaluation of PSCs 315 J-V curve 315 Maximum Power Point Tracking (MPPT) 316

9.2.6 The Systematic Understanding of PSCs 318 Moisture Vulnerability of Perovskite Materials 318 The Role of Grain Boundaries 318 Ion Migration and Hysteresis 322 Interface/Bulk Defects and Passivation 324

9.2.7 PSCs in a Tandem 328 Structures of Perovskite Tandem Cells 328 Transparent Contacts and Recombination Contacts 330

9.3 Remaining Challenges and Prospects of PSCs 331

9.3.1 Lead-Free PSCs 331

9.3.2 Stable and Cheap Contact Materials 336

9.3.3 Strategies toward Stable PSCs 338 Against Moisture 338 Against UV Light 339 Against Heat 341

9.3.4 Large-Area Production of Highly Efficient PSCs 342

References 345

10 Organic-Inorganic Hybrid Perovskite, CH3NH3PbI3 Modifications in Pb Sites from Experimental and Theoretical Perspectives 357
Javier Navas, Antonio Sanchez-Coronilla, Juan Jesus Gallardo, Jose Carlos Pinero, Teresa Aguilar, Elisa I. Martin, Rodrigo Alcantara, Concha Fernandez-Lorenzo and Joaquin Martin-Calleja

10.1 Introduction 358

10.2 Low Doping on Pb Sites 359

10.2.1 Materials and Methods 359 Experimental 359 Computational Details 361

10.2.2 Properties of the Perovskite Prepared 362 XRD 362 Diffuse Reflectance UV-Vis Spectroscopy 365 X-Ray Photoelectron Spectroscopy 366 SEM and Cathodoluminescence 369

10.2.3 Theoretical Analysis 371 Structure and Local Geometry 371 DOS and PDOS Analysis 372 ELF Analysis 376

10.3 High Doping on Pb Sites 378

10.3.1 Properties of the Perovskite Prepared 379 XRD 379 Diffuse Reflectance UV-Vis Spectroscopy 384 X-Ray Photoelectron Spectroscopy 386

10.3.2 Theoretical Analysis 388 Structure and Local Geometry 388 Electron Localization Function 391 DOS and PDOS Analysis 393

10.4 Conclusions 397

References 397

Part 4 Organic Solar Cells 401

11 Increasing the Dielectric Constant of Organic Materials for Photovoltaics 403
Viktor Ivasyshyn, Gang Ye, Sylvia Rousseva, Jan C. Hummelen and Ryan C. Chiechi

11.1 Introduction 404

11.2 Increasing the Dielectric Constant 415

11.2.1 Methodology of Dielectric Constant Measurement 415

11.2.2 High Dielectric Constant Materials 421 High Dielectric Constant Donor Materials 422 High Dielectric Constant Acceptor Materials 429

11.3 Conclusions and Outlook 435

References 436

12 Recent Developments in Dye-Sensitized Solar Cells and Potential Applications 443
Devender Singh, Raman Kumar Saini and Shri Bhagwan

12.1 Solar Energy and Solar Cells 444

12.2 Types of Solar Cells 445

12.2.1 First-Generation Photovoltaic Cells 445 Silicon Single-Crystal-Based Solar Cells 445 Polycrystalline Silicon Based Solar Cells 445 Gallium Arsenide (GaAs)-Based Solar Cells 447

12.2.2 Second-Generation Photovoltaic Cells 447 Amorphous Silicon (a-Si)-Based Solar Cells 447 Cadmium Telluride (CdTe)-Based Solar Cells 448 Copper Indium Diselenide (CuInSe2, or CIS)- Based Solar Cells 448

12.2.3 Third-Generation Photovoltaic Cells 449 Copper Zinc Tin Sulfide (CZTS) and (Its Derivatives) CZTSSe and CZTSe Solar Cells 449 Organic Solar Cells 449 Perovskite Solar Cells 450 Quantum Dot Solar Cell 450

12.3 Dye-Sensitized Solar Cells (DSSCs) 450

12.4 Operation of DSSCs 452

12.4.1 Working System of DSSCs 454

12.5 Fabrication of DSSCs 455

12.5.1 Substrate Selection and Preparation 456 Cutting of the Substrate 456 Cleaning of the Substrate 456 Masking of the Substrate 456

12.5.2 Film Deposition on Substrate 456 Preparation of TiO2 Paste 459 Depositing the TiO2 Layer on the Glass Plate 460

12.5.3 Dye Impregnation on the Electrode 460

12.5.4 Preparation of Counter Electrode 460

12.6 Various Materials Used as Essential Components of DSSCs 461

12.6.1 Transparent Conducting Substrate 461

12.6.2 Photoelectrodes 462 Titanium Oxide (TiO2) 462 Zinc Oxide (ZnO) 463 Niobium Pentoxide (Nb2O5) 464 Ternary Photoelectrode Materials 465 Other Metal Oxides 465

12.6.3 Photosensitizers 466 Metal Complexes as Sensitizers 467

12.6.4 Electrolytes 471 Liquid Electrolytes 472 Solid-State Electrolytes 473 Quasi-Solid Electrolyte 474

12.6.5 Counter Electrodes 474 Platinized Conducting Glass 474 Carbon Materials 474 Conducting Polymers 475

12.7 Advantages and Applications of DSSC 475

12.8 Future Prospect of DSSC 476

12.9 Conclusions 476

References 477

13 Heterojunction Energetics and Open-Circuit Voltages of Organic Photovoltaic Cells 487
Peicheng Li and Zheng-Hong Lu

13.1 Introduction 487

13.2 Ultraviolet Photoemission Spectroscopy 490

13.3 Energy Level Alignment at Heterojunction Interfaces 493

13.3.1 Schottky Barrier, Interfacial Dipole, and Slope Parameter 493

13.3.2 Interfacial Dipole Theory 495

13.3.3 Mapping Energy Level Alignment at Heterojunction Interface 497

13.4 Open-Circuit Voltage of Organic Photovoltaic Cell 499

13.4.1 Two-Diode Model 499

13.4.2 Quasi Fermi Level Model 501

13.4.3 Chemical Equilibrium Model 503

13.4.4 Kinetic Hopping Model 504

References 508

14 Plasma-Enhanced Chemical Vapor Deposited Materials and Organic Semiconductors in Photovoltaic Devices 511
Andrey Kosarev, Ismael Cosme, Svetlana Mansurova, Dmitriy Andronikov, Alexey Abramov and Eugeny Terukov

14.1 Introduction 512

14.2 Experimental 513

14.2.1 Fabrication of PECVD Materials 513

14.2.2 Fabrication of Organic Materials 514

14.2.3 Configurations and Fabrication of Device Structures 516

14.2.4 Characterization of Materials 516

14.2.5 Characterization of Device Structures 521

14.3 Material Results 522

14.3.1 Structure and Composition 522

14.3.2 Optical Properties 526

14.3.3 Electrical Properties 529

14.4 Results for Devices 537

14.4.1 Devices Based on PECVD Materials 537

14.4.2 Devices Based on Organic Materials 538

14.4.3 Hybrid Devices Based on PECVD-Polymer Materials 540

14.4.4 Hybrid Devices Using Crystalline Semicinductors, Non-Crystalline PECVD, and Organic Materials (HJT-OS Structures) 543

14.5 Outlook 546

Acknowledgment 546

References 546

Part 5 Nano-Photovoltaics 551

15 Use of Carbon Nanotubes (CNTs) in Third-Generation Solar Cells 553
LePing Yu, Munkhbayar Batmunkh, Cameron Shearer and Joseph G. Shapter

15.1 Introduction 554

15.1.1 Energy Issues and Potential Solutions 554

15.1.2 Categories of Photovoltaic Devices and Their Development 554

15.2 Carbon Nanotubes (CNTs) 556

15.3 Transparent Conducting Electrodes (TCEs) 556

15.3.1 ITO and FTO 556

15.3.2 CNTs for TCEs 557

15.4 Dye-Sensitized Solar Cells (DSSCs) 563

15.4.1 CNTs-TCFs for DSSCs 563

15.4.2 Semiconducting Layers 565 Nanostructured TiO2 Materials 565 Semiconducting Layers with CNTs 566

15.4.3 Catalyst Layers 570 Platinum (Pt) and Other Catalysts 570

15.5 CNTs in Perovskite Solar Cells 572

15.6 Carbon Nanotube-Silicon (CNT-Si) or Nanotube-Silicon Heterojunction (NSH) Solar Cells 575

15.6.1 Working Mechanism 575

15.6.2 Development of Si-CNT Devices 576

15.6.3 Origin of Photocurrent 577

15.6.4 Effect of the Number of CNT Walls 578

15.6.5 Effect of the Electronic Type of CNTs 579

15.6.6 Effect of CNT Alignment in the Electrode 579

15.6.7 Effect of the Transmittance/Thickness of CNT Films 580

15.6.8 Effect of Doping 580

15.6.9 Intentional Addition of Silicon Oxide Layer 581

15.6.10 Enhancement of Light Absorption 582

15.6.11 Application of Conductive Polymers 584

15.6.12 Discussion 584

15.7 Outlook and Conclusion 585

References 586

16 Quantum Dot Solar Cells 611
Xiaoli Zhao, Chengjie Xiang, Ming Huang, Mei Ding, Chuankun Jia and Lidong Sun

16.1 Introduction 612

16.2 Quantum Dots and Their Properties 612

16.2.1 Fundamental Concepts 612

16.2.2 Size-Dependent Quantum Confinement Effect 613

16.2.3 Multiple Exciton Generation Effect 614

16.2.4 The Kondo Effect 616

16.2.5 Applications 617

16.3 Synthetic Methods for Quantum Dots 618

16.3.1 Hot Injection 618 Theoretical Evaluation of Nucleation and Growth 619 Influence Factors 621 Features 623

16.3.2 Chemical Bath Deposition 624 Theoretical Evaluation of the CBD Method 625 Influence Factors 625 Features 627

16.3.3 Successive Ionic Layer Adsorption and Reaction 628 Theoretical Evaluation of SILAR Method 629 Influence Factors 630 Features 632

16.4 Quantum Dot Solar Cells 633

16.4.1 Schottky Junction Solar Cells 633 Device Structure 633 Preparation Route 635 Materials Selection 635 Photovoltaic Performance 636

16.4.2 Depleted Heterojunction Solar Cells 637 Device Structure 637 Preparation Route 638 Materials Selection 639 Photovoltaic Performance 640

16.4.3 Quantum-Dot-Sensitized Solar Cells 641 Device Structure 641 Preparation Route 642 Materials Selection 643 Photovoltaic Performance 644

16.4 Challenges and Perspectives 645

References 646

17 Near-Infrared Responsive Quantum Dot Photovoltaics Progress, Challenges, and Perspectives 659
Ru Zhou, Jun Xu and Jinzhang Xu

17.1 Introduction 660

17.2 Physical and Chemical Properties 662

17.2.1 Multiple Exciton Generation 662

17.2.2 Quantum Size Effect 663

17.2.3 Other Features 664

17.3 Materials and Film Processing 665

17.3.1 In Situ Strategy 665

17.3.2 Ex Situ Strategy 666

17.3.3 A Comparison between In Situ and Ex Situ 667

17.4 NIR Responsive QDs and Photovoltaic Performance 669

17.4.1 Binary Lead Chalcogenides 669

17.4.2 Binary Silver Chalcogenides 674

17.4.3 Ternary Indium-Based Chalcogenides 676

17.4.4 Ternary and Quaternary Alloyed Compounds 678

17.5 Strategies for Performance Enhancement 682

17.5.1 Light Management 682 Nanophotonic Structuring 682 Plasmonic Enhancement 683

17.5.2 Carrier Management 684 Band Structure Tailoring 684 Surface Engineering 687 Charge Collection Optimizing 692

17.6 New Concept Solar Cells 692

17.6.1 Multiple-Junction CQD Solar Cells 693

17.6.2 Flexible Solar Cells 694

17.6.3 Semitransparent Solar Cells 694

17.6.4 QD/Perovskite Hybrid Solar Cells 696

17.7 Conclusions and Perspectives 699

Acknowledgments 701

References 701

Part 6 Concentrator Photovoltaics and Analysis Models 719

18 Dense-Array Concentrator Photovoltaic System 721
Kok-Keong Chong, Chee-Woon Wong, Tiong-Keat Yew, Ming-Hui Tan and Woei-Chong Tan

18.1 Introduction 722

18.2 Primary Concentrator Non-Imaging Dish Concentrator 722

18.2.1 Geometry of Non-Imaging Dish Concentrator (NIDC) 723

18.2.2 Methodology of Designing NIDC Geometry 726

18.2.3 Coordinate Transformation of Facet Mirror 728

18.2.4 Computational Algorithm 730

18.3 Secondary Concentrator An Array of Crossed Compound Parabolic Concentrator (CCPC) Lenses 733

18.4 Concentrator Photovoltaic Module 740

18.5 Prototype of Dense-Array Concentrator Photovoltaic System (DACPV) 742

18.6 Optical Efficiency of the CCPC Lens 744

18.7 Experimental Study of Electrical Performance 750

18.7.1 Current Measurement Circuit 754

18.8 Cost Estimation of the Dense-Array Concentrator Photovoltaic System Using Two-Stage Non-Imaging Concentrators 757

18.9 Conclusion 758

Acknowledgments 759

References 760

19 Solar Radiation Analysis Model and PVsyst Simulation for Photovoltaic System Design 763
Figen Balo and Lutfu S. Sua

19.1 Introduction 764

19.1.1 Solar Energy in Turkey 764

19.1.2 Climate, Solar Energy Potential, and Electric Production in Erzincan 766

19.2 Data Analysis Model for Solar Radiation Intensity Calculation 768

19.2.1 Horizontal Surface 768 Daily Total Solar Radiation 768 Daily Diffuse Solar Radiation 768 Momentary Total Solar Radiation 769 Momentary Diffuse and Direct Solar Radiation 769

19.2.2 Calculating Solar Radiation Intensity on Inclined Surface 770 Momentary Direct Solar Radiation 770 Momentary Diffuse Solar Radiation 770 Reflecting Momentary Solar Radiation 771 Total Momentary Solar Radiation 771

19.2.3 Data Analysis and Discussion 771

19.3 PVsyst Simulation for the Solar Farm System Design 777

19.3.1 Methodology 777

19.3.2 Findings Obtained with PVsyst Simulation 781

19.4 Conclusions 783

References 784

Index 787

Chapter 1
Emergence of Continuous Czochralski (CCZ) Growth for Monocrystalline Silicon Photovoltaics

Santosh K. Kurinec1*, Charles Bopp1 and Han Xu2

1Electrical and Microelectronic Engineering, Rochester Institute of Technology, Rochester, NY, USA

2GT Advanced Technologies, Hudson, NH, USA

*Corresponding author: skkemc@rit.edu


The Czochralski (CZ) process is the most commonly used method to produce single crystalline silicon for the photovoltaic (PV) and semiconductor industry. As the demand for silicon increases, the pressure on the silicon production industry grows to create higher quantities of the material at reducing prices. Currently, monocrystalline silicon (mono-Si) costs approximately 20% more than the multi-crystalline silicon (mc-Si) as Si-PV substrate. Over the years, CZ-producing vessels have increased in size to support this increased demand. The current CZ vessels are more than double the size, with the ability to produce crystals with twice the diameter and 10 times the mass of the first CZ vessels introduced in the 70s. The increase in height of the pull chamber has in turn caused the depth and width of the molten silicon feed tanks to be increased. The continuous Czochralski (CCZ) method for silicon production has the potential to greatly reduce the cost of silicon wafers. It is an effective method to address the current issues in standard CZ fabrication. With these and cell structure advances, the average manufacturing cost difference between mono- and multi-Si cells is now at US$ 0.015/W. These factors along with higher conversion efficiency rates have resulted in mono-Si cells reaching a dominant position in generation costs. The purpose of this chapter review is to inform what CCZ offers, and the advantages the method provides through engineering advancements as well as through performance of cells constructed with CCZ grown ingots. In addition, CCZ opens the door for reducing the cost of n-type silicon for PV.

Keywords: Continuous Czochralski (CCZ), Mono-Si, Ingot resistivity uniformity, Ga doping in silicon

1.1 Introduction

It is predicted that mono-Si will attain a share of 60% by 2027 over multi-crystalline Si for photovoltaics [1]. Historically, because in the early days of its development, the solar technology was mainly used for space applications and the p-type structure had better resistance to radiations for space applications. P-type wafers are also cheaper due to the CZ ingot process described in the following sections. However, most high-efficiency solar cells realized today are n-type solar cells due to their higher carrier lifetime. The n-type technology is also immune to light-induced degradation (LID), which is caused by formation of boron-oxygen defects in p-type Si. When using n-type solar cells, doped with phosphorus, this effect disappears. Also, n-type solar cells are less prone to metallic impurities of the silicon because of the absence of the boron-oxygen defect. It is predicted that the market share for n-type mono-Si will grow (Figure 1.1).

Figure 1.1 Predicted market share of different wafer types for silicon solar cells [1].

Current mono-Si solar cells are pseudo squares with dimensions 156 × 156 mm2, projected to increase to 161.75 × 161.75 mm2 by 2027. The current CZ crystallization process can produce total ingot mass of 800 kg, which will increase to 1000 kg by 2019. The continuous CZ process has the potential to move far beyond 1000 kg total ingot mass [1]. The following sections describe CZ and CCZ processes.

1.1.1 The Czochralski (CZ) Process

Monocrystalline silicon ingots are grown in a reactor furnace by the Czochralski method named after the Polish scientist Jan Czochralski, who discovered this method in 1916 [2]. The process starts with the stacking of a quartz crucible with polysilicon silicon feedstock, which is then loaded into a furnace. The silicon is heated to around 1500°C to ensure the melting [3]. While the temperature is raised, the air is pumped out of the furnace chamber, and argon is purged through the system. This is done to obtain an inert atmosphere, and the desired pressure is in the range of 15-50 mbar during the pulling process [4]. Then, a rod or cable with a silicon seed is dipped into the molten silicon, and as it is drawn up, a monocrystalline silicon crystal is grown on the seed crystal. Figure 1.2 illustrates the concept of CZ pulling. The vertical pulling movement of the seed rod or cable enables freezing of silicon in monocrystalline form with the seed as the template. The maximum pull rate, vpmax is determined by the heat balance between the heat conducted from the melt to the crystal plus the latent heat of fusion of silicon during freezing and the heat conducted/radiated away by the crystal. It is given by

Figure 1.2 (a) Picture of a commercial crystal puller; (b) crucible with molten Si; (c) polysilicon charge; (d) different stages of CZ growth; (e) grown ingot; (f) shaping pseudo square wafer sawing [7].



vpmax = maximum pull rate in cm/s

L = latent heat of fusion, for Si = 430 cal/g

?S = density of solid silicon = 2.328 g/cm3

s = Stefan Boltzmann constant = 5.67 × 10-5 erg/cm2 s K4

e = emissivity of Si = 0.55

kM = thermal conductivity of molten Si = 0.048 cal/cm s K

TM = melting temperature of Si = 1690 K

r = crystal radius (cm)

1 erg = 2.39 × 10-8 cal

Substituting for the values above, the maximum pull rate for silicon crystal growth is obtained as


The pull rates are adjusted to shape the crystal. Initially pulled quickly, a thin crown is formed that serves as the break off point when the crystal is fully grown. Pull rate then decreases slowly, resulting in a widening of the crystal, producing a taper. When the taper reaches the desired size of the silicon wafer, the pull rate remains constant, growing the body used for wafer production. When the melt is nearly depleted, the pull rate is again increased to form the bottom, which is cone shaped to provide stability in the large crystal [5]. The crystal can then be removed, and the process is repeated. In a typical run, over 100 kg of silicon is added to the crucible. It takes approximately 5 h for the silicon to melt and for the process to begin. The crystal is typically grown at a rate of 2.4 to 3.5 inch per hour for an 8?-diameter ingot [6].

The crucibles used in the CZ process are made of fused silica [8]. High-purity crystalline quartz sand or amorphous quartz powder is first poured into a rotating mold and heat is applied from an electric arc, and the quartz is melted to an amorphous glass. The fusion starts in the inside and spreads out to the mold walls. Gas bubbles of SiO are produced in the melt-crucible interface. The crucible can also react with the carbon in the graphite hot zone parts to form silicon monoxide. The two reactions producing SiO are

In the CZ process, it is unavoidable that a certain amount of oxygen is incorporated from the quartz crucible. In order to remove most of the oxygen and silicon monoxide, a low-pressure argon gas is purged through the furnace chamber. The inert gas removes up to 98%-99% of the oxygen that is dissolved from the crucible [3]. As a result of this, only 1%-2% of the dissolved oxygen from the crucible ends up in the silicon ingot (Figure 1.3). For most semiconductor applications, this is not a concern. However, for high-efficiency solar cells, oxygen impurity is undesirable as oxygen forms precipitates that act as recombination centers, reducing the minority carrier lifetime.

Figure 1.3 Oxygen source from the quartz crucible. Most (<98%) of the dissolved oxygen evaporates as SiO. The remainder is incorporated into the silicon crystal. Carbon comes from the graphite parts.

In addition, the silicon monoxide reacts with the carbon in the graphite support to produce silicon carbide and carbon monoxide through the following reactions [9]:

The minority carrier lifetime in the silicon wafers produced from the ingots grown by the CZ process is greatly influenced by the amount of carbon in the silicon. To achieve long lifetime in the silicon wafers, the oxygen and carbon content has to be reduced by controlling the gas formation in the crucible-melt interface. One method is to apply a strong magnetic field to control the convection in the silicon melt. This is called the MCZ method [10]. Since hot melted silicon conducts electricity, it is subjected to a force created by the interaction between the flow of the melted silicon and the magnetic field. As a result, the flow of the melted silicon is altered. Crystal properties are controlled by taking advantage of this characteristic. It reduces the dissolution of the crucible in the melt by controlling the melt convection. However, the MCZ method becomes expensive, requiring very high magnetic flux densities of ~103 G superconducting magnets with cooling systems. It exceeds the recommended maximum 600 G for 8 h exposure recommended by the American Conference of Governmental Industrial Hygienists (ACGIH).

In general, most impurities tend to segregate into the liquid during crystallization,...

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