Stability and Degradation of Organic and Polymer Solar Cells

Preface xi Acknowledgements  xiii List of Contributors xv 1. The Different PV Technologies and How They Degrade 1 Frederik C. Krebs 1.1 The Photovoltaic Effect and the Overview 1 1.2 The Photovoltaic Technologies 2 1.3 Intrinsic Versus Extrinsic Stability 3 1.3.1 Intrinsic Stability 3 1.3.2 Extrinsic Stability 3 1.4 Degradation – The Culprits, the What, the Why and the How 3 1.5 Some Representative Technologies and How They Degrade 4 1.5.1 Mono- and Polycrystalline Silicon Solar Cells 5 1.5.2 Amorphous, Micro- and Nanocrystalline Silicon Solar Cells 6 1.5.3 CIS/CIGS Solar Cells 8 1.5.4 CdS/CdTe Solar Cells 9 1.5.5 Dye-Sensitized Solar Cells (DSSC) 10 1.5.6 Organic and Polymer Solar Cells (OPV) 11 2. Chemical and Physical Probes for Studying Degradation 17 Birgitta Andreasen and Kion Norrman 2.1 Introduction 17 2.2 Physical Probes 18 2.2.1 UV-vis Spectroscopy 18 2.2.2 Atomic Force Microscopy (AFM) 18 2.2.3 Interference Microscopy 20 2.2.4 Scanning Electron Microscopy (SEM) 21 2.2.5 Fluorescence Microscopy 23 2.2.6 Light-Beam Induced-Current Microscopy (LBIC) 24 2.2.7 Electroluminescence and Photoluminescence Imaging Microscopy (ELI and PLI) 25 2.2.8 X-ray Reflectometry 26 2.3 Chemical Probes 27 2.3.1 Infrared Spectroscopy (IR) 27 2.3.2 Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) 28 2.3.3 X-ray Photoelectron Spectroscopy (XPS) 32 2.4 Summary and Outlook 35 3. Imaging Techniques for Studying OPV Stability and Degradation 39 Marco Seeland, Roland R¨osch and Harald Hoppe 3.1 Introduction to Imaging Techniques 39 3.1.1 Microscopy and Optical Scanning 39 3.1.2 Luminescence Imaging 40 3.1.3 Lock-In Thermography 43 3.1.4 Light-Beam Induced Current 45 3.2 Reports 46 3.2.1 Background: Degradation of OLED Devices 46 3.2.2 Light-Beam Induced Current 50 3.2.3 Luminescence Imaging 54 3.2.4 Optical Microscopy 57 3.2.5 Dark Lock-In Thermography and LBIC 58 3.2.6 Dark Lock-In Thermography and Optical Scanning for Failure Analysis 62 3.3 Discussion: Comparison of Imaging Techniques 63 3.4 Summary 66 4. Photochemical Stability of Materials for OPV 71 Matthieu Manceau, Agnes Rivaton and Jean-Luc Gardette 4.1 Introduction 71 4.2 Methods 72 4.2.1 Aging Condition 72 4.2.1.1 Natural and Artificial Accelerated Aging 72 4.2.1.2 Temperature Effect 73 4.2.1.3 Atmosphere Composition 74 4.2.2 Degradation Monitoring 74 4.2.2.1 Spectroscopies 75 4.2.2.2 Microscopies 80 4.3 State-of-the-Art 82 4.3.1 Degradation of the π-Conjugated Polymer 82 4.3.1.1 Study of the Pioneers: MDMO-PPV and P3HT 82 4.3.1.2 Material Chemical Structure vs. Material Stability 90 4.3.2 Acceptor Material Aging and Blend Degradation 99 4.3.2.1 Acceptor Degradation 99 4.3.2.2 Blend Degradation 99 5. Degradation of Small-Molecule-Based OPV 109 Martin Hermenau, Moritz Riede and Karl Leo 5.1 Comparison to Small-Molecule OLEDs 110 5.1.1 Number of Photoexcitations per Molecule 113 5.2 Comparison to Polymer Solar Cells 115 5.2.1 Sensitivity to Air 115 5.2.2 Temperature Stability 115 5.3 Small-Molecule Organic Materials 116 5.3.1 Active Materials 116 5.3.1.1 Fullerene C60 116 5.3.1.2 Phthalocyanines 117 5.3.1.3 Pentacene 117 5.3.2 Transport- and Exciton-Blocking Materials 119 5.3.2.1 Electron-Transport Materials 119 5.3.2.2 Hole-Transport Materials 123 5.4 Degradation Conditions 125 5.4.1 Oxygen and Water 125 5.4.2 UV Radiation 132 5.5 State-of-the-Art in Lifetime Studies 134 5.6 Summary and Outlook 138 6. Degradation of Polymer-Based OPV 143 Mikkel Jørgensen and Frederik C. Krebs 6.1 Focus on the Degradation and Stability of Polymer Solar Cells 143 6.2 A Chart of Degradation and Stability of Polymer Solar Cells 143 6.3 A Short Account of the OPV Stability/Degradation History 144 6.3.1 The Divisions of Degradation Mechanisms 146 6.3.2 The Methodologies 148 6.4 Modus Operandi for Evolving OPV 148 6.5 The Recent Developments 149 6.5.1 The Photocatalytic Oxides 149 6.5.2 Interlayers 150 6.5.3 The Inverted Structure 151 6.5.4 R2R Processing 152 6.5.5 Lamination and Encapsulation 153 6.5.6 Water Processing 154 6.5.7 Mechanical Degradation – Delamination 155 6.6 Interlaboratory Studies and Round Robins 156 6.7 Outside Studies 157 6.8 How Far Can OPV Be Taken in Terms of Stability 158 7. Test Equipment for OPV Stability 163 Olivier Haillant 7.1 Introduction 163 7.2 Reliability and Durability Testing of PV Products 165 7.2.1 Reliability, a Function of Durability 165 7.2.2 Environmental Durability 166 7.2.3 Durability and Weathering Testing 167 7.3 Laboratory Weathering Testing 168 7.3.1 Acceleration 168 7.3.2 Relevance 169 7.3.3 Precision 170 7.3.4 Introduction to Determination of Acceleration Factors 170 7.3.4.1 Acceleration of Photochemically and Thermally Activated Processes 171 7.3.4.2 Acceleration Related to Thermal Fatigue 171 7.4 Durability Testing Techniques 172 7.4.1 Outdoor Weathering 172 7.4.1.1 Static and Dynamic Outdoor Exposure 172 7.4.1.2 Accelerated Outdoor Exposure 174 7.4.1.3 Companies Servicing Outdoor Exposure 175 7.4.2 Laboratory Weathering 175 7.4.2.1 Introduction 175 7.4.2.2 Filtered xenon arc 178 7.4.2.3 Metal Halide 179 7.4.3 Laboratory Photoaging 180 7.4.3.1 Mercury Arc 180 7.4.3.2 Fluorescent UV Lamps 181 7.4.4 Others 183 7.4.4.1 Light-Soaking Techniques 183 7.4.4.2 UV Concentrators 183 7.4.4.3 Carbon Arc 185 7.5 Conclusion 185 8. Characterization and Reporting of OPV Device Lifetime 193 Suren A. Gevorgyan 8.1 Introduction 193 8.2 Photoelectric Characterization of OPV Devices 194 8.2.1 Photoelectric Characterization Tools 194 8.2.2 Characterization in Controlled Environments 197 8.3 Interlaboratory Studies of OPVs 202 8.3.1 Introduction 202 8.3.2 Interlaboratory Studies of Flexible Large-Area Roll-to-Roll Processed Polymer Solar Cell Modules 203 8.3.3 Interlaboratory Stability Studies of OPVs 204 8.4 Lifetime Testing and Reporting: Standardized Approach 213 8.4.1 Introduction 213 8.4.2 Procedures for Standard Lifetime Measurements 214 8.4.3 Reporting Lifetime 235 8.5 Conclusions 238 9. Concentrated Light for Organic Photovoltaics 243 By Thomas Tromholt 9.1 Introduction 243 9.2 Light-Concentration Setups 245 9.2.1 Refractive Sunlight Concentration 245 9.2.2 Reflective Sunlight Concentration 246 9.2.3 Concentrated Solar Simulation 249 9.3 Experimental Work Performed with Concentrated Light 251 9.3.1 IPV Response to Concentrated Sunlight 251 9.3.2 Polymer Response to Concentrated Light 253 9.3.3 Organic Solar Cell Response to Concentrated Light 257 9.4 Physical Characterization by Concentrated Sunlight 261 9.5 Conclusion 265 10. Barrier Technology and Applications 269 Lars Muller-Meskamp, John Fahlteich and Frederik Krebs 10.1 Encapsulation Requirements 269 10.1.1 Types of Encapsulation 270 10.1.2 Glass/Glass Encapsulation 271 10.1.3 Lamination of Barrier Films 272 10.1.4 Thin-Film Encapsulation 273 10.1.5 Perimeter Sealing 273 10.2 Thin-Film Permeation Physics 274 10.2.1 Solid-State Diffusion and Diffusion in Polymers 274 10.2.2 Fick's First Law of Diffusion 275 10.2.3 Sorption 276 10.2.4 Permeation in Thin Films 277 10.2.5 Models for the Permeation-Coated Polymer Films 278 10.2.6 Temperature Dependence of Permeation 279 10.2.7 Dependence of Water Permeation on Layer Thickness 280 10.2.8 Time Dependence of Permeation 282 10.2.9 Permeation in Multilayer Barriers 284 10.2.10 Pinholes in Multilayer Systems 287 10.3 Measurement of Barrier Properties 288 10.3.1 Gravimetric Cup 289 10.3.2 Carrier-Gas-Based Coulometric Barrier Measurement 289 10.3.3 Mass Spectrometer 290 10.3.4 Direct Pressure Measurement 291 10.3.5 Radioactive Isotopes 292 10.3.6 Calcium Test (Optical or Electrical) 293 10.3.7 Device Testing 294 10.3.8 Standards and Typical Measurement Conditions 295 10.3.9 Test Method Overview 295 10.4 Barrier Technologies 295 10.4.1 Single-Layer Technologies 297 10.4.1.1 Reactive Evaporation 297 10.4.1.2 Magnetron Sputtering 298 10.4.1.3 Plasma-Assisted Chemical Vapor Deposition (PECVD) 302 10.4.1.4 Atomic-Layer Deposition (ALD) 306 10.4.1.5 Summary of Single-Layer Technologies 309 10.4.2 Multilayer Technologies 309 10.5 Barrier Application in OPV 315 10.5.1 Products 316 10.5.2 Barrier Cost and Manufacturability 318 10.6 Conclusion 321 References 322 11. Summary and Outlook 331 Frederik C. Krebs Index 333