Title Page
ABSTRACT
Abbreviations
Contents
Chapter 1. Introduction 17
1.1. Fossil fuel and renewable energy 17
1.2. III-V multijunction solar cells 18
1.3. Wafer bonding and objects 22
Chapter 2. Background knowledge 26
2.1. N-type and p-type semiconductor 26
2.2. Solar cell operating principle 27
2.3. Solar cells main parameters 29
2.3.1. Open circuit voltage (Voc)[이미지참조] 30
2.3.2. Short-circuit current (Isc)[이미지참조] 31
2.3.3. Fill factor (FF) 31
2.3.4. Conversion efficiency (η) 32
2.3.5. Series resistance (Rₛ) 32
2.3.6. Shunt resistance (Rₛₕ) 33
2.4. Solar cells growth 34
2.5. Solar cell fabrication 35
2.5.1. Photolithography 36
2.5.2. Wet etch 37
2.5.3. Metal/semiconductor junction 39
Chapter 3. Single junction solar cells 41
3.1. InGaP single junction solar cells 41
3.1.1. Structure and growth 41
3.1.2. Fabrication and characterization 42
3.2. GaAs SJ SCs 46
3.2.1. Structure and growth 46
3.2.2. Fabrication and characterization 47
3.3. InGaAsP SJ SCs 50
3.3.1. Structure and growth 50
3.3.2. Fabrication and characterization 51
3.4. InGaAs SJ SCs 54
3.4.1. Structure and growth 54
3.4.2. Fabrication and characterization 55
3.5. Conclusion 57
Chapter 4. Lattice-mismatched multijunction solar cells 58
4.1. Wafer bonding and transparent conductive oxide 58
4.2. Flexible type GaAs/InGaAs DJ SCs with ITO:epoxy composite 59
4.2.1. Structure and growth 59
4.2.2. Fabrication and characterization 60
4.3. Rigid-type GaAs/InGaAs DJ SCs using Au:ITO:epoxy composite 70
4.3.1. Introduction 70
4.3.2. Solar cells structure and growth 70
4.3.3. Fabrication and characterization 71
4.4. Conclusion 80
Chapter 5. Lattice-matched multijunction solar cells 81
5.1. Tunnel junction 81
5.2. Latticed-matched multijunction solar cells 83
5.2.1. InGaP/GaAs double junction solar cells (DJ SCs) 83
5.2.2. InGaAsP/InGaAs dual junction solar cells 88
5.3. Conclusion 95
Chapter 6. Summary 96
References 97
List of publications 111
Conferences 112
국문 초록 113
Table 2.1. Etchants and etching rate for III-V solar cells materials 38
Table 2.2. Metal ohmic contact for III-V semiconductors 40
Table 3.1. InGaP SCs fabrication information 43
Table 3.2. Device performance of InGaP SCs before and after ARC 45
Table 3.3. InGaP SCs fabrication information 47
Table 3.4. Device performance of GaAs SCs before and after ARC under illumination 50
Table 3.5. InGaAsP SCs fabrication information 51
Table 3.6. Device performance of InGaAsP SCs before and after ARC 53
Table 3.7. InGaAsP SCs fabrication information 55
Table 3.8. Device performance of InGaAsP SCs before and after ARC 57
Table 4.1. Some parameters of GaAs and InGaAs SJ SCs 58
Table 4.2. Wafer bonding parameters 65
Table 4.3. Solar cells parameters of GaAs/InGaAs bonded DJ SCs 69
Table 4.4. Surface bonding resistance at different Au:ITO ratio 73
Table 4.5. Solar cells parameters of GaAs/InGaAs DJ SCs with ITO:epoxy 78
Table 4.6. Solar cells parameters of GaAs/InGaAs DJ SCs with different ITO: epoxy 79
Table 5.1. Parameters of InGaP/GaAs DJ SCs under illumination 87
Table 5.2. Parameters of DJ SCs with and without lateral etch 93
Table 5.3. Parameters of InGaP/GaAs DJ SCs under illumination 93
Figure 1.1. World total electricity consumption 17
Figure 1.2. World electricity generation by resource 18
Figure 1.3. National Renewable Energy Laboratory 19
Figure 1.4. Interaction of single junction solar with AM1.5G solar spectrum 20
Figure 1.5. Interaction of multijuncion junction solar with AM1.5G solar spectrum 21
Figure 1.6. Methods to approach III-V multijunction solar cells 24
Figure 2.1. Semiconductor materials in the periodic table elements 26
Figure 2.2. N-type (a) and p-type (b) silicon 27
Figure 2.3. The formation of electric field and depletion region in p-n junction (a), electron-hole pair generated under light illumination in energy diagram of p-... 28
Figure 2.4. Current-voltage (I-V) curve of a solar cells 29
Figure 2.5. A solar cell diagram with series resistance 33
Figure 2.6. A solar cell diagram with shunt resistance 33
Figure 2.7. A Veeco D180 MOCVD system 34
Figure 2.8. Fabrication flow for III-V solar cells 35
Figure 2.9. Photolithography and wet etch process 36
Figure 2.10. A rapid thermal annealing (a), an e-beam evaporator and photolithography system (c) 38
Figure 2.11. I-V characteristics of metal/semiconductor junction (a) and experiment data 39
Figure 2.12. Transfer length method (TLM) 39
Figure 3.1. Schematic structure of InGaP SJ SCs 41
Figure 3.2. External quantum efficiency of InGaP SJ SCs 43
Figure 3.3. Dark I-V (a) and illuminated J-Vcurves of InGaP SJ SCs 44
Figure 3.4. Schematic structure of GaAs SJ SCs 46
Figure 3.5. External quantum efficiency of GaAs SJ SCs 48
Figure 3.6. Dark I-V (a) and illuminated J-V curves of GaAs SJ SCs 49
Figure 3.7. Schematic structure of InGaAsP SJ SCs 50
Figure 3.8. External quantum efficiency of InGaAsP SJ SCs 52
Figure 3.9. Dark I-V (a) and illuminated J-V curves of InGaAsP SJ SCs 53
Figure 3.10. Schematic structure of InGaAs SJ SCs 54
Figure 3.11. External quantum efficiency of InGaAs SJ SCs 55
Figure 3.12. Dark I-V (a) and illuminated J-V curves of InGaAs SJ SCs 56
Figure 4.1. Bandgap energy versus lattice constant for III-V semiconductor 58
Figure 4.2. Schematic structure of GaAs (a) and InGaAs (b) solar cells 60
Figure 4.3. ITO NPs and epoxy resin 61
Figure 4.4. Optical microscopy images: kapton film surface (a), InP/metal/kapton (b), GaAs/InGaAs surface before (c) and after (d) ITO:epoxy optimization 62
Figure 4.5. Fabrication flow for flexible type GaAs/InGaAs DJ SCs 63
Figure 4.6. Bonding resistance: sample structure (a) and I-V characteristics 64
Figure 4.7. Bonding transmission: sample structure (a) and transmittance (b) 66
Figure 4.8. SEM images of ITO NPs (a) and GaAs/InGaAs bonded wafer (b) 67
Figure 4.9. Dark I-V and illuminated J-V characteristics of GaAs/InGaAs DJ SCs 68
Figure 4.10. Schematic structure of p⁺⁺-GaAs and p⁺⁺-InGaAs on GaAs and InP substrate, respectively 70
Figure 4.11. Fabrication flaw for rigid-type GaAs/InGaAs DJ SCs 71
Figure 4.12. Bonding resistance: sample structure (a), J-V characteristics (b) and bonding resistance versus Au:ITO ratio (c) 73
Figure 4.13. Bonding interface: structure (a), SEM image of Au particles (b), ITO NPs (c), O.OAu:1ITO (d), 0.2Au:1ITO (e), 0.4Au:1ITO (g), 0.6Au:1ITO (h) and... 75
Figure 4.14. Bonding transmittance of different Au:ITO ratio 76
Figure 4.15. Transmittance versus Au:ITO ratio 76
Figure 4.16. J-V characteristics of GaAs/InGaAs DJ SCs with ITO:epoxy 77
Figure 4.17. J-V curves of GaAs/InGaAs DJ SCs with veried Au:ITO ratio 79
Figure 5.1. Tunnel junction structure 81
Figure 5.2. Schematic representation of the evolution of a tunnel junction when a forward bias is applied: (a) ideal tunnel diode I-V curve, (b) band diagram at low... 82
Figure 5.3. Schematic structure of InGaP/GaAs DJ SCs 84
Figure 5.4. InGaP/GaAs DJ SC after fabrication process: optical microscopy image (a) and SEM image (b) 85
Figure 5.5. I-V characteristic of p⁺⁺-AlGaAs/n⁺⁺-GaAs tunnel junction 85
Figure 5.6. External quantum efficiency of InGaP/GaAs DJ SCs 86
Figure 5.7. J-V characteristic of InGaP/GaAs DJ SCs 87
Figure 5.8. Schematic structure of InGaAsP/InGaAs DJ SCs 88
Figure 5.9. I-V characteristic of p-InP-AuZn/Ni/Au junction 90
Figure 5.10. I-V characteristics of InGaAs-InGaAs tunnel junction 90
Figure 5.11. External quantum efficiency of DJ SCs 91
Figure 5.12. Optical microscopy images of DJ SCs: with lateral etch (a) and without lateral etch (b) 92
Figure 5.13. I-V characteristics of DJ SCs with lateral etch and without lateral etch 92
Figure 5.14. Dark I-V (a) and illuminated J-V (b) of DJ SCs 94