Efficiency Enhancement in Ultrathin Cu(In,Ga)Se2 Solar Cells Prepared on Transparent Conducting Oxide Back Contacts

목차 (Table of Contents)

• Contents
• List of Figures xxvi
• List of Tables xxxviii
• A General overview of the thesis 1
• 1 Introduction 1
• 1.1 The necessity of renewable energy 1
• 1.2 Solar thermal or PV technology 2
• 1.3 Prospects of PV technology 2
• 1.4 Thin film solar cell technology 3
• 1.5 The preference of the CIGSe solar cell over other thin film solar cell technologies 5
• 1.6 The role of constituent layers of a typical CIGSe solar cell 6
• 1.7 Operating principle and the parameters used for the evaluation of a solar cells 11
• 2 Ultrathin CIGSe solar cell prepared on transparent back contacts 17
• 2.1 Semitransparent CIGSe solar cells 17
• 2.1.1 Building PV 18
• 2.1.2 Types of BPV 19
• 2.1.3 Instigation of ST solar cells 20
• 2.1.4 Environmental benefits of BISTPV 21
• 2.1.5 Types of semitransparent solar cells 23
• 2.1.5.1. Aperture-type solar cell 24
• 2.1.5.2. Penetration-type solar cell 25
• 2.1.6. Determination of the transparency of a solar cell 26
• 2.1.7. CIGSe as a potential absorber candidate for making ST solar cell 26
• 2.1.8. Challenges associated with the ultrathinning of the CIGSe absorber 27
• 2.1.8.1. High shunt conductance 27
• 2.1.8.2. Back-surface recombination (BSR) 29
• 2.1.8.3. High bulk recombination 33
• 2.1.9. Choice of bandgap 34
• 2.1.10. Past studies on ultrathin chalcopyrite-based solar cells 40
• 2.1.11. Effect of Ts 42
• 2.1.12. Summary and our approach to increase PV performance in ultrathin wide-bandgap CIGSe solar cells 45
• 2.2 NaF post-deposition treatment of ultrathin CIGSe solar cells (Eg ≈ 1.15 eV) 48
• 2.2.1 The significance of the ultrathin CIGSe solar cells with Eg ≈ 1.15 eV 48
• 2.2.2 Cost benefits associated with the ultrathinning of a CIGSe absorber 51
• 2.2.3 Source of Na in typical CIGSe solar cell 53
• 2.2.4 Provision of Na from an external source 54
• 2.2.5 Influence of Na on the electrical properties of a CIGSe absorber 54
• 2.2.6 Effect of Na on the PV properties of a CIGSe solar cell 55
• 2.2.7 TCO BC as a diffusion barrier for Na and our approach to incorporate Na in the CIGSe absorber 56
• 2.3 The significance of non-uniformities in CIGSe thin film solar cells 57
• 2.3.1 Introduction 57
• 2.3.2 The manifestation of non-uniformities in thin film solar cells 58
• 2.3.3 Degradation induced by inhomogeneities 59
• 2.3.4 Back contact barrier 61
• 2.3.5 The implication of inhomogeneity of BC barrier height 61
• 2.3.6 Why is barrier important? 62
• 2.3.7 Experimental evidence of inhomogeneity in BC barrier 63
• 2.3.8 Simulation results on the fluctuating barrier height in ultrathin solar cells 64
• 2.3.9 How to mitigate detrimental effect of inhomogeneities? 67
• 2.3.10 Why are non-uniformities detrimental in an ultrathin CIGSe solar cell? 71
• 2.3.11 Strategies to reduce the back contact barrier height 72
• 2.3.12 Insertion of WOx layer at the CIGSe/ITO interface to improve hole collection 77
• 2.3.12.1. Potential candidates for better hole collection 78
• 2.3.12.2. WOx prospect as a hole extraction layer in ultrathin CIGSe solar cells 80
• 3 Interface modification by the incorporation of a sulfurized-AgGa layer at the absorber/ITO BC interface in ultrathin CIGSe solar cells (Eg ≈ 1.5 eV) 83
• 3.1 Brief introduction and objective of the study 83
• 3.2 Experimental details 84
• 3.2.1 Preparation of the AGS layer 84
• 3.2.2 The growth of the CIGSe absorber layer 85
• 3.2.3 The completion of a CIGSe solar cell 87
• 3.3 Characterization details 87
• 3.4 Results and discussion 89
• 3.4.1 Selection of an appropriate chalcopyrite absorber for making an ST solar cell 89
• 3.4.1.1. Criterion I: Transmittance 89
• 3.4.1.2. Criterion II: performance 91
• 3.4.2 PV performance of reference CIGSe solar cell (tCIGSe = 300 nm and Eg = 1.5 eV) 92
• 3.4.3 Influence of AGS layer on the CIGSe absorber grain morphology and the corresponding solar cell PV properties 94
• 3.4.4 Ultrathin CIGSe solar cells with the optimum AGS interlayer thickness 100
• 3.4.4.1. Morphological analysis 100
• 3.4.4.2. SIMS depth-dependent elemental distribution 101
• 3.4.4.3. PV characterization 105
• 3.4.4.4. Average visible transmittance 108
• 3.5 Conclusions 112
• 4 The role of AGS interlayer on the CIGSe structural and CIGSe/ITO interface characteristics in ultrathin CIGSe solar cells 114
• 4.1 Brief introduction and the aim of the investigation 114
• 4.2 Experimental details 116
• 4.3 Characterization details 116
• 4.3.1 SCAPS simulation 117
• 4.4 Results and discussion 119
• 4.4.1 Structural analysis 119
• 4.4.2 CIGSe/ITO interface analysis 128
• 4.4.3 Origin of the rollover effect in light-JV curves 135
• 4.5 Conclusions 140
• 5 The influence of AGS layer insertion at absorber/ITO BC interface on the PV properties of ultrathin CIGSe solar cells (tabsorber ≈ 300 nm and Eg ≈ 1.55 eV) prepared at elevated Ts 142
• 5.1 Brief introduction and the objective of the study 142
• 5.2 Experimental details 143
• 5.2.1 The Growth of the reference and modified CIGSe solar cells 143
• 5.3 Device characterization 144
• 5.4 Results and discussion 145
• 5.4.1 Structural analysis 145
• 5.4.2 Morphological analysis 147
• 5.4.3 CIGSe/ITO BC interface analysis 148
• 5.4.4 PV parameters under AM1.5G illumination 151
• 5.5 Conclusions 154
• 6 The role of NaF post-deposition treatment on the PV performance of ultrathin CIGSe solar cells (tabsorber ≈ 460 nm and Eg ≈ 1.15 eV) prepared on the ITO BC 156
• 6.1 Brief introduction and purpose of the study 156
• 6.2 Experimental details 157
• 6.2.1 CIGSe absorber preparation 157
• 6.2.2 Device completion 159
• 6.3 Characterization details 159
• 6.4 Results and discussion 161
• 6.4.1 PV characterization along with the morphological, structural, and topographical analysis 161
• 6.4.2 Temperature-dependent Voc analysis 167
• 6.4.3 CV analysis 170
• 6.4.4 DLCP analysis 172
• 6.4.5 AS analysis 173
• 6.4.6 CIGSe/ITO interface analysis 175
• 6.5 Conclusions 182
• 7 NaF PDT of Ultrathin CIGSe solar cells (tabsorber ≈ 460 nm and Eg ≈ 1.15 eV) prepared on the FTO BC 185
• 7.1 Brief introduction and purpose of the study 185
• 7.2 Experimental details 186
• 7.2.1 Absorber preparation 186
• 7.2.2 Completion of the solar cell 188
• 7.3 Characterization details 188
• 7.4 Results and discussion 188
• 7.4.1 PV properties 188
• 7.5 Conclusions 196
• 8 Ultrathin Cu(In,Ga)Se2 Solar Cells (Eg ≈ 1.15 eV and tabsorber ≈ 450 nm) with improved performance and uniformity upon inserting a WOx Interfacial Layer at the Absorber/ITO BC Interface 198
• 8.1 Brief introduction and the motivation for the current study 198
• 8.2 Experimental details 201
• 8.2.1 Preparation of WOx layer 201
• 8.2.2 Growth of CIGSe absorber 201
• 8.2.3 NaF PDT of the CIGSe absorber 202
• 8.2.4 Device completion 204
• 8.3 Characterization details 206
• 8.4 Results and discussion 207
• 8.4.1 Characterization of WOx layer 208
• 8.4.2 Structural, morphological, and PV properties of CIGSe solar cells 211
• 8.4.3 CIGSe/ITO interface analysis 225
• 8.4.4 Reduced inhomogeneity in PV parameters on introducing a WOx layer at the CIGSe/ITO interface 230
• 8.5 Conclusions 235
• 9 Conclusions and future perspective 238
• 10 References 244
• Papers and patents published from this work 268