Title Page

Contents

Abstract 19

Chapter 1. INTRODUCTION 21

1.1. Introduction to perovskite solar cells 21

1.1.1. Next generation renewable energy source: "Solar Energy" 21

1.1.2. Evolution of photovoltaic devices 23

1.1.3. Next generation photovoltaic device: "Perovskite Solar Cells" 27

1.2. Introduction to transparent conductive electrodes 30

1.2.1. Various transparent conductive electrodes 30

1.2.2. Transparent conductive oxides 33

1.3. Importance of front transparent electrodes 36

1.3.1. Fundamental role of front transparent electrodes 36

1.3.2. Need for emerging front transparent electrodes 38

1.4. Motivation and purpose of research 41

Chapter 2. Efficient performance of perovskite solar cells based on Sn-doped In₂O₃ electrode with artificially controlled preferred orientation 43

2.1. Introduction 43

2.2. Results and discussion 47

2.2.1. Growth mechanism of preferred orientation 47

2.2.2. Structural and morphological analysis by change in preferred orientation 49

2.2.3. Electrical and optical characteristics of ITO electrodes with controlled preferred orientation 53

2.2.4. Analysis of changes in electronic structure and energy level 58

2.2.5. Crystalline and interfacial properties of MAPbI₃ perovskite and NiOx films 64

2.2.6. Photovoltaic characteristics of perovskite solar cells based on preferentially (222) and (400) oriented ITO electrodes 73

2.3. Conclusion 83

2.4. Experimental section 84

Chapter 3. Highly efficient perovskite solar cells exceeding 23% via Sn composition engineering of Sn-doped In₂O₃ electrode 87

3.1. Introduction 87

3.2. Results and discussion 91

3.2.1. Deign of high-quality ITO electrode by Sn composition engineering 91

3.2.2. Analysis of electrical and optical properties for optimizing Sn composition 104

3.2.3. Structural and morphological characterization for Sn composition changes 116

3.2.4. Investigation of film growth mechanism and interfacial properties by thermal annealing effect 121

3.2.5. Optimization of perovskite solar cells based on Sn composition engineered ITO electrodes 129

3.3. Conclusion 141

3.4. Experimental section 142

Summary 148

References 150

논문요약 178

Table 1.2.1. Efficient dopant materials for designing transparent conductive oxide. 35

Table 2.2.1. Interplanar spacing and lattice constants of the (0 and 25)-ITO films calculated and measured from XRD and HRTEM. 67

Table 2.2.2. Relevant device parameters of the PSCs fabricated on different ITO films. Values in parentheses indicate the average values of the device parameters. 75

Table 2.2.3. Fitting parameters for the EIS spectra. The Rs, Rrec and CPE are series resistance, recombination resistance and chemical capacitance, respectively.[이미지참조] 82

Table 3.2.1. Elemental chemical composition and calculated Sn dopant concentration of CEITO films deposited by increasing SnO₂ RF power between... 96

Table 3.2.2. Elemental chemical composition of CEITO films grown at various Sn dopant contents obtained from XPS analysis. 102

Table 3.2.3. Electrical properties (sheet resistance, resistivity, mobility, and carrier concentration) of CEITO electrodes with increasing Sn doping content. 106

Table 3.2.4. Electrical properties and optical properties of CEITO films according to Sn doping content change for comparison with C-ITO film at the... 108

Table 3.2.5. Interplanar spacing and lattice constants of the CEITO films calculated from XRD data. 118

Table 3.2.6. TRPL curves fitting results obtained using bi-exponential decay equation y＝y0 + A1 exp (-t/τ1)+A2 exp(-t/τ2). in which τ₁ is time constant for...[이미지참조] 128

Figure 1.1.1. Next-generation renewable energy sources. 22

Figure 1.1.2. Generational evolution of photovoltaic technology. 26

Figure 1.1.3. World record efficiency chart for photovoltaic devices certificated by the National Renewable Energy Laboratory (NREL). 26

Figure 1.1.4. Atomic structure of perovskite materials. 29

Figure 1.1.5. Typical device architectures of perovskite solar cells. 29

Figure 1.2.1. Various materials candidates for transparent conductive electrodes for perovskite solar cells. 33

Figure 1.2.2. A design method for a practical multi-component TCO for transparent conductive electrodes. 35

Figure 1.3.1. Characteristics (sheet resistance, optical transmittance, surface morphology, columnar structure, and work function) of front transparent... 38

Figure 2.2.1. (a) Preferred orientations of sputtered ITO film by re-sputtering. (b) Relationship between deposition rate and Po₂ of ITO films. 47

Figure 2.2.2. XRD patterns of the as-grown and post-annealed ITO films. 49

Figure 2.2.3. (a) Out-of-plane line-cuts of the GIWAXS spectra for the annealed ITO films fabricated under different Po₂. (b) Schematics of the grains... 50

Figure 2.2.4. Surface FESEM morphology images of the as-grown and annealed ITO films with different O₂ contents. 52

Figure 2.2.5. Electrical properties (sheet resistance, resistivity, mobility, and carrier concentration) of the annealed ITO films grown at different Po₂. 53

Figure 2.2.6. (a) Hypothetical schematics of the grain boundary scattering for 0-ITO and 25-ITO. (b) 2D porous mapping images of the ITO films sputtered... 54

Figure 2.2.7. Optical properties (transmittance, reflectance, and absorbance) of the annealed ITO films grown at different Po₂. 55

Figure 2.2.8. Plots of the refractive index (n) and extinction coefficients (k) as well as of the real (ε₁) and imaginary (ε₂) parts of the annealed ITO films... 56

Figure 2.2.9. Schematic of the energy band for the ITO-adopted high doping level. 58

Figure 2.2.10. (a) Normalized O-K edge XAS spectra and (b) enlargement of the XAS spectra for band edge states below the conduction band of the annealed... 59

Figure 2.2.11. (a) UPS spectra of the secondary electron cut-off and valence band region for ITO films with different O₂ content, with inset at left showing... 62

Figure 2.2.12. Surface FESEM images of the NiOx films deposited on different ITO films.[이미지참조] 64

Figure 2.2.13. (a) Surface FESEM images of the MAPbI₃ perovskite films deposited on different NiOx/ITO films. (b) Distribution histograms of grain size...[이미지참조] 65

Figure 2.2.14. Enlarged cross-sectional HRTEM images of the (0 and 25)-ITO. The inserted FFT pattern images show the crystallinity of the (0 and 25)-ITO. 66

Figure 2.2.15. Cross-sectional HRTEM image of the interface between the MAPbI₃ and NiOx layers according to the preferred orientation of ITO film along...[이미지참조] 67

Figure 2.2.16. (a) 2-D GIWAX spectra for the MAPbI₃ perovskite crystallinity coated on different NiOx/ITO films. (b) 2-D GIWAX pattern images for the...[이미지참조] 68

Figure 2.2.17. Intensity ratio between the (110) and (310) peaks of MAPbI₃ films deposited on different NiOx/ITO films.[이미지참조] 69

Figure 2.2.18. Proposed mechanism of perovskite nucleation and crystal growth according to different preferred orientations of ITO films. 71

Figure 2.2.19. Cross-sectional HRTEM image of PSC fabricated on 0-ITO and 25-ITO. 72

Figure 2.2.20. (a) J-V characteristics of PSCs with various ITO films. Statistical distribution of photovoltaic parameters JSC, VOC, FF and PCE as determined for...[이미지참조] 73

Figure 2.2.21. EQE spectra for the corresponding PSCs. 76

Figure 2.2.22. Light intensity dependent J-V characteristics of the PSCs fabricated on (a) 0-ITO and (b) 25-ITO. Plots of light intensity dependent (c)... 77

Figure 2.2.23. Dark J-V curves of the PSCs with (0, 1, 15, and 25)-ITO. 79

Figure 2.2.24. Nyquist plots of the PSCs with 0-ITO and 25-ITO under dark. 81

Figure 3.2.1. (a) Schematic of co-sputtering process using In₂O₃ and SnO₂ target for fabricating CEITO electrodes. (b) Cross-sectional HRTEM and SAED... 91

Figure 3.2.2. Cubic bixbyite structure of In₂O₃ with non-equivalent cation b and d-sites. 93

Figure 3.2.3. EDS analysis results of CEITO films according to RF power applied to SnO₂ target. 94

Figure 3.2.4. Fitting of XPS spectra for CEITO films deposited with various Sn dopant concentrations. (a) O 1s, (b) In 3d5/2, and (c) Sn 3d5/2 high-resolution...[이미지참조] 97

Figure 3.2.5. Area ratios and sums of In₂O₃-X/In₂O₃, OV/OL, SnO₂/SnO and OV+SnO₂ calculated using the fitted peak areas of O 1s, In 3d5/2 and Sn 3d5/2...[이미지참조] 100

Figure 3.2.6. (a) ToF-SIMS depth profile and (b) distribution and chemical mapping images of 7.50 at.% Sn-doped CEITO and C-ITO. 103

Figure 3.2.7. (a) Sheet resistance, carrier concentration, (b) mobility, and effective mass of CEITO electrodes according to change of Sn doping concentration. 104

Figure 3.2.8. (a) Sheet resistance, resistivity, (b) carrier mobility and concentration of CEITO films grown by subdividing SnO₂ RF power. All CEITO... 107

Figure 3.2.9. Sheet resistance change (△R/R0) of CEITO electrodes as a function of (a) Sn dopant content and (b) thickness for air ambient annealing at a...[이미지참조] 109

Figure 3.2.10. Transmittance and absorbance spectra of the CEITO electrodes in the wavelength region from 350 to 2000 nm. 111

Figure 3.2.11. (a) Tauc plots of ultraviolet-visible (UV-Vis) absorption spectra and extracted (b) optical bandgap values of CEITO films. 113

Figure 3.2.12. (a) Schematic energy band diagrams for Fermi levels (EF) changes of undoped In₂O₃ and CEITO. In the inset, the valence and conduction...[이미지참조] 114

Figure 3.2.13. Changes in average transmittance in the visible light region (400- 800 nm) and near infrared region (800-2000 nm) of CEITO electrodes with... 115

Figure 3.2.14. XRD patterns of CEITO electrodes. The (222) and (400) diffraction peaks, which are the dominatn pahses of CEITO, are enlarged on the right. 116

Figure 3.2.15. Top-view FESEM images of CEITO films deposited at different Sn dopant content. The Sn doping concentration was fine-tuned to the RF power... 119

Figure 3.2.16. AFM surface images of CEITO films grown by increasing Sn dopant content. All CEITO films were deposited with the identical thickness of 300 nm. 120

Figure 3.2.17. (a)Magnified HRTEM images at the interface between the mp-TiO₂/c-TiO₂ layers and the CEITO and C-ITO substrates. (b) Columnar... 121

Figure 3.2.18. AFM surface images for mp-TiO₂ and FAPbI₃ perovskite film formed from different ITO substrates. 123

Figure 3.2.19. (a)Top view SEM images and (b) grain size distribution of FAPbI₃ perovskite films grown at CEITO and C-ITO substrates. 124

Figure 3.2.20. XRD patterns of perovksite films depending on substrates. 125

Figure 3.2.21. Cross-sectional HRTEM images of PSC deivces fabricated at CEITO an C-ITO substrates. Magnified HRTEM image of the FAPbI₃ perovskite... 126

Figure 3.2.22. (a) Steady-state PL spectra of the FAPbI₃ perovskite formed on mp-TiO₂/c-TiO₂/CEITO and C-ITO substrates. (b) TRPL decays of the... 127

Figure 3.2.23. (a) Statistical distribution of photovoltaic parameters (JSC, VOC, FF, and PCE). (b) Current density-voltage (J-V) curves for forward and...[이미지참조] 129

Figure 3.2.24. (a) Statistical distribution of photovoltaic parameters (JSC, VOC, FF, and PCE). (b) Current density-voltage (J-V) curves for forward and...[이미지참조] 131

Figure 3.2.25. (a) The statistics of photoelectric performance parameters (VOC, JSC, FF, PCE) distribution for devices with CEITO and C-ITO substrates. (b)...[이미지참조] 133

Figure 3.2.26. (a) Nyquist plots of PSCs with structure of Au/spiro-OMeTAD/perovskite/mp-TiO₂/c-TiO₂/CEITO and C-ITO substrates. (b)... 136

Figure 3.2.27. (a) Forward and reverse scanned J-V curve of the best performing PSC based on CEITO substrate. (b) J-V curves measured at... 138

Figure 3.2.28. (a) Steady-state PCE measured for 1,500 s at the ambient condition of 21 °C and relative humidity of 27%. (b) PCEs with aging time... 140