Figure 1.1. Average annual growth rates of renewable energy sources. 19

Figure 1.2. Number of publications published per year obtained from a simple and limited literature search using the keywords "dye-sensitized" and "sola" 20

Figure 1.3. Best research cell efficiencies from National Renewable Energy Laboratory(NREL). 21

Figure 1.4. (a) The 90cm² transparent serial-connected monolithic DSSC module from Toyota Central R&D Laboratories., Inc. and AISIN SEIKI Co., LTD., Japan, (b) sandwich Z-interconnected flexible... 22

Figure 2.1. Current density - voltage (J-V) curves in solar cell in dark and under illumination. 26

Figure 2.2. General structure of a dye-sensitized solar cell. 29

Figure 2.3. General band structure for a dye-sensitized solar cell and its operational principle. 30

Figure 2.4. Overview of processes and typical time constants under working condition (1 sun) in a Ru-dye-sensitized solar cell with iodide/triiodide electrolyte. Recombination reactions are indicated by... 32

Figure 2.5. Scanning electron microscope image of a nanocrystalline TiO₂ photoelectrode used in the dye-sensitized solar cell. 39

Figure 2.6. Band structures of several semiconductors. The lower edge of the conduction band (red color) and upper edge of the valence band (green color) are presented along with the band gap in... 40

Figure 2.7. The structure of the most widely used Ru-based photosensitizers. 41

Figure 2.8. Typical Nyquist plot of DSSC. Inset shows the equivalent circuit. 46

Figure 2.9. Equivalent circuit of Bisquert's model. 47

Figure 2.10. Schematic of four different types of photoelectrodes with light scatters used in DSSCs 54

Figure 2.11. Calculated solar absorbance as a function of (a) the radius of scatterers (i.e., large-sized particles), and (b) the wavelength of incident light. The films are 10μm in thickness and formed by... 55

Figure 2.12. Schematic diagram of electron Interception at the SnO₂ photoelectrode/electrolyte interface 56

Figure 2.13. Suggested mechanism to improve the efficiency of DSSCs that were prepared by using (a) neat TiO₂ and (b) size-reduced Fe₂O₃-TiO₂ composite. 57

Figure 2.14. (a) Lateral view FESEM image of TiO₂ nanotubes grown from a 500-nm-thick Ti thin film (sputtered onto FTO glass at 500℃, (b) Response time determined by open circuit voltage... 58

Figure 3.1. Previous work for introduction the cascading band structure. 68

Figure 3.2. Procedure of DSSC fabrication. 72

Figure 3.3. (a) XRD pattern, (b) and (c) TEM images, (d) electron diffraction pattern, (c) HR-TEM image, and (f) the size distribution of the synthesized anatase TiO₂ nanoparticles. 79

Figure 3.4. SEM micrographs showing the top surface of (a) FTO glass and (b) BL-15/FTO. 80

Figure 3.5. Sn 3d transition peaks in XPS spectra of bare SLG and BL-15/SLG. Left and right insets show the O 1s transition peak for BL-15/SLG and deconvolution result of the Sn 3d5/2 peak.(이미지참조) 81

Figure 3.6. (a) XRD patterns and (b) TEM micrographs of the white precipitate, formed during SnCl₄ treatment, before and after sintering at 500℃ for 15 minutes. 82

Figure 3.7. Optical transmittance spectra of SnO₂/SLGs created with different SnCl₄ treatment time. 84

Figure 3.8. (a) Dark J-V curves of modified cells as a function of SnCl₄ treatment time. The modified cells consisted solely of FTO glass, a SnO₂ blocking layer, electrolyte, Pt, and FTO glass. (b) Onset of... 85

Figure 3.9. PL spectra of the TiO₂ layer and TiO₂/BL-15 bi-layer. 86

Figure 3.10. Nyquist plots of C-BL-O and C-BL-15 measured in dark. Inset shows the equivalent circuit. 88

Figure 3.11. J-V curves of the fabricated cells employing bare FTO and SnO₂/FT0. 90

Figure 3.12. (a) Open-circuit voltage, (b) short-circuit current density, (c) fill factor, and (d) conversion efficiency of the fabricated cells employing bare FTO and SnO₂/FTO as a function of... 91

Figure 4.1. SEM images of (a) bare and (b) TiCl₄-treated FTO glass. 106

Figure 4.2. SEM micrographs of freeze-casted TiO₂ phototelectrodes 107

Figure 4.3. TiO₂ wall thickness and lamellar spacing of the freeze-casted TiO₂ Photoelectrodes with lamellar porous structures as a function of slurry concentration. 108

Figure 4.4. Diffused reflectance spectra of the freeze-casted and conventionally screen-printed TiO₂ photoelectrodes. 110

Figure 4.5. Photocurrent density-voltage (J-V) curves of the fabricated cells employing the freeze-casted and conventionally screen-printed TiO₂ photoelectrodes. 112

Figure 4.6. Dark current-voltage (I-V) characteristics of the modified cells. Inset shows the modified cells which consisted solely of FTO glass, TiO₂ blocking layer, electrolyte, Pt, and FTO, but not TiO₂... 113

Figure 4.7. Nyquist plots of C-FC-10(30) and C-SC. The inset shows the equivalent circuit model used for EIS analysis. 114

Figure 5.1. Various one-dimensional (1-D) tungsten oxide nanostructures. 122

Figure 5.2. the first report about dye-sensitized solar cells (DSSCs) based on WO₃. 123

Figure 5.3. Previous works for applying an one-dimensional (1-D) nanostructured photoelectrodes. 124

Figure 5.4. (a) XRD pattern, (b) and (c) TEM, and (d) HR-TEM micrographs of the as-synthesized W18O49 nanorodes. Inset in (b) shows the electron diffraction pattern.(이미지참조) 131

Figure 5.5. (a) XRD pattern, (b) and (c) TEM, and (d) HR-TEM micrographs of the WO₃ nanorods obtained by the heat treatment of the W18O49 nanorodes at 500℃ for 30 minutes in air.(이미지참조) 132

Figure 5.6. SEM images of (a) low and (b) high magnification showing the top view of the WO₃ nanorod film. 133

Figure 5.7. The current density - voltage (J-V) characteristics of the fabricated DSSCs based on photoelectodes made of WO₃ nanorods (dotted line), TiCl₄-treated WO₃ nanorods (straight line), and... 134

Figure 5.8. HR-TEM image of TiCl₄-treated WO₃ nanorods. The FFT patterns are obtained from the nanoparticles on the WO₃ nanorod surface (indicated by red rectangular). 136

Figure 5.9. STEM image of the TiCl₄-treated WO₃ nanorods and their elemental mapping profiles. 137

Figure 5.10. Nyquist curves of DSSCs based on TiCl₄-treated WO₃ nanorods and nanoparticles. 138

Figure 5.11. The incident photon-to-electron conversion efficiency (IPCE) of the fabricated cells based on WO₃ nanorods (dotted line), TiCl₄-treated WO₃ nanorods (straight line), and TiCl₄-treated... 139

Figure 6.1. XRD patterns of (a) BT-2, (b) BF-4, (c) BT-8, (d) BT-24, and (e) BT-120. 152

Figure 6.2. SEM micrographs of (a) BT-2, (b) BT-4, (c) BT-8, (d) BT-24, and (c) BT-120. 153

Figure 6.3. FT-IR spectra of (a) BT-2, (b) BT-4, (c) BT-8, (d) BT-24, and (e) BT-120. 155

Figure 6.4. Current density-voltage (J-V) curves of the fabricated DSSCs based on (a) bare and (b) TiCl₄-treated BaTiO₃ nanoparticles. 156

Figure 6.5. TEM and HR-TEM micrographs of (a and b) bare and (c and d) TiCl₄-treated BT-24. 157

Figure 6.6. XRD patterns in the 2-theta range of 40 to 50 degrees of (a) BT-2, (b) BF-4, (c) BT-8, (d) BT-24, and (e) BT-120. 158

Figure 6.7. Nyquist plots of DSSCs based on the TiCl₄-treated BaTiO₃ nanoparticles. The inset shows the equivalent circuit model used for EIS analysis. 160

Scheme 3.1. Schematic for cascading band structure formed by introducing SnO₂ blocking layer between FTO glass and TiO₂ photoelectrode. 87

Scheme 4.1. Schematic for the four processing steps of the freeze-casting method 99

Scheme 4.2. Schematic for light scattering in the freeze-casted TiO₂ Photoelectrodes 111