In this thesis, ZnO with a new nanostructure was introduced with the advantage of large surface area and good morphology for penetration of the dye solution. Performance and other characteristics of the cells with working electrodes made by this new method were very comparable to those made by conventional methods.
Introduction
Background
- The Sun as unlimited energy resource
- Properties of th Sun Light
Only a small portion of the Sun's total power arrives at Earth, which is far from the Sun. The solar radiation (P0) is the power density of sunlight on the Earth's surface.
Solar Cells
- Introduction
- Theory
Series resistance (Rs) and shunt resistance (Rsh) are typical parasitic resistances for the solar cell. Mainly two factors have an effect on the R's of a solar cell. the internal resistance of solar cells which interferes with the movement of carriers.
Dye Sensitized Solar Cells
Photoelectrochemical method to harness the solar energy
Introduction of Dye sensitized solar cells
- Electron transfer steps of DSC
- Substrates
- Photoanode
- Dyes
- Electrolytes
- Counter Electrode
An important requirement for the photoanode of DSC is high transport mobility of the charge carrier to reduce the resistance to electron transport. Dye absorbs the solar radiation and injects electrons into the conduction band of the TiO2.
Characterization of DSC with Electrocheimcal Impedance Spectroscopy
- Basic
- Physical models for DSC
- Transmission line model
However, the impedance of the capacitor decreases as the frequency increases, the capacitor effectively becomes a short circuit at a sufficiently high frequency. Capacitance is therefore key to understanding the origin of measured resistances. A suitable equivalent circuit of the system is required to extract the physical information from the EIS data.
The electron diffusion current (Jn) is a carrier current with a diffusion coefficient (Dn) and a concentration gradient. The reverse reaction to oxidized dye molecules can be neglected because the kinetics of dye regeneration with 𝐼− ions in the electrolyte is much faster than the reverse reaction. One of the possible methods for monitoring changes in the electron density in the conduction band is to measure the conductivity of the mesoporous oxide.61-63 The most important indirect measurement of the electron density in the conduction band is the measurement of Voc.
In DSC, the conduction band of TiO2 is believed to be located approximately 1.0 eV above the redox potential.64 The electron density of equilibrium with redox (no) system is. One of the important equivalent circuits for DSC is the transmission line (TL) model shown in Figure 2-14. The first arc at the high frequency represents the charge transfer at the interface of the counter electrode and electrolyte.
ZnO nanostructure for photoanode of DSC
- Introduction
- Experimental
- Preparation of ZnO nanostructured photoanode
- Fabrication of dye sensitized solar cells with ZnO photoanode
- Characterization of properties
- Result & Discussion
- Conculsion
It shows a uniform, continuous and porous seed layer with film thickness of ~200 nm. b) shows CPZ layer built by an airbrush method with a layer thickness of ~2 μm. It is thought that the surface of saddle like nanosheets of CPZ layer was exposed with (001) plane of ZnO when it was built up by the airbrush method, so that nanorods could be well grown on it with [001] direction. Thus, the XRD pattern of nanostructure on MSZ layer shows almost random orientation and on CPZ layer shows some preferred orientations with [002] direction.
Raman spectra of ZnO setose nanorods on the CPZ layer which was built by the airbrush method. The photovoltaic performance of the cells are shown in Figure 3-4. IPCE spectra in Figure 3-4. b) show the Jsc expansion of cells with CPZ layer and MSZ layer having maximum absorption of 39% and 25% at 550 nm, respectively. a) J-V curve, (b) incident photocurrent efficiency (IPCE) and (c) Nyquist plots of ZnO. In the CPZ layer there is no barrier to the penetration of the dye solution, the photoanode of the cell with the CPZ layer was completely absorbed by the N719 dye.
The air brushing method provides a well-built seed layer as CPZ layer for the growth of ZnO nanorods. Setose ZnO nanostructure with CPZ layer has advantages for application in DSSCs as large surface area and good morphology for penetrating the dye solution. The CPZ layered cell exhibits developed energy conversion efficiency that surpasses the cells with conventional synthesis method.
Mesoporous carbon for counter electrode of DSC
- Introduction
- Experimental
- Synthesis of OMC–CNT nanocomposites
- DSC tests
- Electrochemical and physicochemical characterizations
- Result & Discussion
- Conclusion
After carbonization and removal of the OMS template with HF, the OMC-CNT nanocomposites were generated. A closer look at the OMC-CNT nanocomposites (Figure 4-2.g and h) revealed that the CNTs protruded from the OMC particles. 57 The structural properties of OMC and OMC-CNT nanocomposites were investigated by X-ray diffraction (XRD) (figures 4-5.a and b).
This indicated that the hexagonal structure of the OMS template was maintained in both the OMC and OMC-CNT replicas, which was consistent with the TEM observations. The key factor in the preparation of OMC-CNT nanocomposites was the use of NiPc as a precursor for the carbon nanostructures. We investigated such a possibility by using OMC-CNT nanocomposites as CE for DSC.
As shown in Figure 4-9, the CEs based on the OMC-CNT nanocomposites and Pt showed very similar shapes in terms of redox peak positions and current densities. The efficiency of cells based on the OMC-CNT nanocomposites, OMC and Pt-based CEs was monitored for 30 days. In particular, the OMC-CNT nanocomposites represent the first example of simultaneous one-step formation of OMCs and CNTs from a single precursor.
Graphene oxide for Counter electrode of DSC
- Introduction
- Experimental
- Preparation of negatively and positively charged GO
- Preparation of rGO/Pt and rGO/Au hybrid films on FTO for the counter
- DSC fabrication
- Characterization
- Result & discussion
- Conclusion
The surface morphologies of the rGO and rGO/metal hybrid films were investigated by scanning electron microscopy (FEI, Nova Nanosem 230). The formation of metal nanoparticles on rGO sheets is well known.113-116 The SEM images of (a) an uncoated FTO surface, (b) Pt thin film coated FTO (i.e. the conventional counter electrode), (c) rGO/Pt - coated FTO, (d) and rGO/Au coated FTO are shown in Figure 5-3. The thin rGO/metal nanoparticle hybrid films were transparent as indicated in insets of Figure 5-3. The rGO/Pt and rGO/Au nanoparticle films showed lower transmittance by 8.2 and 11.6 % at 550 nm, respectively, compared to FTO.
XPS spectrum of the binding energy of (e) the Pt 4f core electron in the rGO/Pt hybrid film, (f) the Au 4f core electron in the rGO/Au hybrid film, (g) the C 1s core electron. That is, the efficiency of DSSC with rGO/Au nanoparticle hybrid thin film counter electrode remained at this level for 1 month without a significant decrease. It was confirmed from SEM images that Au in the rGO/Au nanoparticle hybrid film did not corrode after the operation of the DSSC (Figure 5-7.a).
The stability of rGO/Au nanoparticle films in DSSCs is consistent with the results of Kou et al. The stability of the rGO/Au catalyst was also evident in repeated CV scans of a three-electrode system (Figure 5-7.b), which showed no change in the. Interestingly, the cell efficiencies of rGO/Au and rGO/Ni nanoparticle counter electrodes are comparable or slightly higher compared to that of the conventional Pt counter electrode.
A novel dye coating method for DSC
- Introduction
- Experimental
- Preparation of TiO2 photo-anodes
- Fabrication of DSSCs
- Characterizations
- Results and discussion
- Conclusion
Since the viscosity of ethylene glycol is much lower than glycerol, ethylene glycol can easily penetrate the nano-porous TiO2 electrode and distribute the dye on the surface more efficiently. When the temperature increases to 100 oC, the viscosity of ethylene glycol and glycerol decreases. The reaction time and concentration of N719 dyes in ethylene glycol were investigated simultaneously.
When the concentration of dye is increased from 5 mM to 30 mM in ethylene glycol, cell performance improves. Since ethylene glycol is quite viscous and non-volatile near 100 oC, the working electrode can be protected from ambient oxygen for a short period of time while coating the dye. These reveal any differences between the dyes produced by a conventional low-concentration method or at a higher concentration in ethylene glycol.
The second set and the third set from the bottom are sampled using ethylene glycol at 100 oC for 1 min and 3 min, respectively. A noticeable difference was observed from the sample whose coating was prepared at 160 ◦C. EIS spectra for a sample prepared at 160 oC showed an increased semicircle for the second arc, which represents a resistance at the TiO2/dye/electrolyte interface. These degraded products can diffuse into the electrolyte and also affect the function of the electrolyte, and this increases the third arc (diffusion resistance in an electrolyte). 2) The main framework of N719 molecules can still be adsorbed on TiO2, and the partial ligands can be disassembled from the molecules.
Study of dye adsorbing with DMSO
- Intriduction
- Experimental
- Preparation of TiO 2 photo-anodes
- Preparation of Dye solution
- Device Fabrication and Characterization
- Results and discussion
- Conclusion
Fig.2 shows the performance J-V curve of the prepared enclosures analyzed under the illumination (100mW/cm2). The high efficiency of the sample immersed in DMSO at high temperature is assumed to be high N719 dye adsorption is very effective in efficiency improvement. Fig.3 shows the IR spectra of the N719 dye adsorbed on the TiO2 surfaces with high temperature DMSO immersion and room temperature adsorption in mixed acetonitrile and ethanol solution up to 24 hours immersion.
Fig.4 depicting high temperature and room temperature DRIFT IR spectra of the bare DMSO solvent used for the dye solution. Fig.5 shows the field emission scanning electron microscope (SEM) details of the cross section and morphology of the film. The efficiency of the charge injection process strongly depends on the type of bonding of the ink to the semiconductor.
Field emission line electron microscopy image of a dye-sensitized TiO2 nanocrystalline solar cell fabricated in DMSO solvent (a) Cross-sectional image (b) Morphology image. In this study, an increased efficiency of 10.3% was observed for the adsorption of N719 dye at high temperature (160 °C for 30 s) in DMSO solvent on TiO2 electrodes due to the increased adsorption of the dye and the better anchoring process of the carboxylate and sulfoxide groups of the dye adsorption to the semiconductor surface. High-temperature adsorption in DMSO solvent is effective in improving the adsorption of N719 dye molecules and significantly reducing the immersion time (30 s), which promotes DSC energy generation.
General conclusion
M.; Gratzel, M., High-performance dye-sensitized solar cells based on solvent-free electrolytes produced by eutectic melts. Gratzel, M., CoS replaces Pt as efficient electrocatalyst for triiodide reduction in dye-sensitized solar cells. H.; Kavan, L.; Graetzel, M., Organized Mesoporous TiO2 Films Stabilized by Phosphorus: Application to Dye-Sensitized Solar Cells.
M.; Gratzel, M., High molar extinction coefficient heteroleptic ruthenium complexes for thin film dye-sensitized solar cells.
