CHAPTER 2 CHARACTERIZATION TECHNIQUES

Transcription

1 19 CHAPTER 2 CHARACTERIZATION TECHNIQUES 2.1 INTRODUCTION The characterization of materials is important for understanding their properties and applications. This chapter describes the instruments and experimental methods utilized for various measurements towards the characterization of the synthesized TiO 2 nanostructures. The techniques adopted to characterize the nanoparticles are: X - ray diffraction (XRD), UV - visible spectroscopy, Fourier transforms infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and surface area analysis (BET). The fabrication of DSSC is also discussed. Spectroscopy is a powerful tool to study the structure of nanocrystalline, organic and inorganic materials. Spectroscopy is a technique that uses the interaction of energy with a sample to perform an analysis. The data obtained from spectroscopy is called a spectrum. A spectrum is a plot of the intensity of energy detected versus the wavelength (or mass or momentum or frequency, etc.) of the energy [59]. A spectrum can be used to obtain information about atomic and molecular energy levels, molecular geometries, chemical bonds, interactions of molecules and related processes. Often, spectra are used to identify the components of a sample (qualitative analysis).

2 20 Table 2.1 Characterization techniques and their applications TECHNIQUES 1. X-Ray Diffraction (XRD) 2.Ultraviolet-Visible Spectroscopy (UV/Vis) 3. Fourier Transform Infrared Spectroscopy (FT IR) APPLICATIONS To study the crystalline properties of solid substances To analyze molecular (organic) and ionic species capable of absorbing at UV or Visible wavelengths in dilute solutions To analyze only molecular compounds (organic compounds, natural products, polymers, etc.) 4.Scanning Electron Microscopy (SEM) To study the topography, structure and compositions of metals, ceramics, polymers, composites and biological materials 5. Transmission Electron Microscopy (TEM) 6. Surface area analysis (BET) To study the local structures, morphology, and dispersion of multi component polymers, cross sections and crystallizations of metallic alloys, semiconductors, microstructure of composites, etc. To study the surface area, pore volume, pore diameter, and pore size distribution of nanoparticles. Spectra may also be used to measure the amount of material in a sample (quantitative analysis). Table 2.1 shows the various characterization techniques and their applications. This chapter also encompasses a detailed view of the theoretical aspects, instrumentation techniques of the three major spectroscopic methods namely powder X ray Diffraction, UV-visible, and Fourier Transform Infrared spectroscopy (FT - IR). The next level of characterization is to examine the surface, arrangement of surface atoms and the electronic structure of the nanoparticles. This can be done only by viewing the particles in the nanometre range. There are two main kinds of

3 21 microscopy. The first class of microscopy involves a stationary sample in line with a high - speed electron gun. Both the scanning electron microscope (SEM) and transmission electron microscope (TEM) are based on this technique. Detailed information of surface area measurement and pore size measurement of BET analysis has described in this chapter. 2.2 POWDER X - RAY DIFFRACTION (XRD) Principle Figure 2.1 shows a schematic representation of powder X - ray diffractometer. X-rays are electromagnetic radiation with wavelength in the range nm. It is used in diffraction experiments in the typical wavelength range A. For electromagnetic radiation to be diffracted, the spacing in the grating should be of the same order as the wavelength. In crystals, the typical inter atomic spacing 2-3Å the suitable radiation is X-rays. Hence X-rays can be used to the study crystal structures [60]. Figure 2.1 Powder X - ray diffractometer In this technique, the primary X - rays are made to fall on the sample substance to be investigated. Because of its wave nature, like light waves, X - ray gets diffracted to a certain angle. This angle of diffraction, which differs from that of the incident beam, will give the information regarding the crystal nature of the substance. The wavelength of the X - rays can be varied for the application by using a grating plate.

4 Bragg s Law Bragg diffraction occurs when electromagnetic radiation or subatomic particle waves with wavelength comparable to atomic spacings are incident upon a crystalline sample, scattered by the atoms in the system and undergo constructive interference in accordance to Bragg's law. Figure 2.2 Bragg s Law Considering the conditions necessary to make the phases of the beams coincide when the incident angle equals and reflecting angle (Figure 2.2). The rays of the incident beam are always in phase and parallel up to the point at which the top beam strikes the top layer at atom Z. The second beam continues to the next layer where it is scattered by atom B. The second beam must travel the extra distance AB + BC if the two beams are to continue traveling adjacent and parallel. This extra distance must be an integral (n) multiple of the wavelength (λ) for the phases of the two beams to be the same: nλ = AB+BC (1) Recognizing d as the hypotenuse of the right triangle ABZ, we can use trigonometry to relate d and θ to the distance (AB + BC). The distance AB is opposite θ so, AB = d sinθ (2) Because AB = BC eq. (1) becomes,

5 23 nλ = 2AB (3) Substituting eq. (2) in eq. (3) we have, nλ = 2d sinθ (4) and Bragg's Law has been derived. where, n - order of diffraction λ - the wavelength of x-rays d - the spacing between the planes in the atomic lattice. θ - the angle between the incident ray and the scattering planes. Note that if only two rows of atoms are involved, the transition from constructive to destructive interference as θ changes is gradual. However, if interference from many rows occurs then the constructive interference peaks become very sharp with mostly destructive interference in between. This sharpening of the peaks as the number of rows increases that is very similar to the sharpening of the diffraction peaks from a diffraction grating as the number of slits increases Instrumentation A powder X - ray diffractometer consists of a X - ray source (usually a X - ray tube), a sample stage, a detector and provision to change angle θ (Figure 2.3). The X - ray is focused on the sample at some angle θ, while the detector opposite to the source reads the intensity of the X - ray that receives at 2θ away from the source path. The incident angle is the increased over time while the detector angle always remains 2θ above the source path.

6 24 Figure 2.3 Powder X - ray diffraction X - ray Tubes The most common source of X - rays is an X - ray tube. The tube is evacuated and contains a copper block with a metal target anode and a tungsten filament cathode with a high voltage is applied between them. The filament is heated by a separate circuit, and the large potential difference between the cathode and anode electrons at the metal target. The accelerated electrons knock core electrons out of the metal, and electrons in the outer orbitals drop down to fill the vacancies and thereby, emitting X-rays. The X-rays exit the tube through a beryllium window. Due to massive amounts of heat being produced in this process, the copper block must usually be water cooled X-ray Detectors Most modern equipment do use transducers that produce an electrical signal when exposed to radiation. These detectors are often used as photon counters, so intensities are determined by the number of counts in a certain period of time.

7 Gas-Filled Transducers A gas-filled transducer consists of a metal chamber filled with an inert gas, with the walls of the chamber as a cathode and a long anode in the center of the chamber. When X - rays enters the chamber, its energy ionizes many molecules of the gas. The free electrons then migrate towards the anode and the cations migrate towards the cathode. The electrons that reach the anode cause current to flow, which can be detected. The sensitivity and dead time (when the transducer will not respond to radiation) both depend on the voltage of the transducer is operated at. At high voltage, the transducer is very sensitive but it has a long dead time, whereas at low voltage, the transducer has a short dead time but low sensitivity Scintillation Counters In a scintillation counter, phosphor is placed in front of a photomultiplier tube. When X - rays strike on the phosphor, it produces flashes of light, which are detected by the photomultiplier tubes Semiconductor Transducers A semiconductor transducer has a gold coated p-type semiconductor layered on lithium containing semiconductor intrinsic zone, followed by an n-type semiconductor on the other side of the intrinsic zone. The semiconductor is usually composed of silicon and germanium but germanium is used if the radiation wavelength is very short. The n - type semiconductor is coated by an aluminum contact, which is connected to a pre-amplifier. The entire crystal has a voltage applied across it. When X - ray strikes the crystal, it elevates many electrons in the semiconductor into the conduction band, which causes a pulse of current [61, 62] Applications The X - ray diffraction is a good tool to study the nature of the crystalline substances. In crystals, the ions or molecules are arranged in well-defined positions in planes in three dimensions. The impinging X - rays are reflected by each crystal

8 26 plane. So the planes can not be same or identical for any two chemical substances, this technique provides vital information regarding the arrangement of atoms and the spacing in between them and also to find out the chemical compositions of crystalline substances. The sample under study can be of either a thin layer of crystal or in a powder form. Since, the power of a diffracted beam depends on the quantity of the corresponding crystalline substance. It is also possible to carry out quantitative determinations [63]. 2.3 ULTRAVIOLET - VISIBLE SPECTROSCOPY Principle Molecules absorb energy and this energy can bring out translational, rotational or vibrational motion or ionization of the molecules depending upon the frequency of the electromagnetic radiation. Excited molecules are unstable and quickly drop down to ground state again giving off the received energy in the form electromagnetic radiation. The wavelength and intensity of the electromagnetic radiation absorbed or emitted can be recorded to get a spectrum (Figure 2.4). Spectral analysis yields qualitative and quantitative information about the materials under study [64]. Figure 2.4 Electromagnetic spectrum

9 27 Ultraviolet-visible (UV-vis) spectroscopy is useful tool to characterize the absorption, transmission, and reflection of a variety of compounds and materials, such as pigments, coatings etc. The UV - vis spectra has broad features including sample identification and very useful for quantitative measurements Instrumentation The instruments has the following components: A light source that generates a broad band of electromagnetic radiation A dispersion device that selects a particular wavelength (or, more correctly a waveband) from the broadband radiation of the source A sample area (component) One or more detectors to measure the intensity of radiation Other optical components, such as lenses or mirrors, relay light through the instrument. A schematic representation of a UV/vis spectrophotometer is shown in Figure 2.5. Normal working range for a spectrometer is nm, working beyond 180 nm requires special arrangements [65]. Figure 2.5 Functional block diagram of UV - visible spectrophotometer

10 The Light Source A deuterium discharge lamp for UV region ( nm) A tungsten filament lamp or tungsten-halogen lamp for Visible and NIR regions ( nm) The instrument automatically swaps lamps when scanning between the UV and VIS-NIR regions The Monochromator All monochromators contain the following component parts: An entrance slit A collimating lens A dispersing device A focusing lens An exit slit Ideally, the output from a monochromator is monochromatic light. However, in practice, the output is always a band, optimally symmetrical in shape Dispersion devices Dispersion devices cause different wavelengths of light to be dispersed at different angles. When combined with an appropriate exit slit, these devices can be used to select a particular wavelength (or, more precisely, a narrow waveband) of light from a continuous source. Two types of dispersion devices, prisms and holographic gratings are commonly used in UV-vis spectrophotometers. Light falling on the grating is reflected at different angles, depending on the wavelength. Holographic gratings yield a linear angular dispersion with

11 29 wavelengths and are temperature insensitive. However, they reflect light in different orders, which may overlap. As a result, filters must be used to ensure that only the light from the desired reflection order reaches the detector Detectors A detector converts a light signal into an electrical signal. Ideally, it should give a linear response over a wide range with low noise and high sensitivity. Spectrophotometers normally contain either a photomultiplier tube detector or a photodiode detector. The photomultiplier tube combines signal conversion with several stages of amplification within the body of the tube. It consists of a photoemissive cathode, a number of dynodes (which emit several electrons for each electron striking them) and an anode. Photodiodes are increasingly being used as detectors in modern spectrophotometers. Photodiode detectors have a wider dynamic range and are more robust than photomultiplier tube detectors. In a photodiode, light falling on the semiconductor material allows electrons to flow through it, thereby depleting the charge in a capacitor connected across the material. The amount of charge needed to recharge the capacitor at regular intervals is proportional to the intensity of the light Cells These are containers for the sample and reference solutions. They must be transparent to the radiation passing through. For UV region: Quartz or fused silica cuvettes are usually used. VIS/NIR regions: Silicate glass or plastic cuvettes ( nm) can also be used [66].

12 Applications It is the most widely used technique for quantitative molecular analysis and obeys Beer - Lambert law. Sometimes, it is used in conjunction with other techniques such as NMR, IR, etc., in the identification and structural analysis, of organic compounds. For qualitative analysis it provides valuable information through the absorption spectrum which is unique for a given compound [67-72]. 2.4 SCANNING ELECTRON MICROSCOPY (SEM) Principle In this technique, an electron beam is focused onto sample surface kept in a vacuum by electro-magnetic lenses (since electron possesses dual nature with properties of both particle and wave, hence an electron beam can be focused or condensed like an ordinary light). The beam is then rastered or scanned over the surface of the sample. The scattered electron from the sample is then fed to the detector and then to a cathode ray tube through an amplifier, where the images are formed, which gives the information of the sample [73] Instrumentation It comprises of a heated filament as a source of electron beam, condenser lenses, aperture, evacuated chamber for placing the sample, electron detector, amplifier, CRT with image forming electronics, etc. The SEM is an instrument that produces a largely magnified image by using electrons instead of light to form an image. A schematic diagram of the FE-SEM is shown in Figure 2.6. A beam of electrons is produced at the top of the microscope by an electron gun. The electron beam follows a vertical path through the microscope, which is held within a vacuum chamber.

13 31 Figure 2.6 Functional Block diagram of field emission scanning electron microscope (FE-SEM) The beam travels through electromagnetic fields and lenses, which focus the beam down towards the sample. Once the beam hits the sample, electrons and X - rays are ejected from the sample. Detectors collect these X - rays, backscattered electrons and secondary electrons and convert them into a signal that is sent to a screen similar to a television screen. This produces the final image. In this research work, the powder samples were placed on the carbon tape which is attached to the sample holder. JEOL JSM 6320F (FESEM), F E I Quanta FEG 200 (HRSEM) are used to study the surface morphology of the sample.

14 Applications Scanning electron microscopy has been applied to the surface studies of metals, ceramics, polymers, composites and biological materials for both topography as well as compositional analysis. An extension of this technique is Electron Probe Micro Analysis (EPMA), where the emission of X-rays, from the sample surface, is studied upon exposure to a beam of high energy electrons. Depending on the type of detectors used this method is classified in to two as: Energy Dispersive Spectrometry (EDS) and Wavelength Dispersive Spectrometry (WDS). This technique is used extensively in the analysis of metallic and ceramic inclusions, inclusions in polymeric materials and diffusion profiles in electronic components. 2.5 ENERGY DISPERSIVE X - RAY ANALYSIS (EDAX) Energy dispersive X - ray spectroscopy (EDS or EDX) is an analytical technique used predominantly for the elemental analysis or chemical characterization of a specimen. Being a type of spectroscopy, it relies on the investigation of a sample through interactions between electromagnetic radiation and matter, analyzing X - rays emitted by the matter in this particular case. Its characterization capabilities are due in large part to the fundamental principle that each element of the periodic table has a unique atomic structure allowing X - rays that are characteristic of an element's atomic structure to be uniquely distinguished from each other. To stimulate the emission of characteristic X - rays from a specimen, an high energy beam of charged particles such as electrons or protons or a beam of X - rays is focused into the sample to be characterized. At rest, an atom within the sample contains ground state (or unexcited) electrons situated in discrete energy levels or electron shells bound to the nucleus. The incident beam may excite an electron in an inner shell, prompting its ejection and resulting in the formation of an electron - hole within the atom s electronic structure. An electron from an outer, higher - energy shell then fills the hole, and the difference in energy between the higher - energy shell and the lower energy shell is released in the form of a X - ray. The X - ray released by the electron is then detected and analyzed by the energy dispersive

15 33 spectrometer. These X - rays are characteristic of the difference in energy between the two shells, and the atomic structure of the element form which they were emitted. Figure 2.7 The principle of EDX The excess energy of the electron that migrates to an inner shell (in order to fill the newly - created hole) can do more than emitting a X - ray. Often, the excess energy is transferred to a third electron from a further outer shell, prompting its ejection. This ejected species is called an Auger electron and the method for its analysis is known as Auger Electron Spectroscopy (AES). Energy Dispersive X-Ray spectroscopy (EDS or EDX) is a technique used in conjunction with chemical microanalysis by scanning electron microscopy (SEM) (Figure 2.7). EDS technique detects X - rays emitted from the sample during bombardment by an electron beam to characterize the elemental composition of the volume analyzed. When a sample is bombarded by the electron beam in SEM, the electrons are ejected from atoms comprising the sample surface. EDS X - ray detector measures the relative abundance of X - rays against their energy. The detector is typically a lithium-drifted silicon solid-state device. When an incident X - ray hits

16 34 the detector, which creates a pulse of charge that is proportional to the energy of X - ray. The pulse charge is converted to a pulse voltage (which is proportional to the energy X - ray) by a charge sensitive preamplifier. The signal is then sent to a multichannel analyzer where the pulses are sorted by the tension. The energy, as determined by measuring the voltage per incident X - ray is sent to a computer for display and further data evaluation. The spectrum of X - ray energy versus counts is evaluated to determine the elemental composition of the sample volume. 2.6 TRANSMISSION ELECTRON MICROSCOPY (TEM) Principle In this technique, a beam of high-energy electrons (typically kev) is collimated by magnetic lenses and allowed to pass through a specimen under high vacuum. The transmitted beam and a number of diffracted beams can form a resultant diffraction pattern, which is imaged on a fluorescent screen kept below the specimen. The diffraction pattern gives the information regarding lattice spacing and symmetry of the structure under consideration. Alternatively, either the transmitted beam or the diffracted beams can be made to form a magnified image of the sample on the viewing screen as bright-and dark field imaging modes respectively. This gives information about the size and shape of the micro-structural constituents of the material. High - resolution image contains information about the atomic structure of the material. This can be obtained by recombining the transmitted beam and diffracted beams together [74, 75] Instrumentation It comprises of a tungsten filament or LaB 6 or a field emission gun as source of electron beam, objective lens, imaging lens, CCD camera, monitor, etc. The ray of electrons is produced by a pin-shaped cathode heated up by current. The electrons are vacuumed up by a high voltage at the anode. The acceleration voltage is between 50 and 150 kv. The higher it is, the shorter are the electron waves and the higher is the power of resolution, but this factor is hardly ever limiting. The power of resolution of electron microscopy is usually restrained by the quality of the

17 35 lens-systems and especially by the technique with which the preparation has been made. Modern gadgets have powers of resolution that range from nm. Schematic representation of TEM image is shown in Figure 2.8. The accelerated ray of electrons passes a drill-hole at the bottom of the anode. Its following way is analogous to that of a ray of light in a light microscope. The lens-systems consist of electronic coils generating an electromagnetic field. The ray is first focused by a condenser and then passes through the object, where it is partially deflected. The degree of deflection depends on the electron density of the object. The greater the mass of the atoms, the greater is the degree of deflection. Biological objects have only weak contrasts since they consist mainly of atoms with low atomic numbers (C, H, N, O). Consequently, it is necessary to treat the preparations with special contrast enhancing chemicals (heavy metals) to get at least some contrast. Additionally, they are not thicker than 100 nm, because the temperature rises due to electron absorption. It is generally impossible to examine living things. Figure 2.8 Functional Block diagram of transmission electron microscope

18 36 After passing through the object, the scattered electrons are collected by an objective. Thereby an image is formed, that is subsequently enlarged by an additional lens - system (called projective with electron microscopes). The formed image is made visible on a fluorescent screen or it is documented on photographic material. Photos taken with electron microscopes are always black and white. The degree of darkness corresponds to the electron density (differences in atom masses) of the candled preparation Applications Transmission electron microscopy is used to study the local structures, morphology, dispersion of multi - component polymers, cross sections and crystallization of metallic alloys semiconductors, microstructure of composite materials, etc. The instrument can be extended to include other detectors like Energy Dispersive Spectrometer (EDS) or Energy Loss Spectrometer (ELS) to study about the local chemistry of the material similar to SEM technique [76] 2.7 FOURIER TRANSFORM INFRARED SPECTROSCOPY (FT-IR) Principle It involves the absorption of electromagnetic radiation in the infrared region of the spectrum which results in changes in the vibrational energy of molecule. Since, usually all molecules will be having vibrations in the form of stretching, bending, etc. The absorbed energy will be utilized in changing the energy levels associated with them. It is a valuable and formidable tool in identifying organic compounds which have polar chemical bonds (such as OH, NH, CH, etc.) with good charge separation (strong dipoles) [77-79] Instrumentation It was originally designed as a double beam spectrophotometer comprising IR source (red hot ceramic material), grating monochromator, thermocouple detector, cells made of either sodium chloride or potassium bromide

19 37 materials, etc. In this process, the light is dispersed by the monochromator but, this type of basic design for IR measurements has been outdated. Instead, a newer technique termed Fourier Transform-Infrared (FT-IR) has been in practice. This technique utilises a single beam of un-dispersed light has the instrument components similar to the previous one. Figure 2.9 Functional Block diagram of Fourier transform infrared spectrometer In FT-IR, the un-dispersed light beam is passed through the sample and the absorbance at all wavelengths is received at the detector simultaneously. A computerized mathematical manipulation (known as Fourier Transform ) is performed on this data to obtain absorption data for each and every wavelength. To perform this type of calculations interference of light pattern is required for which the FT-IR instrumentation contains two mirrors; one fixed and one moveable with a beam splitter in between them. Before scanning the sample, a reference or a blank scanning is required. The following is the simplified design of the instrument (Figure 2.9).

20 Applications It finds extensive use in the identification and structural analysis of organic compounds, natural products, polymers, etc. The presence of particular functional group in a given organic compound can be identified. Since every functional group has unique vibrational energy, the IR spectra can be seen as their fingerprints. 2.8 BET ANALYSIS Surface Area Determination The surface of a material is the dividing line between a solid and its surroundings, liquid, gas or another solid. Therefore, the amount of surface or surface area is an important factor in the behavior of a solid. Surface area has strong influence on many factors such as dissolution rates of pharmaceuticals, the activity of industrial catalyst, adsorption capacity of air and water purifiers, and the processing of most powders and porous materials, etc. Whenever solid matter is divided into smaller particles, new surfaces are created thereby increasing the surface area. Similarly, when pores are created within the particle interior (by dissolution, decomposition or some other physical or chemical means) the surface area is also increased. There may be more than 2000 m 2 of surface area in a single gram of activated carbon as an example for gas absorption. The true surface area, including surface irregularities and pore interiors, cannot be calculated from particle size information but is rather determined at the atomic level by the adsorption of an unreactive gas or inert gas. The amount adsorbed, let s call it X, is a function not only of the total amount of exposed surface but also (i) temperature, (ii) gas pressure and (iii) the strength of interaction between gas and solid. Because most gases and solids interact weakly, the surface must be cooled substantially in order to cause measurable amounts of adsorption - enough to cover the entire surface. Where the gas pressure increases, more gas is adsorbed on the surface (in a non - linear way). However, adsorption of a cold gas does not stop when it covers the surface in a complete layer of one molecule thick (let s call the theoretical monolayer amount

21 39 of gas Xm)! As the relative pressure is increased, excess gas is adsorbed to form multilayers. [80, 81] So, gas adsorption - as a function of pressure - does not follow a simple relationship, and we must use an appropriate mathematical model to calculate the surface area. We use the BET equation as follows: 1 1 C 1 P x[( P P ) 1] X C X C P 0 m m 0 (5) where P/P 0 is the gas s relative pressure and constant C is related to the strength of interaction between gas and solid The Principle The gas most commonly used is nitrogen for a number of reasons. In the classical manometric technique, relative pressures less than unity are achieved by creating conditions of partial vacuum (absolute pressures of pure nitrogen below atmospheric pressure). This method is easily automated and the amount of gas adsorbed is made at a number different relative pressures. Usually, the analyzer obtains at least three data points in the relative pressure range between and 0.30 Pa. Experimentally measured data are recorded as pairs of values: the amount of gas adsorbed is expressed as STP volume (VSTP) and the corresponding relative pressure (P/Po). A plot of these data is called an isotherm. The Principle of calculation, the computer program takes over and a least - squares linear regression is used to fit the best straight line through a transformed data set consisting of the following pairs of values: 1/VSTP (Po/P)-1 and P/Po. The monolayer capacity, V m, is calculated from the slope,

22 40 S C 1 (6) V m C and the intercept, i, of the straight line i V 1 (7) m C Solving for V m V m 1 s i (8) The number of molecules in the monolayer is obtained through the number of moles. Vm value is calculated by dividing Vm by the molar volume (MV) for the number of moles. The number of molecules covering the surface in a layer one molecule thick can be determined by multiplying moles by Avogadro s number. If we know how much area one molecule occupies, then the total area can be calculated. Thus the area called as cross - sectional area. Therefore, the total surface area, St, is then calculated from the below equation S t V L A m A V m (9) M v where L AV is Avogadro s number and Am is the cross - sectional area. All surface area results are finally reported normalized by sample weight, or mass, as square meters per gram, written m 2 /g. 2.9 SOLAR CELL FABRICATION The DSSC consists of four components namely: photoanode, dye molecules, electrolytes and photocathode. For the DSSC fabrication, ruthenium (II) N dyes, iodide and tri - iodide electrolytes and Pt - coated photocathodes were purchased from

23 41 commercially available sources and utilized. The surface of a photoanode was modified with synthesized TiO 2 nanostructures by using spray deposition method. The fabrication of DSSC is described clearly here. 1.5 g of synthesized TiO 2 nanostructures and 50 ml of ethanol were grounded in a mortar for few minutes to form colloidal suspensions. Thereafter, five drops of triton - X were added to the solution as an organic binder. Fluorine doped tin oxide (FTO) substrates were cleaned ultrasonically using a mixture of acetone and ethanol. Figure 2.10 I - V curve measurements system at Prof. Kenji Murakami laboratory, Shizuoka University The TiO 2 nanostructures suspension in ethanolic solution was sprayed over the FTO substrate at a substrate temperature of 150 C by spray deposition. TiO 2 coated FTO substrates (photoanodes) were annealed at 450 C for 2 h. Photoanodes were immersed in ethanolic solution with 0.03 M di - tetrabutyl ammonium is - bis (isothiocyanato) bis (2,2 - bipyridyl 4,4 dicarboxylato) ruthenium (II) (N - 719). The dye sensitized photoanode and Pt - coated counter electrode were clamped using clips. Finally, an iodide redox electrolyte was filled between the electrodes via capillary action and DSSC s device were subjected in I - V instrument JASCO, CEP - 25BX, as shown in Figure 2.10.