الفهرس 
Chapter 1Only 14 pages are availabe for public view
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Abstract
Structural, dc and ac electrical conductivity and optical properties were studied for 2\,7\ dichlorofluorescein in thin film form. X-ray diffraction XRD analysis depicts that the investigated compound in thin film forms has amorphous structure but in powder form shows a polycrystalline nature. Atomic force microscope (AFM) measurement of TiO2/FTO shows that the average particles size are 44.437 nm with roughness equals 20.307 nm. The optical properties of 2\,7\ dichlorofluorescein thin films of different thickness are studied. Transmittance and reflectance are measured at room temperature, in the wave length range (350–2500 nm), to calculate the optical constants (refractive index n and absorption index k) by Fresnel’s equations. The allowed optical transitions were found to be indirect transitions. Analysis of the obtained values of the refractive index yielded the optical high frequency dielectric constant and other optical dispersion parameters , . The Dc electrical conductivity for 2\,7\ dichlorofluorescein was measured in the temperature range (303-433 K). The electrical resistance was measured as a function of temperature. The obtained results showed that DCF has two values of activation energy and through the considering range of temperature. The first one is the, intermolecular conduction process which result from traveling of the charge carriers from one kind of macromolecule to another which causes lower value for activation energy (region I). The second process is the intramolecular conduction which results from hopping of electrons from one atomic site to another. Ac electrical conductivity for the investigated DCF as an organic semiconductor was studied as a function of temperature range (303-433 K) and frequency range (500 Hz -5 MHz). The obtained results indicate that ac conductivity depends on both temperature and frequency. The frequency exponent S is related to ac conductivity by the relation where S is temperature independent and lies very close to unity in the temperature range [303-363 K]. This is interpreted according to CBH model between centers forming intimate valence alternation pairs IVAP, S at higher temperatures [373-433 K]; it decreases with increasing temperature which is interpreted according to CBH model between centers forming non-intimate valence alternation pairs NVAP,s for the investigated organic dye. Photovoltaic properties of 2\,7\ dichlorofluorescein dye-sensitized solar cell have been investigated by current–voltage and capacitance–voltage measurements. All the measurements were carried out at room temperature in dark and under different illumination levels. It was found that the deduced value of the short circuit current density (Isc) equal 0.0172 mA and the open circuit voltage (Voc) equals 0.345V. Also from the investigation of the capacitance spectroscopy it was found that, the solar cell capacitance–voltage characteristics exhibit a behavior from the positive capacitance to the negative capacitance.