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العنوان
Study of Some Physical characteristics of an organic dye prepared as thin film form and its photovoltaic applications /
المؤلف
Mahmoud, Nourhan Abd El-Naser El-Sayed.
هيئة الاعداد
باحث / نورهان عبد الناصر السيد محمود
مشرف / كــرم فـتـحـي عـبـدالـرحـمـــــــن
مشرف / ايناس عبدالفتاح الشاذلي
مشرف / جيهان فاروق عبده سالم
تاريخ النشر
2022.
عدد الصفحات
216 p. :
اللغة
الإنجليزية
الدرجة
ماجستير
التخصص
الفيزياء والفلك (المتنوعة)
تاريخ الإجازة
1/1/2022
مكان الإجازة
جامعة عين شمس - كلية العلوم - الفيزياء
الفهرس
Only 14 pages are availabe for public view

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Abstract

Organic semiconductors are an attraction point for scientists. Organic semiconductor is a basic of new electronics due to its advantages. they are less expensive, lighter, and more flexible in shaping and manufacture when compared to an inorganic semiconductor. Organic semiconductors are used in a range of applications such as light emitting diodes (OLEDs), field effect transistors (OFET) and solar cells (OSC). In the first part, the thermal evaporation technique was used to deposit organic thin films of 4-dimethyl amino benzeldine malononitrile (DBM) and their structural, electrical and optical properties were investigated. In the second part, organic solar cell was fabricated. We examined the electrical and photovoltaic properties of these cell to obtain the solar cell parameters optimization and fabrication.
Thermal properties of DBM compound were studied using Differential thermal analysis (DTA) methods. The compound is thermally stable up to its melting point at 435 K. The crystal structure of DBM was determined by X-ray single crystal diffraction using single crystal diffractometer. It was found that the DBM crystallized in the monoclinic system with P21 space group and the lattice parameters are given as a = 16.992 nm, b = 3.910 nm, c = 9.391 nm, α = 90.00◦, β = 123.72◦ and γ = 90.00◦. On the other hand, X-ray powder diffraction of DBM indicated that the material in the powder form is polycrystalline. Miller indices, hkl, values for each diffraction peak in the X-ray powder diffraction spectrum were calculated using a computer program.
Thin films of DBM were prepared using thermal evaporation technique. The molecular structure of DBM films was investigated by Fourier-transform infrared (FTIR). The observed vibrational wavenumbers in FTIR spectra were analysed and assigned to different normal modes of the molecule. FTIR spectra for DBM powder as well as for as-deposited and annealed DBM films reflected the thermal and chemical stability of DBM compound.
Thermal evaporation of DBM led to partially crystalline films oriented to the (520) plane and found that the crystallinty of the films increases as the film thickness increases. The effect of annealing on the nature and degree of crystallinty has been investigated and it was found that the annealing temperature enhances the crystallinity of the DBM thin films. It is observed that the crystallite size increases gradually with the increasing of film thickness. The scanning electron microscope of the as-deposited DBM thin films of different thicknesses supported that the crystallite size increases with increasing the film thickness. Also, the crystallite size increased from 59.2 to 65.771 nm with the annealing temperature.
Optical properties were investigated for as-deposited and annealed DBM films by using spectrophotometric measurement of transmittance and reflectance at normal incidence in the wavelength range of 200-2500 nm. The obtained spectra showed that all the films are transparent above λ > 1000 nm and the measured optical constants (refractive index, n, and absorption index, k) are independent of the film thickness and their values are slightly changed by annealing temperature.
The optical dispersion parameters have been analysed by a single oscillator model. The values of oscillator energy (E_0) and dispersion energy (E_d) were found to be 1.31, 1.19 eV for the as-deposited films and 1.39, 1.68 eV for the annealed film at 373K. The analysis of the spectral behaviour of the absorption coefficient () in the fundamental absorption region was analysed by applying the energy band theory of solid and revealed indirect transitions with a value of energy gap equals to 0.9325 eV followed by Urbach tail. Thermal annealing increases the value of the energy gap and decreases the Urbach tail.
The hot probe method measurements showed that DBM is p type material. The current was measured as a function of voltage at room temperature, which shows that Au electrode formed ohmic contact with DBM compound. The dark electrical resistivity of DBM thin films were measured for the films with different thicknesses and the measurements showed that it decreases with increasing film thickness. The temperature dependence of the electrical conductivities of DBM bulk and thin films were measured in the temperature range from 298 to 423 K. It was found that the conduction is through an activated process having two conduction levels with different activation energies. Also, it was found that the values of activation energies are independent on the film thickness in the thickness range 130-590 nm. The average values of activation energies were found to be 0.74 and 1.137 eV as a change from extrinsic to intrinsic conduction. In addition, the electrical conductivity of DBM films.
The current density-voltage (J-V) and capacitance-voltage (C V) characteristics of DBM thin films with different thicknesses have been investigated. the charge transport phenomenon appears to be space-charge-limited current (SCLC).
However, hybrid organic-inorganic solar cell was fabricated by thin film of DBM deposited on n-Si substrates. The capacitance-voltage characteristics indicated that the junction is of abrupt nature. The dark forward current density-voltage characteristics indicated a tunnelling conduction at relatively low voltages followed by a space charge-limited-conduction mechanism at relatively high voltages. Under illumination, the cell exhibits photovoltaic characteristics with an open-circuit voltage (V_oc) of 0.76, a short-circuit current (I_sc) of 1.2 × 10-9A and a power conversion efficiency (η) of 1.48%.