Browsing by Author "Masresha, Tizazu"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Photovoltaic Properties of Polymer based Bulk Heterojunction Solar Cell Composed of Poly[3-(2,5-Dioctyle-Pheneyl) Thiophene](Pdopt) and (PCBM)
    (Addis Ababa University, 2006-07) Masresha, Tizazu; Tessema, Genene (PhD)
    The Theme of this thesis is to characterize polymer based photovoltaic cell using the J-V measurements and impedance spectroscopy. Absorption spectra of pure (neutral) poly[3-(2,5-dioctyle-pheneyl) thiophene](PDOPT) study showed that the optical band gap of this polymer about 2eV, indicating that it is in the range of inorganic semiconductors. The sandwich structure ITO/PEDOT:PSS/PDOPT:PCBM/Al were utilized to fabricate the device. All the devices which are tested in this work, are bulk heterojunction that are composed of the p-type , PDOPT and n-type fullerene derivative, (phenyl-(6,6’)-c61)-butyric acid methyl ester ( PCBM )blend. The J-V measurements under both illumination dark indicated that the typical diode rectification property with rectification ratio 1.5× 103 at ( ±1.8V ) Such a device of blend ratio 1:2 (PDOPT:PCBM) expected to show a photovoltaic behavior with a power conversion efficiency about 0.028 % under 100mWcm−2
  • No Thumbnail Available
    Item
    Superposition of Squeezed Laser Light Beams
    (Addis Ababa University, 2015-07) Masresha, Tizazu; Kassahun, Fesseha (PhD)
    In this research we have studied the squeezing and statistical properties of a pair of superposed output light beams generated by three-level lasers, with the injected atoms prepared initially in a coherent superposition of the top and bottom levels. In particular, applying the density operator for the superposed output laser light beams together with the Q functions, we have calculated the global and local mean and variance of the photon number as well as the quadrature squeezing. In addition, we have determined the mean and variance of the photon number sum and difference and the photon numbers correlation of a pair of superposed two-mode output light beams. It is found that both the mean photon number and quadrature variance of the superposed output laser light beams is the sum of the mean photon numbers and the quadrature variances of the constituent output light beams. However, the variance of the photon number of the superposed output laser light beams is not the sum of the variances of the photon numbers of the component output laser light beams. Moreover, the global and local quadrature squeezing of a pair of superposed output laser light beams turned out to be the average of the global and local quadrature squeezing of the constituent output light beams. We have also noticed that the squeezing of the superposed output laser light beams is 61.5% below the vacuum state-level. On the other hand, we have seen that the local quadrature squeezing is greater than the global quadrature squeezing. It is found that the maximum local quadrature squeezing is 92.5% and occurs in the frequency = ±0.01. Furthermore, our results have shown that the local quadrature squeezing, unlike the local mean of the phonon number, quadrature variance, and photon number variance does not increase as the value of increases. In addition, our analysis indicates that the quadrature squeezing of the superposition of squeezed laser light beam and a light beam in vacuum state turned out to be just half of the quadrature squeezing of the three-level laser output light beam. Finally, we would like to mention that the photon numbers of a pair of superposed two-mode light beams are correlated