Quantum efficiency and photovol talc §~ ~roperties of a photodiode made of ;/ poly (3-4(-octylphenyl)-2, 2'-bithiophene) (ptopt)

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Addis Ababa University


In this thesis we investigated the photovoltaic properties of poly [3-(4- octylphenyl)-2, 2'-bithiophene] (PTOPT) in the form of AI/PTOPT/ITO sandwich structure. The peaks of the spectral response of the device were found to match with the absorption spectrum of PTOPT for illumination from both the AI and ITO sides. However, the IPCE% obtained when the device was illuminated from the AI side is found to be lower than for illumination from the ITO side. The experimentally collected data on absorption and action spectrum are explained based on the theoretical model proposed by Gosh and Feng. The photovoltaic parameters were determined from the I-V curve recorded by illuminating the photodiode through the AI side with monochromatic light (500 nm) of intensity 7.4 JlW/cm2. No correction was done for reflection from the surface of the AI electrode. A power conversion efficiency of 0.7% and a fill factor of 0.25 were also obtained. The small value of the efficiency is due to the low mobility of the charge carriers of the photodiode. Moreover, the short circuit photocurrent of the device was found to vary with the incident light intensity. The observed variation of the photocurrent with the incident light irradiation (linear at low light intensities and non-linear at higher light intensities) will be explained using a simple kinetic model



Investigated the Photovoltaic Properties