Fatih Ongul

Formation of CdZnS thin films by Zn diffusion

The structural, composition and optical absorption properties of Cd1−xZnxS (CdZnS) thin films fabricated by the reactive diffusion of Zn in CdS have been investigated. These ternary compounds were characterized by x-ray diffraction (XRD), energy dispersive x-ray fluorescence and optical absorption measurements. It is established that thermal annealing of Zn/CdS structure at temperature (400 °C) lower than the melting point of Zn (418 °C) results in the concentration distribution of Zn in CdS film described by an erfc-curve (D = 5 × 10−14 cm2 s−1) and characterizing the free impurity diffusion from a constant source. In contrast to this, the concentration profile of Zn in CdS film at higher annealing temperature (570 °C) is not described by the erfc-curve and shows a nearly stepped form, which is characteristic of reactive diffusion. XRD patterns of Zn/CdS structures annealed at 570 °C showed diffraction peaks of ternary CdZnS compounds. Analysis of the absorption spectrum of such films indicates formation of CdZnS composition with the largest value of energy band gap up to 2.64 eV, exceeding the band gap of CdS (2.43 eV). It is concluded that interdiffusion in Zn/CdS structures at temperatures exceeding the melting point of Zn was accompanied by formation of Cd1−xZnxS ternary compounds. The band gap of this variable band structure changes from 2.64 eV in the near surface region to 2.43 eV (CdS) in the inner region of the film.

Vacuum-free processed bulk heterojunction solar cells with E-GaIn cathode as an alternative to Al electrode

In this paper, the photovoltaic characteristics of bulk heterojunction solar cells employing an eutectic gallium–indium (EGaIn) alloy as a top metal contact which was coated by a simple and inexpensive brush-painting was investigated. The overall solar cell fabrication procedure was vacuum-free. As references, regular organic bulk heterojunction solar cells employing thermally evaporated Aluminum as a top metal contact were also fabricated. Inserting the ZnO layer between the active layer and the cathode electrodes (Al and EGaIn) improved the photovoltaic performance of the herein investigated devices. The power conversion efficiencies with and without EGaIn top electrodes were rather comparable. Hence, we have shown that the EGaIn, which is liquid at room temperature, can be used as a cathode. It allows an easy and rapid device fabrication that can be implemented through a vacuum free process.

Modification of CdTe thin films by Zn reactive diffusion

Formation of Cd1−xZnxTe (CdZnTe) ternary compounds as a result of Zn diffusion in CdTe thin films, the structural and optical properties of CdZnTe compounds and I–V characteristics of CdZnTe/CdTe heterojunctions are presented. X-ray diffraction study of Zn/CdTe structures exposed to thermal annealing indicates the formation of CdZnTe compounds. Analysis of the absorption spectra of Zn/CdTe structures, annealed at 500 °C, and CdTe thin films show that the energy band gap of the former (1.65 eV) is larger than that of the latter (1.50 eV). Such an increase of the band gap of annealed two-layer Zn/CdTe is attributed to the reactive diffusion of Zn in CdTe films accompanied by the formation of Cd1−x ZnxTe compounds with an average value of x = 0.22. The temperature dependence of the effective diffusion coefficient of Zn in CdTe at 430–520 °C is described as D = 2.5 × 10−3 exp(−1.30 kT−1)~cm2 s−1.

Theoretical and experimental investigations of the 2-(4-chlorophenyl)-3-{[5-(2-cyano-2-phenylethenyl)]furan-2-yl}acrylonitrile molecule as a potential acceptor in organic solar cells.

A novel soluble asymmetric acrylonitrile derivative, 2-(4-Chlorophenyl)-3-{[5-(2-cyano-2-phenylethenyl)]furan-2-yl}acrylonitrile (CPCPFA, 3) was synthesized in three steps by Knoevenagel condensation. The structure of the CPCPFA was characterized using UV-vis, FTIR, (1)H NMR, (13)C NMR, and LC-MS. CPCPFA was evaluated as an electron acceptor in bulk heterojunction organic solar cells. Its optical and electronic properties as well as photovoltaic performance were investigated.

4.15 Solar Cells

Global energy problem is one of the most serious among the top 10 problems of the humanity for the next 100 years. The energy need is increasing in proportional to the increase in the world population. Recently, the source for the energy of the world is highly dependent on the fossil fuels, which leads to a climate change due to the increased amount of carbon emissions to the atmosphere. Reducing the depence on fossil fuels and the use of renewable energy sources have been foreseen as two viable strategies to overcome this problem. Political reliability, cost effectivity, and public acceptibility can be counted as the biggest advantages of renewable energy sources.