Ashraf M. Abdel Haleem

Experimental determination of band offsets at the SnS/CdS and SnS/InSxOy heterojunctions

The semidirect x-ray photoelectron spectroscopy technique was used to measure the band alignments at the interface of heterostructures based on SnS. The layers were deposited by electrochemical deposition (ECD), chemical bath deposition (CBD), or photochemical deposition (PCD). The following four kinds of heterojunctions were characterized. (1) ECD-SnS/PCD-CdS. (2) CBD-SnS/PCD-CdS. (3) ECD-SnS/ECD-InSxOy. (4) CBD-SnS/ECD-InSxOy. The valence band offsets ΔEV of those four heterojunctions are determined to be 1.34, 1.59, 0.77, and 0.74±0.3 eV, respectively.

Wide Bandgap InS-based Thin Film: Deposition, Characterization, and Application for SnS Solar Cells

A wide band gap InS-based thin film was deposited onto F-doped SnO2-coated glass by electrochemical deposition from an aqueous solution using a two-step periodic-pulse voltage. The film was characterized optically by a double beam spectrometer, morphologically by a scanning electron microscope. In addition, the composition ratios of the film were measured by Auger electron spectroscopy. Furthermore, the photosensitivity of the film was observed by means of photoelectrochemical measurements, which confirmed that the film showed n-type conduction. Finally, a detailed X-ray photoelectron spectroscopy (XPS) study was performed in order to understand the chemical states of the elements involved in the film composition. The XPS results revealed that the deposited film can be written in the form of InSxOy(OH)z. The film was used along with tin sulfide thin film to fabricate a novel heterojunction.

Analytical modeling of the radial pn junction nanowire solar cells

In photovoltaic solar cells, radial p-n junctions have been considered a very promising structure to improve the carrier collection efficiency and accordingly the conversion efficiency. In the present study, the semiconductor equations, namely Poissons and continuity equations for a cylindrical p-n junction solar cell, have been solved analytically. The analytical model is based on Greens function theory to calculate the current density, open circuit voltage, fill factor, and conversion efficiency. The model has been used to simulate p-n and p-i-n silicon radial solar cells. The validity and accuracy of the present simulator were confirmed through a comparison with previously published experimental and numerical reports.

A numerical simulator for graded-bandgap solar cells

A one-dimensional semiconductor simulator is implemented. This simulator is able to simulate thin film graded-bandgap semiconductors having position dependent device parameters such as: the energy gap, absorption coefficient, the dielectric constant and other parameters. The simulator is able to calculate the conversion efficiency of the solar cells under normal conditions as well as the limiting efficiency of the cells. It calculates the efficiency by solving the coupled semiconductor equations, namely, Poissons equation and the current continuity equations together with the Boltzmann photon equation. The non-avoidable bulk losses due to carriers recombination, namely, radiative and Auger, are carefully considered. The photon-recycling effect is carefully taken into account.

Heterojunction of poly (o-toluidine) and silicon nanowires

Abstract. A nanostructured poly (o-toluidine)/silicon nanowires (NPOT/SiNWs) heterojunction has been fabricated with a low cost and simple techniques, where NPOT has been in situ polymerized upon SiNWs synthesized by chemical etching of a silicon wafer. The morphology of SiNWs before and after deposition of NPOT has been examined by scanning electron microscope (SEM). The chemical composition of NPOT has been investigated by Fourier transform infrared (FTIR), ultraviolet-visible (UV-visible) spectroscopy, and X-ray diffraction (XRD) techniques. NPOT morphology has also been examined by SEM before being deposited on the SiNWs. I-V measurements of the device have been made at room temperature under dark conditions. The heterojunction diode parameters such as turn-on voltage, reverse saturation current (I0), ideality factor (η), barrier height (ΦB) and series resistance (Rs) have been determined from the I−V curves using Schottky equations. The device shows promising characteristics as a candidate for producing heterojunction diodes.

Studies of N-type indium tin sulfide (In x Sn y S) thin films using electrochemical deposition technique

Tin sulfide (SnS) films usually possess p-type electrical conductivity. Indium tin sulfide (In<inf>x</inf>Sn<inf>y</inf>S) thin films were deposited on indium-tin-oxide coated glass by electrochemical deposition from an aqueous solution containing Na<inf>2</inf>S<inf>2</inf>O<inf>3</inf>, SnSO<inf>4</inf>, and In<inf>2</inf>(SO<inf>4</inf>)<inf>3</inf>. Different concentration of In<inf>2</inf>(SO<inf>4</inf>)<inf>3</inf> was added to observe the effects on the structural and electrical properties. All thin films were deposited for the duration of 12 minutes. The thickness of the thin film was measured to be around 0.5 µm. The as-deposited thin films were characterized by scanning electron microscope, X-ray diffraction, Auger electron microscopy (AES) and photo-electro-chemical measurement We observed that the SnS surface morphologies changed when different concentration of indium was added. In this research, a transformation of p-type to n-type conductivity was revealed with additional of In<inf>2</inf>(SO<inf>4</inf>)<inf>3</inf> greater than 1 mM concentration.