Pd-F:SnO2 thin films have been prepared by spray pyrolysis technique. Optimization has been done by doping SnO2 with palladium at varying levels of concentration and then recording sheet resistance. The sheet resistivity has been observed to decrease gradually as at% Pd concentration is increased; an optimum sheet resistivity value of 2.71 × 10 −2 Ω cm has been recorded. The decrease in sheet resistivity has been attributed to presence of Pd ions which contribute in increment of charge carrier density. Using the optimum value of at% Pd doping, the same procedure has been repeated to study the effect of fluorine on Pd:SnO2; an optimum value of 1.64 × 10 Ω cm which is attributed to effects resulting from annealing the samples in nitrogen gas atmosphere.
Focused sunlight can act as a localized source of excess minority carriers in a solar cell. Current signal generated by these carriers gives considerable information about the electrical properties of the cell's material. Point by point current-voltage data were measured for a back point-contact concentrator photovoltaic cell when illuminated by focused sunlight. Two numerical curve fitting procedures: a non-linear two-point interval division and particle swarm optimization algorithm were then applied to extract local parameters (i.e. as function of position) from the current-voltage data at each measurement point. Extracted parameters plotted yields relative spatial information about the electrical properties of a solar cell in a two or three dimensional mapping. The curve fitting routines applied to current-voltage data reveal that performance parameters: short circuit current, open circuit voltage, maximum power and fill factor show distinct variations in the vicinity of the observed current reducing feature. The relative values of the diode ideality factors, series resistance, shunt resistance and reverse saturation currents from both methods showed no significant measurable features that could be distinguished. This shows that the observed reduction in photo-induced current was due to severe recombination in the bulk or around the highly diffused point contacts and not the quality of the multiple p-n junctions of the cell. These approaches allow one to obtain a set of parameters at each local point on the cell which are reasonable and representative of the physical system.
Dye-sensitized solar cells (DSSCs) offer an economically reliable and suitable alternative in moderating the challenges presented by the existing convectional photovoltaic cells. However, the efficiency of dye-sensitized solar cells has remained relatively low. For this reason, this research was aimed at studying the characteristics of TiO 2 compact layer that can be applied in DSSCs as a way of improving efficiency. To achieve this, TiO 2 compact layer was deposited on a conductive glass substrate by using Holmarc's Spray Pyrolysis system, using Ultrasonic Spray Head and spraying in the vertical geometry. X-ray Diffraction studies revealed that TiO 2 compact layer was of anatase phase and had tetragonal crystalline structure. Raman spectroscopy showed that the most intense peak appeared at 142 cm-1 due to the external vibration of the anatase structure. Hall Effect studies revealed that TiO 2 compact layer has a high density of charge carriers' value of 1.25 × 1019 cm-3 hence it can be used in DSSC applications.
Titanium dioxide is a wide band gap semiconductor responsible for the bright white appearance in most substances. This material has many unique properties due to its extraordinary chemical stability. TiO 2 has a conduction band that closely matches the excited energy level of organic dyes hence it is used in fabrication of photo-anode electrode of dye sensitized solar cell. However, the optical properties and the density of states of TiO 2 thin films determine the performance of dye sensitized solar cell fabricated from TiO 2 photo-anode electrode. For this reason, the purpose of this study was to investigate the optical properties and the OJL electronic inter-band transition analysis of TiO 2 nanoparticle thin films. Under the OJL model, the expressions of density of states were specified for the optical transition from the valence band to the conduction band. The TiO 2 nanoparticles were prepared using sol-gel and hydrothermal methods and deposited on a conductive glass substrate by screen printing and spray pyrolysis techniques. SEM analysis revealed that TiO 2 nanoparticles were spongy and had unevenly sphere-shaped profile while TiO 2 nanotubes had a skein-like morphology with abundant number of nanotubes intertwined together. This study showed that TiO 2 thin films have both direct and indirect band-gaps. The OJL Gap energy (E 0) values were observed to be between 30273.2356 and 31072.0000 wavenumbers which translated to band-gap energies between 3.744 and 3.843 eV. From these findings showed that TiO 2 films prepared could be used in the fabrication of high performing dye-sensitized solar cell.
Abstract. Indium Hydroxy Sulphide has demonstrated abundance in resources, low prices, nontoxic characteristics, radiation resistance, high temperature resistance, and chemical stability, and therefore it has become an extremely important photoelectric, photovoltaic, and light sensing thin film material. Some treatment on this material include thermal annealing which is a process used for intrinsic stress liberation, structural improving, and surface roughness to control its electro-optical properties. In a qualitative way, annealing modifies surface morphology, intrinsic parameters, and electron mobility with temperature and time. In this work, an explanation on the surface modification of In(OH) x S y thin films when subjected to an annealing process is discussed. Both electrical and optical effects caused by annealing were carried out and characterizations were performed at different annealing temperatures in nitrogen in the temperature range 373-573 K. Using optical measurements data and simulated data, Scout software was employed and the results showed that increasing annealing temperature causes a slight decrease in transmittance with a consequence of modifying the energy band gaps values between 2.79-3.32 eV. It was concluded that annealing influence optical transmittance and resistance of the film make the thin films potential for photovoltaic, and light sensing applications.
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