CW-Department of Physics
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Item Optimization of Sn.Se, Deposited by Reactive Thermal Evaporation for Solar cell Application(2014) Njoroge, W. K.; Munguti, L. K.; Musembi, R. J.Abstract In this study, tin selenide was prepared at different ratios using tin and selenium pellets in glass tube filled with argon and then heated up to 350'C. The resulting materials were cut Into ingots which were used in preparation of thin films by thermal evaporation. The evaporation was done using Edwards auto 306 coating unit. The chamber pressure was maintained at 5.0 x 10"mbars during the film deposition. Thin films of tin-selenide produced using various ratios were characterized for optical properties and sheet resistance. The optical measurements were done using UV-VJS-NIR spectrophotometer Solid State 3700 DUV in the visible range (380-750nm) and the transmittance spectra data obtained was analyzed using the SCOUT software. The films with ratio of J.I showed the highest transmittance of 85% with a band gap energy obtained 3S 140eV. The electrical characterization measurements were carried out using a four point probe at room temperature (25°(,) to obtain the sheet resistivity. The value of resistivity for was 20.1 .oem.Item Optical Characterization of Compounds for Dye-Sensitized Solar Cell Applications(2014) Njoroge, W. K.; Kabuga, P.; Simiyu, JThe dye Sensitized solar cell can provide an economically credible alternative in miugaring the challenges presented by the current convectional photovoltaic devices. Whereas the se m iconductor assume both the task of light absorption and charge carrier transport, the two functions are separated Light is absorbed b~. a sensitizer \\ hich is anchored to the surface of a wide band semiconductor. Charge separation takes place at the interface via photo-induced electron injection from the dye into the conduction band of the semiconductor Carriers are transported in the conduction band of the semiconductor to the charve collector The use of sensitizers in conjunction with oxide films of nano crystallme morphology has :1 broad :;bs')f])ti0n band and permits to harvest a large fraction of sunlight Nearly quantitative conversion of incident photon into electric current is achieved over a large spectral range extending from the UV ill the ncar l f< region. Overall solar energy to electrical energy conversion efficiencies of over 10% has bee n reported III addition, there are good prospects to produce these cells at lower cost than conventional solar cells The aim of this research is to contribute to the optical characterization of compounds required 111 TiO: based dye sensitized solar cells. To achieve this, several dyes will be used as the electron donating species These dyes will be adsorbed onto a nano-porous titania substrate. The nano-porous TiO: will he' prepared by sol-gel process and its layer will be mounted on a glass substrate bv ernp lov ing scree n printing technique. Using DUV3700 spectrophotometer the TiOc layer will be charac terize d to obtain iio. optical prope n ies which are transmittance and reflectance when in both un-sensiuzed and sens ii ized. An l ,'I:; e lccuolvte solution will be used as the redox couple. This solution \\ill be made of potassium iodide saturated "ith iodine. The solar cell parameters wil l then be determined as a \\'3\ of characterizing tht' solar cell. Thev will include open circuit voltage (Voc), short circuit current (l sc ). fill factor IFFI. efficiencv (Ill and power at maximum power point (Pl1laJ of the solar cell. Finallv , comparison 311(1 appropriate conclusions will be made as to which type ofDSSC is the best as per the dyes usedItem Optoelectronic Properties of Palladium Doped Tin (IV) Oxide (Pd: Sn02) Tlfin Films Deposited by Spray Pyrolysis(2013) Munji, M. K.; Mwathe, P. M.; Musembi, R. J.; Odari, B.V.Palladium Doped Tin (lV) Oxide (Pd: Sn02) thin films were deposited by Spray Pyrolysis technique using an alcoholic precursor solution consisting of Stannic chloride (SnCl~.5H20) and Palladium Chloride (PdCI?j The effect of increasing palladium concentration 011 optical and electrical properties was investigated. Sheet resistivity of the thin films was measured using the four point probe method and laid in the range of 0027- 3.43 Dcm for Pd: SnO:, thin films with Pd content of 0 - 6931% Pd prepared under optimized conditions. The optical properties were studied ill the UV/V1SiN1R region The Optical Band gap of the thin films was ill the range of3.73 - 4.11 eVItem Application of LBIC measurements for characterisation of triple junction solar cells(Elsevier, 2014-04-15) Munji, M. K.; van Dyk, E.E.; Kwarikunda, N.; Vorstera, F.J.; Okullo, W.In this study the Light Beam Induced Current (LBIC) imaging technique was used to characterise InGaP/InGaAs/Ge triple junction solar cells. The study focused on the use of monochromatic and solar light as beam probes to obtain photocurrent response maps from which the presence of any current reducing features on the solar cell were identified. Point illuminated current voltage (I–V) curves were obtained simultaneously while LBIC scanning measurements were being made. Curve fitting using an interval division algorithm based on the single diode model was performed to extract basic point device and performance parameters to give a rough indication of the functioning of the triple junction device. Using red and blue lasers as beam probes, reverse voltage breakdown was observed on the I–V curves which could be attributed to the Ge bottom subcell not being fully activated. The extracted parameters obtained when using monochromatic and solar light beam probes showed a large variation, indicating the dependence of I–V parameters on the spectral content of the beam probe.Item Effect of Sn Doping on the Electrical Properties of as Prepared and annealed ZnO thin films Prepared by Reactive Evaporation(2014) Munji, M. K.; Nyaga, P. K.; Musembi, R. J.Layers of transparent and conductive Sn-doped Zinc oxide (lnO) have been prepared by reacti. e evaporation on glass substrates. The deposition has been done at various doping levels ranging from J % to 8%. Annealing of samples was done using Rapid Thermal Processing (RTP). In this work, Nabertherrn Programmable Furnace system was used and annealing done at 300°C for one hour. Electrical characterization has been done for both prepared and annealed samples using four point probe configuration at room temperature (25°C) to obtain the sheet resistance. The sheet resistance for tin doped zinc oxide reduced with increase in tin doping to a minimum of J J .920cm at 4% tin doping for as prepared samples and I I .890cl11 for annealed samples.Item Analysis of Optimuzed Deposition Temperature of ZnO:Al Thin Film on SnSe ZnO:Al P-N Juction Solar Cell(2014) Munji, M. K.; Mbae, J. G.; Musembi, R. J.Solar energy has revolutionized the energy sector in the entire world by offering affordable, abundant and safe power source to the growing demands. The technology in solar cell production has advanced considerably in recent years Solar cell with very high conversion efficiency has been manufactured The efficiencies of solar cells depend on materials used. Deposition method and deposition conditions as they control the optoelectronic properties of the layers. Solar cell samples pre pared with a coat of ZnO)/AI exhibit 100 little degradation and very good solar cell properties (2hao et 01.,20(2). In this research Zinc Oxide will be doped in various percentages alluminurn ranging from 0% to 6% by mass to increase charge carriers. To obtain the optimum doping concentration, the optical and electrical properties of ZnO: AI thin film samples will be analyzed using a solid spec 3700 DUV optical spectrum analyzer and four point probe method respectively. The thin films of optimized Al doped 2nO will be deposited at different deposition temperature ranging from .4OOK-6OOK and tin selenide by reactive evaporation and evaporation technique respectively using Edward 306.Aulo evaporation system. The absorptance transrnittance and reflectance data of opitim ized ZnOA I in the range from 300nlll-2500nfll Will be obtained using UV-VIS NIR spectrophotometer solid state 3700 DUV. The resulting optical measurements will be analyzed using scout software to determine optical constant for thin solar cells The electrical properties of SnxSey and ZnO Al thin films w ill studied using four points probe method using Keithley 400 source meter using Lab View programme SnxSey-ZnO:AI solar cell will be fabricated using the optimized eloping concentration of AI and deposition temperature The performance of the p-n junction such as short circuit current (l sc). open circuit voltage (Voc ). fill factor (FF) and conversion efficiency (11) will be studied using a solar cell simulatorItem Characterization of TiO2 based dye-sensitized Solar Cell prepared by screen printing method(2014) Munji, M. K.; Muendo, Musila Nicholas; Simiyu, J.The dye-sensitized solar cells can provide an economically credible alternative in mitigating the challenges presented by the current convectional photovoltaic devices. Whereas the semiconductor assume both the task of light absorption and charge carrier transport, the two functions are separated. Light is absorbed by a sensitizer which is anchored 10 the surface of a wide band semiconductor. Charge separation takes place at the interface via photo-induced electron injection from the dye into the conduction band of the semiconductor. Carriers are transported in the conduction band of the semiconductor to the charge collector. The use of sensitizers in conjunction with oxide filrns of nano crystalline morphology provides a broad absorption band and permits to harvest a large fraction of sunlight. Nearly quantitative conversion of incident photon into electric current is achieved over a large spectral range extending from the UV to the near IR region. Overall solar energy to electrical energy conversion efficiencies of over 10% has been reported ln addition, there are good prospects to produce these cells at lower cost than conventional solar cells This research aims at contributing to the foregoing research on characterization of low cost Ti02 based dye sensitized solar cells. To achieve that, black berry dye was used as the electron donating species. Blackberry dye was extracted from blackberry fruit and adsorbed onto a nano-porous titania substrate. The nano-porous Ti02 was prepared by sol-gel process and its layer \NaS mounted on a glass substrate by employing screen printing technique. Using DUV3700 spectrophotometer, the Ti02 layer was characterized \0 obtain its optical properties which are transmittance and reflectance. Graphite coated glass 1\3S used as the counter electrode. An UIo• electrolyte solution was used as the redox couple. This solution was made of potassium iodide saturated with iodine. The solar cell parameters were determined 85 3 way of characterizing the solar cell. They included open circuit voltage (Voc), short circuit current (l sc ). fill factor (FF), power at maximum power point (Prnax) of the solar cell and efficiency (11).Item Experimental analysis and modeling of the< i> IV characteristics of photovoltaic solar cells under solar spectrum spot illumination(Elsevier, 2009-12) Munji, M. K.; van Dyk, E.E.; Vorster, F.J.In this paper, some models that have been put forward to explain the characteristics of a photovoltaic solar cell device under solar spot-illumination are investigated. In the experimental procedure, small areas of the cell were selected and illuminated at different solar intensities. The solar cell open circuit voltage (Voc) and short circuit current (Isc) obtained at different illumination intensities was used to determine the solar cell ideality factor. By varying the illuminated area on the solar cell, changes in the ideality factor were studied. The ideality factor obtained increases with decreasing illumination surface ratio. The photo-generated current at the illuminated part of the cell is assumed to act as a dc source that injects charge carriers into the p–n junction of the whole solar cell while the dark region of the solar cell operates in a low space charge recombination regime with small diffusion currents. From this analysis, a different model of a spot illuminated cell that uses the variation of ideality factor with the illuminated area is proposed.Item Characterization of a low concentrator photovoltaics module(Elsevier, 2012-05) Munji, M. K.; Butler, B.A.; van Dyk, E.E.; Okullo, W.; Booysen, P.Low concentration photovoltaic (LCPV) systems have the potential to reduce the cost per kWh of electricity compared to conventional flat-plate photovoltaics (PV) by up to 50%. The cost-savings are realised by replacing expensive PV cells with relatively cheaper optical components to concentrate incident solar irradiance onto a receiver and by tracking the sun along either 1 axis or 2 axes. A LCPV module consists of three interrelated subsystems, viz., the optical, electrical and the thermal subsystems, which must be considered for optimal module design and performance. Successful integration of these subsystems requires the balancing of cost, performance and reliability. In this study LCPV experimental prototype modules were designed, built and evaluated with respect to optimisation of the three subsystems and overall performance. This paper reports on the optical and electrical evaluation of a prototype LCPV module.Item Characterization of SnxSeylSn02: Co PN Junction Deposited by Spray Pyrolysis for Photovoltaic Application(2014) Munji, M. K.; Gitonga, R.G.This research will involve characterization of Sn.Se.: S1102-Co P-N as a solar cell material. SnSe is Ci p- type semiconductor with a direct band gap and high absorption in the visible region spectrum Cobalt doped rin oxide is not only a direct band gap semiconductor but also has a wide band gap and high transmittance Solar cells making use either of the two materials have been fabricated and have achieved good efficiencies. A solar cell using the two materials for a P-N junction is yet to be fabricated In this.research Co-doped Sn02 and SnSe thin films will be deposited on glass substrates using spray pyrolysis technique. The precursor solution will be prepared by dissolving 0.025 M of stannic chloride (SnCl2.5H2O) and different amounts of cobalt nitrate 6-hydrate (Co (NO;)2:6H20) and 1 - 1 dimethyl selenourea (IC3H8N2Se. Different thin films such as Sn02: CO-SIl02: SnSe and Co-SnO]: Snse \will be prepared Optical properties of thin films will be characterized i.e. absorbance spectra, transmittance and reflectance with UV-VIS-NIR spectrophotometer and the band gap of the films will be analysed by use 01scout software. Electrical characterization especially sheet resistivity wiII be measured using the Four point probe method. Thin films with optimum properties will be used at fabricated a P-N junction through double deposition. I-V characteristics of the junction will be done using. Keithley 2400 source meter and a computet. Fill factor (FF), open circuit voltage (Voc), and efficiency of tile junction wil] be obtainedItem Results of Injection and Tracer Tests in Olkaria East Geothermal Field(Stanford Universit, 1994-01-18) Ambusso, W.This paper presents results of a six month Injection and Tracer test done in Olkaria East Geothermal Field The Injection tests show that commencement of injection prior to onset of large drawdown in the reservoir leads to greater sustenance of well production and can reduce well cycling which is a common feature of wells in Olkaria East Field. For cases where injection is started after some drawdown has occurred in the reservoir, injection while leading to improvement of well output can also lead to increase in well cycling which is a non desirable side effect. Tracer tests reveal slow rate of fluid migration (< 5 m/hr). However estimates of the cumulative tracer returns over the period of injection is at least 31 % which is large and reveals the danger of late time thermal drawdown and possible loss of production. It is shown in the discussion that the two sets of results are consistent with a reservoir where high permeability occurs along contact surfaces which act as horizontal "fractures" while the formations between the "fractures" have low permeability. This type of fracture system will lead to channeled flow of injected fluid and therefore greater thermal depletion along the fractures while formations further from the fracture would still be at higher temperature. In an attempt to try and achieve a more uniform thermal depletion in the reservoir, it is proposed that continuous injection be done for short periods ( - 2years) and this be followed by recovery periods of the nearly the same length of time before resumption of injection again.Item Occurrence and Distribution of high temperature geothermal systems in Kenya(1993) Ambusso, W.; Onacha, S.A.; Omenda, P.A.Item The third East African Regional Astronomy Workshop(2014-02-10) Hashim, N. O.Item Results of Gravity and Ground Magnetic Survey of Menengai Geothermal Field, Kenya.(2011-11) Kemei, J. K.; Langat, G.K.; Ambusso, Willis Jakanyango; Okumu, J.Geothermal energy is increasingly becoming an important source of electricity generation in Kenya. It is estimated that more than 7000MW of electricity can be generated from geothermal prospects in Kenya. Identifying and delineating this resource can be done using geophysical methods. Currently Geothermal Development Company (GDC) has commenced drilling geothermal exploration wells in Menengai area and from the first well the results showed very good results. Gravity and Ground magnetic survey was carried out in Menengai area to map the subsurface structure. The Gravity measurements and total magnetic field intensity was taken with a station spacing of approximately 1km apart. Data reductions has been done and used to plot contour maps of the study area. Both data sets indicate that the northern part of the geothermal field is demagnetized indicating a zone of possible higher temperature and higher degree of hydrothermal alteration and intruded with high density bodies in the upper crust.