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Analysis of sol aging effects on self-cleaning properties of TiO2 thin film

- Lukong, V. T., Ukoba, K. O., Jen, T. C.

Optimization of process parameters for sputtering of hydroxyapatite target on stainless steel

- Oladijo, Segun Stephen

  • Authors: Oladijo, Segun Stephen
  • Date: 2021
  • Subjects: Biomedical materials , Hydroxyapatite coating , Thin films , Steel, Stainless , Sputtering (Physics)
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/481892 , uj:43679
  • Description: Abstract: Biomaterials are natural or synthetic in origin materials ‘other than drug’ or the combination of two or more materials that can be used for some period for the replacement or treatment of any organs, tissue, or body. Metallic biomaterials like titanium, stainless steel, and cobalt alloys are notable materials that are adapted and used for medical applications purpose due to their favorable properties such as toughness, relatively low rate of corrosion, and excellent strength. Biomaterials are essential for the replacement of human joints and requires a long period of time such as 15 years to 20 years for older ages and more than 25 years above for younger age patients to serve as implant in their body and therefore, it is necessary to prolong the service life of biomaterials. In this study, the surface modification process was used for the enhancement of existing materials to improve the surface properties of the samples. For this research work, radio-frequency magnetron sputtering was considered for the deposition of the Hydroxyapatite (HAP) thin-film coating on stainless steel. This is due to its potential surface modification capability of high deposition rate, strong bond affinity, low cost of production, and capability to deposit insulating materials since Hydroxyapatite is known to be a good reinforcement for surface modification due to its favorable properties such as excellent bioactive and biocompatibility. Therefore, RF- magnetron sputtering was used for the deposition of a nanostructured thin film of Hydroxyapatite ceramic on the surface of stainless steel AISI 304. The RF sputtering process parameters (such as the RF-power and the deposition time in the deposition process) were characterized/optimized by Taguchi analysis, and evaluating the thin film phases and wear resistance, and the corrosion resistance was determined by electrochemical techniques. The scanning electron microscope (SEM) equipped with electron discharge microscopy, the atomic force microscope (AFM), X-ray diffraction, and optical microscopy were used to characterize the properties of the HAP thin-film coatings. The mechanical property and the tribological properties of the HAP coating were measured using Vickers hardness and, micro scratch tester. The electrochemical corrosion technique was used to analyze the corrosion behavior of the thin film. Whilst optimization of the process parameter was carried out using L9 Taguchi orthogonal array... , M.Ing. (Mechanical Engineering)
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Fabrication and synthesis of SnOX thin films : a review

- Emeka, Nwanna Charles, Imosili, Patrick Ehi, Jen, Tien-Chien

  • Authors: Emeka, Nwanna Charles , Imosili, Patrick Ehi , Jen, Tien-Chien
  • Date: 2020
  • Subjects: Thin films , Tin oxide , Band gap
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/457872 , uj:40647 , Citation: Emeka, N.C., Imosili, P.E. & Jen, T.C. 2020. Fabrication and synthesis of SnOX thin films : a review.
  • Description: Abstract: Due to its exceptional electrical, optical, chemical and magnetic properties, tin oxide (SnO and SnO2), which is a functional material has gained enormous attention for use in a variety of applications. Films of SnOX have a direct band gap between the ranges of 2.2 and 3.6 eV, with these films finding usefulness in various functions such as; solar cells, transparent conducting oxides for gas sensors, lithium-ion batteries, microelectronics, and use in the optoelectronics industries. In order to satisfy the needs of a broad range of these applications, thin films with an extensive properties span defined by film composition, thickness, structural properties and morphology are required. This article explains the theory and research status of the various manufacturing processes of tin oxide. The purpose is to analyse the effects of the thin films through distinct forms of deposition. The general finding summarized in this research on SnOX showed that various researchers studied specific characteristics of tin oxide properties restricted by experimental conditions.
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Fabrication, simulation and techno-economic evaluation of thin film nanocomposite membrane for acid mine drainage treatment

- Ramokgopa, Selaelo Kholofelo

  • Authors: Ramokgopa, Selaelo Kholofelo
  • Date: 2020
  • Subjects: Water - Purification - Membrane filtration , Acid mine drainage - Purification , Nanocomposites (Materials) , Thin films
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/480084 , uj:43447
  • Description: Abstract: Thin Film Composite (TFC) membrane technology has been applied in the removal of various pollutants from wastewater. TFC membranes have small pore sizes which enable the rejection of multivalent ions such as those found in Acid Mine Drainage (AMD). Also, nanoparticles with desirable properties have been added to TFC membranes to form Thin Film Nanocomposite (TFN) membranes with potentially enhanced properties. A great opportunity is provided for novel and sustainable development of TFN membranes with Carbon Nanotube (CNTs) for the treatment of AMD. CNT-Infused TFN membranes were synthesized to investigate the feasibility for use in synthetic AMD treatment. Flux and rejection under various operating conditions were measured. The addition of CNTs improved flux by up to 50% and reduced heavy metal concentration in AMD up to 95%. Furthermore, rejection followed the sequence Mg2+>Fe3+>Al3+. Design of Experiments (DOE) was used to determine the effects of process parameters (heavy metal concentration, pressure and MWCNT loading) on process optimisation and semi-empirical modelling techniques were conducted on the experimental data. Response Surface Methodology (RSM) was used to evaluate model outputs and Analysis of variance (ANOVA) was used for model validation. Iron concentration, pressure and CNT loading were found to have the most significance on the process followed by magnesium concentration and aluminium concentration according to RSM results... , M.Tech. (Chemical Engineering)
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Preparation and characterization of NbxOy thin films : a review

- Emeka, Nwanna Charles, Imoisili, Patrick Ehi, Jen, Tien-Chien

A two-dimensional simulation of atomic layer deposition process on substrate trenches

- Olotu, Olufunsho Oladipo

  • Authors: Olotu, Olufunsho Oladipo
  • Date: 2019
  • Subjects: Atomic layer deposition , Thin films , Nanostructured materials
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/413228 , uj:34805
  • Description: Abstract: In the cause of the increasing need for miniaturisation of devices, a more sophisticated nano-manufacturing technique of component was rummage around for, which has led to the adoption of atomic layer deposition (ALD) technique due to its competency of accomplishing superb uniformity, conformality, pinhole-free and ultra-thinness. In this dissertation, the ALD process within the cavity and surface of substrate trench was studied numerically with the intent to optimise the deposition process while formulating suitable ALD recipe. In the cause of optimising the process of an atomic layer deposition (ALD) for trenched substrate, a numerical model was presented, and two-dimensional simulations of the ALD process of substrate trenches in an arbitrary reactor were performed. Here, the deposition of aluminium oxide (Al2O3) was illustrated with trimethylaluminum (TMA) and ozone (O3) precursors as Aluminum (Al) and oxygen (O2) sources respectively while inert argon was used as purging gas in an arbitrary reactor. The flow is similar to a typical top-to-bottom type ALD reactor. The gases are assumed to enter at an inlet temperature of 150°C while the substrate, reactor walls and outlet temperature of 250°C is used. The TMA and O3 precursors are both pulsed separately, according to the sequence, into the reactor at 0.085 m/s for 0.2 and 1 second, respectively. While inert-purge gas (Ar) is used to purge the reactor domain at 0.17 m/s for 5 seconds between the pulse and exposure times. For this work the ALD sequence follows in a pulse-exposure-purge-exposure-pulse-exposure-purge manner to form a complete ALD cycle. After the reactive and inert-gases have flown and penetrated into the trenched substrate the excess and by-products are then exhausted past the edges of the trenched substrate towards the outlet of the reactor. The reactor flow domain is meshed into 67023 nodes. The ALD process within the arbitrary reactor is investigated by numerical simulating the reactor using computational fluid dynamics (CFD) within commercial software packages ANSYS FLUENT and CHEMKINPRO. This transient process is implemented by the coupled algorithm approach... , M.Ing. (Mechanical Engineering)
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Study on doctor blade and spin coated cuingase2 thin films

- Singh, Abhay Kumar, Jen, Tien-Chien

The study of bionanocomposite thin films and their crystal growth behaviour

- Malwela, Thomas

  • Authors: Malwela, Thomas
  • Date: 2014-10-08
  • Subjects: Nanocomposites (Materials) , Composite materials - Effect of high temperatures on , Crystal growth , Thin films
  • Type: Thesis
  • Identifier: uj:12544 , http://hdl.handle.net/10210/12337
  • Description: Ph.D. (Chemistry) , This study focuses on the morphology and crystal-growth behaviour of polyactide (PLA)-based blends and blends modified with organoclay thin films. The study further examined the effect of blending and the incorporation of organoclays on the enzymatic degradation behaviour. Thin films of unmodified and nanoclay-modified PLA/poly(butylene succinate) (PBS) blends were cast on a glass substrate by a spin coater, while thin films of biodegradable PLA/poly[(butylene succinate)-coadipate] PBSA blends and blends containing organoclays were cast on a silicon (100) wafer substrate. The morphology and crystal growth behaviour of the thin films crystallized at different temperatures were examined with an atomic force microscopy (AFM) equipped with a hot-stage scanner. In PLA/PBS blend thin films, AFM images showed that the size of the dispersed PBS phase was influenced by C30B clay loading on the blends. The dispersed size reduced on the addition of C30B clay up to 2 wt%, beyond which, dispersed size began to increase. Transmission electron microscopy studies indicated that this behaviour was due to the preferential location of silicates in the PBS phase than in the PLA phase. For thin films annealed at 60 °C, the additi on of organoclays to the blend quenched the growth of edge-on lamellae. The crystalline morphologies at 120 °C were dominated by edge-on lamellae grown, around the PBS phase to form spherulites. Morphologies of thin films crystallized at 120 °C from melt were dominated by the flat-on lamellae, while those crystallized at 70 °C from melt were dominated by the edge-on lamellae. In the case of PLA/PBSA blend thin films, the results indicated that the size and distribution of the dispersed phase were directly related to the blend composition. The crystal growth behaviours indicated the presence of homogeneous and heterogeneous nucleations, and the nature of nucleation was directly related to the blend ratio and the temperature at which crystallization occurred. Therefore, this study will facilitate the understanding of crystal growth behaviour in a confined environment and will enable the modulation of the blend properties.
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Fabrication and characterization of CuInSe₂/CdS/ZnO thin film solar cells

- Chenene, Manuel Luis

  • Authors: Chenene, Manuel Luis
  • Date: 2012-08-20
  • Subjects: Thin films , Solar cells , Photovoltaic cells , Chalcopyrite
  • Type: Thesis
  • Identifier: uj:2836 , http://hdl.handle.net/10210/6271
  • Description: M.Sc. , I-III-VI2 compound semiconductors are important photovoltaic (PV) materials with optical and electrical properties that can be tuned for optimum device performance. Recent studies indicated that the efficiencies (1) > 18%) of CuInSe2/CdS/ZnO thin film devices are in good agreement with that of standard silicon cells. In this study, CuInSe 2 absorber films with excellent material properties were produced by relatively simple and reproducible two-stage growth techniques. In these approaches, metallic precursors (Cu/InSe, InSe/Cu, Cu/InSe/Cu and InSe/Cu/InSe) were deposited by thermal evaporation from specially designed graphite heaters at temperatures around 200°C. In the second stage of the process, the alloys were exposed to elemental Se vapour or H2Se/Ar gas. A systematic study was conducted in order to determine optimum growth parameters for the different deposition processes. Optimum material properties (homogeneous and dense films with a high degree of compositional uniformity) were obtained when InSe/Cu/InSe precursors were selenized in elemental Se vapour or H2Se/Ar gas. Comparative studies also indicated that the reaction kinetics is enhanced when H2Se/Ar is used as chalcogen source. Fully selenized films were obtained at temperatures as low as 450°C in a H2Se/Ar atmosphere, compared to temperatures of 600°C in the case of Se vapour. The optical and electrical properties of the absorber layers were accurately controlled by small variations in the bulk composition of the films. A standard CdS/ZnO window layer technology was also developed in our laboratories and preliminary solar cell devices were fabricated and evaluated.
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Comparison of the structural properties of a-Si:H and CulnSe₂ on glass and flexible substrates

- Langa, Dolly Frans

  • Authors: Langa, Dolly Frans
  • Date: 2012-03-14
  • Subjects: Thin films , Photovoltaic cells , Polycrystalline semiconductors , Amorphous semiconductors , Semiconductor films , Metallic films
  • Type: Thesis
  • Identifier: uj:2168 , http://hdl.handle.net/10210/4540
  • Description: M.Sc. , Thin film solar cells based on polycrystalline indium diselenide (CulnSe₂) and amorphous silicon (a-Si:H) are promising candidates for the efficient conversion of sunlight into useable, cheap electrical energy. However, typical device structures are rather complex and consists of semiconductor/metal contacts as well as complicated p - n and p - i - n heterojunctions. In this study, CulnSe₂ absorber layers with excellent material properties were prepared by the selenization of metallic alloys. The a-Si:H thin films were deposited by radio frequency (RF) glow discharge in vacuum. The polycrystalline and amorphous absorber layers were deposited on glass and flexible substrates. In each case, a systematic study was conducted in which all the relevant processing parameters were varied over a broad range. These studies indicated that the structural features of the substrate significantly influence the structural features of the semiconductor thin films. The flexible substrate (kapton) was characterized by the presence of ridges, which distorted the growth behavior of the films. Deposition of ln/Cu/ln metallic alloys onto Mo coated glass (kapton) resulted in discontinuous metallic alloys, which were characterized by the presence of separated elongated island structures. The structural features of the precursors were maintained in the absorber film after selenization in elemental Se vapor. The morphological features of the CulnSe₂ absorber films were also critically influenced by the reaction temperature And reaction period to Se. The structural features on a-Si:H was significantly influenced by the structural features of the particular substrate used. Atomic force microscopy (AFM) imaging in combination with statistical analysis revealed higher roughness values when the amorphous semiconductor materials were deposited onto kapton, which negatively impacts on the device properties of solar cell devices.
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Optimization of quaternary and pentenary chalcopyrite for applications in thin film solar cells

- Chenene, Manuel Luis

  • Authors: Chenene, Manuel Luis
  • Date: 2011-11-08
  • Subjects: Thin films , Solar cells , Photovoltaic cells , Chalcopyrite
  • Type: Thesis
  • Identifier: uj:7264 , http://hdl.handle.net/10210/3938
  • Description: Ph.D. , One of the solutions to the high cost of solar modules is the development of thin film solar cell technologies, which enable material saving, few processing steps, good stability in outdoor testing, high conversion efficiency and flexibility for large area coatings. Polycrystalline CuInSe2 (CIS) thin films and related quaternary and pentenary compounds such as Cu(In,Ga)Se2 (CIGS) and Cu(In,Ga)(Se,S)2 (CIGSS) are the most promising thin film candidates to fulfil the requirements of economically viable solar modules. Presently CIS, CIGS and CIGSS thin film solar cells are prepared mostly by two – stage deposition processes, where Cu-In-Ga alloys are deposited, followed by selenization and/or sulfurization using H2Se/Ar and/or H2S/Ar gases, Se and/or S vapours. Key problems related to this approach are (1) the widely reported compositional change and loss of material during the annealing and selenization stages, and (2) the formation of a graded film structure with most of the Ga residing at the back of the film, due to the difference in the reaction rates between the binary selenides. The present study aims to develop CIGS quaternary and CIGSS pentenary thin film absorbers which are substantially homogeneous and single phase. In order to achieve this aim different deposition processes were developed. This included thermal evaporation of pulverized compound materials from a single crucible with and without subsequent reaction of the precursors in Se vapour or H2Se/Ar atmosphere. Alternatively, controlled partial selenization/sulfurization of the Cu-In-Ga magnetron sputtered precursor films under controlled conditions of reaction time, temperature and gas phase concentration were applied to produce CIGSS films. The latter approach allowed homogeneous incorporation of Ga and S species into CIS compound material, and with that a corresponding increase of band gap of the material in the active region of the solar cell. CIGS quaternary and CIGSS pentenary based solar cells were completed by depositing a CdS buffer layer of around 50 nm thickness, high resistivity ZnO and low resistivity Al – doped ZnO with thicknesses of about 50 nm and 0.5 μm respectively. I-V measurements on fabricated solar cells, under standard A.M. 1.5 conditions, demonstrated good solar cell device quality with efficiencies of about 10 % and 15% respectively.
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Structural analysis of polycrystalline CuInSe₂ thin films

- Bekker, Willem Johannes

  • Authors: Bekker, Willem Johannes
  • Date: 2010-11-22T09:49:56Z
  • Subjects: Thin films , Solar cells , Photovoltaic cells , Polycrystalline semiconductors , Chalcopyrite
  • Type: Thesis
  • Identifier: uj:7018 , http://hdl.handle.net/10210/3525
  • Description: M.Sc. , CuInSe2 (CIS) is considered to be one of the most promising candidates for high efficiency thin film solar cells. The reaction of metallic alloys to a reactive selenium atmosphere (H2Se/Ar or elemental Se vapour) is a promising growth technique to produce CIS thin films of high crystalline quality. However, up to now, the control of the final film quality has been critically influenced by the loss of material and subsequent formation of detrimental binary phases during the high temperature selenization stages. In this study, it is shown that this phenomenon is strongly related to the selenization temperature and, in particular, the ramping procedure followed to the final selenization temperature. Metallic alloys which were selenized in H2Se/Ar at 400°C or slowly heated in 20 minutes to temperatures around 400°C were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) to have nonuniform surface morphologies, highly defected 0.8-2 !lm sized grains and to contain Cuselenide binary phases. Energy dispersive X-ray spectroscopy (EDS) analysis confirmed the generally reported sharp increase in the Cu/In atomic ratio for these classes of samples. In contrast, rapid heating (in 2 minutes) of identical metallic alloys to temperatures above 400°C, resulted in uniform, dense films with low defect density 1 !lm sized grains void of any evidence of secondary phases. X-ray fluorescence (XRF) Kal,2 measurements of metallic alloys at different stages of selenization revealed no evidence of material losses. XRF depth profiles, however, explained this discrepancy by revealing a pronounced segregation of In towards the Mo back contact when the samples were selenized at 400°C, or slowly heated to temperatures around 400°C. This segregation was dramatically reduced in films rapidly heated and selenized at temperatures above 400°C. For the purpose of comparison, metallic alloys were also reacted to elemental Se vapour. The structural features (grain size and preferred orientation) ofthese films differed significantly from those selenized under similar conditions in H2Se/Ar. The results from this study, including photoluminescence (PL) measurements obtained from these films, were used to affect the fabrication of CIS absorbers with excellent material properties and solar cell devices with moderate conversion efficiencies.
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Formation of CuIn(Se,S)₂ and Cu(In,Ga)(Se,S)₂ thin films by chalcogenization of sputtered metallic alloys

- Sheppard, Charles Johannes

  • Authors: Sheppard, Charles Johannes
  • Date: 2009-04-23T08:17:38Z
  • Subjects: Thin films , Sputtering (Physics) , Alloys , Solar cells , Chalcopyrite , Photovoltaic cells
  • Type: Thesis
  • Identifier: uj:8306 , http://hdl.handle.net/10210/2435
  • Description: Ph.D. , The reaction of direct current (DC) magnetron sputtered metallic CuIn and CuInGa alloys to a reactive H2Se/Ar/H2S gaseous atmosphere is an attractive industrial production process to produce Cu-based chalcopyrite absorber films for applications in high efficiency photovoltaic modules. This deposition process is generally referred to as a two-step deposition technology. However, the obvious technological advantages of this deposition technology are overshadowed by growth-related anomalies, such as the separation or at least partial separation of the ternary phases (i.e. CuInSe2, CuGaSe2 and CuInS2) during the high temperature chalcogenization. This in turn prevents the effective band-gap widening of the semiconductor alloys in order to achieve open-circuit voltages in excess of 600mV, which is a critical prerequisite for the optimal performance of thin film solar modules. Against this background, a detailed study was undertaken in order to understand the formation kinetics of quaternary CuIn(Se,S)2 and pentenary Cu(In,Ga)(Se,S)2 alloys deposited with a reproducible two-step growth technology. The main objective of this study was to optimize a complex set of experimental parameters in order to deposit homogenous alloys in which the band-gap value of the resulting semiconductor film could be modified in order to maximize the operating parameters of photovoltaic devices. This was achieved by the homogenous incorporation of S and/or Ga into the chalcopyrite lattice, resulting in shrinkage of the lattice parameters and hence increase in band-gap value Eg. However, the substitution of In with Ga and Se with S proved to be a complex process. It was, for example, observed that separation or at least partial separation of the ternary phases already occurs during the chemical reaction between the hydrogen selenides (H2Se) gas and the metallic precursors. Detailed studies indicated that this phenomenon was strongly related to the selenization parameters (e.g. reactive gas concentration, and reaction temperature and time) as well as the Cu/(In + Ga) atomic ratio. In optimized processes, the metallic precursor films were partially selenized in order to produce at least one partially reacted Cu-III-VI2 ternary alloy and group Cu-VI and III-VI binary phases. The partially selenized alloys were subsequently sulphurized under optimal thermal conditions in a H2S:Ar gas mixture to produce homogeneous single-phase quaternary and pentenary chalcopyrite alloys. X-ray diffraction (XRD) studies revealed that the lattice parameters of the chalcopyrite lattice decreased linearly with the incorporation of S and/or Ga, according to the predictions of Vegard’s law. Gracing incidence x-ray diffraction (GIXRD) studies on the compound semiconductors revealed that the lattice parameters remained virtually constant through the entire depth of the layer. Optical studies revealed a shift in the band-gap value of the absorber films as function of the S concentration. The band-gap of the absorber films could be varied between 0.99 and 1.35eV by controlling the S/Se anion ratio during the diffusion process, while maintaining the Ga/III atomic ratio constant at 0.25. Solar cells were completed by chemical bath deposition (CBD) of CdS and radio frequency (RF) sputtered intrinsic and highly conductive ZnO films onto the absorber films. The cells were evaluated under standard A.M. 1.5 conditions. Devices manufactured from CuIn(Se,S)2 and Cu(In,Ga)(Se,S)2 based alloys demonstrated average open-circuit voltages (Voc) and short-circuit current densities (Jsc) values of 470 and 650 mV and 20 and 33 mA.cm-2, respectively. A plot of the open-circuit voltage as function of the band-gap revealed an experimental relationship of: Voc = (Eg/q – 0.6) mV for Eg < 1.3 eV. The fill factor (FF) values varied between 35 and 56% and device efficiencies () between 4 and 13%, depending on the S/Se anion ratio and Ga incorporation. The findings from the studies clearly indicated that a better understanding of the CuIn(Se,S)2 and Cu(In,Ga)(Se,S)2 formation process led to absorber material with improved material properties. It was also demonstrated that it is possible to produce a homogenous CuIn(Se,S)2 and Cu(In,Ga)(Se,S)2 absorber films with the scalable two-step deposition process.
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Structural and optical characterization of Si:H and ZnO

- Sheppard, Charles Johannes

  • Authors: Sheppard, Charles Johannes
  • Date: 2008-10-28T06:19:00Z
  • Subjects: Thin films , Solar cells , Amorphous substances , Silicon , Semiconductors
  • Type: Thesis
  • Identifier: uj:13542 , http://hdl.handle.net/10210/1365
  • Description: M.Sc. , Thin film solar cell devices based on amorphous silicon absorber films are promising candidates for the efficient conversion of sunlight into useable, cheap electrical energy. However, typical device structures are rather complex and consist of semiconductor/metal contacts as well as a complicated p-i-n junction. Against this background, the present study focussed on the optimization of certain key components of the device, including the transparent conductive oxide, amorphous silicon absorber layers and substrate/metal structures. These thin films were deposited by direct current (DC) magnetron sputtering and radio frequency (RF) capacitativecoupled gas discharge. In each case, a systematic study was conducted in which all the relevant processing parameters were varied over a broad range. The material quality of the respective films was subsequently correlated against the growth parameters. In the case of DC magnetron sputtered ZnO, w hich is generally used as a transparent conductive oxide in the device structure, the material quality were critically influenced by geometric orientation of the sample with respect to the target, the substrate-target distance, deposition power, working pressure and substrate temperature. Optimum structural, optical and electrical properties were obtained in the case of samples deposited at an angle of 80° with respect to the surface of the target. Bombardment damage was to a large extent prevented when the samples were placed at a vertical substrate-to-target distance of 70 mm, 75 mm away from the center zone of the plasma. The optimum substrate temperature, deposition power and working pressure was experimentally found to be 100°C; 600 mW/cm2 and 5.25 ´ 10-3 Torr, respectively. The structural features of the substrates influenced the morphology and optical properties of the DC sputtered metallic films. In general, the surface roughness increased when the glass substrates were replaced by kapton. The glass/silver structures were characterized by relatively smooth surface morphologies, while glass/aluminium films exhibited spike-like growth features. The material properties of intrinsic amorphous silicon were influenced by the RF power, substrate temperature and deposition pressure. A systematic study revealed optimum structural, optical and electrical properties at depositions powers around 43 mW/cm2, substrate temperatures close to 200°C and deposition pressures in the order of 500 mT. , Professor V. Alberts
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The effect of temperature, time and gas flow rate on the growth and characterization of Cu(In,Ga)Se₂ (CIGS) absorbers for thin film solar cells

- Ejigu, Efrem Kebede

  • Authors: Ejigu, Efrem Kebede
  • Date: 2008-10-28T06:18:30Z
  • Subjects: Thin films , Solar cells , Photovoltaic cells , Polycrystalline semiconductors
  • Type: Thesis
  • Identifier: uj:13538 , http://hdl.handle.net/10210/1361
  • Description: M.Sc. , Current solar cell research programmes in general aim to develop a high conversion efficiency photovoltaic (PV) module from high quality thin films. In this study, Cu (In,Ga)Se2 (CIGS) thin films were grown and characterized. These films were grown by selenization of Cu-In-Ga precursors. These precursors were prepared by co-sputtering In and (Cu, Ga). All the precursors were grown on Mo coated soda lime glass substrates. The selenization was conducted under different conditions in Ar/H2Se atmosphere, i.e. taking different values of flow rate of H2Se (5.00, 1.00, 0.25 mol%) in Ar, temperature (350, 450, 550 ºC) and time (10, 20, 30, 40, 50, 60 min). At each selenization condition, two samples were placed at different positions in the chamber. The structural properties of the produced films were analyzed by the techniques of X-ray Diffraction (XRD) for phases, Scanning Electron Microscopy (SEM) for morphology and Energy Dispersive Spectroscopy (EDS) for the bulk composition. The effect of temperature variation, the effect of flow rate variation and the effect of time variation were analyzed by comparing the structural properties as analyzed by the techniques mentioned. All in all this specific study delivers important information about the sensitivity of Cu(In,Ga)Se2 (CIGS) thin films to the temperature, gas flow rate and exposure time of the selenization step. , Doctor C.A. Engelbrecht Professor Vivian Alberts
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Deposition of single-phase Cu(In,Ga)Se₂ thin films

- Mhlungu, Buyisiwe M.

  • Authors: Mhlungu, Buyisiwe M.
  • Date: 2008-10-28T06:18:11Z
  • Subjects: Thin films , Solar cells , Photovoltaic cells , Semiconductors , Chalcopyrite , Gallium
  • Type: Thesis
  • Identifier: uj:13534 , http://hdl.handle.net/10210/1359
  • Description: M.Sc. , Thin film solar cell devices based on chalcopyrite absorber layers have reached a high performance level over the last few years, especially on laboratory scale. Despite this progress, there is still an urgent need to develop an industrial easily scalable deposition technology for depositing chalcopyrite thin films on a large scale. In this study, homogeneous single-phase quaternary Cu(In1-xGax)Se2 thin films were prepared with a reproducible two-step growth technique. The growth process is based on the controlled selenization of sputtered metallic CuIn0.75Ga0.25 alloys in a H2Se/Ar gas mixture at atmospheric pressure. Attention was mainly focused on the optimization of the reaction parameters such as the temperature profiles, gas concentrations and reaction periods. In an optimal reaction process, the reaction velocities of the binary selenide phases were carefully controlled to prevent the formation of stable group I-III-VI2 ternary alloys during the initial selenization step. The composite alloys were subsequently annealed in an inert atmosphere, followed by a second selenization step to promote the homogeneous alloying of gallium with partially formed CuInSe2. Glancing incident angle x-ray diffraction (GIXRD) at incident angles between 0.2º and 10º revealed virtually no shift in d-spacing with sample depth, which confirmed the monophasic nature of the quaternary alloys. Optical measurements revealed an increase in the band gap value of the chalcopyrite alloy due to the homogeneous incorporation of gallium into the CuInSe2 structure. Solar cell devices were fabricated by depositing cadmium sulphide (CdS) buffer layers and zinc oxide (ZnO) window layers onto the CuIn0.75Ga0.25Se2 absorber films. These devices were measure under standard A.M. 1.5 conditions and favorable conversion efficiencies were demonstrated. , Prof. V. Alberts
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Optimization of the Ga and S diffusion processes in Cu(In,Ga)Se₂ thin films

- Dejene, Francis Birhanu

  • Authors: Dejene, Francis Birhanu
  • Date: 2008-10-27T10:00:20Z
  • Subjects: Thin films , Photovoltaic cells , Solar cells , Gallium , Selenium
  • Type: Thesis
  • Identifier: uj:13513 , http://hdl.handle.net/10210/1355
  • Description: Ph.D. , Thin film photovoltaic modules based on Cu(In,Ga)Se2 (CIGS) thin films possess attributes that enable them to compete effectively with silicon-based modules. These attributes are stability, high efficiency, and low material cost. A very promising industrial related process to produce the chalcopyrite absorber layers involves the selenization of metallic precursors. However, recent literature suggests that it is extremely difficult to incorporate an appreciable amount of gallium into the active region of the CIGS thin film. Regardless of its location in the precursor stack, gallium has been observed to segregate to the back of the film during the high temperature selenization step. Consequently, the resulting films are phase-segregated with CuGaSe2 near the Mo electrode and CuInSe2 at the film surface. In this study, the incorporation of gallium and sulfur into CuInSe2 thin films was systematically investigated to establish a scientific and engineering base for the fabrication of homogeneous CuIn(Se,S)2 and Cu(In,Ga)Se2 quaternary alloys with optimum band gap values between 1.1 and 1.2 eV. The selenization of seleniumcontaining (i.e. Cu/InSe, InSe/Cu and InSe/Cu/InSe) precursors in elemental Se vapour at temperatures around 550°C resulted in CuInSe2 thin films with superior structural properties. In an attempt to increase the band gap of these films, the selenium species were replaced by sulfur species during a solid-state diffusion process. Alternatively, gallium was introduced into the structure by replacing the InSe/Cu/InSe precursors with InSe/Cu/GaSe precursors. Important process parameters such as the deposition temperature of precursor elements, the selenization temperature in elemental Se vapour, as well as the concentration of gallium in the alloys were optimized during subsequent studies. From these systematic studies optimum experimental conditions were determined for the deposition of homogeneous Cu(In,Ga)Se2 thin films. The monophasic nature of the quaternary alloys was confirmed by XRD studies, revealing a shift in the lattice spacing due to the homogeneous incorporation of gallium into the chalcopyrite lattice. Completed solar cell devices revealed open-circuit voltages above 500mV, which confirmed the increase in the band gap value of the absorber films. , Professor V. Alberts
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