Browsing by Author "Lane, D W"
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Item Open Access Close space sublimation of CdTe for solar cells and the effect of underlying layers(2010-03-23T16:35:28Z) Wakeling, B R; Lane, D WThis work has focused on the design, construction and testing of a close space sublimation system for CdTe deposition. In addition, it also focused on variations to the treatment and fabrication procedures of the transparent conducting oxide and CdS layers prior to the CdTe deposition, in order to influence the structure and electrical properties of the CdTe/CdS interface. CdTe was deposited by the physical vapour process, close space sublimation. The equipment used was custom built for this work and is therefore described in detail. Some of the deposition parameters of the equipment were varied in order to allow a comparison between the equipment in this work and those reported in the literature. Bilayers of CdS have been created by depositing two individual CdS layers, on top of one another, whilst also varying the annealing treatment of the first layer. These bilayers were included in devices and which subsequently underwent a series of etches to allow analysis of the materials. The bilayers were shown to effect the preferred orientation of the CdTe layer deposited on top, but the results suggested the bilayers had a negative effect on the amount of current recombination in the depletion region. The roughness of the transparent conducting oxide coated glass substrates used in this work, was proposed as a way of influencing the roughness of the CdS layer deposited on top and therefore the roughness of the layer the CdTe is deposited on. It was proposed that the CdTe material deposited on a roughened substrate may have an increased grain size; no evidence for this was found for samples including CdS layers. A second phase of CdTe was observed and assigned to the presence of a CdSxTe1−x alloy. The sulphur content of the alloy was found to increase as the roughness of the substrate increased. CdS was deposited by the wet chemistry process chemical bath deposition. In situ monitoring of the deposition was carried out by studying the re ection of light from the interface at the end of an optical fibre placed within the solution. The results indicated that the in situ monitoring was sensitive to the initial deposition but the sensitivity reduced as the film thickness approached 150 nm. The in situ monitoring technique and ellipsometry measurements of the CdS showed good agreement with the theory of two deposition mechanisms occurring during the deposition. The results showed that CdS grown by chemical bath deposition has a two layer structure consistent with; a low density CdS grown by homogeneous deposition, on top of dense CdS grown by ion by ion deposition. An ellipsometry model for the CdS and CdTe layers is presented, along with its optical properties over the wavelength range 245 to 1690 nm.Item Open Access The copper-bismuth-sulphur material system and thin film deposition of Cu3BiS3 by sputtering and evaporation for the application of photovoltaic cells(2016-06-02) McCracken, R O; Lane, D WThe semiconducting sulphosalt Wittichenite has been identified as a possible absorber material for thin film photovoltaic devices. It has the chemical formula Cu3BiS3 and its component elements are those of low toxicity and high abundance making it a very attractive prospect for photovoltaic devices. The copper bismuth sulphur material system is not very well understood and information on it limited to a few small regions. To aid understanding of this system a pseudo-binary phase diagram along the CuS-Bi join of the Cu-Bi-S ternary phase diagram was constructed by making bulk samples of various compositions along the join and analysing them using X-ray diffraction and differential scanning calorimetry. This join was chosen because is crosses the point at which Cu3BiS3 would be expected to occur due to its stoichiometry. The CuS-Bi phase diagram shows Cu3BiS3 forms across a wide compositional range but is mixed with either bismuth metal or copper sulphides depending on composition. Films of Cu3BiS3 were made using sputtered copper and bismuth films annealed in a sulphur atmosphere and thermal co- evaporation of copper sulphide and bismuth.Item Open Access High throughput combinatorial screening of Cu-Zn-Sn-S thin film libraries for the application of Cu2ZnSnS4 photovoltaic cells(2014-11-07) Hutchings, K D; Lane, D WThe naturally occurring mineral of Cu2ZnSnS4 (CZTS) is a promising alternative absorber layer for thin film based photovoltaic devices. It has the remarkable advantage that it consists of abundant, inexpensive and non-toxic elements compared to its crystallographically related and highly successful counterparts: the Cu(In,Ga)(S,Se)2 (CIGSSe) and CuIn(S, Se)2 (CISSe) material systems. Therefore, there is real commercial potential for reduced material costs and improved device efficiencies. A two-stage high throughput combinatorial process for the fabrication of Cu-Zn-Sn-S thin film libraries is presented, which consists of either sequentially stacking or co-depositing Cu,Sn and Zn precursor layers by DC magnetron sputtering followed by a sulphurisation process. Sputtering conditions and target-substrate geometry are developed to give compositionally graded Cu-Zn-Sn precursor layers spanning a wide spatial region around the point of stoichiometry. Conversion into Cu-Zn-Sn-S libraries is achieved by thermally evaporating a uniform layer of sulphur directly onto the metal alloy and annealing the sample at 500 °C in a furnace. Effects of the precursor composition on the structural properties of the films prior to the incorporation of sulphur are investigated. The sulphurised libraries are then studied by Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy as a function of composition, to assess the effects on morphology and phase formation. Observations of changes in lattice parameters and crystallinity are clear. The opto-electronic and electrical properties of the CZTS film libraries are measured using photoconductivity and hot point probe techniques, respectively. Changes in the band gap and conductivity type are studied as a function of atomic ratios. Based on high performing compositions, devices have been fabricated with the highest achieving cell at 1.26 %. The observations are discussed in the context of the particular compositions and synthesis conditions, and recommendations are made for further work.Item Open Access The use of low cost virtual reality and digital technology to aid forensic scene interpretation and recording(2011-01-11) Chan, A; Lane, D WCrime scenes are often short lived and the opportunities must not be lost in acquiring sufficient information before the scene is disturbed. With the growth in information technology (IT) in many other scientific fields, there are also substantial opportunities for IT in the area of forensic science. The thesis sought to explore means by which IT can assist and benefit the ways that forensic information can be illustrated and elucidated in a logical manner. The central research hypothesis considers that through the utilisation of low cost IT, the visual presentation of information will be of significant benefit to forensic science in particular for the recoding of crime scenes and its presentation in court. The research hypothesis was addressed by first exploring the current crime scene documentation techniques; their strengths and weaknesses, giving indication to the possible niche that technology could occupy within forensic science. The underlying principles of panoramic technology were examined, highlighting its ability to express spatial information efficiently. Through literature review and case studies, the current status of the technology within the forensic community and courtrooms was also explored to gauge its possible acceptance as a forensic tool. This led to the construction of a low cost semi-automated imaging system capable of capturing the necessary images for the formation of a panorama. This provides the ability to pan around; effectively placing the viewer at the crime scene. Evaluation and analysis involving forensic personnel was performed to assess the capabilities and effectiveness of the imaging system as a forensic tool. The imaging system was found to enhance the repertoire of techniques available for crime scene documentation; possessing sufficient capabilities and benefits to warrant its use within the area of forensics, thereby supporting the central hypothesis.