<p>Thin-film solar cells based around the absorber material CuIn_1-xGa_xSe₂ (CIGS) are studied with respect to their stability characteristics, and different ways of modelling device operation are investigated. Two ways of modelling spatial inhomogeneities are detailed, one fully numerical and one hybrid model. In the numerical model, thin-film solar cells with randomized parameter variations are simulated showing how the voltage decreases with increasing material inhomogeneities.</p><p>With the hybrid model, an analytical model for the p-n junction action is used as a boundary condition to a numerical model of the steady state electrical conduction in the front contact layers. This also allows for input of inhomogeneous material parameters, but on a macroscopic scale. The simpler approach, compared to the numerical model, enables simulations of complete cells. Effects of material inhomogeneities, shunt defects and grid geometry are simulated.</p><p>The stability of CIGS solar cells with varying absorber thickness, varying buffer layer material and CIGS from two different deposition systems are subjected to damp heat treatment. During this accelerated ageing test the cells are monitored using characterization methods including J-V, QE, C-V and J(V)_T. The degradation studies show that the typical V_OC decrease experienced by CIGS cells subjected to damp heat is most likely an effect in the bulk of the absorber material.</p><p>When cells encapsulated with EVA are subjected to the same damp heat treatment, the effect on the voltage is considerably reduced. In this situation the EVA is saturated with moisture, representing a worst case scenario for a module in operation. Consequently, real-life modules will not suffer extensively from the V_OC degradation effect, common in unprotected CIGS devices.</p>

Robust ion-exchanged glass waveguides exhibit low optical losses in a broad spectral range and they allow integration of several devices on the same chip due to their planar structure. Consequently, they can be a low cost alternative to semiconductors for fabricating various integrated optical devices. Two high performance photonic devices were designed and realized, demonstrating the potential of glass waveguides. The well-controlled silver-film ion-exchange process allowed the fabrication of: i) a highly sensitive biosensor based on optical absorption and, ii) a low loss hybrid electro-optic (EO) polymer modulator with a narrow coplanar electrode gap. The single-mode, channel integrated optical ion-exchange waveguide on borosilicate glass (Corning 0211) is described for broad spectral band (400-650 nm) detection and analysis of heme-containing protein films at a glass/water interface. The evanescent wave interaction is improved significantly by fabricating ion-exchange waveguides with a step-like index profile. Silver nano-particle formation is reduced in order to achieve low loss in the Soret-band (~400 nm). Unlike other surface-specific techniques (e.g. SPR, interferometry) that probe local refractive-index changes and therefore are susceptible to temperature fluctuations, the integrated optical waveguide absorption technique probes molecular-specific transition bands and is expected to be less vulnerable to environmental perturbations. The hybrid integration of phosphate glass (IOG-1) and EO polymer is realized for the first time. The critical alignment steps which are typically required for hybrid optoelectronic devices are eliminated with a simple alignment-free fabrication technique. The low loss adiabatic transition from glass to EO polymer waveguide is enabled by gray scale patterning of the novel EO polymer, AJLY. Total insertion loss of 5 dB and electrode gap of 8 μm is obtained for an optimized device design. EO polymer poling at 135 ºC and 75 V/μm is enabled by the sol-gel buffer layer.

Transparent conducting oxide (TCOs) thin films, including non-stoichiometric tin doped indium oxide (ITO) and aluminium doped zinc oxide (AZO), have found considerable applications in various displays, solar cells, and electrochromic devices, due to their unique combination of high electrical conductivity and optical transparency. TCO thin films are normally fabricated by sputtering, thermal vapour deposition and sol-gel method. Among them, sol-gel processing, which was employed in this project, is no doubt the simplest and cheapest processing method, The main objectives of this project were to produce indium tin oxides (ITO) and zinc aluminium oxides (AZO) nanoparticles with controlled particle size and morphology and to fabricate TCO thin films with high optical transmittance and electrical conductivity. In this research, hydrothermal method was used to synthesise ITO and AZO nanoparticles. Tin oxides, zinc oxides, ITO and AZO particles with the particle size ranging from 10 nm to several micrometers and different morphologies were synthesised through controlling the starting salts, alkaline solvents and hydrothermal treatment conditions. ITO and AZO thin films were fabricated via sol-gel technique through dip coating method. The effects of the starting salts, alkaline solvents, surfactant additives and coating and calcination conditions on the formation of thin films were investigated. XRD, TEM, FEG-SEM, DSC-TGA, UV-Vis spectrometer and four-point probe resistance meter were used to characterise the crystallinity, particle size, morphology, optical transmittance and sheet resistance of the particles and thin films. Crack-free thin films with high optical transmittance (>80% at 550 nm) and low sheet resistances (2.11 kΩ for ITO and 26.4 kΩ for AZO) were obtained in optimised processing conditions.

The microelectronics industry requires continuous advances due to ever-evolving technology and the corresponding need for higher density substrates with smaller features. Specifically, new dielectric materials with enhanced electrical properties are needed. At the same time, adhesion must be maintained in order to preserve package reliability and mechanical performance. As a result, this research investigates the use of thin glass sheets as an alternative substrate material as it offers a number of advantages including coefficient of thermal expansion similar to silicon, good dielectric properties and optical transparency to assist in the alignment of buried features. As part of this project it was necessary to deposit metallic coatings onto the glass sheets to create electrical tracks, pads and microvias. In order to meet these requirements, the metallisation of both smooth as received glass surfaces and surfaces roughened by laser machining using electroless copper and nickel deposition were investigated. This study resulted in a number of important conclusions about the roles of chemical bonding and mechanical anchoring in both the adhesion and catalyst adsorption, that are key factors in the electroless metallisation process.....

Thin film material properties and measurement characterisation techniques are crucial for the development of micro-electromechanical systems (MEMS) devices. Furthermore, as the technology scales down from microtechnology towards nanotechnology, nanoscale materials such as carbon nanotubes (CNTs) are required in electronic devices to overcome the limitations encountered by conventional materials at the nanoscale. The integration of CNTs into micro-electronics and material applications is expected to provide a wide range of new applications. The work presented in this thesis has contributed to the development of thin film material characterisation through research on the thermal conductivity measurement and the control of the residual stress of thin film materials used commonly in MEMS devices. In addition, the use of CNTs in micro-electronics and as filler reinforcement in composite materials applications have been investigated, leading to low resistivity CNTs interconnects and CNTs-Polyimide (PI) composites based resistive humidity sensors. In the first part of this thesis, the thermal conductivity of conductive thin films as well as the control of the residual stress arising from fabrication process in PI micro-cantilevers have been studied. A MEMS device has been developed for the thermal conductivity characterisation of conductive thin films showing good agreement with thermal conductivity of bulk material. Low energy Ar+ ion bombardment in a plasma has been used to control the residual stress present in PI cantilevers. Appropriate ion energy and exposure time have led to stress relaxation of the beams resulting in a straight PI cantilever beam. In the second part of this thesis, low resistivity CNTs interconnects have been developed using both dielectrophoresis (DEP) and Focused Ion Beam (FIB) techniques. An investigation of the effects of CNT concentration, applied voltage and frequency on the CNTs alignment between Al and Ti electrodes has resulted in the lowering of the CNTs’ resistance. The deposition of Pt contact using FIB at the CNTs-metal electrodes interface has been found to decrease the high contact resistances of the devices by four and two orders of magnitude for Al and Ti electrodes respectively. The last part of this thesis focuses on the preparation of CNTs-PI composite materials, its characterisation and its application as resistive humidity sensor. The integration of CNTs inside the PI matrix has resulted in enhancing significantly the electrical and mechanical properties of the composites. In particular, a DEP technique employed to induce CNTs alignment inside the PI matrix during curing has been attributed to play an important role in improving the composite properties and lowering the percolation threshold. In addition, the fabrication and testing of CNTs-PI resistive humidity sensors have been carried out. The sensing performance of the devices have shown to be dependent highly on the CNT concentration. Finally, the alignment of CNTs by DEP has improved the sensing properties of CNTs-PI humidity sensors and confirmed that the change of resistance in response to humidity is governed by the change of the CNTs’ resistances due to charge transfer from the water molecules to the CNTs.

To accelerate environmentally friendly thin film photovoltaic (PV) technologies, copper-based chalcogenides are attractive as absorber materials. Chalcopyrite copper indium gallium selenide (CIGS ≡ CuIn1–xGaxSe2) is today a commercially important PV material, and it is also in many aspects a very interesting material from a scientific point of view. Copper zinc tin sulfide selenide (CZTSSe ≡ Cu2ZnSn(S1–xSex)4) is considered as an emerging alternative thin film absorber material. Ternary Cu2SnS3 (CTS) is a potential absorber material, thus its related alloys Cu2Sn1–xGexS3 (CTGS) and Cu2Sn1–xSixS3 (CTSS) are attractive due to the tunable band gap energies. CuSb(Se1–xTex)2 and CuBi(S1–xSex)2 can be potential as ultra-thin (≤ 100 nm) film absorber materials in the future. In the thesis, analyses of these Cu-based chalcogenides are based on first-principles calculations performed by means of the projector augmented wave method and the full-potential linearized augmented plane wave formalisms within the density functional theory as implemented in the VASP and WIEN2k program packages, respectively. The electronic and optical properties of CIGS (x = 0, 0.5, and 1) are studied, where the lowest conduction band (CB) and the three uppermost valence bands (VBs) are parameterized and analyzed in detail. The parameterization demonstrates that the corresponding energy dispersions of the topmost VBs are strongly anisotropic and non-parabolic even very close to the Γ-point. Moreover, the density-of-states and constant energy surfaces are calculated utilizing the parameterization, and the Fermi energy level and the carrier concentration are modeled for p-type CIGS. We conclude that the parameterization is more accurate than the commonly used parabolic approximation. The calculated dielectric function of CuIn0.5Ga0.5Se2 is also compared with measured dielectric function of CuIn0.7Ga0.3Se2 collaborating with experimentalists. We found that the overall shapes of the calculated and measured dielectric function spectra are in good agreement. The transitions in the Brillouin zone edge from the topmost and the second topmost VBs to the lowest CB are responsible for the main absorption peaks. However, also the energetically lower VBs contribute significantly to the high absorption coefficient. CTS and its related alloys are explored and investigated. For a perfectly crystalline CTS, reported experimental double absorption onset in dielectric function is for the first time confirmed by our calculations. We also found that the band gap energies of CTGS and CTSS vary almost linearly with composition over the entire range of x. Moreover, those alloys have comparable absorption coefficients with CZTSSe. Cu2XSnS4 (X = Be, Mg, Ca, Mn, Fe, Ni, and Zn) are also studied, revealing rather similar crystalline, electronic, and optical properties. Despite difficulties to avoid high concentration of anti-site pairs disordering in all compounds, the concentration is reduced in Cu2BeSnS4 partly due to larger relaxation effects. CuSb(Se1–xTex)2 and CuBi(S1–xSex)2 are suggested as alternative ultra-thin film absorber materials. Their maximum efficiencies considering the Auger effect are ~25% even when the thicknesses of the materials are between 50 and 300 nm. / <p>QC 20170523</p>

Les concentrateurs Falcon permettent de séparer des particules en fonction de leur densité. Leur capacité à traiter des débits de suspension importants rend leur utilisation courante dans les procédés miniers. Dans les gammes de tailles ultrafines (entre 1 et 100 μm), leur coupure devient à la fois granulométrique et densimétrique. Ce travail a porté sur la compréhension de leur physique et de ses limites. Une analyse de leurs mécanismes de séparation a abouti à une loi d’échelle analytique, validée expérimentalement. Des investigations plus complètes appliquées aux suspensions ultrafines ont été réalisées numériquement. Finalement un critère physique liant la gamme de taille à séparer aux densités des différentes fractions a été explicité et appliqué à la valorisation de sédiments fins. / Enhanced gravity separators are widely used in minerals beneficiation, as their superior gravity field enables them to separate particles within narrow classes of density and size. This study aims to shed light on the Falcon concentrator’s ability to separate particles with size and density ranges lower than usual, 1 to 100 micrometers and 1.2 to 3.0 s.g. respectively. Differential particle settling being identified as the prevailing separation mechanism under such conditions, this study couples a theoretical and numerical approach with targeted experiments to build a predictive Falcon separation model that embeds phenomenological fluid and particle flow analysis. Based on this model, physical limitations were identified and quantified through explicit relations between operating parameters, and particle size and density ranges. Falcon’s efficiency to beneficiate dredged sediments was characterized in this way.

GaN and its alloys with Al and In belong to the group III nitride semiconductors and are today the materials of choice for efficient white light emitting diodes (LEDs) enabling energy saving solid state lighting. Currently, there is a great interest in the development of novel inexpensive techniques to fabricate hybrid LEDs combining high quality III-N quantum well (QW) structures with inexpensive colloidal nanoparticles or conjugated polymers. Such hybrid devices are promising for future micro-light sources in full-color displays, sensors and imaging systems. Organics can be engineered to emit at different wavelengths or even white light based on functional groups or by blend of several polymers. This is especially important for the green region, where there is still a lack of efficient LEDs. Besides optoelectronics, other applications such as biochemical sensors or systems for water splitting can be realized using GaN-based nanostructures. Despite a significant progress in the field, there is still a need in fundamental understanding of many problems and phenomena in III-nitride based nanostructures and hybrids to fully utilize material properties on demand of specific applications. In this thesis, hybrid structures based on AlGaN/GaN QWs and colloidal ZnO nano-crystals have been fabricated for down conversion of the QW emission utilizing non-radiative (Förster) resonant energy transfer. Time-resolved photoluminescence (TRPL) was used to investigate the QW exciton dynamics depending on the cap layer thickness in the bare QW and in the hybrid samples. Although the surface potential influences the exciton dynamics, the maximum pumping efficiency assuming a non-radiative energy transfer mechanism was estimated to be ~40 % at 60 K in the structure with thin cap layer of 3 nm. Since bulk GaN of large area is difficult to synthesize, there is a lack of native substrates. Thus, GaN-based structures are usually grown on SiC or sapphire, which results in high threading dislocation density in the active layer of the device and can be the reason of efficiency droop in GaN based LED structures. Fabricating GaN nanorods (NR) can be a way to produce GaN with lower defect density since threading dislocations can be annihilated toward the NR wall during growth. Here, GaN(0001) NRs grown on Si(111) substrates by magnetron sputtering using a liquid Ga target have been investigated. A high quality of NRs have been confirmed by transmission electron microscopy (TEM) and TRPL. Two strong near band gap emission lines at ~3.42 eV and ~3.47 eV related to basal plane stacking faults (SF) and donor-bound exciton (DBE), respectively, have been observed at low temperatures. TRPL properties of the SF PL line suggest that SFs form a regular structure similar to a multiple QWs, which was confirmed by TEM. The SF related PL measured at 5 K for a single NR has a significantly different polarization response compared to the GaN exciton line and is much stronger polarized (&gt; 40 %) in the direction perpendicular to the NR growth axis. Hybrids fabricated using GaN NRs and the green emitting polyfluorene (F8BT) have been studied using micro-TRPL. In contrast to the DBE emission, the recombination time of the SF-related emission was observed to decrease, which might be due to the Förster resonance energy transfer mechanism. Compared to chemical vapor deposition, sputtering allows synthesis at much lower temperatures. Here, sputtering was employed to grow InAlN/GaN heterostructures with an indium content targeted to ~18 %, which is lattice matched to GaN. This means that near strain-free GaN films can be synthesized. It was found that using a lower temperature (~25 C) while depositing the top InAlN results in an improved interface quality compared to deposition at 700 C. In latter case, regions of quaternary alloy of InAlGaN forming structural micro-defects have been observed at the top InAlN/GaN interface in addition to optically active flower-like defect formations.

We report the possibility to control the tilting of nanoneedles and nanowires by using structured sapphire substrates. The advantage of the reported strategy is to obtain well oriented growth along a single direction tilted with respect to the surface normal, whereas the growth in other directions is suppressed. In our particular case, the nanostructures are tilted with respect to the surface normal by an angle of 58°. Moreover, we demonstrate that variation of the nanostructures shape from nanoneedles to cylindrical nanowires by using SiO2 layer is observed.

Although the passive films that form on stainless steels have been extensively studied, the concentration depth profiles are not fully understood. Their thinness makes passive films hard to study, but angle-resolved X-ray photoelectron spectroscopy (ARXPS) is a non-destructive technique that can be used to obtain depth information. An iterative approach to deconvolute ARXPS measurements into depth profiles is discussed, and the chemistry of passive films on a molybdenum-containing 316L stainless steel is investigated. Bipolar electrochemistry, in which the sample is placed along an electric field created by two driving electrodes in an electrolyte, is investigated as a screening tool. It is shown that the method is useful to create corrosion gradients on 304 stainless steel, both under pitting and non-pitting conditions. Chromium carbide thin films were deposited by magnetron sputtering with a variety of deposition parameters on stainless steel, and subsequently analyzed. It is shown that these films present a promising material system for protective coatings to improve the corrosion resistance of stainless steels while also maintaining other useful properties, such as low interfacial contact resistance. Particular attention is given to the electrochemical evaluation of the films, whose high carbon concentrations necessitates different interpretations of the electrochemical results compared to for stainless steels.