This thesis presents studies on light management in optoelectronic devices. The broad aim of the thesis is to improve the efficiency of optoelectronic devices by optimised light usage. The studies emphasise the design and fabrication of nanostructures for optimised photon control. A key hypothesis guiding the research is that better designs can be achieved by ab initio identification of their desired Fourier properties. The specific devices studied are organic Distributed Feedback (DFB) lasers, organic solar cells and silicon solar cells. The impact of a substructured grating design capable of affording unprecedented control over the balance between feedback and output coupling in DFB organic lasers was investigated both experimentally and theoretically. It was found experimentally that such gratings can halve the threshold of organic DFB lasers. The reduction in the laser threshold is associated with reduced output coupling and higher feedback provided by the substructured gratings. The possibility of improving the efficiency of organic solar cells by trapping light into the absorbing medium was investigated. It was found that the low refractive index of the organic gain medium compromises the light trapping performance. It was found that strong absorption enhancement, however, can be achieved using plasmonic nanostructures. Finally, a novel design concept for light trapping in silicon solar cells is proposed. This design takes advantage of grating structures with long periods that are capable of providing broad-band light trapping, which is an important requirement for silicon solar cells. The design is based on a supercell that enables better light injection through manipulation of the grating's Fourier properties. The design idea leads to the formation of quasi-random nanostructures that afford great versatility for photon control. Strong light trapping was achieved and characterised both theoretically and experimentally.

The polarization dependent diffraction efficiency and imaging properties of high numerical aperture (N.A.) holographic optical elements (HOEs) were investigated to determine the suitability of these elements for magneto-optic data storage head applications. Two-wave first-order coupled wave theory was combined with a local planar grating model to determine the s and p-polarization diffraction efficiency characteristics of these HOEs. Experimental results for 0.55 N.A. focusing HOEs fabricated in silver halide photographic emulsions and dichromated gelatin films demonstrated that the p-to-s-polarization diffraction efficiency ratio at the Bragg angle corresponded with theoretical results to within 5%. Diffraction based wave propagation theory and a geometrical ray trace model were used to evaluate the imaging performance of these elements. Results from the diffraction based wave propagation model showed that the HOEs imaging performance had very minimal polarization dependence. The ray trace model indicated precise alignment and good wavelength stability are needed to achieve diffraction limited performance.

Some basic concepts and principles of optical dielectric slab waveguiding and experimental methodology involving characterisation of waveguide films are introduced, Results from the characterisation of thin polymeric waveguide films and measurements of refractive indices of the films are presented. The birefringence of some polymer films is analysed and discussed. The photostabilities of several dopants (DEMI, Ultra-DEMI, Dicyclohexyl-DEMI, Mor2, Morpip and DCM) are investigated in a polymer matrix (PMMA), and their measured photostabilities are presented. These organic chromophores change their properties in the course of photodegradation. Degradation experiments are carried out by exposing the doped waveguide films to light in air, vacuum and nitrogen environments. The degradation mechanisms of these chromophores are discussed. It is found that the degradation of the DEMI, Ultra-DEMI, Dicyclohexyl-DEMI and DCM are due to photooxidation, their photostabilities are much higher in vacuum than in air. The Mor2 and Morpip degrade by direct photodecomposition, their photostabilities are in the same order when exposed to light in their main absorption bands. The oxygen free environment (e.g. vacuum) is essential to increase their photostabilities. A beam branching effect in DCM doped waveguide film is observed. Stacked multi-layer waveguides are investigated as possible humidity sensors. Symmetric structure (PMMA/P-4VP/PMMA/P-4VP/PMMA) (P4VP-I) and unsymmetric structure (Si02/P-4VP/Zeonex/P-4VP/Air) (P4VP-II) are studied. Special procedures and process have been developed to fabricate multi-layer waveguide structures in experiments. It is found that both structures have good reversibilities and show reasonable stabilities. 30 ppm concentrations of water vapour can be detected by the P4VP-II structure. The experimental results show that the overall response of P4VP-II structure exhibits good linearity with increase of the concentration of water vapour. The structures can not only measure the phase shift of interference, but also can measure the direction of fringe movement. The sensitivity of the structure can be further improved by using different combinations of polymers in the structure.

This thesis focuses on the preparation parameter and characterization of boron and boron nitride thin film. System is built composing of designing the geometry, substrate and target holder, pumping parts and plasma generated parts. Experiments with various conditions have been tried and the optimized condition is found for the film growth rate. Many ways of characterization includes: X-ray diffraction, Scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy have been tried to identify the material composition.

The interaction of a high power laser beam with the lattice of transparent optical materials induces internal strains in the latter. Attention is focused on optical materials of zinc blende structure and excitation at the 10.6-(mu)m wavelength of the laser. A lattice dynamical treatment is presented to obtain the laser induced internal strains in terms of the lattice Green's functions, the transverse effective charge and the Raman coefficient. The transverse effective charge and the Raman coefficient are then thoroughly discussed and discrepancies in previous works concerning these parameters are resolved. / The imperfect lattice Green's functions are utilized to calculate the expected magnitude of the actual strains induced in real crystals taking into account the effect of lattice point defects. The mechanical laser damage thresholds at the 10.6-(mu)m CO(,2) laser wavelength are then obtained specifically for SiC, GaAs, InSb, ZnS, ZnSe, and CdTe materials, in good agreement with the available measured values.

Thesis (Ph. D.)--Washington State University, December 2008. / Title from PDF title page (viewed on Apr. 13, 2009). "School of Mechanical and Materials Engineering." Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (leaves 123-131).

High Concentrated Photovoltaics (H-CPV) promise a more efficient, higher power output than traditional photovoltaic modules. This is achieved by concentrating sunlight onto a small triple junction (CTJ) InGaP/InGaAs/Ge cell (ranging from 3.14 mm2 to 1 cm2) by using precision optical systems. These systems utilise non-imaging optics to concentrate and distribute the incident solar flux uniformly onto the CTJ device receiver to achieve maximum performance and power output from an H-CPV module. However, the performance of the device can be reduced due to the partial or complete absorption of a range of wavelengths present in the solar spectrum by the optical materials that are used for concentration. An investigation to determine the current density topographies of each subcell in a CTJ cell by multiple raster scans of an optical fibre receiver of a spectrometer in the plane of the aperture of the secondary’s optical element was conducted. Results showed that the physical properties of the optical elements’ material absorbed different amounts of the spectral content with respect to the subcell photosensitive wavelength regions. The facet properties of the primary optical Fresnel lens showed that the more rounded the Fresnel facets were, the lower the concentration of sunlight incident onto the CTJ cell. The increase in facet numbers showed an increase in scattering of the incident sunlight and chromatic aberrations. Chromatic aberration created by the refractive optics showed a variation in the amount of concentration on each individual subcell as well as the difference in intensity profiles across for the different subcells. Based on these results and the development of new multi-junction devices by industry, the performance of a four and six-junction device with the optical materials was investigated by simulations. The simulations showed that the careful integration of an additional subcell in a multi-junction device could rectify current mismatch between the subcells in the device. Based on the simulations, the best performing multi-junction cell was identified as the four-junction device that showed a cell and module efficiency under operation of 42.5 % and 35.5 %, respectively. Additionally, based on the performance results observed from the H-CPV module, the development of an HCPV module that would attempt to harness the incident tracked diffuse sunlight available to a concentrator photovoltaic (CPV) module for additional energy yield was undertaken. The part of the study comprised of measurements of the solar source, design of a prototype Hybrid High Concentrator Photovoltaic (HH-CPV) module. Results showed that power generation from the H-CPV system was highly dependent on the DNI levels and fluctuates greatly with variation in the DNI. The irradiance levels within the diffuse regions of the H-CPV module showed that the baseplate and vertical sides had an average irradiance range of 140-450 and 50-225 W.m-2, respectively. Irradiance topographic raster scans revealed that the baseplate and vertical sides had a relatively uniform intensity distribution and was identified as favourable sites for diffuse cell population. Simulations of various PV technologies showed the most suitable technology for the placement within the cavity of the HH-CPV module. The developed HH-CPV module was finalized with the utilization of CIS modules to harness the diffuse irradiance. During a 3 month power monitoring of the HH-CPV system, it was determined that the major power generation for the HH-CPV module come from the CPV component, while the CIS modules showed a minor power contribution. The total energy yield for the monitoring period was 45.99, 3.89 and 1.76 kW.h for the CPV, four-vertical sides and baseplate components, respectively. The increase in energy yield of the HH-CPV module when compared to the standard H-CPV module was determined to be 12.35 % for the monitoring period. The incorporation of the CIS modules into the H-CPV module to create the HH-CPV module did increase the energy yield of the module during high DNI conditions and did offset the almost zero power generation during low DNI conditions.

No description available.

Solar energy is one of the fastest growing forms of energy generation due to its low cost, lack of emissions, minimal maintenance, and excellent durability. However, like any other technology, it is also not free from defects and degradation, which limit its performance in the real world. Most of the degradation is related to metal contacts, which also happens to be one of the most expensive items in manufacturing, comprising almost half of the cost of converting a silicon wafer into a photovoltaic (PV) cell. Therefore, studying contact degradation to make them reliable and free of defects is the key to achieving high energy yields. High efficiency PV modules that are both cheap and reliable with an extended lifetime ultimately reduce the levelized cost of energy. This study aims to characterize contact degradation in solar cells to identify the root causes of performance losses and develop alternate solutions to metallization. Electrical and optical characterizations were performed on both accelerated-aged and field-exposed solar cells and modules to look for specific performance losses. Furthermore, materials characterization was performed on selected samples to understand the potential root causes and factors affecting the degradation. Unencapsulated solar cells mainly consisting of newer cell technologies and metallization were exposed to acetic acid to simulate field conditions and understand the effect on contact corrosion. Finally, a low-cost novel contact technology called the "transferred foil contact" was developed that can be used as the back contact of a highly efficient silicon heterojunction solar cell, to minimize recombination, and potentially combine cell metallization and interconnection. An overview of the solar energy history and current state-of-the-art is first discussed, followed by a chapter on solar cell device physics and contact technology. The following chapters discuss the different degradation mechanisms in terms of the process-structure-properties relationships of the PV materials.