Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Mayor, James Rhett; Committee Member: Garimella, Srinivas; Committee Member: Jeter, Sheldon. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (M. Phil.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 97-102).

With the increasing demand for energy throughout the world, the environment around us is getting severely affected. The conventional energy sources (coal, oil and gas) are unfortunately the biggest polluters of the environment. The aforementioned energy sources emit greenhouse gases like carbon dioxide and methane, which are responsible for global warming and ozone layer depletion. The only feasible answer to this problem is to reduce the use of the conventional energy sources and focus more on other energy sources. The renewable energy sources (solar, wind and hydro) have been present in nature, but the technology to harvest these energies have always been relatively expensive until recently. The biggest advantage of using renewable energy sources is the fact that these energy sources will never run out and they also do not pollute the environment as their more conventional counterparts. With more research being conducted into better ways of storing the power trapped from the renewable energy sources and the relative difficulty of obtaining the ever-depleting conventional energy sources, the future for renewable energy sources definitely looks better than at any time in the past

This research analyses the California Solar Initiative (CSI) Program data to identify and describe peer effects and price elasticity to adoption affecting the patterns of residential PV adoption. Descriptive statistics and adoption trends are analyzed to explore the impacts of peer effects and third-party owned system on the diffusion of residential solar PV in California. As the residential solar PV technology is still in an early stage of market formation, understanding the patterns of adoption in relatively more mature market can have broad implications for wider diffusion of the technology at the national level. In the first part of the thesis, I build an econometric model to estimate the influence of system cost and peer effects on the rate of diffusion at the zip code-level. The results reveal significant and positive installed base effects in the rate of future adoption. These results provide support to the hypothesis that peer effects help accelerate the adoption of new technologies. The cost-to-customer reduction is negative and significant at the state level. The impact of installed base in inducing new adoption is larger in zip codes with higher overall adoptions. The second part of the thesis presents trends in installation and choice of system capacity of major adoption clusters in California and analyzes the spread of third-party owned systems. Evidence from major adoption clusters in California has shown that growth in leasing adoption exhibits exponential characteristics while growth of customer owned system shows strongly linear feature. This suggests that third-party owned systems play a role in expanding the solar PV market to a significantly large population, especially given that this business would significantly reduces information cost associated with PV adoption. These results offer direct policy and marketing insights that would be useful in speeding up the diffusion of residential PV. / text

Highly glazed facades of commercial buildings are desirable from the point of view of architects, building owners, and building occupants because they create visual connections with the outdoors, offer the possibility for a naturally-lit workplace, and satisfy certain aesthetic desires. The physical properties of glass, however—even when part of the best current window systems—means that this form of environmental separation is highly vulnerable to thermal flux from and to the outdoor environment. The transmission of solar radiation to the perimeter spaces represents an important source of thermal influx, and is typically controlled with shading devices. At best, shading devices create a secondary thermal barrier between indoor and outdoor environments, which can lower energy consumption, decrease peak load, allow for smaller HVAC systems, and provide better occupant comfort. The physical influence of indoor blinds, though, is not always so straightforward. They tend to create two primary effects that operate in opposing directions in regards to energy consumption: (1) they reflect a portion of shortwave solar radiation entering the building back to the outdoors, and (2) they significantly increase the window surface area available for convective heat transfer, which can increase the convective fraction of solar gain, and potentially increase the magnitude of the instantaneous cooling load. For these reasons, the overall impact of interior blinds on equipment load and energy consumption is difficult to foresee. This study describes the results of experiments that tested various configurations of blinds in an outdoor test chamber that simulates conditions in a highly-glazed commercial office building. A simulation model that gives good agreement with experimental results was simultaneously developed. This model will allow retroactive parametric testing of blind parameters for the same given weather and internal load conditions. / text

Organic solar cells (OSCs) have shown great promise in becoming the next generation of renewable energy due to its low cost, simple manufacturing process and flexibility. A method of efficiency improvement in OSCs is by incorporating metallic nanoparticles (NPs). While various reports have reported that incorporation of NPs improve OSC efficiencies due to the Localized Surface Plasmon Resonance (LSPR) effect, the investigations have lacked depth and a detailed investigation is necessary to fully understand the device mechanisms of these OSCs. In this thesis, we first investigate OSCs incorporating Au NPs into the hole collection Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) layer. Our theoretical and experimental results show that the very strong near field around Au NPs due to LSPR mainly distributes laterally along the PEDOT:PSS rather than vertically into the adjacent active layer, leading to minimal enhancement of light absorption in the active layer. With optical effects proven to be minor contributors to device performance improvements, we investigate the electrical properties of the OSCs and obtain insights into the detailed device mechanisms. Improvements in power conversion efficiency (PCE) of solar cells are found to originate from the enlarged active layer/PEDOT:PSS interfacial area and improved PEDOT:PSS conductivity. At high NP concentrations, reduced exciton quenching at donor/acceptor junctions is found to cause PCE deterioration. Next, the effects of Au NPs incorporated into the active layer of OSCs with a newly synthesized donor polymer are investigated in detail. Our experimental and theoretical results both show that LSPR introduced by the NPs can enhance the light absorption in the active layer of OSCs because the strong LSPR near field mainly distributes laterally along the active layer. Combined with our previous study, our results strongly suggest that NPs have to be incorporated in the active layer in order to harvest light by the LSPR effect. Meanwhile, our results show that the electrical properties of NPs improve at low concentration of NPs. When NP concentration is increased, the electrical properties deteriorates and counter-diminish the optical enhancement from LSPR and reduces the overall performance improvement. Finally, we demonstrate efficiency improvement in OSCs by ~22% through incorporating Au NPs into all polymer layers. Au NPs are found to have distinct mechanisms in improving device performance when incorporated in different polymer layers. Our results indicate that the efficiency improvement is the accumulated effects of incorporating NPs in the individual layers and that coupling is not observed in this device configuration. On the whole, our findings highlight the importance that both optical and electrical properties need to be studied and optimized simultaneously for achieving enhancement in PCE of OSCs. We have carried out a detailed study on incorporating NP in various layers and our results are highly useful for the design of high efficiency OSCs incorporating metallic NPs. / published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

Sunlight is sustainable, clean and readily available energy source, which is one of the potential alternatives to the traditional energy sources. Recently, the organic photovoltaics (OPVs), in particular polymer solar cells (PSCs), have attracted increasing attention owing to their outstanding properties such as low cost, lightweight, flexible, allowing vacuum-free fabrication process and thin-film architecture. These advantageous material and manufacturing features of PSCs provide the opportunities for many novel applications. However, the lower power conversion efficiencies (PCEs) of PSCs compared to inorganic solar cells hinder their competition in the marketplace. This thesis covers the basic principles of the PSC, strategies for enhancing PCEs as well as the recent development of PSCs. The importance of the source materials has been also demonstrated and discussed. Due to a large number of possibilities, limited resources and time, it is not feasible to do all the work experimentally. Therefore, for continuing advance development of PSCs, the device performance should be modeled as a function of material parameters, which requires the knowledge of material properties, in particular the complex index of refraction N= n - ik. Accurate determination of the optical functions of the active layers and light trapping layers commonly used in PSCs by using the spectroscopic ellipsometry (SE) has been demonstrated. In order to acquire reliable solutions, the methodology including multiple sample analysis, combinations of different measurement techniques, selection of models, the rigorous fitting procedures and the independent verification have been proposed. The obtained information can be used in the simulation to optimize device architectures, model device performance as well as characterize novel materials. / published_or_final_version / Physics / Doctoral / Doctor of Philosophy

Organic solar cells (OSCs) have attracted intense attention in recent years due to their advantages of low cost, easy fabrication, and high flexibility compared to its inorganic counterparts. However, due to the conflicts between the short diffusion length of excitons and long absorption length of incident photons, the thickness of OSCs is typically thin, and thus power conversion efficiency (PCE) is generally lower than traditional silicon solar cells. Therefore, an exquisite design of light trapping schemes is essential to the PCE improvement. Generally, physical guideline of light trapping involves two main approaches: geometric optics methods and wave optics methods. The former aims at elongating optical path inside the photoactive layer and thus enhancing photon absorption. For organic thin film solar cells with typical active layer thickness of 100 nm-200 nm, which is in subwavelength scale, we cannot investigate light harvesting mechanism simply by the geometric optics methods and instead wave optics properties should be considered. In this thesis, two different light trapping enhancement designs are proposed. In order to simulate these structures, we built up programs for absorption power calculation based on scattering matrix method (SMM) by rigorously solving Maxwell’s equations. It is worth to point out that, different from the widely-used calculation method by Absorption = 1-Transmission-Reflection, our algorithm can extract the net optical absorption of the active layer rather than the whole OSCs. This improvement is very important because metal absorption, which does not contribute to exciton generation, can be excluded from the result. In Chapter 3, design of organic solar cell incorporating periodically arranged gradient type active layer is presented. This design can enhance light harvesting with patterned organic materials themselves (i.e. self-enhanced active layer design) to avoid degrading electrical performance in contrast to introducing inorganic concentrators into the active layers such as silicon and metallic nanostructures. Our numerical results show that the OSC with a self-enhanced active layer, compared with the conventional planar active layer configuration, has broadband and wide-angle range absorption enhancement due to better geometric impedance matching and prolonged optical path. In Chapter 4, OSC with interstitial lattice patterned metal nanoparticles (NPs) is proposed, which can improve the light blocking of traditional square lattice patterned NPs structure and achieve broadband absorption enhancement. Compared to square lattice design, the plasmonic mode couplings between individual NPs in the interstitial lattice are more versatile and much stronger. Moreover, plasmonic modes can couple to the guided modes, resulting in large enhancement factor at some wavelengths. These works provide a theoretical foundation and engineering reference for high performance OSC designs. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Organic solar cell (OSC) is a highly promising research field with a strong potential to realize low cost solar cells with flexibility and light weight. Although OSC power conversion efficiency (PCE) exceeding 9% has been achieved recently, great efforts are still needed to strive a PCE over 10% making OSC ready for commercialization. Besides the demand of high PCE, other considerations, such as easy solution process, stability and large area processing, are also required for mass production in future. With the understanding of key technical issues that still challenge OSC towards widely spread applications, our worksarefocusingon1) applying the solution processed inorganic materials to ameliorate the intrinsic drawback in OSCs; and 2)proposing novel and simple solution process to improve electrical properties of OSCs by controlling the film quality thus the electrical properties during the film formation process. Detailed work is listed below: 1. Incorporating of metal nanoparticles (NPs) for improving OSC efficiency Metal NPs are selected as the candidate for improving OSC efficiency through their unique optical and electrical properties. Our results show that (1a) When meal NPs are incorporated in the hole transport layer (HTL) poly-(3, 4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), the PCE of OSCs are improved due to enhanced conductivity and rough surface. (1b) When metal NPs are embedded in the active layer, OSC performance can be further enhanced due to improvement in light absorption and electrical properties. When we incorporate Au NPs in all organic layers of OSCs, accumulation improvements in OSC performances can be achieved. (1c) When metal NPs are incorporated in electron transport layer of TiO2, the experimental results show that the enhanced charge extraction under solar illumination can be attributing to the UV-excited electrons transfer from TiO2electron transport layer and storage by Au NPs. 2. Solution processed metal oxide thin film for high efficient hole transporting layer (HTL) The solution-processed transition metal oxides (TMOs) have attracted great attention due to their superior air-stability properties and universal energy level alignment with organic materials. In this thesis, we propose a one-step method to synthesize low-temperature solution-processed TMOs such as molybdenum oxide and vanadium oxide, with good film quality, desirable electrical properties, and improved device stability, for HTLs applications. 3. Self-assemble metal oxide for high efficient electron transporting layer (ETL) We propose a self-assemble and solution-processed method in fabricating ETLs composed of TiO2 NPs that can simultaneously achieve good film uniformity and homogeneity, and electron transport properties. We believe this new method will be capable for large-area applications in future. 4. Vertical morphology control for active layer. Besides carrier transport layers, the morphology of the active layer will significantly affect its electrical and optical properties and thus device performance. We propose up-side-down method to modify the nano-morphology blend along vertical direction, which is beneficial to vertical charge transport and thus producing higher OSC performances. The film-growth dynamics of polymer blends is studied, which has been neglected in most study of OSC morphology by others. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Dye sensitized solar cells (DSSCs) have received extensive attention among solar cells in recent years as the production cost is comparatively low and photovoltaic performance is good. Apart from TiO2, SnO2-based DSSCs are of great interest since SnO2 has a wide band gap and high mobility. Though the conversion efficiency of SnO2-based DSSCs is still not comparable to TiO2-based DSSCs, there is room for improvement to fabricate an efficient device. In this study, different commercial SnO2 nanoparticles have been compared. The number of SnO2 layers and paste formulation have been optimized. The effects of TiCl4 and TTIP treatments have been investigated. In order to further optimize the performance of SnO2-based DSSCs, different strategies have been adopted to increase dye loading, facilitate electron transport and enhance photon absorption. Different dopants (Zn, Mg and Ag) have been introduced to SnO2 pastes. It is found that cells with Zn dopants perform the best with increased dye uptake. SnO2 nanorods have been synthesized and mixed with SnO2 nanoparticles. More nanorods result in faster electron transport and hence increase the conversion efficiency. In addition, different gold nanostructures (nanostars, nanorods and nanocubic Au) have been synthesized and incorporated into SnO2 photoanodes to study the plasmonic effects. It can be observed that nanocubic Au demonstrates the largest improvement in conversion efficiency. The obtained results will be discussed in detail. / published_or_final_version / Physics / Master / Master of Philosophy