835 research outputs found
Characterization of n-type Silicon Oxide for Use in Thin Film Solar Cells
No full textThis thesis studied the characteristics and applications of n-type silicon oxide (SiOx) produced through plasma enhanced chemical vapor deposition were studied through. n-type SiOx has shown excellent results in various applications of solar cell technology including back reflectors and intermediate reflecting layers. These results can aid in making amorphous silicon cells thinner. Thinner cells are not only cheaper and less resource intensive but are known to be much less susceptible to degradation, which is a major research goal in amorphous silicon solar cells. This thesis used three experiments to characterize and utilize n-type SiOx. First, the effects of varying deposition parameters of SiOx films were analyzed. SiOx layers were then applied as back reflectors of p-i-n amorphous silicon solar cells. Finally, SiOx was integrated into a two-period, one-dimensional photonic crystal. Forward power, pressure, CO2 flow and PH3 flow during deposition were varied to study their effects on SiOx films. Optical and electrical characteristics, as well as the deposition rate, of the films were measured as each deposition parameter was varied. Raman spectroscopy was also used to analyze the crystalline silicon structures in the material. These measurements showed that an increase in the oxygen content of SiOx enhanced its optical characteristics, while decreasing its electrical characteristics. CO2 flow as well as power and pressure had significant an impact on the oxygen content. Furthermore, it was found that increasing PH3/SiH4 flow ratio above 0.024 decreased the doping concentration of the SiOx film and had adverse effects on both the conductivity and activation energy of the films. Raman spectroscopy results suggested that the SiOx contained 5-7 nm crystalline silicon features. SiOx layers were deposited on amorphous silicon cells using both a p-i-n-SiOx configuration, as well as a p-i-SiOx configuration that contained no n-type amorphous silicon layer. In addition to varying the SiOx deposition parameters, the thickness of the n-type amorphous silicon layer was also varied. These cells were measured in a solar simulator and an external quantum effficiency setup. The p-i-n-SiOx solar cells achieved an initial efficiency of 10.8 % and a JSC of 16.65 ma/cm2. This was a relative efficiency enhancement of 15.3 % and a relative JSC enhancement of 17.5 % over standard p-i-n solar cells. p-i-SiOx cells achieved an initial efficency of 9.85 % and JSC of 16.55 mA/cm2. Degradation tests showed stabilized efficiencies of 8.2 % for p-i-n-SiOx cells and 7.9 % for p-i-SiOx cells. The external quantum efficiency results showed significant improvement of p-i-n-SiOx cells over p-i-n cells in the red spectra, which are attributed to enhanced reflection. There was also significant improvement in the blue spectra, which is attributed to enhanced electron collection at the back of the solar cell. SiOx was also integrated into a photonic crystal using n-type amorphous silicon as the second material. The photonic crystal was designed through careful tuning using the Advanced Semiconductor Analysis (ASA) simulation package. The results were very promising and showed how photonic crystals can be finely tuned for specific solar cell applications such as an intermediate reflecting layer for a micromorph cell.Sustainable Energy TechnologiesElectrical Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc
Doped nanocrystalline silicon oxide for use as (intermediate) reflecting layers in thin-film silicon solar cells
No full textIn summary, this thesis shows the development and nanostructure analysis of doped silicon oxide layers. These layers are applied in thin-film silicon single and double junction solar cells. Concepts of intermediate reflectors (IR), consisting of silicon and/or zinc oxide, are applied in tandem cells. Multi-stack Bragg reflector IRs are tested in tandem cells, increasing the top cell current output. Finally, mechanical polishing is applied on intermediate reflectors, creating asymmetrically textured IRs. Doped silicon oxide layers have proven their versatility as multipurpose layers in thin-film silicon solar cells. In chapter 3, the search for device grade n- and p-doped silicon oxide material is described. The nanostructure of silicon oxide films with a wide array of optical and electrical properties is studied in detail by TEM, Raman, FTIR and XPS. Silicon oxide is found to be a very heterogeneous material with complex nanostructure. Both the amorphous and crystalline phases of silicon oxide are studied in detail. Differences are found between the p- and n-doped materials. It is found that the n-doped material has a nanostructure of silicon crystal grains embedded in an amorphous silicon oxide matrix. The p-doped material, however, contains silicon filaments in an amorphous silicon oxide matrix. These filaments are of intrinsic amorphous silicon with crystalline silicon grains. Intrinsic amorphous silicon is mainly responsible for good conductivity in both n-doped and p-doped silicon oxide, however, minimum crystalline content is also required. Finally, the relations between each phase and element content is related to optical and electrical properties. N-doped silicon oxide used as a back reflector in single junction solar cells reflects unabsorbed light back into the absorber layer, increasing its current output. The blue part of the spectrum is absorbed in one pass, therefore the response in the red part of the spectrum is expected to increase. However, an increase in the blue part of the spectrum is observed as well and is the topic of chapter 4. This increase is attributed to a combination of factors, but mostly to the prevention of a native oxide formation on the standard a-Si:H n-layer. The standard n-layer is covered with the n-doped silicon oxide layer which prevents the standard layer from oxidizing in ambient air. The silicon oxide also provides a better contact interface with silver. Other factors increasing the blue response include: 1. The lower activation energy of n-doped silicon oxide in comparison with the standard a-Si:H n-layer. 2. The changing of the band states due to the larger bandgap of n-doped silicon oxide in reference to n-doped a-Si:H. 3. The thinner a-Si:H n-layer as the one in the reference cell is twice as thick. 4. The lower parasitic plasmonic absorption in the silver back contact due to the common interface with silicon oxide. P-doped silicon oxide exhibits anti-reflective properties, increasing cell current output in the blue part of the spectrum as well. An initial efficiency of 11.4% is achieved with the application of both p- and n-doped silicon oxide layers in a single junction a-Si:H solar cell. Intermediate reflector concepts are explored in chapter 5. Distributed Bragg Reflectors (DBR) have tunable reflective properties and are an interesting candidate for intermediate reflectors in tandem cells. They exhibit nearly the same reflectance range under various angles of incidence. DBRs can be easily designed with the help of optical simulation software such as ASA. The design sequence is as follows: 1. The desired reflectance range inside a solar cell is simulated by varying the thickness of each material. 2. This stack is then simulated in a glass – air environment. 3. The stack is deposited on a glass substrate. 4. The measured reflectance is compared with the air – glass simulation. If a good fit is achieved, the DBR will give the desired simulated reflectance inside the cell. DBRs greatly enhance the top cell current in a tandem cell, reaching up to 13,5 mA/cm2 in a 175 nm-thick a-Si:H layer. Current matching and lowering of Voc remain issues. Texture control in the IR is important in order to provide good light scattering for both the top and bottom cells of a tandem and to provide a good substrate for the growth of a defect-free nanocrystalline absorber layer. An approach to modify the texture of ZnO serving as an asymmetric IR in a tandem cell is developed. Because of the excellent performance of the top amorphous silicon cell deposited on an Asahi VU substrate, it is beneficial to keep this substrate texture for the top cell and integrate different textures (with larger surface features) in the layers processed after the top cell. Two approaches to create an asymmetrically-textured IR are chosen: wet etching and mechanical polishing. The wet etching approach is done with two dilution levels of HCl. Then the IR interface facing the top cell has a typical Asahi VU texture while the IR interface facing the bottom cell has larger surface features beneficial for long-wavelength scattering. The second approach is about applying mechanical polishing to silicon oxide and ZnO IRs. This approach successfully flattened the Asahi-induced texture, leaving it in the IR interface facing the top cell and on the other flat side allowing higher-quality nc-Si:H growth.Electric Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc
The &Spaces Library
No full textCapstone project for LIS 2005 involving the redesign of public library institutions with a focus on physical space. Conference poster, PowerPoint, and paper attached
Bifacial Photovoltaic Technology: Recent Advancements, Simulation and Performance Measurement
No full textIn this chapter, we introduce the physic principle and applications of bifacial PV technology. We present different bifacial PV cell and module technologies as well as investigate the advantages of using bifacial PV technology in the field. We describe the measurement and modeling of Albedo, which is one of the important factors for the energy yield of bifacial PV technology. For an accurate assessment of the performance ratio of bifacial PV strings, it is necessary to measure the albedo irradiance using an albedometer or the front- and rear-side plane of array (POA) irradiance. We also discuss the advanced techniques for the characterization of bifacial PV modules. By means of simulation, we give insight into what boundary conditions result in new bifacial technology gains and the influence of the mounting position of irradiance sensors. We executed several simulations by varying the sensor positions on the rear side of the PV modules, different places, different albedo numbers, mounting heights, different geographical locations with various tilts, seasons, and weather types. To validate the simulation results, we performed various experiments in the field under different conditions. The results prove that the bifacial gain is highly dependent on the mounting heights of PV modules, tilt angles, weather conditions, latitude, and location.Photovoltaic Materials and Device
Modelling of bifacial photovoltaic farms to evaluate the profitability of East/West vertical configuration
No full textEast/West (E/W) vertical bifacial photovoltaic (PV) modules can achieve higher profits than the conventional North/South (N/S) tilted configuration depending on the design choices and external conditions. In this study a model based on 2D view factor concept is developed to estimate the power generated by a large-scale bifacial PV farm, considering the non-uniformity of the incident irradiance and the spectral impact. A validation using measured data is performed, focusing on the non-uniformity of the rear irradiance. This model is used to compare the profitability between E/W vertical and N/S tilted PV farm configurations, considering higher prices during noon with respect to morning/evening periods. The results identify the ratio between these two price values as the key variable that influences the comparison between the PV farm configurations. Specifically, a sufficiently high price ratio ensures the higher profitability of E/W vertical modules, however, the exact value is dependent on the location and the design variables. In general, higher row-to-row distance and lower diffuse fraction enhance the profitability of the E/W vertical over the N/S tilted configuration. On the other hand, elevation of the modules, curtailment strategies and hybrid solutions have a minor influence.Team Jan-Willem van WingerdenPhotovoltaic Materials and Device
Micro-textures for efficient light trapping and improved electrical performance in thin-film nanocrystalline silicon solar cells
No full textElectrical Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc
Time-varying, ray tracing irradiance simulation approach for photovoltaic systems in complex scenarios with decoupled geometry, optical properties and illumination conditions
No full textThe accurate computation of the irradiance incident on the surface of photovoltaic modules is crucial for the simulation of the energy yield of a photovoltaic system. Depending on the geometrical complexity of the surroundings, different approaches are commonly employed to calculate the irradiance on the photovoltaic system. In this article, we introduce a backward ray tracing simulation approach to calculate the irradiance on photovoltaic systems in geometrically complex scenarios. We explain how the repetition of time-consuming simulation steps can be avoided with the proposed approach by storing a selection of the results from the most computationally expensive parts of the problem, and we show that the irradiance calculated with the proposed approach is in good agreement with the results of Radiance, a well-established irradiance simulation tool. Furthermore, we present an experimental validation carried out using a pyranometer and a reference cell over a period of 6 months in a complex scenario, which shows errors lower than 5% in the calculation of the daily irradiation. Finally, we compare high-resolution spectral simulations with measurements taken with a spectroradiometer under different sky conditions. The proposed approach is particularly well-suited for the simulation of bifacial and tandem photovoltaic modules in complex urban environments, for it enables the efficient simulation of high-resolution spectral irradiance in scenarios with time-varying reflectance properties.Photovoltaic Materials and DevicesElectrical Sustainable Energ
Annual Reproductive Cycle and Meat Yield of the Wedge Clam Donax trunculus Linnaeus, 1758 from Black Sea
No full textThe study aims to determine the reproductive cycle, the condition index, meat yield, shell component index, shell thickness index and gonad index of bivalve Donax trunculus inhabiting the Kefken-Babal & imath; location on the Black Sea in relation to environmental parameters between November 2013 and October 2014. Its gonadal development began in November. D. trunculus was in the inactive stage during autumn. Spawning was observed from May (18 degrees C) to August (28 degrees C). Sex ratios were not equal and number of males was higher during the study period (1.13:1) with one hermaphrodite individual only. Being synchronous between sexes based on histological analysis, the reproductive cycle consists of six stages. The study showed that the most ideal period to harvest of D. trunculus was between December and May, especially when the meat yield and condition index were determined to be highest.Trkiye Bilimsel ve Teknolojik Arascedil;timath;rma Kurumu , Trkiye [TOVAG-113O381]; Scientific and Technological Research Council of Turkey (TUBITAK) [TOVAG-113O381]This research was supported through project (grand numbers TOVAG-113O381) funded by the Scientific and Technological Research Council of Turkey (TUBITAK)
Red wine polyphenols prevent metabolic and cardiovascular alterations associated with obesity in Zucker fatty rats (Fa/Fa)
No full textPeer reviewe
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