1,721,060 research outputs found
Metal Halide Perovskites for Blue and Near-Infrared Optically Pumped Lasers
No full textPerovskites have been researched as materials with desirable properties for electro-optical applications, such as a laser that utilizes the perovskite as a gain medium for lasing. Through experimental and theoretical studies, researchers have made perovskite lasers available for a large part of the visible spectrum. Moreover, tunable perovskite lasing over a wide spectrum of wavelengths has been achieved by controlling the makeup and stoichiometry of the perovskite gain material. However, lasing has not been achieved in the near-infrared (~900 nm) and the blue (~400 nm) ends of the spectrum. Thus, to address these gaps in perovskite lasing, perovskite thin films have been fabricated in the hopes of achieving tunable lasing in these spectrums. To achieve lasing, the perovskite precursor solution can be spun onto a grating and optically pumped. Furthermore, to validate the adequacy of a perovskite thin film for lasing, it is optically pumped with increased excitation intensity and tested for photoluminescence and amplified spontaneous emission. Findings are presented in this thesis for various methods and experiments used to fabricate thin-film perovskites and evaluate their performance and adequacy for lasing in the blue and near-infrared spectral regions. Ultimately, amplified spontaneous emission was not achieved from any of the perovskite thin films studied. However, observations (e.g., the presence of mid-gap trap states and oxidation) and experimental results were obtained which will aid future research of perovskite lasers. Photoluminescent emission was achieved for MAPbSnI3 and MAPbCl3 (MA: methylammonium) thin films, which emitted in the near-infrared and blue, respectively. Additionally, experiments were carried out to explore and improve the performance of the perovskites used to achieve photoluminescent emission
Cloud Detection and Sun Visibility Forecasting via Full-Sky Imaging and Computer Vision
No full textIn 2012, renewable energy composed about 12.5% of total energy production in the United States, of which over half was generated by wind. More recently, solar power generation through photovoltaics has continued to grow at record levels as cost and scalability challenges have been overcome. The variability of solar power continues to be an obstacle for high-penetration of solar power. In particular, successful grid integration has a higher necessity for accurate intra-hour solar forecasting to cope with clouds, and as forecasting methods improve, microgrids will more safely be able to become more dependent on solar power generation.
This research discusses the development of an intra-hour sun visibility system. Sun visibility is used as an approximate indicator for solar irradiance. The primary hardware aspect of the system is a camera with a 150° fisheye lens; a neutral density filter is utilized to attenuate the brightness of the sun. The system software contains three primary modules: hardware interfacing, feature detection, and visibility forecasting. Computer vision techniques are employed for sun detection, cloud detection, and cloud movement detection. Multiple series of test images representing different partly cloudy days were used to simulate forecasting. Up to 5-minute forecasts were producible, and 1-minute forecasts had the highest average accuracy of 67%. This points to some limitations of direct-camera sky imaging and light attenuation. It is concluded that many techniques implemented extract cloud features effectively; however, the shifts in cloud shape and speed continue to be a challenge to practically model and forecast intra-hour, in the sub-kilometer range
Suppression of Photoinduced Anion Segregation in Mixed-Halide Perovskites
No full textMixed-halide perovskites are highly attractive in the field of materials science and engineering due to the ability to tune their bandgap across the entire visible spectrum. However, the full range of bandgap tunability cannot be achieved during operational conditions (e.g. illumination and voltage bias) of perovskite devices due to the phenomenon of halide segregation, which results in an undesirable change to the intended bandgap of the perovskite and a reduction to the amount of usable phase space. This problem can be remediated through the implementation of a disulfide additive, T2, into the perovskite, as the mild reducing ability of T2 has potential to inhibit the initial iodide oxidation step of halide segregation. Here, photoluminescence spectroscopy is used to demonstrate the ability of T2 to suppress halide segregation, and subsequent experimentation provides new insight into the importance of additive redox potential in the suppression of halide segregation
Metal Halide Perovskites for Blue and Near-Infrared Optically Pumped Lasers
No full textPerovskites have been researched as materials with desirable properties for electro-optical applications, such as a laser that utilizes the perovskite as a gain medium for lasing. Through experimental and theoretical studies, researchers have made perovskite lasers available for a large part of the visible spectrum. Moreover, tunable perovskite lasing over a wide spectrum of wavelengths has been achieved by controlling the makeup and stoichiometry of the perovskite gain material. However, lasing has not been achieved in the near-infrared (~900 nm) and the blue (~400 nm) ends of the spectrum. Thus, to address these gaps in perovskite lasing, perovskite thin films have been fabricated in the hopes of achieving tunable lasing in these spectrums. To achieve lasing, the perovskite precursor solution can be spun onto a grating and optically pumped. Furthermore, to validate the adequacy of a perovskite thin film for lasing, it is optically pumped with increased excitation intensity and tested for photoluminescence and amplified spontaneous emission. Findings are presented in this thesis for various methods and experiments used to fabricate thin-film perovskites and evaluate their performance and adequacy for lasing in the blue and near-infrared spectral regions. Ultimately, amplified spontaneous emission was not achieved from any of the perovskite thin films studied. However, observations (e.g., the presence of mid-gap trap states and oxidation) and experimental results were obtained which will aid future research of perovskite lasers. Photoluminescent emission was achieved for MAPbSnI3 and MAPbCl3 (MA: methylammonium) thin films, which emitted in the near-infrared and blue, respectively. Additionally, experiments were carried out to explore and improve the performance of the perovskites used to achieve photoluminescent emission
Metal Halide Perovskites for Blue and Near-Infrared Optically Pumped Lasers
No full textPerovskites have been researched as materials with desirable properties for electro-optical applications, such as a laser that utilizes the perovskite as a gain medium for lasing. Through experimental and theoretical studies, researchers have made perovskite lasers available for a large part of the visible spectrum. Moreover, tunable perovskite lasing over a wide spectrum of wavelengths has been achieved by controlling the makeup and stoichiometry of the perovskite gain material. However, lasing has not been achieved in the near-infrared (~900 nm) and the blue (~400 nm) ends of the spectrum. Thus, to address these gaps in perovskite lasing, perovskite thin films have been fabricated in the hopes of achieving tunable lasing in these spectrums. To achieve lasing, the perovskite precursor solution can be spun onto a grating and optically pumped. Furthermore, to validate the adequacy of a perovskite thin film for lasing, it is optically pumped with increased excitation intensity and tested for photoluminescence and amplified spontaneous emission. Findings are presented in this thesis for various methods and experiments used to fabricate thin-film perovskites and evaluate their performance and adequacy for lasing in the blue and near-infrared spectral regions. Ultimately, amplified spontaneous emission was not achieved from any of the perovskite thin films studied. However, observations (e.g., the presence of mid-gap trap states and oxidation) and experimental results were obtained which will aid future research of perovskite lasers. Photoluminescent emission was achieved for MAPbSnI3 and MAPbCl3 (MA: methylammonium) thin films, which emitted in the near-infrared and blue, respectively. Additionally, experiments were carried out to explore and improve the performance of the perovskites used to achieve photoluminescent emission
Ink Engineering for Uniform Metal Halide Perovskite Thin Films
No full textHybrid perovskite materials, specifically methylammonium lead iodide
(MAPbI3 or CH3NH3PbI3), are exceptionally attractive for thin film photovoltaic
applications due to their tunable optoelectronic properties, high power-conversion
efficiencies in the lab, solution processability, and versatility of fabrication. Despite
these promising attributes, one notable issue is the tendency for halide perovskites
to crystallize rapidly during deposition, making it difficult to create smooth,
continuous films, which are necessary to prevent shorting of thin film devices. Rapid
crystallization occurs because thin films are spin coated from unstable solutions of
methylammonium iodide (MAI): lead iodide (PbI2) in dimethylformamide (DMF).
Common prevention efforts include solution processing via additives that increase
solubility to slow crystallization. Though there has been some success, the additive
selection process and implementation is extremely empirical (trial and error) and
often unfit for scaling up in a manufacturing process. Thus the goal of this research
was to engineer a simplified solution processing that decouples crystal growth from
spin coating that reliably produces high quality solutions and films. Here is presented
a novel room temperature flash precipitation nanoparticle synthesis that employs a
turbulent mixer. The optimal ligand:precursor ratio for the system’s current
materials is DDAI:MAI:PbI2 = 0.5:1.10:1 where there is a 10% excess of MAI and 0.5
mL of 50 mg/ml DDAI stock solution in DMF. Solutions and films are further
enhanced through a non-solvent composition of 90% chloroform and 10%
dichlorobenzene (10 ml total). These system parameters culminated in the fabrication
of an LED. The LED achieved a maximum external quantum efficiency of 0.4% with
a turn-on voltage of about 3.2 V and a maximum luminance of 24.8 cd/m2 under the
applied voltage of 6 V. It is promising that even without complete optimization, this
ink engineering process was able to create working LEDs. With continued
exploration, this processing methodology has the potential to make a meaningful
contribution to the perovskite and optoelectronics research communities
The Solar Potential: Evaluation Solar Energy Policies in the United States
No full textRenewable resources have become the focal point of national policy frameworks across the globe. In an effort to combat climate change and air pollution, nations have turned their interest to solar renewable energy to replace fossil fuels. Solar energy has become one of the fastest growing and highest used renewable energy sources, and it continues to grow as new technology is applied along with new thorough research.
Of the leading nations, the United States has quickly taken up adapting solar into its energy policy framework. The federal government has implemented many policies to help get the growth of the solar industry off the ground, of which they created the Federal Investment Tax Credit. The FITC was, and still is, an instrumental part of promoting the residential and commercial solar sectors. Along with the FITC, general policies include Net Energy Metering, Solar Leasing, Solar Power Purchase Agreements, Renewable Portfolio Standards, and Renewable Energy Credits.
In order to further understand the importance of solar policies in this thesis, I focus my attention on three states: California, New Jersey, and New York. Each one of these states provide a different view and interpretation of how policies can impact the status of state level solar industries. Throughout the thesis, I aim to make the connections that these policies, both federal and states, are the key factors that separate the U.S solar industry from that of the global solar industry
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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