1,343 research outputs found
Performance of Major League Baseball Players during Their “Free Agency” Season
Do pro athletes try harder and perform better during their free agency year? Each year this question is asked in many professional sports. The purpose and objective of this project is to discover whether Major League Baseball players actually have better statistics during their free agency year. The result will add creditability to one side of the issue at hand. Data collected consists of offensive statistics in the year prior to their free agency year, their free agency year itself and the year after their free agency season. A simple paired T-test was applied for six major offensive categories: HR/AB, RBI/AB, AVG, OBP, SLG, and OPS. Two analyses were taken. The first analysis was between the year before their free agency season and their contract year and the second was between their free agency season and the year after. All data was compiled into spreadsheets and T-tests were conducted. Analysis confirmed that athletes showed an increase in their numbers from the year before the free agency year to their free agency year in all six categories, but only a significant increase in one category, RBI/AB. Data also showed that from their free agent year to the following year there was a significant drop off in statistics in all six categories. As a result, on average, athletes do tend to perform better during their free agency season. However, since there were only two significant increases in statistics, motivation to get a bigger contract cannot be the only reason for the increase in statistics. There were other reasons that affected an athlete’s performance from year to year independent of whether it was their free agent year or not. These reasons are explored in more detail within the paper
Suppressing Deep Traps in PbS Colloidal Quantum Dots via Facile Iodide Substitutional Doping for Solar Cells with Efficiency >10%
Surface passivation of PbS colloidal quantum dots (QDs) with iodide has been used in highly efficient solar cells. Iodide passivation is typically achieved by ligand exchange processes on QD films. Complementary to this approach, herein we present a non-intrusive solution-based strategy for doping QDs with iodide to further optimize solar cell performance. The doping step is applied in-situ at the end of the synthesis of the QDs. The optimum precursor I/Pb ratio is found to be in the 1.5-3% range at which iodide substitutes S without excessively altering the dots´ surface chemistry. This allows for band engineering and decreasing the density of deep trap states of the QDs which taken together lead to PbS QD solar cells with efficiency in excess of 10%.Peer ReviewedPostprint (author's final draft
Solution-Processed, Solid-State Solar Cells based on Environmentally Friendly AgBiS2 Nanocrystals
Solution-processed inorganic solar cells are a promising low-cost alternative to firstgeneration
solar cells.1,2 Solution processing at low temperatures and the use of nontoxic
and abundant elements can help minimize cost and facilitate regulatory acceptance.
However, until now there has been no material that exhibits all of these features while
demonstrating promising efficiencies. Many of the most promising solution-processed
inorganic solar cells contain toxic elements such as lead or cadmium (perovskites,2,3 PbS,4
CdTe,5,6 CdS(Se)7,8) or scarce elements like tellurium or indium (CdTe, CIGS(Se)/CIS9,10).
Others require high-temperature processes such as selenization or sintering or rely on
vacuum deposition techniques ((Sb2S(Se)3,11–13 SnS,14,15 CZTS(Se)16). Here, we present
AgBiS2 nanocrystals as a novel nontoxic,17 earth-abundant18 material for highperformance,
solution-processed solar cells fabricated in ambient conditions at low
temperatures (≤100°C). The AgBiS2 nanocrystals have favorable properties for solar-cell
applications including a near-ideal bandgap and strong, broad absorption. We
demonstrate a Newport certified power conversion efficiency of 6.3% with no hysteresis
and a remarkably high short-circuit current density of about 22 mA·cm-2 for an active
layer thickness of only ~35 nm.Peer ReviewedPostprint (author's final draft
Photo-FETs: phototransistors enabled by 2D and 0D nanomaterials
The large diversity of applications in our daily lives that rely on photodetection technology requires photodetectors with distinct properties. The choice of an adequate photodetecting system depends on its application, where aspects such as spectral selectivity, speed, and sensitivity play a critical role. High-sensitivity photodetection covering a large spectral range from the UV to IR is dominated by photodiodes. To overcome existing limitations in sensitivity and cost of state-of-the-art systems, new device architectures and material systems are needed with low-cost fabrication and high performance. Low-dimensional nanomaterials (0D, 1D, 2D) are promising candidates with many unique electrical and optical properties and additional functionalities such as flexibility and transparency. In this Perspective, the physical mechanism of photo-FETs (field-effect transistors) is described and recent advances in the field of low-dimensional photo-FETs and hybrids thereof are discussed. Several requirements for the channel material are addressed in view of the photon absorption and carrier transport process, and a fundamental trade-off between them is pointed out for single-material-based devices. We further clarify how hybrid devices, consisting of an ultrathin channel sensitized with strongly absorbing semiconductors, can circumvent these limitations and lead to a new generation of highly sensitive photodetectors. Recent advances in the development of sensitized low-dimensional photo-FETs are discussed, and several promising future directions for their application in high-sensitivity photodetection are proposed.Peer ReviewedPostprint (author's final draft
Strategies for controlled electronic doping of colloidal quantum dots
Over the last several years tremendous progressed progress has been made in incorporating
Colloidal Quantum Dots (CQDs) as photoactive components in optoelectronic devices. A
significant part of that progress is associated with significant advancements made in
achievingon controlled electronic doping of the CQDs and thus improving the electronic
properties of CQDs solids. Today, a variety of strategies exists towards that purpose and this
minireview aims at surveying major published works in this subject. Additional attention is
given to the many challenges associated with the task of doping CQDs as well as to the
optoelectronic functionalities and applications being realized when successfully achieving light
and heavy electronic doping of CQDs.Peer ReviewedPostprint (author's final draft
Ag2ZnSnS4 Nanocrystals Expand the Availability of RoHS Compliant Colloidal Quantum Dots
The demonstration of the quantum confinement effect in colloidal quantum dots (QDs) has been extensively studied and exploited mainly in Pb and Cd chalcogenide systems. There has been an urgent need recently for the development of non(less)-toxic colloidal QDs to warrant compliance with current safety regulations (Restriction of Hazardous Substances (RoHS) Directive 2002/95/EC). Herein, we report Pb/Cd-free, solution processed luminescent Ag2ZnSnS4 (AZTS) colloidal QDs. We present a selective and controlled amine and thiol-free synthesis of air stable luminescent AZTS QDs by the hot injection technique. By controlling the reaction conditions we obtain controlled size variation and demonstrate the quantum confinement effect that is in good agreement with the theoretically calculated values. The band gap of the AZTS QDs is size-tunable in the near-infrared from 740 to 850 nm. Finally, we passivate the surface with Zn-oleate, which yields higher quantum yield (QY), longer lifetime, and better colloidal stability.Peer ReviewedPostprint (published version
MoS2-HgTe Quantum Dot Hybrid Photodetectors beyond 2 ÎĽm
Mercury telluride (HgTe) colloidal quantum dots (CQDs) have been developed as promising materials for the short and mid-wave infrared photodetection applications because of their low cost, solution processing and size tunable absorption in the short wave- and mid- infrared spectrum. However, the lowmobility and poor photo-gain have limited the responsivity of HgTe CQDs-based photodetectors to only tens of mA/W. Here, we integrated HgTe CQDs on a TiO2 encapsulated MoS2 transistor channel to form hybrid phototransistors with high responsivity of ~106 A/W, the highest reported to date for HgTe QDs. By operating the phototransistor in the depletion regime enabled by the gate modulated current of MoS2, the noise current is significantly suppressed leading to an experimentally measured specific detectivity D* of ~1012 Jones at a wavelength of 2 ÎĽm. This work demonstrates for the first time the potential of the hybrid 2D/QD detector technology in reaching out to wavelengths beyond 2 ÎĽm with compelling sensitivity.Peer ReviewedPostprint (author's final draft
The Role of Surface Passivation for Efficient and Photostable PbS Quantum Dot Solar Cells
Peer ReviewedPostprint (author's final draft
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