Theory of enhanced dynamical photo-thermal bi-stability effects in cuprous oxide/organic hybrid heterostructure

We theoretically demonstrate the formation of multiple bi-stability regions in the temperature pattern on the interface between a cuprous oxide quantum well and DCM2:CA:PS organic compound. The Frenkel molecular exciton of the DCM2 is brought into resonance with the $1S$ quadrupole Wannier-Mott exciton in the cuprous oxide by "solvatochromism" with CA. The resulting hybrid is thermalized with surrounding helium bath. This leads to strongly non-linear temperature dependence of the laser field detuning from the quadrupole exciton energy band which is associated with the temperature induced red shift of the Wannier exciton energy. Numerical up and down-scan for the detuning reveals hysteresis-like temperature distribution. The obtained \emph{multiple} bi-stability regions are at least three orders of magnitude bigger ($meV$) than the experimentally observed bi-stability in bulk cuprous oxide ($\mu eV$). The effective absorption curve exhibits highly asymmetrical behavior for the Frenkel-like (above the $1S$ energy) and Wannier-like (below the $1S$ energy) branches of the hybrid.Comment: 6 pages, 7 Figure

Catenary vaults: a solution to low-cost housing in South Africa

This research report discusses the design approach of catenary vaults in the application of low-cost housing. It investigates the most efficient design, materials and construction methods to provide a sustainable and durable solution to low-cost housing. Investigation into various materials was carried out and two specific blocks are used in the construction process: the dry-stack interlocking block and the splitter-brick block. An innovative method of designing catenary curves was developed: The Segmental Equilibrium Method. This design approach focuses on equilibrium equations to define the geometric shape of a catenary under various loading. The method incorporates dead, live and wind loads. The solution obtained is exact and thus proves to be the most superior method in designing catenary curves. The method was compared to the Finite Element Analysis and errors ranged from 0% to 8.9%. Finite Element collaborated with the Segmental Equilibrium Method and verified that the proposed method of analysis can be used in the design of catenary curves. Finite Element Method was used to analyse temperature loading on the catenary curve. A tensile stress of 0.95N/mm² and compressive stress of 1.02N/mm² were obtained. These values are within the materials capacity of the brick (1.1N/mm² Tension and 7-10 N/mm² Compression). The final structure was built using a sliding steel form work. The construction process was closely documented and is discussed in the report. The problems during construction and solutions are presented. A cost analysis was carried out and compared to other leading projects in South Africa. It was found that the structure is economically competitive, with an average cost of R95 000 ($9 500). The report concludes that thin shelled structures, in particular catenary vaults, are a viable option for low-cost housing in South Africa

Plexcitons: Dirac points and topological modes

Plexcitons are polaritonic modes that result from the strong coupling between excitons and plasmons. We consider plexcitons emerging from the interaction of excitons in an organic molecular layer with surface plasmons in a metallic film. We predict the emergence of Dirac cones in the two-dimensional bandstructure of plexcitons due to the inherent alignment of the excitonic transitions in the organic layer. These Dirac cones may open up in energy by simultaneously interfacing the metal with a magneto-optical layer and subjecting the whole system to a perpendicular magnetic field. The resulting energy gap becomes populated with topologically protected one-way modes which travel at the interface of this plexcitonic system. Our theoretical proposal suggests that plexcitons are a convenient and simple platform for the exploration of exotic phases of matter as well as of novel ways to direct energy flow at the nanoscale

Origin of Efficiency Roll-Off in Colloidal Quantum-Dot Light-Emitting Diodes

We study the origin of efficiency roll-off (also called “efficiency droop”) in colloidal quantum-dot light-emitting diodes through the comparison of quantum-dot (QD) electroluminescence and photoluminescence. We find that an electric-field-induced decrease in QD luminescence efficiency—and not charge leakage or QD charging (Auger recombination)—is responsible for the roll-off behavior, and use the quantum confined Stark effect to accurately predict the external quantum efficiency roll-off of QD light-emitting diodes.United States. Department of Energy (DE-SC0001088

Creating a Brand on the Identity of a Sports Club: Preliminary Report Creating a Brand on the Identity of a Sports Club

Creating a sports club brand is an important strategic marketing activity. The quality of the content of a sports club brand can be communicated effectively by promoting its key features. A sports club’s identity is a critical marketing feature that significantly contributes to differentiation on the market. The paper aims to argue the importance and the marketing practice in Croatian sport of implementing a sports club’s identity in its brand image. The research has been conducted during year of 2019 using qualitative and quantitative methods through different sport case studies of three famous basketball and two famous football clubs from Croatia. Although communication of the brand image through its identity is increasingly encouraged in recent scientific literature, it is not yet a common practice in sports in Croatia. Results shows there are no clear links between the brand image and the identity even in Croatian famous professional sport clubs. The sports club’s identity is recognized in terms of its existence, social significance, activities, and development to date. The sports brand identity should com- municate the core values of the sports club identity. A distinct brand of a sports club is imperative for desirable positioning in the wider environment. The identity of a sports club is a valuable marketing and strategic element of its brand. The distinctiveness of a sports club brand significantly depends on the implementation of its identity in its image. In sport marketing practice in Croatia it needs to be change

Organic materials able to detect analytes

The present invention generally relates to polymers with lasing characteristics that allow the polymers to be useful in detecting analytes. In one aspect, the polymer, upon an interaction with an analyte, may exhibit a change in a lasing characteristic that can be determined in some fashion. For example, interaction of an analyte with the polymer may affect the ability of the polymer to reach an excited state that allows stimulated emission of photons to occur, which may be determined, thereby determining the analyte. In another aspect, the polymer, upon interaction with an analyte, may exhibit a change in stimulated emission that is at least 10 times greater with respect to a change in the spontaneous emission of the polymer upon interaction with the analyte. The polymer may be a conjugated polymer in some cases. In one set of embodiments, the polymer includes one or more hydrocarbon side chains, which may be parallel to the polymer backbone in some instances. In another set of embodiments, the polymer may include one or more pendant aromatic rings. In yet another set of embodiments, the polymer may be substantially encapsulated in a hydrocarbon. In still another set of embodiments, the polymer may be substantially resistant to photobleaching. In certain aspects, the polymer may be useful in the detection of explosive agents, such as 2,4,6-trinitrotoluene (TNT) and 2,4-dinitrotoluene (DNT)

State-of-the-Art Perovskite Solar Cells Benefit from Photon Recycling at Maximum Power Point

Photon recycling is required for a solar cell to achieve an open-circuit voltage ($V_{OC}$) and power conversion efficiency (PCE) approaching the Shockley-Queisser theoretical limit. In metal halide perovskite solar cells, the achievable performance gains from photon recycling remain uncertain due to high variability in perovskite material quality and the non-radiative recombination rate ($k_{1}$). In this work, we study state-of-the-art $\textrm{Cs}_{0.05}(\textrm{MA}_{0.17}\textrm{FA}_{0.83})_{0.95}\textrm{Pb}(\textrm{I}_{0.83}\textrm{Br}_{0.17})_{3}$ films and analyze the impact of varying non-radiative recombination rates on photon recycling and device performance. Importantly, we predict the impact of photon recycling at the maximum power point (MPP), demonstrating an absolute PCE increase of up to 2.0% in the radiative limit, primarily due to a 77 mV increase in $V_{MPP}$. Even with finite non-radiative recombination, benefits from photon recycling can be achieved when non-radiative lifetimes and external LED electroluminescence efficiencies measured at open-circuit, $Q_{e}^{LED}(\textrm{V}_{OC})$, exceed 2 $\mu$s and 10%, respectively. This analysis clarifies the opportunity to fully exploit photon recycling to push the real-world performance of perovskite solar cells toward theoretical limits.Comment: Main text: 16 pages and 6 figures, SI: 22 pages and 21 figure

Improved performance and stability in quantum dot solar cells through band alignment engineering

Solution processing is a promising route for the realization of low-cost, large-area, flexible and lightweight photovoltaic devices with short energy payback time and high specific power. However, solar cells based on solution-processed organic, inorganic and hybrid materials reported thus far generally suffer from poor air stability, require an inert-atmosphere processing environment or necessitate high-temperature processing [superscript 1], all of which increase manufacturing complexities and costs. Simultaneously fulfilling the goals of high efficiency, low-temperature fabrication conditions and good atmospheric stability remains a major technical challenge, which may be addressed, as we demonstrate here, with the development of room-temperature solution-processed ​[ZnO over ​PbS] quantum dot solar cells. By engineering the band alignment of the quantum dot layers through the use of different ligand treatments, a certified efficiency of 8.55% has been reached. Furthermore, the performance of unencapsulated devices remains unchanged for over 150 days of storage in air. This material system introduces a new approach towards the goal of high-performance air-stable solar cells compatible with simple solution processes and deposition on flexible substrates.National Science Foundation (U.S.)Hertz FoundationSamsung Advanced Institute of TechnologyNational Institutes of Health (U.S.) (Massachusetts Institute of Technology. Laser Biomedical Research Center. Contract 9-P41-EB015871-26A1)National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (MIT Center for Materials Science and Engineering. Award DMR-08-19762

Practical Roadmap and Limits to Nanostructured Photovoltaics

The significant research interest in the engineering of photovoltaic (PV) structures at the nanoscale is directed toward enabling reductions in PV module fabrication and installation costs as well as improving cell power conversion efficiency (PCE). With the emergence of a multitude of nanostructured photovoltaic (nano-PV) device architectures, the question has arisen of where both the practical and the fundamental limits of performance reside in these new systems. Here, the former is addressed a posteriori. The specific challenges associated with improving the electrical power conversion efficiency of various nano-PV technologies are discussed and several approaches to reduce their thermal losses beyond the single bandgap limit are reviewed. Critical considerations related to the module lifetime and cost that are unique to nano-PV architectures are also addressed. The analysis suggests that a practical single-junction laboratory power conversion efficiency limit of 17% and a two-cell tandem power conversion efficiency limit of 24% are possible for nano-PVs, which, when combined with operating lifetimes of 10 to 15 years, could position them as a transformational technology for solar energy markets.Eni-MIT Alliance Solar Frontiers Program (Eni S.p.A. (Firm))National Science Foundation (U.S.). Graduate Research Fellowship ProgramLink FoundationHertz Foundation (Fellowship