2,868 research outputs found
Statutory regulation of the secular curriculum in England and consequences for legal liability
Full text linkThe extent and scope of state regulation of the secular curriculum and of the quality of educational provision in schools in England has grown virtually beyond recognition in the past 15 years. Within that period, England has moved from being one of the least legally regulated systems to one of the most highly regulated in Europe, a transformation which has been by no means without political, educational and legal controversy. ... This article will first address the question as to why the government decided to develop a highly detailed and prescriptive regulatory framework for the curriculum in England, placing this reform in the context of other related educational reforms during the same period. The second part of the article will examine some key elements of the regulatory framework itself and will discuss in particular the manner in which it is formulated and promulgated by the central government. ... The final part of the article will consider the potential for legal challenge by aggrieved parties - parents or children - in respect of the substantive content, quality or delivery of the curriculum in schools. It will consider the limited litigation that has arisen so far in England relating to the substance of educational provision, and whether the establishment of a detailed regulatory framework for the curriculum increases the likelihood of litigation in this context. (DIPF/Orig.
High Thickness Tolerance in AllâPolymerâBased Organic Photovoltaics Enables Efficient and Stable InâDoor Operation
Get PDFOrganic photovoltaics (OPVs) have great potential to drive lowâpower consumption electronic devices under indoor light due to their highly tunable optoelectronic properties. Thick devices (>300 nm photoâactive junctions) are desirable to maximize photocurrent and to manufacture largeâscale modules via solutionâprocessing. However, thick devices usually suffer from severe charge recombination, deteriorating device performances. Herein, the study demonstrates excellent thickness tolerance of allâpolymerâbased PVs for efficient and stable indoor applications. Under indoor light, device performance is less dependent on photoactive layer thickness, exhibiting the best maximum power output in thick devices (34.7 ”W cmâ2 in 320â475 nm devices). Thick devices also exhibit much better photostability compared with thin devices. Such high thickness tolerance of allâpolymerâbased PV devices under indoor operation is attributed to strongly suppressed spaceâcharge effects, leading to reduced bimolecular recombination losses in thick devices. The unbalanced charge carrier mobilities are identified as the main cause for significant spaceâcharge effects, which is confirmed by driftâdiffusion simulations. This work suggests that allâpolymerâbased PVs, even with unbalanced mobilities, are highly desirable for thick, efficient, and stable devices for indoor applications
Slower carriers limit charge generation in organic semiconductor light-harvesting systems
Get PDFBlends of electron donating and accepting organic semiconductors are widely used as photoactive materials in next generation solar cells and photodetectors. The yield of free charges in these systems is often determined by the separation of interfacial electron-hole pairs, which is expected to depend on the ability of the faster carrier to escape the Coulomb potential. Here we show, by measuring geminate and non-geminate losses and key transport parameters in a series of bulk-heterojunction solar cells, that the charge-generation yield increases with increasing slower carrier mobility. This is in direct contrast with the well-established Braun model where the dissociation rate is proportional to the mobility sum, and recent models that underscore the importance of fullerene aggregation for coherent electron propagation. The behavior is attributed to the restriction of opposite charges to different phases, and to an entropic contribution that favors the joint separation of both charge carriers
Parameterization of Metallic Grids on Transparent Conductive Electrodes for the Scaling of Organic Solar Cells
Get PDFRequirements for Making Thick Junctions of Organic Solar Cells based on Nonfullerene Acceptors
Get PDFHanding over the Reinsâthe Changing Relationship between People and Policy in the South Australian Rangelands
Get PDFSensitivity of Sub-Bandgap External Quantum Efficiency Measurements of Solar Cells under Electrical and Light Bias
Get PDFThe measurement of the external quantum efficiency (EQE) for photocurrent generation at photon energies below the bandgap of semiconductors has always been an important tool for understanding phenomena such as charge photogeneration via tail and trap states. The shape of the subgap EQE can also reveal the subtle but important physics of inter- and intramolecular states that lay at the heart of charge photogeneration in molecular systems such as organic semiconductors. In this work, we examine the influence of optical and electrical noise on the sensitivity of EQE measurements under different electrical and optical bias conditions and demonstrate how to enhance the dynamic range to an unprecedented >100 dB. We identify and study several apparatus-and-device-related factors limiting the sensitivity including: the electrical noise floor of the measurement system; flicker and pick-up noise; probe light source stray light; the photon noise of the light bias source; the electrical noise of the voltage bias source; and the shunt-resistance-limited thermal and electrical shot noise of the device. By understanding and minimizing the influence of these factors we are able to detect EQE signals derived from weak subgap absorption features in both organic and inorganic solar cell systems at photon energies well below their bandgaps
Quantitative photoluminescence of broad band absorbing melanins: A procedure to correct for inner filter and re-absorption effects
Full text linkWe report methods for correcting the photoluminescence emission and
excitation spectra of highly absorbing samples for re-absorption and inner
filter effects. We derive the general form of the correction, and investigate
various methods for determining the parameters. Additionally, the correction
methods are tested with highly absorbing fluorescein and melanin (broadband
absorption) solutions; the expected linear relationships between absorption and
emission are recovered upon application of the correction, indicating that the
methods are valid. These procedures allow accurate quantitative analysis of the
emission of low quantum yield samples (such as melanin) at concentrations where
absorption is significant.Comment: 20 pages, 13 figure
Decision-tree early warning score (DTEWS) validates the design of the National Early Warning Score (NEWS)
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