Statutory regulation of the secular curriculum in England and consequences for legal liability

The 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.

Slower carriers limit charge generation in organic semiconductor light-harvesting systems

Blends 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

On the Electro‐Optics of Carbon Stack Perovskite Solar Cells

Mesoporous carbon stack architecture is attracting considerable interest as a candidate for scalable, low‐cost perovskite solar cells amenable to high‐throughput manufacturing. These cells are characterized by microns‐thick mesoporous titania and zirconia layers capped by a nonselective carbon electrode with the whole stack being infused with a perovskite semiconductor. Although the architecture does not deliver the >20% power conversion efficiencies characteristic of perovskite planar and mesoporous geometries, it does produce cells with respectable efficiencies >16%, which is unexpected due to the carbon electrode being a nonideal anode and the active layers being so thick. Optimization of these cells requires an understanding of the coupled efficiencies of light absorption, charge generation, and extraction which is currently unavailable. Herein, a combined experimental‐simulation study that elucidates photogeneration and extraction is reported. By determining the optical constants of the individual components and using effective‐medium approximations, the internal quantum efficiencies (IQE) in both the titania and zirconia layers are determined to be ≈85%. Numerical drift‐diffusion simulations indicate that this high IQE is a consequence of the thick junctions reducing minority carrier concentrations at the electrodes, thereby decreasing surface recombination. This insight can now be used to tune the carbon stack for efficiency and simplicity

Sensitivity of Sub-Bandgap External Quantum Efficiency Measurements of Solar Cells under Electrical and Light Bias

The 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

We 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