Examining architectures of photoanode-photovoltaic tandem cells for solar water splitting

Given the limitations of the materials available for photoelectrochemical water splitting, a multiphoton (tandem) approach is required to convert solar energy into hydrogen efficiently and durably. Here we investigate a promising system consisting of a hematite photoanode in combination with dye-sensitized solar cells with newly developed organic dyes, such as the squaraine dye, which permit new configurations of this tandem system. Three configurations were investigated: two side-by-side dye cells behind a semitransparent hematite photoanode, two semitransparent dye sensitized solar cells (DSCs) in front of the hematite, and a trilevel hematite/DSC/DSC architecture. Based on the current-voltage curves of state-of-the-art devices made in our laboratories, we found the trilevel tandem architecture (hematite/SQ1 dye/N749 dye) produces the highest operating current density and thus the highest expected solar-to-hydrogen efficiency (1.36% compared with 1.16% with the standard back DSC case and 0.76% for the front DSC case). Further investigation into the wavelength-dependent quantum efficiency of each component revealed that in each case photons lost as a result of scattering and reflection reduce the performance from the expected 3.3% based on the nanostructured hematite photoanodes. We further suggest avenues for the improvement of each configuration from both the DSC and the photoanode part

LARVA - safer monitoring of real-time Java programs (tool paper)

The use of runtime verification, as a lightweight approach to guarantee properties of systems, has been increasingly employed on real-life software. In this paper, we present the tool LARVA, for the runtime verification of properties of Java programs, including real-time properties. Properties can be expressed in a number of notations, including timed-automata enriched with stopwatches, Lustre, and a subset of the duration calculus. The tool has been successfully used on a number of case-studies, including an industrial system handling financial transactions. LARVA also performs analysis of real-time properties, to calculate, if possible, an upper-bound on the memory and temporal overheads induced by monitoring. Moreover, through property analysis, LARVA assesses the impact of slowing down the system through monitoring, on the satisfaction of the properties.peer-reviewe

Stable Ta2O5 Overlayers on Hematite for Enhanced Photoelectrochemical Water Splitting Efficiencies

Hematite (α‐Fe2O3) is one of the most promising photoanodes for water oxidation, however the efficiencies of current hematite materials remain low. Surface trap states are often reported as one of the factors which limit the activity of hematite photoelectrodes, often leading to undesirable surface pinning and trap‐mediated recombination. The deposition of ultra‐thin Al2O3 overlayers is known to enhance hematite activity through passivation of surface states, however Al2O3 is rapidly degraded at normal hematite operating pH values (pH≈13). This study reports atomic layer deposition (ALD) of Ta2O5 thin films as stable, passivating overlayers on a range of hematite photoelectrodes and demonstrates that enhanced activity correlates with observed changes in trap‐state dynamics