Plasmonic Nanostructure Design for Efficient Light Coupling into Solar Cells

We demonstrate that subwavelength scatterers can couple sunlight into guided modes in thin film Si and GaAs plasmonic solar cells whose back interface is coated with a corrugated metal film. Using numerical simulations, we find that incoupling of sunlight is remarkably insensitive to incident angle, and that the spectral features of the coupling efficiency originate from several different resonant phenomena. The incoupling cross section can be spectrally tuned and enhanced through modification of the scatterer shape, semiconductor film thickness, and materials choice. We demonstrate that, for example, a single 100 nm wide groove under a 200 nm Si thin film can enhance absorption by a factor of 2.5 over a 10 μm area for the portion of the solar spectrum near the Si band gap. These findings show promise for the design of ultrathin solar cells that exhibit enhanced absorption

Universal optical transmission features in periodic and quasiperiodic hole arrays

We investigate the influence of array order in the optical transmission properties of subwavelength hole arrays, by comparing the experimental spectral transmittance of periodic and quasiperiodic hole arrays as a function of frequency. We find that periodicity and long-range order are not necessary requirements for obtaining enhanced and suppressed optical transmission, provided short-range order is maintained. Transmission maxima and minima are shown to result, respectively, from constructive and destructive interference at each hole, between the light incident upon and exiting from a given hole, and surface plasmon polaritons (SPPs) arriving from individual neighboring holes. These SPPs are launched along both illuminated and exit surfaces, by diffraction of the incident and emerging light at the neighboring individual subwavelength holes. By characterizing the optical transmission of a pair of subwavelength holes as a function of hole-hole distance, we demonstrate that a subwavelength hole can launch SPPs with an efficiency up to 35%, and with an experimentally determined launch phase φ = π/2, for both input-side and exit-side SPPs. This characteristic phase has a crucial influence on the shape of the transmission spectra, determining transmission minima in periodic arrays at those frequencies where grating coupling arguments would instead predict maxima

Electrooptic Modulation in Thin Film Barium Titanate Plasmonic Interferometers

We demonstrate control of the surface plasmon polariton wavevector in an active metal−dielectric plasmonic interferometer by utilizing electrooptic barium titanate as the dielectric layer. Arrays of subwavelength interferometers were fabricated from pairs of parallel slits milled in silver on barium titanate thin films. Plasmon-mediated transmission of incident light through the subwavelength slits is modulated by an external voltage applied across the barium titanate thin film. Transmitted light modulation is ascribed to two effects, electrically induced domain switching and electrooptic modulation of the barium titanate index

Enhanced Radiative Emission Rate and Quantum Efficiency in Coupled Silicon Nanocrystal-Nanostructured Gold Emitters

We report local-field-enhanced light emission from silicon nanocrystals close to a film of nanoporous gold. We resolve photoluminescence as the gold−Si nanocrystal separation distance is varied between 0 and 20 nm and observe a fourfold luminescence intensity enhancement concomitant with increases in the coupled silicon nanocrystal/nanoporous gold absorbance cross section and radiative decay rate. A detailed analysis of the luminescence data indicated a local-field-enhanced quantum efficiency of 58% for the Si nanocrystals coupled to the nanoporous gold layer

How Much can Guided Modes Enhance Absorption in Thin Solar Cells?

Absorption enhancement in thin metal-backed solar cells caused by dipole scatterers embedded in the absorbing layer is studied using a semi-analytical approach. The method accounts for changes in the radiation rate produced by layers above and below the dipole, and treats incoherently the subsequent scattering of light in guided modes from other dipoles. We find large absorption enhancements for strongly coupled dipoles, exceeding the ergodic limit in some configurations involving lossless dipoles. An antireflection-coated 100-nm layer of a-Si:H on Ag absorbs up to 87% of incident above-gap light. Thin layers of both strong and weak absorbers show similar strongly enhanced absorption

An Experimental and Theoretical Investigation of 1-Butanol Pyrolysis

Bioalcohols are a promising family of biofuels. Among them, 1-butanol has a strong potential as a substitute for petrol. In this manuscript, we report on a theoretical and experimental characterization of 1-butanol thermal decomposition, a very important process in the 1-butanol combustion at high temperatures. Advantage has been taken of a flash pyrolysis experimental set-up with mass spectrometric detection, in which the brief residence time of the pyrolyzing mixture inside a short, resistively heated SiC tube allows the identification of the primary products of the decomposing species, limiting secondary processes. Dedicated electronic structure calculations of the relevant potential energy surface have also been performed and RRKM estimates of the rate coefficients and product branching ratios up to 2,000 K are provided. Both electronic structure and RRKM calculations are in line with previous determinations. According to the present study, the H2O elimination channel leading to 1-butene is more important than previously believed. In addition to that, we provide experimental evidence that butanal formation by H2 elimination is not a primary decomposition route. Finally, we have experimental evidence of a small yield of the CH3 elimination channel

The influence of physical activity performed at 20-40 years of age on cardiovascular outcomes in medical patients aged 65-75

Summary Introduction Several studies show that physical activity can reduce the risk of cardiovascular disease, but the vast majority of these focus on the short- to intermediate-term benefits or refer to very specific populations. This observational study was conducted to determine whether physical activity performed during the third or fourth decade of life influences the occurrence of cardiovascular events in patients aged 65-75 years. Materials and methods We studied a cohort of 2191 unselected patients admitted to Internal Medicine Departments. Data were collected on the patients' medical history and their physical activity level when they were 20 to 40 years old. For the latter purpose, we used a specific questionnaire to assess the levels of physical activity related to the patients' job, daily life, leisure time, and sports. Results Almost half (44.2%) of the patients we evaluated reported moderate-intense physical activity when they were 20-40 years old. Around one third (35.8%) of the patients had experienced at least one major cardiovascular event, and there was a slight trend towards fewer cardiovascular events in patients with histories of physical activity (mean risk reduction: 4%, multivariate analysis). More evident benefits were observed in the subgroup of patients with diabetes, where cardiovascular outcomes were much better in patients who had been physically active than in those with sedentary life-styles (mean risk reduction: 24%). Conclusions Given its design, our study may have underestimated the cardiovascular benefits of physical activity. Nonetheless, our results suggest that moderate-intense exercise during young adulthood may have limited beneficial effects on cardiovascular disease in old age, except in specific high-risk populations (diabetic patients). More evident benefits are probably associated with regular physical activity throughout life

Highly stable and efficient all-inorganic lead-free perovskite solar cells with native-oxide passivation

There has been an urgent need to eliminate toxic lead from the prevailing halide perovskite solar cells (PSCs), but the current lead-free PSCs are still plagued with the critical issues of low efficiency and poor stability. This is primarily due to their inadequate photovoltaic properties and chemical stability. Herein we demonstrate the use of the lead-free, allinorganic cesium tin-germanium triiodide (CsSn0.5Ge0.5I3) solid-solution perovskite as the light absorber in PSCs, delivering promising efficiency of up to 7.11%. More importantly, these PSCs show very high stability, with less than 10% decay in efficiency after 500 h of continuous operation in N2 atmosphere under one-sun illumination. The key to this striking performance of these PSCs is the formation of a full-coverage, stable native-oxide layer, which fully encapsulates and passivates the perovskite surfaces. The native-oxide passivation approach reported here represents an alternate avenue for boosting the efficiency and stability of lead-free PSCs