Black silicon solar cells with interdigitated back-contacts achieve 22.1% efficiency.

The nanostructuring of silicon surfaces--known as black silicon--is a promising approach to eliminate front-surface reflection in photovoltaic devices without the need for a conventional antireflection coating. This might lead to both an increase in efficiency and a reduction in the manufacturing costs of solar cells. However, all previous attempts to integrate black silicon into solar cells have resulted in cell efficiencies well below 20% due to the increased charge carrier recombination at the nanostructured surface. Here, we show that a conformal alumina film can solve the issue of surface recombination in black silicon solar cells by providing excellent chemical and electrical passivation. We demonstrate that efficiencies above 22% can be reached, even in thick interdigitated back-contacted cells, where carrier transport is very sensitive to front surface passivation. This means that the surface recombination issue has truly been solved and black silicon solar cells have real potential for industrial production. Furthermore, we show that the use of black silicon can result in a 3% increase in daily energy production when compared with a reference cell with the same efficiency, due to its better angular acceptance.

Surface passivation and optical characterization of Al2O3/a-SiCx stacks on c-Si substrates.

The aim of this work is to study the surface passivation of aluminum oxide/amorphous silicon carbide (Al2O3/a-SiCx) stacks on both p-type and n-type crystalline silicon (c-Si) substrates as well as the optical characterization of these stacks. Al2O3 films of different thicknesses were deposited by thermal atomic layer deposition (ALD) at 200 °C and were complemented with a layer of a-SiCx deposited by plasma-enhanced chemical vapor deposition (PECVD) to form anti-reflection coating (ARC) stacks with a total thickness of 75 nm. A comparative study has been carried out on polished and randomly textured wafers. We have experimentally determined the optimum thickness of the stack for photovoltaic applications by minimizing the reflection losses over a wide wavelength range (300-1200 nm) without compromising the outstanding passivation properties of the Al2O3 films. The upper limit of the surface recombination velocity (S eff,max) was evaluated at a carrier injection level corresponding to 1-sun illumination, which led to values below 10 cm/s. Reflectance values below 2% were measured on textured samples over the wavelength range of 450-1000 nm.

Thermal emission of macroporous silicon chirped photonic crystals.

In this Letter we report on the thermal properties of macroporous silicon photonic crystals with the unit cell gradually varied along the pore axis. We show experimentally that arbitrarily large omnidirectional total-reflectance bands can be produced with such structures. We also demonstrate that those bands can be effectively used to reduce thermal radiation in large spectral bands.

Integrating multi-unit electrophysiology and plastic culture dishes for network neuroscience.

The electrophysiological characterisation of cultured neurons is of paramount importance for drug discovery, safety pharmacology and basic research in the neurosciences. Technologies offering low cost, low technical complexity and potential for scalability towards high-throughput electrophysiology on in vitro neurons would be advantageous, in particular for screening purposes. Here we describe a plastic culture substrate supporting low-complexity multi-unit loose-patch recording and stimulation of developing networks while retaining manufacturability compatible with low-cost and large-scale production. Our hybrid polydimethylsilane (PDMS)-on-polystyrene structures include chambers (6 mm in diameter) and microchannels (25 microm x 3.7 microm x 1 mm) serving as substrate-embedded recording pipettes. Somas are plated and retained in the chambers due to geometrical constraints and their processes grow along the microchannels, effectively establishing a loose-patch configuration without human intervention. We demonstrate that off-the-shelf voltage-clamp, current-clamp and extracellular amplifiers can be used to record and stimulate multi-unit activity with the aid of our dishes. Spikes up to 50 pA in voltage-clamp and 300 microV in current-clamp modes are recorded in sparse and bursting activity patterns characteristic of 1 week-old hippocampal cultures. Moreover, spike sorting employing principal component analysis (PCA) confirms that single microchannels support the recording of multiple neurons. Overall, this work suggests a strategy to endow conventional culture plasticware with added functionality to enable cost-efficient network electrophysiology.

Sub-wavelength patterning of the optical near-field.

We report the sub-wavelength patterning of the optical near-field by total internal reflection illumination of a regular array of resonant gold nano-particles. Under appropriate conditions, the in-plane coupling between Localized Surface Plasmon (LSP) fields gives rise to sub-wavelength light spots between the structures. Measurements performed with an Apertureless Scanning Near-Field Optical Microscope (ASNOM) show a good agreement with theoretical predictions based on the Green dyadic method. This concept might offer a convenient way to elaborate extended optical trap landscapes for manipulation of sub-micrometer systems.