We investigate the optical and opto-electronic properties of black silicon (b-Si) nanostructures passivated with Al 2O 3. The b-Si nanostructures significantly improve the absorption of silicon due to superior anti-reflection and light trapping properties. By coating the b-Si nanostructures with a conformal layer of Al 2O 3 by atomic layer deposition, the surface recombination velocity can be effectively reduced. We show that control of plasma-induced subsurface damage is equally important to achieve low interface recombination. Surface recombination velocities of S eff 13 cm / s have been measured for an optimized structure which, like the polished reference, exhibits lifetimes in the millisecond range

A three‐dimensional photonic crystal intermediate reflector for enhanced light trapping in tandem solar cells is presented. The intermediate reflector consists of a transparent and conductive ZnO:Al inverted opal sandwiched in between the top amorphous silicon and bottom microcrystalline silicon cell.

Understanding the impact of order and disorder is of fundamental importance to perceive and to appreciate the functionality of modern photonic metasurfaces. Metasurfaces with disordered and amorphous inner arrangements promise to mitigate problems that arise for their counterparts with strictly periodic lattices of elementary unit cells such as, e.g., spatial dispersion, and allows the use of fabrication techniques that are suitable for large scale and cheap fabrication of metasurfaces. In this study, we analytically, numerically and experimentally investigate metasurfaces with different lattice arrangements and uncover the influence of lattice disorder on their electromagnetic properties. The considered metasurfaces are composed of metal-dielectric-metal elements that sustain both electric and magnetic resonances. Emphasis is placed on understanding the effect of the transition of the lattice symmetry from a periodic to an amorphous state and on studying oblique illumination. For this scenario, we develop a powerful analytical model that yields, for the first time, an adequate description of the scattering properties of amorphous metasurfaces, paving the way for their integration into future applications.

We study numerically in detail optical effects occurring during the interaction of light with dielectric gratings and explain how they can be exploited to enhance light absorption in thin‐film solar cells. We analyze in depth two scenarios with practical relevance where dielectric gratings are incorporated. The first is an one‐dimensional, binary grating, which can be manufactured lithographically. The second is a two‐dimensional grating of dielectric spheres that can be fabricated employing self organization processes on pre‐textured substrates. From a universally valid point of view, we finally outline strategies to optimize the geometry of textured surfaces permitting for a maximization of absorption in a solar cell. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Black silicon with aspect ratios up to 10 and an average optical reflectance of only 2.5% over the whole absorbing spectral range was covered perfectly conformal with a transparent conductive oxide. The thin film was deposited by thermal ALD and exhibited a resistivity of 1.1 Ohm cm. This concept promises a new design for an efficient heterojunction silicon solar cell.

We present experimental results and rigorous numerical simulations on the optical properties of Black Silicon surfaces and their implications for solar cell applications. The Black Silicon is fabricated by reactive ion etching of crystalline silicon with SF6 and O2. This produces a surface consisting of sharp randomly distributed needle like features with a characteristic lateral spacing of about a few hundreds of nanometers and a wide range of aspect ratios depending on the process parameters. Due to the very low reflectance over a broad spectral range and a pronounced light trapping effect at the silicon absorption edge such Black Silicon surface textures are beneficial for photon management in photovoltaic applications. We demonstrate that those light trapping properties prevail upon functionalization of the Black Silicon with dielectric coatings, necessary to construct a photovoltaic system. The experimental investigations are accompanied by rigorous numerical simulations based on three dimensional models of the Black Silicon structures. Those simulations allow insights into the light trapping mechanism and the influence of the substrate thickness onto the optical performance of the Black Silicon. Finally we use an analytical solar cell model to relate the optical properties of Black Silicon to the maximum photo current and solar cell efficiency in dependence of the solar cell thickness. The results are compared to standard light trapping schemes and implications especially for thin solar cells are discussed

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