L.V. Mercaldo

Silicon oxide based n-doped layer for improved performance of thin film silicon solar cells

We propose the use of n-doped silicon oxide as alternative n-layer in thin film Si p-i-n solar cells. By varying input gas ratios, films with a wide range of optical and electrical properties are obtained. Applying these layers in solar cells, good electrical and optical properties are demonstrated. A relative efficiency increase up to 13.6% has been observed on the cells adopting a simple Ag back contact. A similar spectral response as with the cell with standard n-layer plus ZnO/Ag back contact is obtained. The deposition of a buffer layer at the back contact can therefore be avoided.

First and second-order Raman scattering in Si nanostructures within silicon nitride

First and second-order Raman analysis on annealed silicon nitride films is reported. Possible formation of amorphous Si nanoparticles after an intermediate treatment is deduced from the occurrence of a resonant spectrum. After nucleation of Si nanocrystals, with a model description of the first-order spectra it is possible to access information regarding mean radius, size dispersion, and crystalline phase fraction consistent with the fundamental data derived from microscopy. Substantial increase in second to first order intensity ratio is also observed: Enhanced electron–phonon coupling in both amorphous and crystalline Si nanoparticles is suggested.

Self-organized broadband light trapping in thin film amorphous silicon solar cells.

Nanostructured glass substrates endowed with high aspect ratio one-dimensional corrugations are prepared by defocused ion beam erosion through a self-organized gold (Au) stencil mask. The shielding action of the stencil mask is amplified by co-deposition of gold atoms during ion bombardment. The resulting glass nanostructures enable broadband anti-reflection functionality and at the same time ensure a high efficiency for diffuse light scattering (Haze). It is demonstrated that the patterned glass substrates exhibit a better photon harvesting than the flat glass substrate in p-i-n type thin film a-Si:H solar cells.

Light trapping efficiency of periodic and quasiperiodic back-reflectors for thin film solar cells: A comparative study

Recently, great efforts have been carried out to design optimized metallic nano-grating back-reflectors to improve the light absorption in thin film solar cells. In this work, we compare the performances of deterministic aperiodic backreflectors in the form of 1-D nanogratings based on the generalized Fibonacci deterministic aperiodic sequence with a standard periodic one. The case of study here analyzed relies on a realistic solar cell model, where light absorption is evaluated only in the intrinsic region of an amorphous silicon P-I-N junction. We found that the results of comparison are strongly influenced by the amorphous silicon extinction coefficient within the near-infrared wavelength range, where most photonic-plasmonic modes (responsible for the light absorption enhancement typically observed when structured metal nanogratings are employed) are excited. In particular, with device-grade hydrogenated amorphous silicon, we demonstrate that Fibonacci-like backreflectors are able to provide an absorpt...

Photoluminescence properties of partially phase separated silicon nitride films

Photoluminescence properties of partially phase separated amorphous silicon nitride films, lying in between homogeneous materials and composites embedding pure Si nanoparticles, have been investigated. With excitation energy above the Tauc gap, the emission band systematically blue-shifts and broadens with decreasing silicon content, suggesting tail to tail recombination as the prevailing luminescence mechanism. With subgap excitation, the response is instead peaked at 1.7 eV independently of the stoichiometry, likely as an effect of the spatial fluctuations of the gap. In this case, excitation and emission selectively occur in the Si rich domains within the material, and direct band to band recombination is proposed as the possible dominant process. Another effect of the nonuniform material composition is likely the unusual S-shaped evolution of the integrated photoluminescence intensity versus temperature observed for the sample richest in Si. This behavior has been described with a phenomenological mod...

Plasmonic Light Trapping in Thin-Film Solar Cells: Impact of Modeling on Performance Prediction

We present a comparative study on numerical models used to predict the absorption enhancement in thin-film solar cells due to the presence of structured back-reflectors exciting, at specific wavelengths, hybrid plasmonic-photonic resonances. To evaluate the effectiveness of the analyzed models, they have been applied in a case study: starting from a U-shaped textured glass thin-film, µc-Si:H solar cells have been successfully fabricated. The fabricated cells, with different intrinsic layer thicknesses, have been morphologically, optically and electrically characterized. The experimental results have been successively compared with the numerical predictions. We have found that, in contrast to basic models based on the underlying schematics of the cell, numerical models taking into account the real morphology of the fabricated device, are able to effectively predict the cells performances in terms of both optical absorption and short-circuit current values.

Nanosphere lithography for advanced all fiber Sers probes

In this work, we report a straightforward and cost-effective fabrication route for the development of nano-patterned optical fiber tips. The technique is based on self-assembling polystyrene microspheres at the air/water interface and on their successive transferring on the fiber tip of single mode optical fiber. By applying to the fiber further treatments like particle size reduction, metal coating and sphere removal, different periodic structures have been conveniently realized. The morphological analysis reveals indeed the successful creation on the optical fiber tip of regular metallic-dielectric spheres’ arrays as well as metallic patterns with dimensional features down to a submicron scale. Finally, as proof of concept, we demonstrated the capability of the realized patterns to work as efficient Surface Enhanced Raman Spectroscopy (SERS) fiber probes.

MoOx as hole-selective collector in p-type Si heterojunction solar cells

We investigated the possible application of molybdenum oxide (MoOx) on the backside of p-type SHJ solar cells as substitute for the silicon-based back surface field layer. Solar cells with 4 cm2 area were fabricated on FZ c-Si(p) wafers, passivated with ultrathin i-a-Si:H buffers. A nanocrystalline n-SiOx emitter was applied while on the backside we applied 20 nm-thick p-type a-Si:H or evaporated MoOx (10 nm). Symmetric samples were additionally prepared to compare the effects on wafer passivation of MoOx versus the more conventional p-a-Si:H layer. For flat devices we have observed a Voc increase of ∼40 mV with MoOx replacing p-a-Si:H, with fill factors ∼73% in both the cases. Globally an efficiency increase of 1% absolute has been achieved moving to the MoOx hole collector. The feasibility of the MoOx/Ag backside configuration has been demonstrated also for textured p-type SHJ solar cells, reaching so far an efficiency of 18.1%.

Reproducible SERS substrates on optical fiber tips by nanosphere lithography

This paper reports on the assessment of a simple and economical self-assembly methodology to obtain reproducible substrates onto the optical fiber tip for surface-enhanced Raman spectroscopy (SERS) applications. The method relies on the use of the nanosphere lithography of the optical fiber end facet. A careful analysis has been carried out to investigate the capability of the proposed procedure to realize repeatable pattern on the optical fiber tip. Finally, we demonstrate the effective application of the patterned OFTs as SERS nanoprobes.

Relevance Of TCO workfunction in n-silicon oxide emitter - c-Si (p) heterojunction solar cell

The amorphous /crystalline silicon heterojunction solar cells have largely demonstrated their usefulness to reach high efficiency. We have adopted a different and wider bandgap emitter based on silicon oxide, n-SiOx. A central role in this type of structure is played from the TCO workfunction whose value affects strongly the heterojunctions band structure at the emitter interface. RF magnetron sputtered TCO obtained with different deposition parameters, have been made in order to optimize their use in our heterojunction solar cell. Numerical simulation on the SiOx HJ, with TCO having proper workfunction value, show potential efficiency conversion well over the 23%. New Roman Bold font. An example is shown next.