Light Trapping Applications Research Articles

Manipulating optical reflections using engineered nanoscale metasurfaces

We propose a comprehensive scheme for the efficient design of graded optical metasurfaces capable of rerouting the impinging energy at will in a flexible way. We show that carefully designed conjoined optical nanoelements may be used as basic building blocks to arbitrarily shape the reflected phase front, while providing large controllability and low loss over deeply subwavelength thicknesses. The metasurface elements are designed using transmission line concepts combined with nanocircuit theory, and they can be realized with conventional lithographic techniques. Based on these concepts, we put forward a fast and accurate analytical model to design the optical analog of reflectarrays for light bending, steering, and focusing. The proposed designs show large efficiency over a broad angular spectrum, accompanied by broad bandwidths of operation. Our technique may lead to significant advances in the field of planarized nanophotonics and light manipulation over a surface, with potential applications in light trapping and efficient photonic couplers.

Printable Surface Holograms via Laser Ablation

Holographic displays are used for applications in data storage, light trapping, security, sensing, and optical devices. Currently available fabrication techniques for holography remain expertise-dependent, costly, and time-consuming, limiting the widespread personalized use of holograms. The development of efficient and low-cost techniques for the rapid fabrication of holograms is required for practical applications. In this report, we use a single 6 ns laser pulse to record holographic surface gratings by ablation in well-ordered printed ink on a substrate. The entire hologram fabrication process can be completed within a few minutes. The photonic features of the prepared holograms have been modeled computationally and characterized experimentally. We demonstrate the versatility of our fabrication method by preparing 2D and 3D holograms on both optically transmissive and opaque surfaces. We anticipate that our strategy to fabricate holograms through laser ablation may hold great potential in personalized data storage, optical, and security applications.

Focused ion beam strategy for nanostructure milling in doped silicon oxide layer for light trapping applications

Focused ion beam milling is used to nanopattern doped silicon oxide layer in view of light trapping application in thin film photovoltaics. Different working conditions, such as ion beam currents, milling times, dwell times, etc., are optimized in order to improve the nanochannel shape by reducing the effect of redeposition of sputtered target material on the sidewalls. This phenomenon, due to ion beam striking on the target layer, induces a V-shape instead of the desired box-shape for the nanochannels. A suitable milling strategy is here explored to reduce this effect. The results show that the parallel scan routine with “bottom to top” direction gives a more appropriate shape. Also parallel multi-pass milling and 3 × 1017 ions/cm2 ion dose result in reduced redeposition. Sputtering yield is calculated both experimentally and theoretically, and correlated with the redeposition. Due to the focused ion beam peculiarity, nanopatterning can be achieved, without utilizing an etching mask or resist layer, which is advantageous for fabrication of prototype devices.

Nanomoulding of Functional Materials, a Versatile Complementary Pattern Replication Method to Nanoimprinting

We describe a nanomoulding technique which allows low-cost nanoscale patterning of functional materials, materials stacks and full devices. Nanomoulding combined with layer transfer enables the replication of arbitrary surface patterns from a master structure onto the functional material. Nanomoulding can be performed on any nanoimprinting setup and can be applied to a wide range of materials and deposition processes. In particular we demonstrate the fabrication of patterned transparent zinc oxide electrodes for light trapping applications in solar cells.

UV-nanoimprint lithography and large area roll-to-roll texturization with hyperbranched polymer nanocomposites for light-trapping applications

Light-trapping textures were produced in hyperbranched polymer (HBP) silica nanocomposites using a UV-nanoimprint lithography (UVNIL) replication method, either in batch or roll-to-roll processes. The hardness of the HBP was found to increase by a factor of 2.5 with the addition of 50vol% of nanoparticles. A nickel master with random sub-micron pyramidal structures was used to imprint nanocomposites containing up to 20vol% of silica on a polyethylene naphthalate (PEN) substrate. The influence of nanoparticle fraction and pressure on the texture morphology and light scattering properties of the replicas was studied using scanning electron microscopy and optical analysis. The roughness and coherence length of the textures were similar to those of the master for all investigated compositions and process pressures. Likewise, the light scattering performance of aluminum-coated texturized nanocomposites was identical to that of the metal template, with a haze of 90% over the 400–800nm spectral range. Thin film amorphous silicon solar cells were deposited on the texturized substrates using a large-area roll-to-roll process. The photocurrent of these devices was found to be 23% higher than the reference value of a flat cell.

Optical properties of gold and aluminium nanoparticles for silicon solar cell applications

The optical properties of metal nanoparticles are explored as a function of lateral size, shape, aspect-ratio and metal type. Simulations based on the discrete dipole approximation are compared with experimental measurements of arrays of metal nanoparticles fabricated by electron-beam lithography. Careful selection of experimental parameters ensures minimization of far-field and near-field coupling, and inhomogeneous broadening, thus allowing comparison with single particle simulations. The optical properties of Au nanoparticles are compared with similar Al nanoparticles for each particle type. For solar cell light-trapping applications, we require metal nanoparticles that exhibit extinction peaks near the band-edge region of the absorbing material, as well as low absorption and large optical cross-sections. Al nanoparticles are shown to be of interest for amorphous silicon solar cells, but their applications for polycrystalline solar cells is limited by the presence of an interband region in the near-infrared. The opposite is found for Au nanoparticles, which feature an interband threshold region in the visible that makes their optical properties unsuitable for amorphous silicon but very suitable for crystalline and polycrystalline silicon solar cells.

Chemical synthesis of silver nanoparticles for solar cell applications

AbstractA novel approach to fabricate silver nanoparticles for light trapping applications in silicon based solar cells has been demonstrated. Silver nanoparticles of various sizes have been synthesized by chemical reduction reactions. The particle size in the colloidal solutions was varied by using two different reducing compounds in addition to altering the compositions of the mixtures. In the present work, deposition of the silver nanoparticles onto a conventional bulk silicon solar cell shows an increase in the quantum efficiency at longer wavelengths, indicating the utilization of incident radiation that is normally lost in poor absorbing silicon (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)