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We present subwavelength nanostructures with a periodic array that transitions from hemispherical to spherical shapes, achieving efficient broadband anti-reflection (AR) in organic solar cells (OSCs). Optimizing the shapes and geometrical parameters of an antireflective subwavelength nanostructure (ARSN) enhances absorption in the active layer across a broad wavelength range through reduced reflection. An OSC integrated with an optimized front-mounted ARSN, featuring a diameter of 100 nm, a spacing of 20 nm, and an aspect ratio of 0.9, achieves a short-circuit current density (J SC) of 27.89 mA/cm2, approximately 8.61 % higher than that of a conventional planar OSC. Additionally, we examine the AR properties of the ARSN by analyzing the optical admittance diagram, following the modeling of the ARSN using the effective medium approximation. This approach can be applied to other wavelength regions and a range of applications, including optoelectronic devices, displays, absorbers, and metasurfaces. [ABSTRACT FROM AUTHOR]

High index nanostructures lead to unique light-matter interactions and strong optical resonances for potential light trapping applications and improved optical performances. In this work, Gaussian shaped subwavelength 3D nanostructures are introduced and rapid prototyping of these nanostructures is carried out on silicon (Si) in a single-step using focused ion beam (FIB) milling. The tapered geometry of Gaussian pillar structures provided reflection suppression from the smaller tip in contrast to its extended base, enabling trapping of light, confirmed through light reflection calculations and hot spots observed through absorption density distributions. The nature of accelerated ions in a FIB system is directly used and highly ordered Gaussian pillar like subwavelength nanostructures are fabricated in a single-step on Si. Simulations and experiments demonstrate nanostructure evolution from periodically spaced subwavelength nanoholes to Gaussian pillar structures with tuning of beam processing parameters, providing fabrication flexibility. The proposed light management structures, investigated through Finite Difference Time Domain (FDTD) calculations, exhibit 10–20% reflection for a broadband visible wavelength range against planar Si and previously reported Si structures (such as nano-cones, nano-wires, nano-pyramids etc.). Experimental results support theoretical predictions and provide evidence for antireflection properties from the fabricated nanostructures. Considering the rapid fabrication approach and tunable nature of Gaussian shaped nanostructures, exhibiting unique optical properties; this work provides realization of nanoscale light management 3D structures for localized light trapping and antireflection applications. Image 1 • A novel method for rapid prototyping of highly ordered, light management subwavelength 3D nanostructures by direct, single-step FIB milling process. • Unique 3D nanostructures in the form of Gaussian pillar-like structures fabricated on Si exploiting the Gaussian nature of the incident ion beam. • Reflection suppression from smaller tip in contrast to extended base of 3D structures: Enhanced light trapping and antireflection properties. [ABSTRACT FROM AUTHOR]

Abstract The optical properties of localized surface plasmon resonances (LSPR) sustained by self-assembled silver nanoparticles are of great interest for enhancing light trapping in thin film photovoltaics. First, we report on a systematic investigation of the structural and the optical properties of silver nanostructures fabricated by a solid-state dewetting process on various substrates. Our study allows to identify fabrication conditions in which circular, uniformly spaced nanoparticles are obtainable. The optimized NPs are then integrated into plasmonic back reflector (PBR) structures. Second, we demonstrate a novel procedure, involving a combination of opto-electronic spectroscopic techniques, allowing for the quantification of useful and parasitic absorption in thin photovoltaic absorber deposited on top of the PBR. We achieve a significant broadband useful absorption enhancement of 90% for 0.9 µm thick μc-Si:H film and demonstrate that optical losses due to plasmonic scattering are insignificant below 730 nm. Finally, we present a successful implementation of a plasmonic light trapping scheme in a thin film a-Si:H solar cell. The quantum efficiency spectra of the devices show a pronounced broadband enhancement resulting in remarkably high short circuit current densities (J sc). [ABSTRACT FROM AUTHOR]

Abstract: Color filtering via interaction of visible light with nanostructured surfaces offers high resolution printing of structural colors. A novel approach for color filtering in reflection mode via direct fabrication of subwavelength nanostructures on high‐index, low‐loss, and inexpensive silicon (Si) substrate is developed. Nanostructures having a unique geometry of tapered holes are fabricated exploiting the Gaussian nature of a gallium source focused ion beam (FIB). The fabrication process is rapid and single‐step, i.e., without any pre‐ or postprocessing or mask preparation in contrast to previously reported nanostructures for color filtering. These nanostructures are tunable via FIB parameters and a wide color palette is created. Finite‐difference time‐domain (FDTD) calculations reveal that the unique tapered nanohole geometry facilitates enhanced color purity via selective absorption of a narrow band of incident light wavelengths and makes it possible to obtain a wide variety of colors suitable for realistic color printing applications. The proposed approach is demonstrated for color printing applications via fabrication of butterflies and letters on Si. [ABSTRACT FROM AUTHOR]

Nanostructured surfaces are common in nature and exhibit properties such as antireflectivity (moth eyes), self-cleaning (lotus leaf), iridescent colors (butterfly wings), and water harvesting (desert beetles). We now understand such properties and can mimic some of these natural structures in the laboratory. However, these synthetic structures are limited since they are not easily mass produced over large areas due to the limited scalability of current technologies such as UV-lithography, the high cost of infrastructure, and the difficulty in nonplanar surfaces. Here, we report a solution process based on block copolymer (BCP) self-assembly to fabricate subwavelength structures on large areas of optical and curved surfaces with feature sizes and spacings designed to efficiently scatter visible light. Si nanopillars (SiNPs) with diameters of 115 ± 19 nm, periodicity of 180 ± 18 nm, and aspect ratio of 2-15 show a reduction in reflectivity by a factor of 100, <0.16% between 400 and 900 nm at an angle of incidence of 30°. Significantly, the reflectivity remains below 1.75% up to incident angles of 75°. Modeling the efficiency of a SiNP PV suggests a 24.6% increase in efficiency, representing a 3.52% (absolute) or 16.7% (relative) increase in electrical energy output from the PV system compared to AR-coated device. [ABSTRACT FROM AUTHOR]

Despite the 'darker than black' association attributed to carbon nanotube forests, here is shown that it is also possible to grow these structures, over heat-sensitive substrates, featuring highly transmissive characteristics from the UV to infrared wavelengths, for forest heights as high as 20 μm. The optical transmission is interpreted in terms of light propagation along channels that are self-generated by localized bundling of tubes, acting as waveguides. A good correlation is shown between the distribution of diameter sizes of these sub-wavelength voids and the transmission spectrum of the forests. For the shorter visible and near-UV wavelengths, this model shows that light propagates by channeling along individual vertical voids in the forests, which elucidates the origin for the widely-reported near-zero reflectance values observed in forests. For the longer infrared wavelengths, the mode spreads over many nanotubes and voids, and propagates along a 'homogeneous effective medium'. The strong absorption of the forest at the shorter wavelengths is correlated in terms of the stronger attenuation inside a waveguide cavity, according to the λ−1/2 attenuation dependency of standard waveguide theory. The realization of this material can lead to novel avenues in new optoelectronic device design, where the carbon nanotube forests can be used as highly conducting 'scaffolds' for optically active materials, whilst also allowing light to penetrate to significant depths into the structure, in excess of 20 μm, enabling optical functionality. [ABSTRACT FROM AUTHOR]

Recently, a large number of experimental and theoretical works have revealed a variety of plasmonic nanostructures with the capabilities of Fano resonance (FR) generation. Among these structures, plasmonic oligomers consisting of packed metallic nanoelements with certain configurations have been of significant interest. Oligomers can exhibit FR independently of the polarization direction based on dipole-dipole antiparallel modes without the need to excite challenging high-order modes. The purpose of this review article is to provide an overview of recent achievements on FR of plasmonic nanostructures in recent years. Meanwhile, more attention is given to the optical properties of plasmonic oligomers due to the high potential of such structures in optical spectra engineering. [ABSTRACT FROM AUTHOR]

Abstract: Porous nanostructures on BK7 glass manufactured by chemical treatment are able to function as antireflection (AR) components over a wide spectral range and have potential to achieve high laser damage resistance. The damage-resistant properties of antireflective porous glasses with nearly 100% transmittances exposed to pulse lasers with three different central wavelengths were investigated in this paper. The laser damage tests showed that the LIDTs under the irradiation of 12ns 1064nm pulses, 10ns 532nm pulses and 8ns 355nm pulses are 58J/cm2, 20J/cm2 and 12J/cm2, respectively. These values are much higher than those of AR coated glasses, but are almost the same level of un-etched substrate. To understand possible damage mechanisms, the role of electric field distribution inside the porous structure during the laser radiation process was investigated by a three-dimensional finite difference time-domain method. The temperature distribution resulting from the internal electric field may be a main factor to induce the damage. In addition, the involved defects during the etching process are also responsible for the damage in the porous structure. Finally, some possible approaches to improve the LIDT are proposed. [Copyright &y& Elsevier]

Plasmonic resonances with a Fano lineshape observed in metallic nanoclusters often arise from the destructive interference between a dark, subradiant mode and a bright, super-radiant one. A flexible control over the Fano profile characterized by its linewidth and spectral contrast is crucial for many potential applications such as slowing light and biosensing. In this work, we show how one can easily but significantly tailor the overall spectral profile in plasmonic nanocluster systems, for example, quadrumers and pentamers, by selectively altering the particle shape without a need to change the particle size, interparticle distance, or the number of elements of the oligomers. This is achieved through decomposing the whole spectrum into two separate contributions from subgroups, which are efficiently excited at their spectral peak positions. We further show that different strengths of interference between the two subgroups must be considered for a full understanding of the resulting spectral lineshape. In some cases, each subgroup is separately active in distinct frequency windows with only small overlap, leading to a simple convolution of the subspectra. Variation in particle shape of either subgroup results in the tuning of the overall spectral lineshape, which opens a novel pathway for shaping the plasmonic response in small nanoclusters. [ABSTRACT FROM AUTHOR]

Two-photon lithography is a potential route to produce high-resolution 3D ceramics. However, the large shrinkage due to the elimination of an important organic counterpart of the printed material during debinding/sintering remains a lock to further development of this technology. To limit this phenomenon, an original approach based on a composite resin incorporating 45 wt% ultrasmall (5 nm) zirconia stabilized nanoparticles into the zirconium acrylate precursor is proposed to process 3D zirconia microlattices and nanostructured optical surfaces. Interestingly, the nanoparticles are used both as seeds allowing control of the crystallographic phase formed during the calcination process and as structural stabilizing agent preventing important shrinkage of the printed ceramic. After 3D photolithography and pyrolysis, the weight and volume loss of the microstructures are drastically reduced as compared to similar systems processed with the reference resin without nanoparticles, and stable 3D microstructures of cubic zirconia are obtained with high spatial resolution. In the case of a patterned surface, the refractive index of 2.1 leads to a diffraction efficiency large enough to obtain microfocusing with linewidths of 0.1 µm, and the demonstration of a microlens array with a period as small as 0.8 µm., (© 2021 The Authors. Small published by Wiley-VCH GmbH.)