Single-step manufacturing of hierarchical dielectric metalens in the visible

Metalenses have shown a number of promising functionalities that are comparable with conventional refractive lenses. However, current metalenses are still far from commercialization due to the formidable fabrication costs. Here, we demonstrate a low-cost dielectric metalens that works in the visible spectrum. The material of the metalens consists of a matrix-inclusion composite in which a hierarchy satisfies two requirements for the single-step fabrication; a high refractive index and a pattern-transfer capability. We use a UV-curable resin as a matrix to enable direct pattern replication by the composite, and titanium dioxide nanoparticles as inclusions to increase the refractive index of the composite. Therefore, such a dielectric metalens can be fabricated with a single step of UV nanoimprint lithography. An experimental demonstration of the nanoparticle composite-based metalens validates the feasibility of our approach and capability for future applications. Our method allows rapid replication of metalenses repeatedly and thereby provides an advance toward the use of metalenses on a commercial scale. Current metalenses are far from commercialization due to fabrication cost and low throughput. Here, the authors use a UV-curable resin as a matrix for direct pattern replication by the composite and TiO2 nanoparticles to increase the refractive index of the composite, allowing dielectric metalenses to be manufactured in a single step.11Ysciescopu

Selectively patterned TiO2 nanorods as electron transport pathway for high performance perovskite solar cells

conversion efficiency and simple fabrication process. One of the various approaches to increase the efficiency of PSCs is to change the material or structure of the carrier transport layer. Here, optically long and electrically short structural concept is proposed to enhance the characteristics of a PSC by employing selectively grown single crystalline TiO2 nanorods. The approach has the merit of increasing the electron-hole separation effectively and enables a thicker active layer to be coated without electrical loss by using TiO2 nanorods as an electron pathway. Moreover, selectively grown TiO2 nanorods increase the optical path of the incident light via scattering effects and enable a smooth coating of the active layer. Nanoimprint lithography and hydrothermal growth were employed to fabricate selectively grown TiO2 nanorod substrates. The fabricated solar cell exhibits an efficiency of 19.86% with a current density, open-circuit voltage, and fill factor of 23.13 mA/cm(2), 1.120 V, and 76.69%, respectively. Time-resolved photoluminescence, ultraviolet-visible (UV-Vis) spectroscopy, and the incident photon to current efficiency (IPCE) analysis were conducted to understand the factors responsible for the improvement in characteristics of the fabricated PSCs

Fabrication of perovskite solar cell with high short-circuit current density (J(SC)) using moth-eye structure of SiOX

The performance of solar cells is determined by three factors: the open-circuit voltage (V-OC), short-circuit current density (J(SC)), and fill factor (FF). The V-OC and FF are determined by the material bandgap and the series/shunt resistance, respectively. However, J(SC) is determined by the amount of incident light in addition to the bandgap of the material. In this study, a moth-eye pattern was formed on a glass surface via direct printing to increase the amount of incident light and thus increase J(SC). The moth-eye pattern is a typical antireflection pattern that reduces the reflection by gradually increasing the refractive index. A flat perovskite solar cell (F-PSC) and a moth-eye patterned perovskite solar cell (M-PSC) had J(SC) values of 23.70 and 25.50 mA/cm(2), respectively. The power-conversion efficiencies of the F-PSC and M-PSC were 19.81% and 21.77%, respectively

Hexagonal array micro-convex patterned substrate for improving diffused transmittance in perovskite solar cells

In the past decade, the fastest development in solar cell research has occurred for perovskite solar cells. Owing to the favorable properties of perovskite materials, perovskite solar cells exhibit excellent power conversion efficiencies and there appears great potential for future development. In this paper, we report the fabrication of a substrate with excellent optical properties by incorporating hexagonal array micro-convex (HAMC) nanostructures in it before integration with the electrode (indium tin oxide and zinc oxide) and the halide for use in organic-inorganic perovskite solar cells. This was fabricated using nanoimprint lithography which showed excellent throughput and involved simple processing methods. The HAMC nanostructured substrate showed strong light scattering as compared to that of the conventional substrate. This resulted in the increase of current density of the fabricated solar cell from 19.45 mA/cm2 (un-patterned substrate) to 20.92 mA/cm2 (nanostructured substrate) with accompanying increase in the external quantum efficiency and a satisfactory performance by the perovskite solar cell

Metal–Organic Framework-Templated PdO-Co₃O₄ Nanocubes Functionalized by SWCNTs: Improved NO₂ Reaction Kinetics on Flexible Heating Film

Detection and control of air quality are major concerns in recent years for environmental monitoring and healthcare. In this work, we developed an integrated sensor architecture comprised of nanostructured composite sensing layers and a flexible heating substrate for portable and real-time detection of nitrogen dioxide (NO₂). As sensing layers, PdO-infiltrated Co₃O₄ hollow nanocubes (PdO-Co₃O₄ HNCs) were prepared by calcination of Pd-embedded Co-based metal–organic framework polyhedron particles. Single-walled carbon nanotubes (SWCNTs) were functionalized with PdO-Co₃O₄ HNCs to control conductivity of sensing layers. As a flexible heating substrate, the Ni mesh electrode covered with a 40 nm thick Au layer (i.e., Ni­(core)/Au­(shell) mesh) was embedded in a colorless polyimide (cPI) film. As a result, SWCNT-functionalized PdO-Co₃O₄ HNCs sensor exhibited improved NO₂ detection property at 100 °C, with high sensitivity (<i>S</i>) of 44.11% at 20 ppm and a low detection limit of 1 ppm. The accelerated reaction and recovery kinetics toward NO₂ of SWCNT-functionalized PdO-Co₃O₄ HNCs were achieved by generating heat on the Ni­(core)/Au­(shell) mesh-embedded cPI substrate. The SWCNT-functionalized porous metal oxide sensing layers integrated on the mechanically stable Ni­(core)/Au­(shell) mesh heating substrate can be envisioned as an essential sensing platform for realization of low-temperature operation wearable chemical sensor

High thermoelectric figure of merit of porous Si nanowires from 300 to 700 K.

Thermoelectrics operating at high temperature can cost-effectively convert waste heat and compete with other zero-carbon technologies. Among different high-temperature thermoelectrics materials, silicon nanowires possess the combined attributes of cost effectiveness and mature manufacturing infrastructures. Despite significant breakthroughs in silicon nanowires based thermoelectrics for waste heat conversion, the figure of merit (ZT) or operating temperature has remained low. Here, we report the synthesis of large-area, wafer-scale arrays of porous silicon nanowires with ultra-thin Si crystallite size of ~4 nm. Concurrent measurements of thermal conductivity (κ), electrical conductivity (σ), and Seebeck coefficient (S) on the same nanowire show a ZT of 0.71 at 700 K, which is more than ~18 times higher than bulk Si. This ZT value is more than two times higher than any nanostructured Si-based thermoelectrics reported in the literature at 700 K. Experimental data and theoretical modeling demonstrate that this work has the potential to achieve a ZT of ~1 at 1000 K

Methylammonium Chloride Induces Intermediate Phase Stabilization for Efficient Perovskite Solar Cells

One of the most effective methods to achieve high-performance perovskite solar cells has been to include additives that serve as dopants, crystallization agents, or passivate defect sites. Cl-based additives are among the most prevalent in literature, yet their exact role is still uncertain. In this work, we systematically study the function of methylammonium chloride (MACl) additive in formamidinium lead iodide (FAPbI3)-based perovskite. Using density functional theory, we provide a theoretical framework for understanding the interaction of MACl with a perovskite. We show that MACl successfully induces an intermediate to the pure FAPbI3 ??-phase without annealing. The formation energy is related to the amount of incorporated MACl. By tuning the incorporation of MACl, the perovskite film quality can be significantly improved, exhibiting a 6?? increase in grain size, a 3?? increase in phase crystallinity, and a 4.3?? increase in photoluminescence lifetime. The optimized solar cells achieved a certified efficiency of 23.48%

Spontaneous Registration of Sub-10 nm Features Based on Subzero Celsius Spin-Casting of Self-Assembling Building Blocks Directed by Chemically Encoded Surfaces

For low-cost and facile fabrication of innovative nanoscale devices with outstanding functionality and performance, it is critical to develop more practical patterning solutions that are applicable to a wide range of materials and feature sizes while minimizing detrimental effects by processing conditions. In this study, we report that area-selective sub-10 nm pattern formation can be realized by temperature-controlled spin-casting of block copolymers (BCPs) combined with submicron-scale-patterned chemical surfaces. Compared to conventional room-temperature spin-casting, the low temperature (<i>e.g.</i>, −5 °C) casting of the BCP solution on the patterned self-assembled monolayer achieved substantially improved area selectivity and uniformity, which can be explained by optimized solvent evaporation kinetics during the last stage of film formation. Moreover, the application of cold spin-casting can also provide high-yield <i>in situ</i> patterning of light-emitting CdSe/ZnS quantum dot thin films, indicating that this temperature-optimized spin-casting strategy would be highly effective for tailored patterning of diverse organic and hybrid materials in solution phase