Diphylleia grayi-Inspired Intelligent Hydrochromic Adhesive Film.

Diphylleia grayi-inspired hydrochromic nano/microstructured films have received much attention for its promising smart hydrochromic applications owing to their simple and low-cost but energy-effective strategy. A new type of water-switchable glazing film patterned with various nano/micro air-hole inverse opal arrays is introduced by selectively removing nano/microsphere polystyrene arrays embedded in the surface of polydimethylsiloxane (PDMS) films. Using the significant contrast ratio of the bleaching and the scattering states, we have optimized the switching properties of Mie scattered patterns. As a result, we obtained a single inverse opal layer-embedded PDMS adhesive film with hexagonally close-packed 1 µm air-hole arrays as an optimum scattered film. The differences of diffusive transmittance and optical haze values between the dry and the wet states of the best scattered film reached 44.93% (ΔTD.T = 59.11-14.18%) and 54.88% (ΔH = 69.42-14.54%), respectively. In addition, using the best-optimized inverse opal layer-embedded PDMS film, we fabricated a perfectly imitated Diphylleia grayi structure for camouflage application and an intelligent hydrochromic window device. The dynamic water modulation of the scattered opaque and nonscattered transparent state of the inverse opal-patterned PDMS adhesive film can provide an advanced platform structure in the area of hydrochromic technology for smart windows, camouflage, and clear umbrellas for rainy days.

Newly Developed Broadband Antireflective Nanostructures by Coating a Low-Index MgF2 Film onto a SiO2 Moth-Eye Nanopattern.

A newly developed nanopatterned broadband antireflective (AR) coating was fabricated on the front side of a glass/indium tin oxide/perovskite solar cell (PSC) by depositing a single interference layer onto a two-dimensional (2D)-patterned moth-eye-like nanostructure. The optimized developed AR nanostructure was simulated in a finite-difference time domain analysis. To realize the simulated developed AR nanostructure, we controlled the SiO2 moth-eye structure with various diameters and heights and a MgF2 single layer with varying thicknesses by sequentially performing nanosphere lithography, reactive ion etching, and electron-beam evaporation. Optimization of the developed AR nanostructure, which has a 100 nm-thick MgF2 film coated onto the SiO2 moth-eye-like nanostructure (diameter 165 nm and height 400 nm), minimizes the reflection loss throughout the visible range. As a result, the short-circuit current density (JSC) of the newly AR-coated PSC increases by 11.80%, while the open-circuit voltage (VOC) remains nearly constant. Therefore, the power conversion efficiency of the newly developed AR-decorated PSC increases by 12.50%, from 18.21% for a control sample to 20.48% for the optimum AR-coated sample. These results indicate that the newly developed MgF2/SiO2 AR nanostructure can provide an advanced platform technology that reduces the Fresnel loss and therefore increases the possibility of the commercialization of glass-based PSCs.

Stable and Colorful Perovskite Solar Cells Using a Nonperiodic SiO2/TiO2 Multi-Nanolayer Filter.

While research on building-integrated photovoltaics (BIPVs) has mainly focused on power-generating window applications, the utilization of other underutilized surface areas in buildings, including exteriors, facades, and rooftops, has still not been fully explored. The most important requirements for BIPVs are color, power conversion efficiency (PCE), and long-term stability. In this work, we achieved colorful (red, green, blue, RGB) perovskite solar cells (PSCs) with minimized PCE loss (<10%) and enhanced photostability by exploiting the optical properties of nonperiodic multi-nanolayer, narrow-bandwidth reflective filters (NBRFs). The NBRFs were fabricated by multilayering high-index TiO2/low-index SiO2 in a nonperiodic manner, which allowed devices to demonstrate various colors with effectively suppressed unwanted baseline ripple-shape reflectance. The PCEs of PSCs with nonperiodic RGB-NBRFs were 18.0%, 18.6%, and 18.9%, which represent reductions of only 10%, 7%, and 6% of PCE values, respectively, compared to a black control PSC (20.1%). Moreover, the photostability of the PSCs was substantially improved by using the NBRFs because of ultraviolet blocking in the TiO2 layers. The G-PSC retained 65% of the initial PCE after 60 h of continuous illumination (AM 1.5G one sun) at the maximum power point, whereas the black PSC retained only 30%. Aesthetic color value, low PCE loss, and enhanced photostability of PSCs were simultaneously achieved by employing our NBRFs, making this a promising strategy with potential applicability in power-generating building exteriors.

Dual wavelength lasing of InGaN/GaN axial-heterostructure nanorod lasers.

Optical confinement effects are investigated in InGaN/GaN axial-heterostructure nanolasers. Cylindrical nanorods with GaN/InGaN/GaN structures are prepared using combined processes of top-down and bottom-up approaches. The lasing of InGaN is observed at a low threshold (1 µJ cm-2), which is attributed to an efficient carrier transfer process from GaN to InGaN. The lasing of GaN is also found in the threshold range of 10-20 µJ cm-2 with a superlinear increase in emission intensity and high quality factors (Q = 1000), implying that dual wavelengths of lasing are tunable as a function of excitation intensity. The non-classical Fabry-Pérot modes suggest strong light-matter interactions in nanorods by optical confinement effects. The polarization of lasing indicates that the non-classical modes are in the identical transverse mode, which supports the formation of exciton-polaritons in nanorods. Polariton lasing in a single axial-heterostructure nanorod is observed for the first time, which proposes small-sized light sources with low threshold, polarized light, and tunable wavelengths in a single nanorod.

RGB-Colored Cu(In,Ga)(S,Se)2 Thin-Film Solar Cells with Minimal Efficiency Loss Using Narrow-Bandwidth Stopband Nano-Multilayered Filters.

Colorful Cu(In,Ga)(S,Se)2 (CIGSSe) thin-film solar cells were achieved by integrating a narrow-bandwidth stopband filter (NBSF) on a CIGSSe cell. The full range of visible color of NBSF could be realized by depositing one-dimensional nano-multilayers of alternating high-index (Al2O3) and low-index (SiO2) films while controlling the thickness of each layer and the number of stacked layers. Particularly, high-purity red, green, and blue (RGB) colors were generated on black CIGSSe cells with minimal harvest efficiency drop, showing power conversion efficiency (PCE) losses for the red and green CIGSSe cells of 4.2 and 1.2%, respectively, with no reduction in the PCE of the blue CIGSSe cell. The minimal drop in the harvest efficiency was attributed to the antireflection effect of the NBSF and the low overlap between the reflectance spectrum of NBSFs with a narrow stopband and the absorption spectrum of CIGSSe. The esthetic value could be further enhanced through the color variation of the RGB NBSF with viewing angle, so-called pearl-like colors. The synergetic effect of minimal efficiency loss, full color realization, and the pearl-like color change of the newly developed NBSFs can make CIGSSe cells applicable to building-integrated photovoltaics.

Enhanced DC-Operated Electroluminescence of Forwardly Aligned   p/MQW/n InGaN Nanorod LEDs via DC Offset-AC Dielectrophoresis.

We introduce an orientation-controlled alignment process of p-GaN/InGaN multiquantum-well/n-GaN (p/MQW/n InGaN) nanorod light-emitting diodes (LEDs) by applying the direct current (DC) offset-alternating current (AC) or pulsed DC electric fields across interdigitated metal electrodes. The as-forwardly aligned p/MQW/n InGaN nanorod LEDs by a pulsed DC dielectrophoresis (DEP) assembly process improve the electroluminescence (EL) intensities by 1.8 times compared to the conventional AC DEP assembly process under DC electric field operation and exhibit an enhanced applied current and EL brightness in the current-voltage and EL intensity-voltage curves, which can be directly used as the fundamental data to construct DC-operated nanorod LED devices, such as LED areal surface lightings, scalable lightings (micrometers to inches) and formable surface lightings. The enhancement in the applied current, the improved EL intensity, and the increased number of forwardly aligned p/MQW/n InGaN nanorods in panchromatic cathodoluminescence images confirm the considerable enhancement of forwardly aligned one-dimensional nanorod LEDs between two opposite electrodes using DC offset-AC or a pulsed DC electric field DEP assembly process. These DC offset-AC or pulsed DC electric field DEP assembly processes suggest that designing for these types of interactions could yield new ways to control the orientation of asymmetric p/MQW/n InGaN diode-type LED nanorods with a relatively low aspect ratio.

Multiple-Color-Generating Cu(In,Ga)(S,Se)2 Thin-Film Solar Cells via Dichroic Film Incorporation for Power-Generating Window Applications.

There are four prerequisites when applying all types of thin-film solar cells to power-generating window photovoltaics (PVs): high power-generation efficiency, longevity and high durability, semitransparency or partial-light transmittance, and colorful and aesthetic value. Solid-type thin-film Cu(In,Ga)S2 (CIGS) or Cu(In,Ga)(S,Se)2 (CIGSSe) PVs nearly meet the first two criteria, making them promising candidates for power-generating window applications if they can transmit light to some degree and generate color with good aesthetic value. In this study, the mechanical scribing process removes 10% of the window CIGSSe thin-film solar cell with vacant line patterns to provide a partial-light-transmitting CIGSSe PV module to meet the third requirement. The last concept of creating distinct colors could be met by the addition of reflectance colors of one-dimensional (1D) photonic crystal (PC) dichroic film on the black part of a partial-light-transmitting CIGSSe PV module. Beautiful violets and blues were created on the cover glass of a black CIGSSe PV module via the addition of 1D PC blue-mirror-yellow-pass dichroic film to improve the aesthetic value of the outside appearance. As a general result from the low external quantum efficiency (EQE) and absorption of CIGSSe PVs below a wavelength of 400 nm, the harvesting efficiency and short-circuit photocurrent of CIGSSe PVs were reduced by only ∼10% without reducing the open-circuit voltage (VOC) because of the reduced overlap between the absorption spectrum of CIGSSe PV and the reflectance spectrum of the 1D PC blue-mirror-yellow-pass dichroic film. The combined technology of partial-vacancy-scribed CIGSSe PV modules and blue 1D PC dichroic film can provide a simple strategy to be applied to violet/blue power-generating window applications, as such a strategy can improve the transparency and aesthetic value without significantly sacrificing the harvesting efficiency of the CIGSSe PV modules.

Horizontally assembled green InGaN nanorod LEDs: scalable polarized surface emitting LEDs using electric-field assisted assembly.

In this study, we report the concerted fabrication process, which is easy to transform the size of active emitting area and produce polarized surface light, using the electric-field-assisted assembly for horizontally assembled many tiny nanorod LEDs between two metal electrodes. We fabricate the millions of individually separated 1D nanorod LEDs from 2D nanorod arrays using nanosphere lithography, etching and cutting process of InGaN/GaN LED structure on a flat sapphire substrate. The horizontally assembled InGaN-based nanorods LED device shows bright (~2,130 cd/m(2)) and uniform polarized (polarization ratio, ρ = ~0.61) green emissions from large area (0.7 cm × 0.6 cm) planar surface. The realization of a horizontally assembled nanorod LED device can prove the concept of an innovative idea to fabricate formable and scalable polarized surface LED lighting.