Solar steam generation has been achieved by surface plasmon heating with metallic nanoshells or nanoparticles, which have inherently narrow absorption bandwidth. For efficient light-to-heat conversion from a wider solar spectrum, we employ adiabatic plasmonic nanofocusing to attain both polarization-independent ultrabroadband light absorption and high plasmon dissipation loss. Here we demonstrate large area, flexible thin-film black gold membranes, which have multiscale structures of varying metallic nanoscale gaps (0–200 nm) as well as microscale funnel structures. The adiabatic nanofocusing of self-aggregated metallic nanowire bundle arrays produces average absorption of 91% at 400–2,500 nm and the microscale funnel structures lead to average reflection of 7% at 2.5–17 μm. This membrane allows heat localization within the few micrometre-thick layer and continuous water provision through micropores. We efficiently generate water vapour with solar thermal conversion efficiency up to 57% at 20 kW m−2. This new structure has a variety of applications in solar energy harvesting, thermoplasmonics and related technologies.
The ability to render objects invisible with a cloak that fits all objects and sizes is a longstanding goal for optical devices. Invisibility devices demonstrated so far typically comprise a rigid structure wrapped around an object to which it is fitted. Here we demonstrate smart metamaterial cloaking, wherein the metamaterial device not only transforms electromagnetic fields to make an object invisible, but also acquires its properties automatically from its own elastic deformation. The demonstrated device is a ground-plane microwave cloak composed of an elastic metamaterial with a broad operational band (10-12 GHz) and nearly lossless electromagnetic properties. The metamaterial is uniform, or perfectly periodic, in its undeformed state and acquires the necessary gradient-index profile, mimicking a quasi-conformal transformation, naturally from a boundary load. This easy-to-fabricate hybrid elastoelectromagnetic metamaterial opens the door to implementations of a variety of transformation optics devices based on quasi-conformal maps.
Here, excitation orthogonalized red/green/blue upconversion luminescence (UCL)-based full-color tunable rareearth (RE) ion-doped upconversion nanophosphors (UCNPs) are reported. The LiREF 4 -based core/sextuple-shell (C/6S) UCNPs are synthesized, and they consist of a blue-emitting core, green-emitting inner shell, and red-emitting outer shell, with inert intermediate and outermost shells. The synthesized C/6S UCNPs emit blue, green, and red light under 980, 800, and 1532 nm, respectively. Importantly, by combining incident near-infrared (NIR) light with various wavelengths (800, 980, and 1532 nm), full-color UCL including blue, cyan, green, yellow, orange, red, purple, and white UCL is achieved from the single C/6S UCNP composition. The color gamut obtained from the C/6S UCNPs shows 101.6% of the sRGB standard color gamut. Furthermore, transparent C/6S UCNP-polydimethylsiloxane (PDMS) composite is prepared. Full-color display realized in the transparent C/6S UCNP-PDMS composite indicates the feasibility of constructing the C/6S UCNP-based three-dimensional volumetric displays with wide color gamut.
Flexible
perovskite solar cells attract significant attention because
of their high accessibility in device fabrication, inexpensive fabrication
process, and remarkable power conversion efficiency (PCE). Solvent
engineering has been an important protocol for synthesizing high-quality
perovskite thin films. Toxic antisolvents such as chlorobenzene (CB)
are necessary to obtain desirable film morphologies. This study proposes
a novel green antisolvent, butyl acetate (BA). It exhibits low toxicity,
but its physical properties are similar to those of CB. The difference
between the solubility parameters of antisolvents and dimethyl sulfoxide
(DMSO) determines the volume of residual DMSO within perovskite–DMSO
complexes. During spin coating, BA leaves excess DMSO more effectively
than CB because of larger differences in solubility parameters, facilitating
the gradual nucleation and growth of perovskite grains. The resulting
enlarged grains (>1 μm) reduce trap density and improve charge
carrier mobility, resulting in a significant enhancement in the device
performance (PCE = 19.78%) and environmental stability (PCE retention
of 97.4% after 1000 h). Furthermore, highly efficient and flexible
devices are available as indoor light energy harvesters. At 400 lx
of a white light-emitting diode, a bent device with a bending radius
of 10 mm exhibits a remarkable maximum power density of 0.063 mW cm–2 and PCE of 23.33%.
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