Delayed school start time is associated with better sleep, mental health, and life satisfaction among residential high-school students: a prospective study.

This study examined the longer-term individual- and school-level changes in students 7 months after a 1-hour delay in school start time (SST). Two cohorts of grade 11 students (N = 227; 60.8% female, age = 17.

Broadband electrically controlled reflective metasurface for reconfigurable circularly polarized wavefront manipulation.

A broadband, electrically controlled, reconfigurable, circularly polarized reflective metasurface is presented. The chirality of the metasurface structure is changed by switching active elements, which benefits from the tunable current distributions generated by the elaborately designed structure under x-polarized and y-polarized waves. Notably, the proposed metasurface unit cell maintains a good circular-polarization efficiency in a broadband range of 6.

Processing of Lead Halide Perovskite Thin Films Studied with In-Situ Real-Time X-ray Scattering.

Lead halide perovskites have been of paramount interest for solution-processable solar cells, reaching power conversion efficiencies larger than 25%. In this spotlight, we will provide a systematic overview of the influence of different solution-based processing routes of lead halide perovskites on their phase transformation and conversion as revealed through in-situ X-ray-scattering experiments. These experiments were performed in conditions closely mimicking thin film processing methods and conditions used for thin film solar cell device fabrication and therefore provide critical information about the mechanism of the phase transformation, its onset, the kinetics, as well as the emergence and disappearance of various (meso)phases along the way.

Printed Memtransistor Utilizing a Hybrid Perovskite/Organic Heterojunction Channel.

Neuromorphic computing has the potential to address the inherent limitations of conventional integrated circuit technology, ranging from perception, pattern recognition, to memory and decision-making ( 2019, 52 (4), 964-974) ( 2004, 431 (7010), 796-803) ( 2013, 8 (1), 13-24). Despite their low power consumption ( 2016, 16 (11), 6724-6732), traditional two-terminal memristors can perform only a single function while lacking heterosynaptic plasticity ( 2013, 24 (38), 382001). Inspired by the unconditioned reflex, multiterminal memristive transistors (memtransistor) were developed to realize complex functions, such as multiterminal modulation and heterosynaptic plasticity ( 2018, 554, (7693), 500-504).

Perovskite Solar Cells toward Eco-Friendly Printing.

Eco-friendly printing is important for mass manufacturing of thin-film photovoltaic (PV) devices to preserve human safety and the environment and to reduce energy consumption and capital expense. However, it is challenging for perovskite PVs due to the lack of eco-friendly solvents for ambient fast printing. In this study, we demonstrate for the first time an eco-friendly printing concept for high-performance perovskite solar cells.

Wide-Band-Gap Mixed-Halide 3D Perovskites: Electronic Structure and Halide Segregation Investigation.

Mixed-halide organolead perovskites ( ) are of great interest for both single-junction and tandem solar cells because of their wide band gap. In this study, we investigate the family of mixed iodide/bromide (I/Br) and bromide/chloride (Br/Cl) perovskites, revealing the strong influence of halide substitution on electronic properties, morphology, film composition, and phase segregation. A qualitative blue shift with the I → Br → Cl series was observed, with the resulting optical absorption ranging from 420 to 800 nm covering nearly the entire visible region.

Ruddlesden-Popper-Phase Hybrid Halide Perovskite/Small-Molecule Organic Blend Memory Transistors.

Controlling the morphology of metal halide perovskite layers during processing is critical for the manufacturing of optoelectronics. Here, a strategy to control the microstructure of solution-processed layered Ruddlesden-Popper-phase perovskite films based on phenethylammonium lead bromide ((PEA) PbBr ) is reported. The method relies on the addition of the organic semiconductor 2,7-dioctyl[1]benzothieno[3,2-b]benzothiophene (C -BTBT) into the perovskite formulation, where it facilitates the formation of large, near-single-crystalline-quality platelet-like (PEA) PbBr domains overlaid by a ≈5-nm-thin C -BTBT layer.

Systematic Study on the Morphological Development of Blade-Coated Conjugated Polymer Thin Films via In Situ Measurements.

The morphology of conjugated polymer thin films, determined by the kinetics of film drying, is closely correlated with their electrical properties. Herein, we focused on dramatic changes in the thin-film morphology of blade-coated poly{[,'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]--5,5'-(2,2'-bithiophene)} caused by the effect of solvent and coating temperature. Through in situ measurements, the evolution of polymer aggregates and crystallites, which plays a decisive role in the formation of the charge-transport pathway, was observed in real time.

Role of Alkali-Metal Cations in Electronic Structure and Halide Segregation of Hybrid Perovskites.

The ability to control or prevent phase segregation in perovskites is crucial to realizing stable and tunable mixed-halide optoelectronic devices. In this work, we systematically examine the impact of alkali-metal-cation (Cs and K) concentration on the band structure, chemical composition, phase segregation, and polycrystalline microstructure on formamidinium-dominated mixed-halide mixed-cation perovskite films. It was found that the incorporation of Cs and K cations decreases the work function and the core levels of all components shift toward higher binding energy consistent with n-doping the perovskite film, which facilitates electron transfer to the electron transport layer TiO.

Interfacial Engineering at the 2D/3D Heterojunction for High-Performance Perovskite Solar Cells.

Perovskite solar cells based on two-dimensional/three-dimensional (2D/3D) hierarchical structure have attracted significant attention in recent years due to their promising photovoltaic performance and stability. However, obtaining a detailed understanding of interfacial mechanism at the 2D/3D heterojunction, for example, the ligand-chemistry-dependent nature of the 2D/3D heterojunction and its influence on charge collection and the final photovoltaic outcome, is not yet fully developed. Here we demonstrate the underlying 3D phase templates growth of quantum wells (QWs) within a 2D capping layer, which is further influenced by the fluorination of spacers and compositional engineering in terms of thickness distribution and orientation.

Kinetic Stabilization of the Sol-Gel State in Perovskites Enables Facile Processing of High-Efficiency Solar Cells.

Perovskite solar cells increasingly feature mixed-halide mixed-cation compounds (FA MA Cs PbI Br ) as photovoltaic absorbers, as they enable easier processing and improved stability. Here, the underlying reasons for ease of processing are revealed. It is found that halide and cation engineering leads to a systematic widening of the anti-solvent processing window for the fabrication of high-quality films and efficient solar cells.

Surface Impedance of Metasurfaces/Graphene Hybrid Structures.

Understanding and manipulation of surface impedance in graphene hybrid structure is a significant issue for applications of graphene-based optoelectronics devices. In order to achieve this purpose in the terahertz region, analytical expressions for the impedances of metasurface were derived, which allows us to easily understand the relationship between physical dimensions and impedance. Simulation results show an excellent agreement with the analytical predictions.

Dynamical Transformation of Two-Dimensional Perovskites with Alternating Cations in the Interlayer Space for High-Performance Photovoltaics.

The two-dimensional (2D) perovskites stabilized by alternating cations in the interlayer space (ACI) define a new type of structure with different physical properties than the more common Ruddlesden-Popper counterparts. However, there is a lack of understanding of material crystallization in films and its influence on the morphological/optoelectronic properties and the final photovoltaic devices. Herein, we undertake in situ studies of the solidification process for ACI 2D perovskite (GA)(MA) Pb I (⟨ n⟩ = 3) from ink to solid-state semiconductor, using solvent mixture of DMSO:DMF (1:10 v/v) as the solvent and link this behavior to solar cell devices.

A Low-Profile Dual-Layer Patch Antenna with a Circular Polarizer Consisting of Dual Semicircular Resonators.

In this paper, a circular polarizer comprising dual semicircular split-rings (DSSRs) is presented. By placing it above an elliptical radiator that radiates linearly polarized (LP) waves, dual-layer patch antennas capable of radiating right-hand (RH) or left-hand (LH) circularly polarized (CP) waves are achieved in terms of the different offset direction of the bottom splits of the DSSRs. Because of both the capacitive coupling to the radiator and the degenerate modes existing in the excited DSSRs, the DSSRs collaboratively result in a circularly polarized radiation, successfully converting incident LP waves into CP ones.

Ultra-thin and broadband tunable metamaterial graphene absorber.

A broadband tunable metamaterial graphene absorber is investigated in this paper. The unit cell of the proposed metamaterial graphene absorber is composed of four patch resonators. By tuning the chemical potential of graphene and the geometric size of each patch, the simulated total reflectivity is less than -10 dB from 22.

Tunable reflector with active magnetic metamaterials.

We placed active magnetic metamaterials on metallic surface to implement a tunable reflector with excellent agile performance. By incorporating active elements into the unit cells of the magnetic metamaterial, this active magnetic metamaterial can be tuned to switch function of the reflector among a perfect absorber, a perfect reflector and a gain reflector. This brings about DC control lines to electrically tune the active magnetic metamaterial with positive loss, zero loss and even negative loss.