Covalent organic frameworks (COFs) as a new class of crystalline, porous materials have attracted extensive attention in the fields of photocatalytic and photovoltaic applications. Generally, donor-acceptor (DA) structures play an important role in the charge separation efficiency of solar cells. In this study, two DA-COFs with high crystallinity, good porosity, and excellent stability are incorporated into the FAPbI 3 layer of perovskite solar cells. This addition of DA-COFs reduces the defect concentration and shallows the defect state. The donor-acceptor system in COFs also possesses strong charge-transfer pathway, which strongly prevents charge recombination to afford more efficient charge separation efficiency. The highest power-conversion efficiency of perovskite solar cells constructed with DA-COFs is 23.19% with excellent humidity stability of the solar cells. Therefore, this work provides a pathway for using DA-COFs to fabricate perovskite solar cells with higher efficiency and stability.
External photo-stimuli on heterojunctions commonly induce an electric potential gradient across the interface therein, such as photovoltaic effect, giving rise to various present-day technical devices. In contrast, in-plane potential gradient along the interface has been rarely observed. Here we show that scanning a light beam can induce a persistent in-plane photoelectric voltage along, instead of across, silicon-water interfaces. It is attributed to the following movement of a charge packet in the vicinity of the silicon surface, whose formation is driven by the light-induced potential change across the capacitive interface and a high permittivity of water with large polarity. Other polar liquids and hydrogel on silicon also allow the generation of the in-plane photovoltage, which is, however, negligible for nonpolar liquids. Based on the finding, a portable silicon-hydrogel array has been constructed for detecting the shadow path of a moving Cubaris. Our study opens a window for silicon-based photoelectronics through introducing semiconductor-water interfaces.
Anisotropic mechanics of van der Waals (vdWs) materials offers opportunity to peel off individual atomic layers, initiating a 2D revolution in the fields of materials science, physics, and chemistry. The elasticity, bending, and fracture strength of most of their 2D derivatives are also orientation‐dependent, which not only determines the reliability of devices based on 2D materials but also offers a vast playground for atomic manufacturing with tunable functions. Therefore, a comprehensive understanding of the anisotropic mechanical properties of 2D materials is imminent. In this review, the anisotropic mechanical properties of 2D materials are summarized in attempt to capture the current progress in this field, as well as the route toward their applications. Following a brief discussion of the anisotropic lattice structures of 2D materials, unique experimental methodologies that have been developed to characterize their anisotropic mechanics are discussed. Then, the review pivots on recent processes in anisotropic elastic, fracture, friction, and bending properties of 2D materials. Unique applications of these anisotropic properties, such as mechanical fabrication of atomic precision, as well as anisotropic strain‐induced piezoelectric and band modulation, are further highlighted. Finally, besides emphasizing the need for breakthrough in anisotropic mechanics, prospects for the developments of this field are suggested.
The shrinking size and compact structure of modern precision equipment require ultra-thin but reliable functional coating. Few layers of hexagonal boron nitride (h-BN) and graphene have a dense hexagonal lattice, distinguished electrical conductivity, good lubricity, excellent thermal and chemical stability, and can be both fabricated in large area with high quality, making them ideal candidates for atomically thin multifunctional coatings. In this review, we summarize the performance of h-BN and graphene coatings from four aspects, anti-corrosion and anti-oxidation, wetting, lubrication and electromagnetic interference shielding. Possible failure routes for their long term protection against oxidation and corrosion are comprehensively discussed, accompanying with the optimization routes. We further suggest prospects for developments of h-BN and graphene coatings.
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