The stabilization of black-phase formamidinium lead iodide (α-FAPbI3) perovskite under various environmental conditions is considered necessary for solar cells. However, challenges remain regarding the temperature sensitivity of α-FAPbI3 and the requirements for strict humidity control in its processing. Here we report the synthesis of stable α-FAPbI3, regardless of humidity and temperature, based on a vertically aligned lead iodide thin film grown from an ionic liquid, methylamine formate. The vertically grown structure has numerous nanometer-scale ion channels that facilitate the permeation of formamidinium iodide into the lead iodide thin films for fast and robust transformation to α-FAPbI3. A solar cell with a power-conversion efficiency of 24.1% was achieved. The unencapsulated cells retain 80 and 90% of their initial efficiencies for 500 hours at 85°C and continuous light stress, respectively.

High-index crystal facets, denoted by a set of Miller indices {hkl} with at least one index greater than unity, possess a high density of low-coordinated atoms, steps, edges, and kinks that serve as highly active catalytic sites. [1][2][3] High-index surfaces normally grow faster than lowindex ones and are usually lost during crystal growth due to minimization of the total surface energy. Although the selective exposure of high-index facets at the surface is an important and challenging research topic, much progress has been made in the formation of many kinds of relevant noble metal nanocrystals, which have been extensively applied in catalytic reactions, including those in fuel cells, [4] photocatalysis, [5][6][7] electrocatalysis, [8,9] and petroleum catalytic reforming. [10] However, the generation of metal oxide micro-and nanocrystallites with high-index surfaces is comparatively more difficult due to the presence of strong metal-oxygen bonds and diverse crystal packing structures. [11] Only a few binary metal oxides, such as Co 3 O 4 , [12] anatase TiO 2 , [13][14][15] Fe 3 O 4 , [16] Cu 2 O, [17,18] and SnO 2 , [19] have been successfully achieved. Multinary metal oxide crystals are relatively more meaningful than binary ones because they not only possess more complex functions, but their properties also be readily adjusted by tuning the ratio of the component elements. Bismuth vanadate (BiVO 4 ) attracts intense interest as one of the most promising visible-light-active photocatalysts for water oxidation, due to its appropriate valence band edge located at ≈2.4 eV versus normal hydrogen electrode (NHE). [20] Varieties of morphological BiVO 4 , which are generally enclosed by lowindex {111}, {110}, or {100} planes, were formed through control of the synthetic methods and experimental conditions. [21][22][23] The photocatalytic behavior of BiVO 4 is highly dependent on its surface structure, in which photogenerated electrons and holes can be preferentially separated and accumulated on {010} and {110} facets, respectively, via the driving force created by the different band energies of the two facets. [24,25] Herein, we report the synthesis unprecedented 30-faceted BiVO 4 polyhedra predominantly surrounded by high-index {132}, {321}, and {121} facets. These BiVO 4 materials exhibit 3-5 time enhancements in O 2 evolution from photocatalytic water oxidation, relatively to that of low-indexed counterparts. Theory calculations reveal that the high-index surfaces are energetically favorable for water dissociation and exhibit a notable reduction in the overpotential (0.77-1.14 V) of the oxygen Unprecedented 30-faceted BiVO 4 polyhedra predominantly surrounded by {132}, {321}, and {121} high-index facets are fabricated through the engineering of high-index surfaces by a trace amount of Au nanoparticles. The growth of high-index facets results in a 3-5 fold enhancement of O 2 evolution from photocatalytic water splitting by the BiVO 4 polyhedron, relative to its low-index counterparts. Theory calculations reveal th...

A water oxidation side reaction on a photoelectrochemical charging supercapacitor is completely suppressed by controlling the thickness of a capacitive material.

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binding energy, and high charge transport mobility. [1] The record power conversion efficiency of solar cells based on perovskite materials have recently reached up to 25.5%, [2] not far off traditional crystalline silicon solar cells.In a typical perovskite solar cell, the perovskite layer is sandwiched between a transparent electrode and a reflective back electrode, and electron transport layer (ETL) and hole transport layer are usually inserted between the perovskite and the electrodes to facilitate majority charge transport and to block minority charge carriers. The performance of perovskite solar cells is strongly related to the properties of the charge transport layers, especially the underneath layer on which the perovskite was cast, such as ETL in case of conventional n-i-p device architecture. In particular, the polarity of the substrates determines the nature of perovskite layer and specifically its doping state (n, p, or intrinsic) near the charge-extraction layers, [3] and the surface energy and morphology of the underneath layer affects the crystallization of the perovskite thin films. In addition, the interface issues in terms of interfacial nonradiative recombination and energy level alignment between the ETL and perovskite play an important role in the device performance, hysteresis phenomenon, and operational stability of the corresponding solar cells. [4] Furthermore, the optical constant of the underneath layer determines the light incidence and optoelectric field distribution. [5] Solution-processed tin oxide (SnO 2 ) is ubiquitously used as the electron transport layer (ETL) in perovskite solar cells, while the main concerns related to the application of SnO 2 nanoparticles are the self-aggregation potential and infeasible energy level adjustment, leading to inhomogeneous thin films and mismatched energy alignment with perovskite. Herein, a novel route is developed by adding a functional titanium diisopropoxide bis(acetylacetonate) (TiAcAc) molecule, comprising TiO 4 4core, functional CO, and long alkene groups, into the SnO 2 nanoparticle solution, to optimize the electronic transfer property of SnO 2 for efficient perovskite solar cells. It is found that the TiO 4 4can be used to tune the electronic property of the SnO 2 layer, and the long alkenes can act as a stabilizer to avoid the nanoparticle aggregation and electronic glue among the SnO 2 nanoparticles in the eventual nanoparticulate thin film, enhancing its homogeneity and conductivity. Furthermore, the residual CO groups on the ETL surface can strongly associate with the Pb 2+ and improve the interface intimacy between the ETL and perovskite. As a result, the efficiency of perovskite solar cells can be boosted from 18% to above 20% with significantly reduced hysteresis by employing SnO 2 -TiAcAc as electron transport layer, indicating a great potential for efficient perovskite solar cells.

In the current study, novel environmentally friendly and interfacially active carbon nanotubes/SiO 2 nanomaterials (CNTs/SiO 2 ) for emulsified crude oil separation were prepared via grafting nano-SiO 2 on the surface of oxidized carbon nanotubes (Ox-CNTs). The structure of the as-prepared CNTs/SiO 2 was characterized by Fourier transform infrared spectroscopy, UV−visible absorption spectra, Raman spectra, X-ray diffraction spectra, thermogravimetric analysis, field-emission scanning electron microscope, and energy-dispersive X-ray spectroscopy. Besides, three-phase contact angles (θ) were employed to evaluate the wettability of CNTs/SiO 2 . Also, it was found that the θ value of CNTs/SiO 2 was about 90°. The nanomaterials with interfacial activity can spontaneously assemble at the oil−water interface, thus improving the droplet coalescence in the emulsion. Afterward, the demulsification performance was evaluated in crude-oil emulsions using the bottle test, which demonstrated that the demulsification efficiency demulsification efficiency could reach 87.40%. Also, the water phase was clear, while the optimum concentration and sedimentation time were 500 ppm and 30 min, respectively. Furthermore, the possible demulsification mechanism was evaluated by an optical microscope. The findings in this work might provide a novel environmentally friendly and interfacially active nanomaterial as a crude oil demulsifier.

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