Origin of Persisting Photoresponse of One-Year Aged Two-Dimensional Lead Halide Perovskites Stored in Air under Dark Conditions.

Two-dimensional halide perovskites are promising for advanced photonic, optoelectronic, and photovoltaic applications. However, their long-term stability is still a critical factor limiting their implementation into further commercial applications. Here, we present an environmental stability analysis of BA(MA)PbI (BA = CHN, MA = CHN) two-dimensional perovskites with the lowest quantum well thicknesses of = 1 and = 2, after 1 year of aging under ambient humidity, oxygen content, and light conditions.

Revealing Intrinsic Functionalization, Structure, and Photo-Thermal Oxidation in Hexagonal Antimonene.

Antimonene is one of the more exciting members of the post-graphene family with promising applications in optoelectronics, energy storage and conversion, catalysis, sensing or biomedicine. Efforts have been focused on developing a large-scale production route, and indeed, through a colloidal approach, high-quality few-layers antimonene (FLA) hexagons have been recently obtained. However, their oxidation behavior remains unexplored, as well as their interface, inner structure, and photothermal properties.

Elastic and inelastic strain in submicron-thick ZnO epilayers grown on r-sapphire substrates by metal-organic vapour phase deposition.

A significant part of the present and future of optoelectronic devices lies on thin multilayer heterostructures. Their optical properties depend strongly on strain, being essential to the knowledge of the stress level to optimize the growth process. Here the structural and microstructural characteristics of sub-micron a-ZnO epilayers (12 to 770 nm) grown on r-sapphire by metal-organic chemical vapour deposition are studied.

Revealing Giant Exciton Fine-Structure Splitting in Two-Dimensional Perovskites Using van der Waals Passivation.

Organic-inorganic layered perovskites are currently some of the most promising 2D van der Waals materials. Low crystal quality usually broadens the exciton line width, obscuring the fine structure of the exciton in conventional photoluminescence experiments. Here, we propose a mechanical approach to reducing the effect of spectral diffusion by means of hBN capping on layered perovskites, revealing the exciton fine structure.

Tin perovskite solar cells with >1,300 h of operational stability in N through a synergistic chemical engineering approach.

Despite the promising properties of tin-based halide perovskites, one clear limitation is the fast Sn oxidation. Consequently, the preparation of long-lasting devices remains challenging. Here, we report a chemical engineering approach, based on adding Dipropylammonium iodide (DipI) together with a well-known reducing agent, sodium borohydride (NaBH), aimed at preventing the premature degradation of Sn-HPs.

Boosting Long-Term Stability of Pure Formamidinium Perovskite Solar Cells by Ambient Air Additive Assisted Fabrication.

Due to the high industrial interest for perovskite-based photovoltaic devices, there is an urgent need to fabricate them under ambient atmosphere, not limited to low relative humidity (RH) conditions. The formamidinium lead iodide (FAPI) perovskite α-black phase is not stable at room temperature and is challenging to stabilize in an ambient environment. In this work, we show that pure FAPI perovskite solar cells (PSCs) have a dramatic increase of device long-term stability when prepared under ambient air compared to FAPI PSCs made under nitrogen, both fabricated with -methylpyrrolidone (NMP).

Extrinsic Effects on the Optical Properties of Surface Color Defects Generated in Hexagonal Boron Nitride Nanosheets.

Hexagonal boron nitride (hBN) is a wide-band gap van der Waals material able to host light-emitting centers behaving as single photon sources. Here, we report the generation of color defects in hBN nanosheets dispersed on different kinds of substrates by thermal treatment processes. The optical properties of these defects have been studied using microspectroscopy techniques and far-field simulations of their light emission.

Two-Dimensional Indium Selenide for Sulphur Vapour Sensing Applications.

Surface-to-volume ratio in two-dimensional (2D) materials highlights among their characteristics as an inherent and intrinsic advantage taking into account their strong sensitivity to surface effects. For this reason, we have proposed in this work micromechanically exfoliated 2D nanosheets of InSe as an optical vapour sensor. As a proof of concept, we used 2-mercaptoethanol as the chemical analyte in vapour phase to monitor the change of the InSe photoluminescence (PL) before and after exposure to the analyte.

Out-of-plane orientation of luminescent excitons in two-dimensional indium selenide.

Van der Waals materials offer a wide range of atomic layers with unique properties that can be easily combined to engineer novel electronic and photonic devices. A missing ingredient of the van der Waals platform is a two-dimensional crystal with naturally occurring out-of-plane luminescent dipole orientation. Here we measure the far-field photoluminescence intensity distribution of bulk InSe and two-dimensional InSe, WSe and MoSe.

Optical Contrast and Raman Spectroscopy Techniques Applied to Few-Layer 2D Hexagonal Boron Nitride.

The successful integration of few-layer thick hexagonal boron nitride (hBN) into devices based on two-dimensional materials requires fast and non-destructive techniques to quantify their thickness. Optical contrast methods and Raman spectroscopy have been widely used to estimate the thickness of two-dimensional semiconductors and semi-metals. However, they have so far not been applied to two-dimensional insulators.

Formation of Si/SiO Luminescent Quantum Dots From Mesoporous Silicon by Sodium Tetraborate/Citric Acid Oxidation Treatment.

We propose a rapid, one-pot method to generate photoluminescent (PL) mesoporous silicon nanoparticles (PSiNPs). Typically, mesoporous silicon (meso-PSi) films, obtained by electrochemical etching of monocrystalline silicon substrates, do not display strong PL because the silicon nanocrystals (nc-Si) in the skeleton are generally too large to display quantum confinement effects. Here we describe an improved approach to form photoluminescent PSiNPs from meso-PSi by partial oxidation in aqueous sodium borate (borax) solutions.

Enhancing the photocatalytic properties of PbS QD solids: the ligand exchange approach.

Surface engineering of nanomaterials is a promising tool towards the design of new materials for conversion of solar energy into chemical energy. In this work, we examine the influence of ligand exchange on the photocatalytic performance of solution-processed PbS films. We test different ligands such as oleylamine (OAm), 1,2-ethanedithiol (EDT), 3-mercaptopropionic acid (MPA) and tetrabutylammonium iodide (TBAI).

Charge Transport in Trap-Sensitized Infrared PbS Quantum-Dot-Based Photoconductors: Pros and Cons.

Control of quantum-dot (QD) surface chemistry offers a direct approach for the tuning of charge-carrier dynamics in photoconductors based on strongly coupled QD solids. We investigate the effects of altering the surface chemistry of PbS QDs in such QD solids via ligand exchange using 3-mercaptopropionic acid (MPA) and tetrabutylammonium iodide (TBAI). The roll-to-roll compatible doctor-blade technique was used for the fabrication of the QD solid films as the photoactive component in photoconductors and field-effect phototransistors.

Quantum size confinement in gallium selenide nanosheets: band gap tunability versus stability limitation.

Gallium selenide is one of the most promising candidates to extend the window of band gap values provided by existing two-dimensional semiconductors deep into the visible potentially reaching the ultraviolet. However, the tunability of its band gap by means of quantum confinement effects is still unknown, probably due to poor nanosheet stability. Here, we demonstrate that the optical band gap band of GaSe nanosheets can be tuned by ∼120 meV from bulk to 8 nm thick.

Ultrapure laser-synthesized Si nanoparticles with variable oxidation states for biomedical applications.

We employ a method of femtosecond laser fragmentation of preliminarily prepared water-dispersed microcolloids to fabricate aqueous solutions of ultrapure bare Si-based nanoparticles (Si-NPs) and assess their potential for biomedical applications. The nanoparticles appear spherical in shape, with low size dispersion and a controllable mean size, from a few nm to several tens of nm, while a negative surface charge (-35 mV ± 0.10 according to z-potential data) provides good electrostatic stabilization of colloidal Si-NP solutions.

111 oriented gold nanoplatelets on multilayer graphene as visible light photocatalyst for overall water splitting.

Development of renewable fuels from solar light appears as one of the main current challenges in energy science. A plethora of photocatalysts have been investigated to obtain hydrogen and oxygen from water and solar light in the last decades. However, the photon-to-hydrogen molecule conversion is still far from allowing real implementation of solar fuels.

Nanotexturing To Enhance Photoluminescent Response of Atomically Thin Indium Selenide with Highly Tunable Band Gap.

Manipulating properties of matter at the nanoscale is the essence of nanotechnology, which has enabled the realization of quantum dots, nanotubes, metamaterials, and two-dimensional materials with tailored electronic and optical properties. Two-dimensional semiconductors have revealed promising perspectives in nanotechnology. However, the tunability of their physical properties is challenging for semiconductors studied until now.

Reversible chemisorption of sulfur dioxide in a spin crossover porous coordination polymer.

The chemisorption of sulfur dioxide (SO2) on the Hofmann-like spin crossover porous coordination polymer (SCO-PCP) {Fe(pz)[Pt(CN)4]} has been investigated at room temperature. Thermal analysis and adsorption-desorption isotherms showed that ca. 1 mol of SO2 per mol of {Fe(pz)[Pt(CN)4]} was retained in the pores.