Low-dimensional perovskite nanoplatelet synthesis using in situ photophysical monitoring to establish controlled growth.

Perovskite nanoparticles have attracted the attention of research groups around the world for their impressive photophysical properties, facile synthesis and versatile surface chemistry. Here, we report a synthetic route that takes advantage of a suite of soluble precursors to generate CsPbBr3 perovskite nanoplatelets with fine control over size, thickness and optical properties. We demonstrate near unit cell precision, creating well characterized materials with sharp, narrow emission lines at 430, 460 and 490 nm corresponding to nanoplatelets that are 2, 4, and 6 unit cells thick, respectively. Nanoplatelets were characterized with optical spectroscopy, atomic force microscopy, scanning electron microscopy and transmission electron microscopy to explicitly correlate growth conditions, thickness and resulting photophysical properties. Detailed in situ photoluminescence spectroscopic studies were carried out to understand and optimize particle growth by correlating light emission with nanoplatelet growth across a range of synthetic conditions. It was found that nanoplatelet thickness and emission wavelength increase as the ratio of oleic acid to oleyl amine or the reaction temperature is increased. Using this information, we control the lateral size, width and corresponding emission wavelength of the desired nanoplatelets by modulating the temperature and ratios of the ligand

General Thermal Texturization Process of MoS_2 for Efficient Electrocatalytic Hydrogen Evolution Reaction

Molybdenum disulfide (MoS_2) has been widely examined as a catalyst containing no precious metals for the hydrogen evolution reaction (HER); however, these examinations have utilized synthesized MoS_2 because the pristine MoS_2 mineral is known to be a poor catalyst. The fundamental challenge with pristine MoS_2 is the inert HER activity of the predominant (0001) basal surface plane. In order to achieve high HER performance with pristine MoS_2, it is essential to activate the basal plane. Here, we report a general thermal process in which the basal plane is texturized to increase the density of HER-active edge sites. This texturization is achieved through a simple thermal annealing procedure in a hydrogen environment, removing sulfur from the MoS_2 surface to form edge sites. As a result, the process generates high HER catalytic performance in pristine MoS_2 across various morphologies such as the bulk mineral, films composed of micron-scale flakes, and even films of a commercially available spray of nanoflake MoS_2. The lowest overpotential (η) observed for these samples was η = 170 mV to obtain 10 mA/cm_2 of HER current density

General Thermal Texturization Process of MoS_2 for Efficient Electrocatalytic Hydrogen Evolution Reaction

Molybdenum disulfide (MoS_2) has been widely examined as a catalyst containing no precious metals for the hydrogen evolution reaction (HER); however, these examinations have utilized synthesized MoS_2 because the pristine MoS_2 mineral is known to be a poor catalyst. The fundamental challenge with pristine MoS_2 is the inert HER activity of the predominant (0001) basal surface plane. In order to achieve high HER performance with pristine MoS_2, it is essential to activate the basal plane. Here, we report a general thermal process in which the basal plane is texturized to increase the density of HER-active edge sites. This texturization is achieved through a simple thermal annealing procedure in a hydrogen environment, removing sulfur from the MoS_2 surface to form edge sites. As a result, the process generates high HER catalytic performance in pristine MoS_2 across various morphologies such as the bulk mineral, films composed of micron-scale flakes, and even films of a commercially available spray of nanoflake MoS_2. The lowest overpotential (η) observed for these samples was η = 170 mV to obtain 10 mA/cm_2 of HER current density

Formation mechanism of Cu2ZnSnSe4 absorber layers during selenization of solution deposited metal precursors

Phase-pure Cu2ZnSnSe4 (CZTSe) layers are necessary for achieving efficient thin film solar cells. This requires the knowledge of intermediate phases and their existence regions during the evolution of the CZTSe phase within its homogeneity range. Here we investigate the growth mechanism of different phases when solution deposited metal salt precursors are selenized into CZTSe layers. A combination of in situ and ex situ X-ray diffraction, Raman spectroscopy, energy dispersive X-ray spectroscopy (EDX) and scanning electron microscopy at successively increasing substrate temperatures is used to track evolving crystal phases. The growth starts with the fast formation of binary Cu–Se phases that are present between 190 °C and 320 °C. Overlapping diffraction patterns of CZTSe/Cu2SnSe3/ZnSe phases evolve from 280 °C onwards and remain until a final temperature of 550 °C. The ternary Cu2SnSe3 phase co-existing with CZTSe between 340 °C and 370 °C is confirmed by Raman spectroscopy and point EDX measurements. No individual zinc or tin binary phases can be detected. We propose the kinetically driven formation mechanism, which starts with the selenization of Cu requiring the lowest activation energy for reaction, and then proceeds via the gradual incorporation of Sn and Zn to yield the final CZTSe phase