Showing papers by "Ludvik Martinu published in 2016"

Alkali Metal Halide Salts as Interface Additives to Fabricate Hysteresis-Free Hybrid Perovskite-Based Photovoltaic Devices

Abstract: A new method was developed for doping and fabricating hysteresis-free hybrid perovskite-based photovoltaic devices by using alkali metal halide salts as interface layer additives. Such salt layers introduced at the perovskite interface can provide excessive halide ions to fill vacancies formed during the deposition and annealing process. A range of solution-processed halide salts were investigated. The highest performance of methylammonium lead mixed-halide perovskite device was achieved with a NaI interlayer and showed a power conversion efficiency of 12.6% and a hysteresis of less than 2%. This represents a 90% improvement compared to control devices without this salt layer. Through depth-resolved mass spectrometry, optical modeling, and photoluminescence spectroscopy, this enhancement is attributed to the reduction of iodide vacancies, passivation of grain boundaries, and improved hole extraction. Our approach ultimately provides an alternative and facile route to high-performance and hysteresis-free p...

Ultralow refractive index optical films with enhanced mechanical performance obtained by hybrid glancing angle deposition.

Abstract: Ultralow refractive index materials (n less than 1.38 at 550 nm) are of particular interest in the context of antireflective coatings, allowing one to enhance their overall optical performance. However, application of such materials is typically limited by their mechanical properties. In this study, we explore the characteristics of a new category of hybrid (organic/inorganic) SiOCH thin films prepared by glancing angle deposition (GLAD) using electron beam evaporation of SiO2 in the presence of an organosilicon precursor. The resulting layers exhibited n as low as 1.2, showed high elastic rebound, and generally better mechanical properties than their inorganic counterparts. In addition, hybrid GLAD films were found to be highly hydrophobic. The performance of the films is discussed in terms of their hybridicity (organic/inorganic) ratio determined by infrared spectroscopic ellipsometry as well as the presence of anisotropy assessed by the nanostructure-based spectroscopic ellipsometry model. Finally, we demonstrate successful implementation of the ultralow-index material in a complete antireflective stack.

Wear properties of Fe3Al-based HVOF coatings strengthened with in-situ precipitated nitride and boride particles

Abstract: Iron aluminide coatings reinforced with in-situ precipitated TiN, TiB2 and Fe2B particles were synthesized from Fe3Al, BN and Ti powders using a combination of high-energy ball milling and high velocity oxy-fuel (HVOF) process. In the present work, we investigate the effect of the BN/Ti contents on the microstructure and characteristics of the HVOF coatings and we discuss their tribological properties. The microstructure and composition of powders and coatings were investigated using X-ray diffraction, differential thermal analysis and optical and scanning electron microscopies. The wear rate was evaluated by tribometry in a pin-on-disc configuration, and the mechanical properties were obtained using indentations. X-ray analysis of the coatings prepared from the as-milled powders revealed evidence of TiN, TiB2 and Fe2B peaks. The microhardness (4.3 GPa) and the wear resistance (3 × 10− 4 mm3/Nm) of the coating prepared from the pure Fe3Al powder were increased 3.3 times and by about three orders of magnitude, respectively, when 70 wt% of Fe3Al was milled with 10 wt% of BN and 20 wt% of Ti. Fatigue and abrasive wear were found to be the predominant degradation mechanisms during sliding against an alumina ball of the pure Fe3Al and composite HVOF coatings, respectively. Adhesive wear also contributed to the material loss as confirmed by EDS analysis that revealed a transfer of the coating material to the counterpart.

Continuous ultrathin silver films deposited on SiO2 and SiNx using a self-assembled monolayer

Abstract: In this letter, we study the deposition of ultrathin silver films on silicon oxide and nitride surfaces functionalized with self-assembled monolayers of (3-mercaptopropyl)-trimethoxysilane. First, we compare both solution and vapour-phase functionalization techniques and find the greatest improvement in electrical and optical properties using deposition from solution. Using X-ray photoelectron spectroscopy, we demonstrate that the formation of silver-sulfur covalent bonds is at the root of the improved wetting confirmed by ellipsometry, sheet resistance measurement, and atomic force microscopy. Second, we show that this technique can be extended to functionalize silicon nitride. Finally, we demonstrate a simple, but efficient, low-emissivity optical filter.

Flash post-discharge emission in a reactive HiPIMS process

Abstract: In the present work, time-, space- and species-resolved optical emission spectroscopy has been applied to investigate post-pulse behavior of the reactive High Power Impulse Magnetron Sputtering (HiPIMS) process with a partially poisoned target. Following each pulse, at a high O2/Ar ratio, a well-defined post-discharge emission zone detaches from the target during the first few microseconds of the electron cool-down; this zone exhibits high emission intensity in the near-surface region, and it moves toward the substrate holder. We link this behavior to a localized high density of metastable molecular oxygen, and to the electron attachment dissociation of oxygen.

Low Emissivity Coatings Incorporating Thermochromic VO2: Performance Enhancement and New opportunities

Abstract: Thermochromic VO2 films are of interest for energy saving applications. Incorporating VO2 in a typical low emissivity-type structure (dielectric|VO2|Ag|dielectric) one can obtain a higher luminance transmittance Tlum while maintaining a respectable solar transmission variation Tsol vs. temperature. Samples possessing a Tlum of over 50%, a Tsol higher than 5% and a low emissivity in the infrared are demonstrated.

Optical Films with Enhanced Mechanical Performance Obtained by Hybrid Glancing Angle Deposition

Abstract: Optical and mechanical properties of organic/inorganic thin films prepared by glancing angle deposition of SiO2 and WO3, in the presence of vapors of an organosilicon compound are discussed and correlated with their composition and microstructure.