Search results for "passiv"
showing 10 items of 512 documents
Influence of an elastic stress on the conductivity of passive films
2001
Abstract The electrochemical impedance was measured over a large range of frequency and under straining condition in sodium chloride solution. The Mott-Schottky analysis, performed at high frequency, appears as very useful method to study the effect of an elastic stress on the capacitance values. The results obtained indicate that the semi-conductive properties of passive films formed on a type 316 L stainless steel (SS) are not markedly modified by an elastic stress when applied after ageing. In contrast, passive films formed in the presence of elastic stress have a higher donor and acceptor concentration than those formed in a stress-free state, suggesting that the passive film conductivi…
From Gold Nanoseeds to Nanorods: The Microscopic Origin of the Anisotropic Growth
2016
Directly manipulating and controlling the size and shape of metal nanoparticles is a key step for their tailored applications. In this work, molecular dynamics simulations were applied to understand the microscopic origin of the asymmetric growth mechanism in gold nanorods. Different factors influencing the growth were selectively included in the models to unravel the role of the surfactants and ions. In the early stage of the growth, when the seed is only a few nanometers large, a dramatic symmetry breaking occurs as the surfactant layer preferentially covers the (100) and (110) facets, leaving the (111) facets unprotected. This anisotropic surfactant layer in turn promotes anisotropic gro…
Tuning Charge Carrier Dynamics and Surface Passivation in Organolead Halide Perovskites with Capping Ligands and Metal Oxide Interfaces
2018
Organolead halide perovskites have emerged as exciting optoelectronic materials but a complete understanding of their photophysical properties is still lacking. Here, a morphological series of methylammonium lead bromide (MAPbBr 3 ) perovskites are studied by transient optical spectroscopies over eight orders of magnitude in timescale to investigate the effect of nanostructuring and surface states on the charge carrier dynamics. The sample preparation route and corresponding morphology changes influence the position of the optical features, recombination dynamics, excitation fluence dependence, and dramatically impact surface trap passivation. Growth of the perovskite layer in the presence …
New process of silicon carbide purification intended for silicon passivation
2017
Abstract In this work, we report on a new, efficient and low cost process of silicon carbide (SiC) powder purification intended to be used in photovoltaic applications. This process consists on the preparation of porous silicon carbide layers followed by a photo-thermal annealing under oxygen atmosphere and chemical treatment. The effect of etching time on impurities removal efficiency was studied. Inductively coupled plasma atomic emission spectrometry (ICP-AES) results showed that the best result was achieved for an etching time of 10 min followed by gettering at 900 °C during 1 h. SiC purity is improved from 3N (99.9771%) to 4N (99.9946%). Silicon carbide thin films were deposited onto s…
HCl gas gettering for crystalline silicon thin film solar cells
2011
Crystalline silicon thin film (cSiTF) solar cells could be an attractive alternative for standard silicon solar cells. Only a small amount of the expensive high purity silicon is needed for the epitaxial deposition on a low-cost silicon substrate made from e.g. metallurgical grade (MG) or upgraded metallurgical grade (UMG) silicon. The resulting product is called epitaxial wafer equivalent (EpiWE) because it can be processed in a standard wafer cell production. MG-Si and UMG-Si still contain a huge amount of metallic impurities. These impurities have to be removed by gettering methods in order to prevent diffusion into the highly pure active silicon layer during the high-temperature deposit…
Minority Carrier Lifetime Variations in Multicrystalline Silicon Wafers with Temperature and Ingot Position
2017
The minority carrier lifetimes of multicrystalline silicon wafers are mapped using microwave photoconductive decay for different temperatures and ingot positions. Wafers from the top of the ingot display larger areas with lower lifetimes compared to wafers from the bottom. The lifetimes of low-lifetime areas are found to increase with the temperature, while the lifetimes of some high-lifetime areas decrease or remain unchanged. The relative improvement of the low-lifetime areas is considerably larger than the relative change in the high-lifetime areas. We suggest that the above-mentioned observations explain, at least partially, why previous studies have found the relative temperature coeff…
Temperature Sensitivity of Multicrystalline Silicon Solar Cells
2019
This paper presents an experimental investigation of the temperature coefficients of multicrystalline silicon solar cells. The aim was to determine if some cell parameters can affect positively the temperature sensitivity without detrimental impact on the efficiency. Commercial solar cells with different bulk resistivities, compensation levels, and cell architectures have been studied. We report that the base net doping, the location of the solar cell along the brick and the cell architecture have significant impacts on the temperature coefficients. Moreover, we show how the change in recombination mechanisms along the ingot height affects the temperature coefficients. The compensation leve…
Improved stability of black silicon detectors using aluminum oxide surface passivation
2021
Publisher Copyright: © 2021 ESA and CNES We have studied how high-energy electron irradiation (12 MeV, total dose 66 krad(Si)) and long term humidity exposure (75%, 75 °C, 500 hours) influence the induced junction black silicon or planar photodiode characteristics. In our case, the induced junction is formed using n-type silicon and atomic-layer deposited aluminum oxide (Al2O3), which contains a large negative fixed charge. We compare the results with corresponding planar pn-junction detectors passivated with either with silicon dioxide (SiO2) or Al2O3. The results show that the induced junction detectors remain stable as their responsivity remains nearly unaffected during the electron beam…
Anisotropic optical response of GaN and AlN nanowires.
2012
We present a theoretical study of the electronic structure and optical properties of free-standing GaN and AlN nanowires. We have implemented the empirical tight-binding method, with an orbital basis sp(3), that includes the spin-orbit interaction. The passivation of the dangling bonds at the free surfaces is also studied, together with the effects on the electronic structure of the nanowire. For both GaN and AlN nanowires, we have found a remarkable anisotropy of the optical absorption when the light-polarization changes, showing in the case of GaN a dependence on the nanowire size.
Reduced Recombination Losses in Evaporated Perovskite Solar Cells by Postfabrication Treatment
2021
The photovoltaic perovskite research community has now developed a large set of tools and techniques to improve the power conversion efficiency (PCE). One such arcane trick is to allow the finished devices to dwell in time, and the PCE often improves. Herein, a mild postannealing procedure is implemented on coevaporated perovskite solar cells confirming a substantial PCE improvement, mainly attributed to an increased open-circuit voltage (V\(_{OC}\)). From a V\(_{OC}\) of around 1.11 V directly after preparation, the voltage improves to more than 1.18 V by temporal and thermal annealing. To clarify the origin of this annealing effect, an in-depth device experimental and simulation character…