Search results for "Passivation"
showing 10 items of 91 documents
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…
Molecular Passivation of MoO3: Band Alignment and Protection of Charge Transport Layers in Vacuum-Deposited Perovskite Solar Cells
2019
Vacuum-deposition of perovskite solar cells can achieve efficiencies rivalling solution-based methods and it allows for more complex device stacks. MoO3 has been used to enhance carrier extraction to the transparent bottom electrode in a p-i-n configuration, here we show that by inserting an organic charge transport molecule it can also be used on the top of a perovskite absorber in a n-i-p configuration. This strategy enables the first vacuum-deposited perovskite solar cells with metal oxides as charge transporting layers for both electrons and holes leading to power conversion efficiency > 19 %.
Mass‐Spectrometric Imaging of Electrode Surfaces—a View on Electrochemical Side Reactions
2020
Abstract Electrochemical side reactions, often referred to as “electrode fouling”, are known to be a major challenge in electro‐organic synthesis and the functionality of modern batteries. Often, polymerization of one or more components is observed. When reaching their limit of solubility, those polymers tend to adsorb on the surface of the electrode, resulting in a passivation of the respective electrode area, which may impact electrochemical performance. Here, matrix‐assisted laser‐desorption/ionization mass spectrometry (MALDI‐MS) is presented as valuable imaging technique to visualize polymer deposition on electrode surfaces. Oligomer size distribution and its dependency on the contact …
Incorporation of potassium halides in the mechanosynthesis of inorganic perovskites: feasibility and limitations of ion-replacement and trap passivat…
2018
Potassium halides (KX; X = I, Br, or Cl) were incorporated as partial replacements of CsBr in the mechanosynthesis of CsPbBr3. This led to partial substitution of both monovalent ions forming mixed Cs1−xKxPbBr3−yXy perovskites. Longer photoluminescence lifetimes were also observed, possibly linked to the formation of a non-perovskite KPb2X5 passivating layer.
Highly photoluminescent, dense solid films from organic-capped CH3NH3PbBr3 perovskite colloids
2018
The preparation of densely-packed films from hybrid lead halide perovskite nanocrystals is not trivial, as during assembly into the solid state both the charge transport and photoluminescence can be substantially altered. The objective of the present study was to retain the pre-engineered confined morphologies of hybrid lead halide perovskite nanocrystals in densely-packed solid films by using short organic ligands. Therefore, the roles of the organic ligands would be to provide stable colloids and a good passivation of the nanoparticle surface, as well as to enable the efficient assembly of the nanoparticles in the solid state. We report here an effective and reproducible process to deposi…
Efficient Photo- and Electroluminescence by Trap States Passivation in Vacuum-Deposited Hybrid Perovskite Thin Films
2018
Methylammonium lead iodide (MAPI) has excellent properties for photovoltaic applications, although it typically shows low photoluminescence quantum yield. Here, we report on vacuum-deposited MAPI perovskites obtained by modifying the methylammonium iodide (MAI) to PbI2 ratio during vacuum deposition. By studying the excitation density dependence of the photoluminescence lifetime, a large concentration of trap states was deduced for the stoichiometric MAPI films. The use of excess MAI during vacuum processing is capable of passivating these traps, resulting in luminescent films which can be used to fabricate planar light-emitting diodes with quantum efficiency approaching 2%.
Mechanism of large oscillations of anodic potential during anodization of silicon in H3PO4/HF solutions
2000
Abstract Effect of large oscillations of electrical potential during anodic polarization of silicon in electrolytes composed of phosphoric and hydrofluoric acids has been reported. The oscillations last hours without damping if experimental conditions are optimal. Changes of temperature, anodic current density, intensity of stirring, etc. quench them or convert into less periodic ones. The oscillations are of very high amplitude (typically 15 V) with a period ranging from 18 to 30 s. Scanning electron microscopy (SEM)-imaging of the samples experiencing the oscillatory kinetic behaviour shows unambiguously that the stage of the anodic voltage growth is assisted by the formation of a thin (5…