| 1. |
- Brophy, Rachel Elizabeth, et al.
(författare)
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Effect of Pressure on the Dynamics of Iodide Defects in Methylammonium Lead Iodide: An Atomistic Simulation
- 2023
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Ingår i: Journal of Physical Chemistry C. - 1932-7447 .- 1932-7455. ; 127:17, s. 7938-7943
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Tidskriftsartikel (refereegranskat)abstract
- The diffusion of iodide defects has been considered the most important degradation mechanism of methylammonium lead iodide (MAPI) in solar cells. The present study demonstrates the importance of the pressure inside this material on the dynamics of iodide defects, using molecular dynamics simulations. It is known that the diffusion coefficient of an iodide vacancy is an order of magnitude higher than that of interstitial iodide. We show that this difference systematically increases with increased tensile strain and that both diffusion coefficients tend to zero when a compressive strain is applied. This result suggests that compression of the MAPI can be a good solution to reduce its degradation rate. Besides, the statistical aspect of deriving the diffusion coefficient from the mean squared displacement (MSD) is discussed in terms of the initial conditions (positions and velocities) of the atoms and the simulation time, considering different seeds of the pseudorandom number generator used in the simulations performed with the LAMMPS software.
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| 2. |
- Brophy, Rachel Elizabeth, et al.
(författare)
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OH - ions can reduce the iodide migration in MAPI
- 2023
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Ingår i: Proceedings of the International Semiconductor Conference, CAS. ; , s. 139-142
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Konferensbidrag (refereegranskat)abstract
- One of the main degradation mechanisms of methylammonium lead iodine (MAPI), which is an important material for perovskite based solar cells, is the migration of iodide ions. It is believed that this phenomenon is in fact dominated by the diffusion of iodide vacancies. In this paper, we suggest that the addition of a small amount of OH- ions can help suppress the migration of iodide and increase the overall stability of the material. Through the use of molecular dynamics simulations, we show that the OH- ions can bind to the positively charged iodide vacancies and can block the access of the negative iodide ions into those vacancies.
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| 3. |
- Kateb, Movaffaq, 1985, et al.
(författare)
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Epitaxial growth and characterization of (001) [NiFe/M]20 (M = Cu, CuPt and Pt) superlattices
- 2023
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Ingår i: Surfaces and Interfaces. - : Elsevier BV. - 2468-0230. ; 38
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Tidskriftsartikel (refereegranskat)abstract
- We present optimization of [(15 Å) Ni80Fe20/(5 Å) M]20 single crystal multilayers on (001) MgO substrates, with M being Cu, Cu50Pt50 and Pt. These superlattices were characterized by high resolution X-ray reflectivity (XRR) and diffraction (XRD) as well as polar mapping of important crystal planes. It is shown that cube on cube epitaxial relationship can be obtained when depositing at substrate temperature of 100 °C regardless of the lattice mismatch (5% and 14% for Cu and Pt, respectively). At lower substrate temperatures poly-crystalline multilayers were obtained while at higher substrate temperatures {111} planes appear at ∼10° off normal to the film plane. It is also shown that as the epitaxial strain increases, the easy magnetization axis rotates towards the direction that previously was assumed to be harder, i.e. from [110] to [100], and eventually further increase in the strain makes the magnetic hysteresis loops isotropic in the film plane. Higher epitaxial strain is also accompanied with increased coercivity values. Thus, the effect of epitaxial strain on the magnetocrystalline anisotropy is much larger than what was observed previously in similar, but polycrystalline samples with uniaxial anisotropy (Kateb et al. 2021).
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| 4. |
- Kateb, Movaffaq, 1985, et al.
(författare)
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Nanoscale Elasto-Capillarity in the Graphene-Water System under Tension: Revisiting the Assumption of a Constant Wetting Angle
- 2023
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Ingår i: Langmuir. - 1520-5827 .- 0743-7463. ; 39, s. 12610-12617
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Tidskriftsartikel (refereegranskat)abstract
- Wetting highly compliant surfaces can cause them to deform. Atomically thin materials, such as graphene, can have exceptionally small bending rigidities, leading to elasto-capillary lengths of a few nanometers. Using large-scale molecular dynamics (MD), we have studied the wetting and deformation of graphene due to nanometer-sized water droplets, focusing on the wetting angle near the vesicle transition. Recent continuum theories for wetting of flexible membranes reproduce our MD results qualitatively well. However, we find that when the curvature is large at the triple-phase contact line, the wetting angle increases with decreasing tension. This is in contrast to existing macroscopic theories but can be amended by allowing for a variable wetting angle.
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