| 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, et al.
(författare)
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On the role of ion potential energy in low energy HiPIMS deposition : An atomistic simulation
- 2021
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Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 426
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Tidskriftsartikel (refereegranskat)abstract
- We study the effect of the so-called ion potential or non-kinetic energies of bombarding ions during ionized physical vapor deposition of Cu using molecular dynamics simulations. In particular we focus on low energy high power impulse magnetron sputtering (HiPIMS) deposition, in which the potential energy of ions can be comparable to their kinetic energy. The ion potential, as a short-ranged repulsive force between the ions of the film-forming material and the surface atoms (substrate and later deposited film), is defined by the Ziegler-Biersack-Littmark potential. Analyzing the final structure indicates that, including the ion potential leads to a slightly lower interface mixing and fewer point defects (such as vacancies and interstitials), but resputtering and twinning have increased slightly. However, by including the ion potential the collision pattern changes. We also observed temporary formation of a ripple/pore with 5 nm height when the ion potential is included. The latter effect can explain the pores that have been observed experimentally in HiPIMS deposited Cu thin films by atomic force microscopy.
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| 4. |
- Sultan, Muhammad Taha, et al.
(författare)
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Structural and photoluminescence study of TiO2 layer with self-assembled Si1-xGex nanoislands
- 2020
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 128:8
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Tidskriftsartikel (refereegranskat)abstract
- We study the surface morphology and growth process of SiGe nanoislands on TiO2 films, deposited over Si (001) substrates by high power impulse magnetron sputtering, followed by varying annealing parameters (i.e., 500-750 degrees C for 30min to 20h). Structural analysis was performed by atomic force microscopy, scanning electron microscopy, and grazing incidence x-ray diffraction. Two structural schemes were taken into consideration, i.e., SiGe grown over pre-annealed TiO2 (scheme I) and as-grown TiO2 (scheme II). Photoluminescence (PL) study of the structures revealed spectral features comprised of multiple peak features related to localized and surface states within the oxide layer, along with a peak due to the SiGe nano-islands. It was observed that the spectral feature and intensity depend on the surface morphology and the crystallinity of the underlying TiO2 layer. The structures were subjected to low temperature PL measurements, and the spectra were de-convoluted in order to validate the origin of the obtained spectra. Structural analysis revealed that pre-annealing the underlying polycrystalline TiO2 film, prior to deposition of SiGe layers (scheme I), facilitates the formation of SiGe nanoislands, preferably along the grain boundaries (due to their higher interfacial energy). In comparison, for the case of SiGe deposited over as-grown TiO2 (scheme II), annealing of the structure resulted in random distribution of nanoislands across the entire film. The size of the nanoislands grew with increased annealing time up until the point they started to coalesce, forming discontinuous SiGe layers and eventually leading to melting of the layer.
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