| 1. |
- Brophy, Rachel Elizabeth, et al.
(author)
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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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In: Journal of Physical Chemistry C. - 1932-7447 .- 1932-7455. ; 127:17, s. 7938-7943
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Journal article (peer-reviewed)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.
(author)
-
OH - ions can reduce the iodide migration in MAPI
- 2023
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In: Proceedings of the International Semiconductor Conference, CAS. ; , s. 139-142
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Conference paper (peer-reviewed)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. |
- Erlingsson, Sigurdur I., et al.
(author)
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Reversal of Thermoelectric Current in Tubular Nanowires
- 2017
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 119:3
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Journal article (peer-reviewed)abstract
- We calculate the charge current generated by a temperature bias between the two ends of a tubular nanowire. We show that in the presence of a transversal magnetic field the current can change sign; i.e., electrons can either flow from the hot to the cold reservoir, or in the opposite direction, when the temperature bias increases. This behavior occurs when the magnetic field is sufficiently strong, such that Landau and snaking states are created, and the energy dispersion is nonmonotonic with respect to the longitudinal wave vector. The sign reversal can survive in the presence of impurities. We predict this result for core-shell nanowires, for uniform nanowires with surface states due to the Fermi level pinning, and for topological insulator nanowires.
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| 4. |
- Sultan, Muhammad Taha, et al.
(author)
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Enhanced photoconductivity of SiGe nanocrystals in SiO2 driven by mild annealing
- 2019
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In: Applied Surface Science. - : ELSEVIER SCIENCE BV. - 0169-4332 .- 1873-5584. ; 469, s. 870-878
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Journal article (peer-reviewed)abstract
- Photosensitive films based on finely dispersed semiconductor nanocrystals (NCs) in dielectric films have great potential for sensor applications. Here we report on preparation and characterization of photosensitive Si1-xGex NCs sandwiched between SiO2 matrix. A radio-frequency magnetron sputtering was applied to obtain a multilayer-structures (MLs) by depositing SiO2/SiGe/SiO2 films on Si (0 0 1) substrate. The Si1-xGex NCs were formed by a post-deposition annealing at 100-700 degrees C for 1-5 min. The effect of annealing temperature and time on MLs morphology and NCs size and density was studied using grazing incidence X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy and measurements of spectral distribution of photocurrent. It is demonstrated how the photoconductive properties of the MLs can be enhanced and tailored by controlling the NCs formation conditions and the presence of stress field in MLs and defects acting as traps and recombination centers. All these features can be adjusted/controlled by altering the annealing conditions (temperature and time). The MLs photosensitivity was increased of more than an order of magnitude by the annealing process. A mechanism, where a competition between crystallization process (NCs formation and evolution i.e. size and shapes) and stress field appearance determines the peak position in the photocurrent spectra, was identified.
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