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Imani, Roghayeh
Publications (5 of 5) Show all publications
Abdi-Jalebi, M., Pazoki, M., Philippe, B., Dar, M. I., Alsari, M., Sadhanala, A., . . . Friend, R. H. (2018). Dedoping of Lead Halide Perovskites Incorporating Monovalent Cations. ACS Nano, 12(7), 7301-7311
Open this publication in new window or tab >>Dedoping of Lead Halide Perovskites Incorporating Monovalent Cations
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2018 (English)In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 12, no 7, p. 7301-7311Article in journal (Refereed) Published
Abstract [en]

We report significant improvements in the optoelectronic properties of lead halide perovskites with the addition of monovalent ions with ionic radii close to Pb2+. We investigate the chemical distribution and electronic structure of solution processed CH3NH3PbI3 perovskite structures containing Na+, Cu+, and Ag+, which are lower valence metal ions than Pb2+ but have similar ionic radii. Synchrotron X-ray diffraction reveals a pronounced shift in the main perovskite peaks for the monovalent cation-based films, suggesting incorporation of these cations into the perovskite lattice as well as a preferential crystal growth in Ag+ containing perovskite structures. Furthermore, the synchrotron X-ray photoelectron measurements show a significant change in the valence band position for Cu- and Ag-doped films, although the perovskite bandgap remains the same, indicating a shift in the Fermi level position toward the middle of the bandgap. Such a shift infers that incorporation of these monovalent cations dedope the n-type perovskite films when formed without added cations. This dedoping effect leads to cleaner bandgaps as reflected by the lower energetic disorder in the monovalent cation-doped perovskite thin films as compared to pristine films. We also find that in contrast to Ag+ and Cu+, Na+ locates mainly at the grain boundaries and surfaces. Our theoretical calculations confirm the observed shifts in X-ray diffraction peaks and Fermi level as well as absence of intrabandgap states upon energetically favorable doping of perovskite lattice by the monovalent cations. We also model a significant change in the local structure, chemical bonding of metal-halide, and the electronic structure in the doped perovskites. In summary, our work highlights the local chemistry and influence of monovalent cation dopants on crystallization and the electronic structure in the doped perovskite thin films.

Keywords
monovalent cations, dedoped perovskite thin films, enhanced optoelectronic quality, substitutional doping, interstitial doping
National Category
Materials Chemistry Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-364505 (URN)10.1021/acsnano.8b03586 (DOI)000440505000097 ()29953817 (PubMedID)
Funder
Swedish Research CouncilSwedish Energy AgencySwedish Foundation for Strategic Research StandUpEU, Horizon 2020, 687008Swedish National Infrastructure for Computing (SNIC), snice 2017-01-15; snice 2016-10-23
Available from: 2018-11-05 Created: 2018-11-05 Last updated: 2019-02-19Bibliographically approved
Imani, R., Qiu, Z., Younesi, R., Pazoki, M., Fernandes, D. L. A., Mitev, P. D., . . . Tian, H. (2018). Unravelling in-situ formation of highly active mixed metal oxide CuInO2 nanoparticles during CO2 electroreduction. Nano Energy, 49, 40-50
Open this publication in new window or tab >>Unravelling in-situ formation of highly active mixed metal oxide CuInO2 nanoparticles during CO2 electroreduction
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2018 (English)In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 49, p. 40-50Article in journal (Refereed) Published
Abstract [en]

Technologies and catalysts for converting carbon dioxide (CO2) to immobile products are of high interest to minimize greenhouse effects. Copper(I) is a promising catalytic active state of copper but hampered by the inherent instability in comparison to copper(II) or copper(0). Here, we report a stabilization of the catalytic active state of copper(I) by the formation of a mixed metal oxide CuInO2 nanoparticle during the CO2 electroreduction. Our result shows the incorporation of nanoporous Sn:In2O3 interlayer to Cu2O pre-catalyst system lead to the formation of CuInO2 nanoparticles with remarkably higher activity for CO2 electroreduction at lower overpotential in comparison to the conventional Cu nanoparticles derived from sole Cu2O. Operando Raman spectroelectrochemistry is employed to in-situ monitor the process of nanoparticles formation during the electrocatalytic process. The experimental data are collaborated with DFT calculations to provide insight into the electro-formation of the type of Cu-based mixed metal oxide catalyst during the CO2 electroreduction, where a formation mechanism via copper ion diffusion across the substrate is suggested.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2018
Keywords
Cuprous oxide, Copper indium oxide, CO2 electroreduction, Operando Raman spectroelectrochemistry, Density functional theory
National Category
Physical Chemistry Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-358275 (URN)10.1016/j.nanoen.2018.04.013 (DOI)000434829500006 ()
Funder
Stiftelsen Olle Engkvist ByggmästareGöran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of TechnologyJ. Gust. Richert stiftelseSwedish National Infrastructure for Computing (SNIC), 2017-1-57Swedish National Infrastructure for Computing (SNIC), 2016-10-23
Available from: 2018-08-30 Created: 2018-08-30 Last updated: 2019-03-29Bibliographically approved
Pazoki, M., Röckert, A., Wolf, M. J., Imani, R., Edvinsson, T. & Kullgren, J. (2017). Electronic structure of organic–inorganic lanthanide iodide perovskite solar cell materials. Journal of Materials Chemistry A, 5, 23131-23138
Open this publication in new window or tab >>Electronic structure of organic–inorganic lanthanide iodide perovskite solar cell materials
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2017 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 5, p. 23131-23138Article in journal (Refereed) Published
Abstract [en]

The emergence of highly efficient lead halide perovskite solar cell materials makes the exploration and engineering of new lead free compounds very interesting both from a fundamental perspective as well as for potential use as new materials in solar cell devices. Herein we present the electronic structure of several lanthanide (La) based materials in the metalorganic halide perovskite family not explored before. Our estimated bandgaps for the lanthanide (Eu, Dy, Tm, Yb) perovskite compounds are in the range of 2.0–3.2 eV showing the possibility for implementation as photo-absorbers in tandem solar cell configurations or charge separating materials. We have estimated the typical effective masses of the electrons and holes for MALaI3 (La= Eu, Dy, Tm, Yb) to be in the range of 0.3–0.5 and 0.97–4.0 units of the free electron mass, respectively. We have shown that the localized f-electrons within our DFT+U approach, make the dominant electronic contribution to the states at the top of the valence band and thus have a strong impact on the photo-physical properties of the lanthanide perovskites. Therefore, the main valence to conduction band electronic transition for MAEuI3 is based on inner shell f-electron localized states within a periodic framework of perovskite crystal by which the optical absorption onset would be rather inert with respect to quantum confinement effects. The very similar crystal structure and lattice constant of the lanthanide perovskites to the widely studied CH3NH3PbI3 perovskite, are prominent advantages for implementation of these compounds in tandem or charge selective contacts in PV applications together with lead iodide perovskite devices

National Category
Physical Chemistry Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-332883 (URN)10.1039/C7TA07716E (DOI)000415070100029 ()
Available from: 2017-11-02 Created: 2017-11-02 Last updated: 2019-02-19Bibliographically approved
Imani, R., Dillert, R., Bahnemann, D. W., Pazoki, M., Apih, T., Kononenko, V., . . . Iglic, A. (2017). Multifunctional Gadolinium-Doped Mesoporous TiO2 Nanobeads: Photoluminescence, Enhanced Spin Relaxation, and Reactive Oxygen Species Photogeneration, Beneficial for Cancer Diagnosis and Treatment. Small, 13(20), Article ID 1700349.
Open this publication in new window or tab >>Multifunctional Gadolinium-Doped Mesoporous TiO2 Nanobeads: Photoluminescence, Enhanced Spin Relaxation, and Reactive Oxygen Species Photogeneration, Beneficial for Cancer Diagnosis and Treatment
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2017 (English)In: Small, ISSN 1613-6810, E-ISSN 1613-6829, Vol. 13, no 20, article id 1700349Article in journal (Refereed) Published
Abstract [en]

Materials with controllable multifunctional abilities for optical imaging (OI) and magnetic resonant imaging (MRI) that also can be used in photodynamic therapy are very interesting for future applications. Mesoporous TiO2 sub-micrometer particles are doped with gadolinium to improve photoluminescence functionality and spin relaxation for MRI, with the added benefit of enhanced generation of reactive oxygen species (ROS). The Gd-doped TiO2 exhibits red emission at 637 nm that is beneficial for OI and significantly improves MRI relaxation times, with a beneficial decrease in spin-lattice and spin-spin relaxation times. Density functional theory calculations show that Gd3+ ions introduce impurity energy levels inside the bandgap of anatase TiO2, and also create dipoles that are beneficial for charge separation and decreased electron-hole recombination in the doped lattice. The Gd-doped TiO2 nanobeads (NBs) show enhanced ability for ROS monitored via center dot OH radical photogeneration, in comparison with undoped TiO2 nanobeads and TiO2 P25, for Gd-doping up to 10%. Cellular internalization and biocompatibility of TiO2@xGd NBs are tested in vitro on MG-63 human osteosarcoma cells, showing full biocompatibility. After photoactivation of the particles, anticancer trace by means of ROS photogeneration is observed just after 3 min irradiation.

National Category
Condensed Matter Physics Materials Chemistry Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-325694 (URN)10.1002/smll.201700349 (DOI)000401519900017 ()
Available from: 2017-06-27 Created: 2017-06-27 Last updated: 2017-07-04Bibliographically approved
Pazoki, M., Jacobsson, J. T., Cruz, S., Johansson, M. B., Imani, R., Kullgren, J., . . . Boschloo, G. (2017). Photon Energy-Dependent Hysteresis Effects in Lead Halide Perovskite Materials. The Journal of Physical Chemistry C, 121(47), 26180-26187
Open this publication in new window or tab >>Photon Energy-Dependent Hysteresis Effects in Lead Halide Perovskite Materials
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2017 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 47, p. 26180-26187Article in journal (Refereed) Published
Abstract [en]

Lead halide perovskites have a range of spectacular properties and interesting phenomena and are a serious candidate for the next generation of photovoltaics with high efficiencies and low fabrication costs. An interesting phenomenon is the anomalous hysteresis often seen in current-voltage scans, which complicates accurate performance measurements but has also been explored to obtain a more comprehensive understanding of the device physics. Herein, we demonstrate a wavelength and illumination intensity dependency of the hysteresis in state-of-the-art perovskite solar cells with 18% power conversion efficiency (PCE), which gives new insights into ion migration. The perovskite devices show lower hysteresis under illumination with near band edge (red) wavelengths compared to more energetic (blue) excitation. This can be rationalized with thermalization-assisted ion movement or thermalization-assisted vacancy generation. These explanations are supported by the dependency of the photovoltage decay with illumination time and excitation wavelength, as well as by impedance spectroscopy. The suggested mechanism is that high-energy photons create hot charge carriers that either through thermalization can create additional vacancies or by release of more energetic phonons play a role in overcoming the activation energy for ion movement. The excitation wavelength dependency of the hysteresis presented here gives valuable insights into the photophysics of the lead halide perovskite solar cells.

National Category
Physical Chemistry Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-334350 (URN)10.1021/acs.jpcc.7b06775 (DOI)000417228500005 ()
Funder
ÅForsk (Ångpanneföreningen's Foundation for Research and Development), 43294-1StandUp
Available from: 2017-11-22 Created: 2017-11-22 Last updated: 2019-02-19Bibliographically approved
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