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Pazoki, M. & Edvinsson, T. (2019). Nature of the excited state in lead iodide perovskite materials: Time-dependent charge density response and the role of the monovalent cation. Physical Review B, 100(4), Article ID 045203.
Open this publication in new window or tab >>Nature of the excited state in lead iodide perovskite materials: Time-dependent charge density response and the role of the monovalent cation
2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 4, article id 045203Article in journal (Refereed) Published
Abstract [en]

Charge density response is responsible for the excited-state properties of lead iodide perovskites and is related to both the light absorption properties as well as subsequent electronic and lattice relaxation in the system, important for the working conditions of the material in solar cell applications. Here we investigate the nature of the excited state and its relation to pathways for electronic and lattice relaxations by performing time-dependent density-functional theory (TDDFT). Charge density response upon photoexcitation close to the band edge and deeper into the absorption spectra are investigated for three lead perovskite compounds with different A-site monovalent cations CsPbI3, CH2(NH2)(2)PbI3 (FAPbI(3)), and CH3NH3PbI3 (MAPbI(3)). The carrier cooling mechanism is analyzed and shows that the initial force acting on the nuclei follows the symmetry of the ground-state electronic structure upon photoexcitation with a force parallel to the polarization of the incoming light. This effect is investigated for the three different compounds and shows an initial force for induced ionic movement that depends on both the underlying symmetry of the inorganic lattice as well as on the type and orientation of the organic cation. The excess energy after thermalization under blue-light illumination is large enough for overcoming the activation energy for iodide migration and can thus trigger vacancy formation. Iodide vacancies are seen to be dipole-field compensated by the organic cation, with a shielding of the local field, and thus form an explanation for the defect tolerance found in these systems under photovoltaic operation. A partial charge transfer from the inorganic cage to the monovalent organic cation is predicted with TDDFT calculations for blue- and UV-light illumination with a population of antibinding orbitals in the N-H bond in both CH3NH3 (MA) and CH2(NH2)(2 )(FA), where the implication for this is discussed in terms of the intrinsic photo stability of organic cation containing lead perovskites. The results show the importance of a fundamental understanding of the excited-state properties of perovskite material to reveal the underlying mechanism for the defect tolerance and thus high photovoltaic performance when using organic dipolar cations as well as a rationale for using mixed halide perovskites to decrease the halide migration, effect of vacancy formation, and stability issues under blueand UV-light illumination.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Condensed Matter Physics Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-390785 (URN)10.1103/PhysRevB.100.045203 (DOI)000475499700006 ()
Funder
Swedish Energy Agency, 43294-1Swedish National Infrastructure for Computing (SNIC), snic2018-3-228Swedish National Infrastructure for Computing (SNIC), snic20171-158Swedish National Infrastructure for Computing (SNIC), snic2018-3-352
Available from: 2019-08-16 Created: 2019-08-16 Last updated: 2019-08-16Bibliographically approved
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
Phuyal, D., Safdari, M., Pazoki, M., Liu, P., Philippe, B., Kvashnina, K. O., . . . Gardner, J. (2018). Electronic Structure of Two-Dimensional Lead(II) Iodide Perovskites: An Experimental and Theoretical Study. Chemistry of Materials, 30(15), 4959-4967
Open this publication in new window or tab >>Electronic Structure of Two-Dimensional Lead(II) Iodide Perovskites: An Experimental and Theoretical Study
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2018 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 30, no 15, p. 4959-4967Article in journal (Refereed) Published
Abstract [en]

Layered two-dimensional (2D) hybrid organic-inorganic perovskites (HOP) are promising materials for light-harvesting applications because of their chemical stability, wide flexibility in composition and dimensionality, and increases in photovoltaic power conversion efficiencies. Three 2D lead iodide perovskites were studied through various X-ray spectroscopic techniques to derive detailed electronic structures and band energetics profiles at a titania interface. Core-level and valence band photoelectron spectra of HOP were analyzed to resolve the electronic structure changes due to the reduced dimensionality of inorganic layers. The results show orbital narrowing when comparing the HOP, the layered precursor PbI2, and the conventional 3D (CH3NH3)PbI3 such that different localizations of band edge states and narrow band states are unambiguously due to the decrease in dimensionality of the layered HOPs. Support from density functional theory calculations provide further details on the interaction and band gap variations of the electronic structure. We observed an interlayer distance dependent dispersion in the near band edge electronic states. The results show how tuning the interlayer distance between the inorganic layers affects the electronic properties and provides important design principles for control of the interlayer charge transport properties, such as the change in effective charge masses as a function of the organic cation length. The results of these findings can be used to tune layered materials for optimal functionality and new applications.

National Category
Condensed Matter Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-361922 (URN)10.1021/acs.chemmater.8b00909 (DOI)000442186500014 ()
Funder
StandUpSwedish Energy AgencySwedish Research CouncilKnut and Alice Wallenberg Foundation
Note

De två första författarna delar förstaförfattarskapet.

Available from: 2018-09-27 Created: 2018-09-27 Last updated: 2018-11-02Bibliographically approved
Pazoki, M. & Edvinsson, T. (2018). Metal replacement in perovskite solar cell materials: chemical bonding effects and optoelectronic properties. SUSTAINABLE ENERGY & FUELS, 2(7), 1430-1445
Open this publication in new window or tab >>Metal replacement in perovskite solar cell materials: chemical bonding effects and optoelectronic properties
2018 (English)In: SUSTAINABLE ENERGY & FUELS, ISSN 2398-4902, Vol. 2, no 7, p. 1430-1445Article, review/survey (Refereed) Published
Abstract [en]

The composition of lead halide perovskite materials has been explored extensively over the last few years and as a consequence, different materials have been introduced into the perovskite solar cell family with diverse physical properties. Herein, we present recent progress within the framework of lead replacement that has led to new solar cell compounds by partial exchange or full substitution of lead with other metals. Lead replacement with divalent metals, tin and germanium perovskites as well as alkaline earth metals, and lanthanides are reviewed and discussed with respect to the chemical bonding effects and their relationship with the optoelectronic and charge mobility properties. The physical properties of the materials and the related device performances are also discussed with respect to the metal cation bonding within the perovskite lattice using transition metals and monovalent and trivalent metals.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2018
National Category
Condensed Matter Physics Materials Chemistry Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-366460 (URN)10.1039/c8se00143j (DOI)000436519000003 ()
Funder
Swedish Energy Agency, 43294-1
Available from: 2018-11-22 Created: 2018-11-22 Last updated: 2018-11-26Bibliographically approved
Phuyal, D., Jain, S. M., Philippe, B., Johansson, M. B., Pazoki, M., Kullgren, J., . . . Rensmo, H. (2018). The electronic structure and band interface of cesium bismuth iodide on a titania heterostructure using hard X-ray spectroscopy. Journal of Materials Chemistry A, 6(20), 9498-9505
Open this publication in new window or tab >>The electronic structure and band interface of cesium bismuth iodide on a titania heterostructure using hard X-ray spectroscopy
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2018 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 6, no 20, p. 9498-9505Article in journal (Refereed) Published
Abstract [en]

Bismuth halide compounds as a non-toxic alternative are increasingly investigated because of their potential in optoelectronic devices and their rich structural chemistry. Hard X-ray spectroscopy was applied to the ternary bismuth halide Cs3Bi2I9 and its related precursors BiI3 and CsI to understand its electronic structure at an atomic level. We specifically investigated the core levels and valence band using X-ray photoemission spectroscopy (PES), high-resolution X-ray absorption (HERFD-XAS), and resonant inelastic X-ray scattering (RIXS) to get insight into the chemistry and the band edge properties of the two bismuth compounds. Using these element specific X-ray techniques, our experimental electronic structures show that the primary differences between the two bismuth samples are the position of the iodine states in the valence and conduction bands and the degree of hybridization with bismuth lone pair (6s(2)) states. The crystal structure of the two layered quasi-perovskite compounds plays a minor role in modifying the overall electronic structure, with variations in bismuth lone pair states and iodine band edge states. Density Functional Theory (DFT) calculations are used to compare with experimental data. The results demonstrate the effectiveness of hard X-ray spectroscopies to identify element specific bulk electronic structures and their use in optoelectronic devices.

National Category
Materials Chemistry Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-357561 (URN)10.1039/c8ta00947c (DOI)000433427300020 ()
Funder
Swedish Research Council, 2014-6019Swedish Research Council, 2016-4524Swedish Energy Agency, P43549-1Swedish Foundation for Strategic Research , 15-0130Wallenberg Foundations, 2012.0031StandUp
Available from: 2018-08-20 Created: 2018-08-20 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., Cappel, U. B., Johansson, E. M. J., Hagfeldt, A. & Boschloo, G. (2017). Characterization techniques for dye-sensitized solar cells. Energy & Environmental Science, 10(3), 672-709
Open this publication in new window or tab >>Characterization techniques for dye-sensitized solar cells
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2017 (English)In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 10, no 3, p. 672-709Article, review/survey (Refereed) Published
Abstract [en]

Dye-sensitized solar cells (DSCs) have been widely studied in the last two decades and start to be commercialized in the photovoltaic market. Comprehensive characterization is needed to fully understand and optimize the device performance and stability. In this review, we summarize different characterization methods for dye-sensitized solar cells with liquid redox electrolytes or solid state hole transporting materials, most of which can also be used for similar devices such as perovskite based thin film solar cells. Limitations and advantages of relevant methods for studying the energy levels and time scales involved in charge transfer processes as well as charge transport related characteristic lengths are discussed. A summary of recent developments in DSCs and the importance of measured parameters for the device optimization procedure are mentioned at the end.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2017
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-320102 (URN)10.1039/c6ee02732f (DOI)000396430700002 ()
Available from: 2017-04-26 Created: 2017-04-26 Last updated: 2017-04-26Bibliographically approved
Dennis Larsson, E., Pazoki, M., Hermansson, K. & Kullgren, J. (2017). Computational Green Chemistry. In: : . Paper presented at Swedish e-Science Academy 2017.
Open this publication in new window or tab >>Computational Green Chemistry
2017 (English)Conference paper, Poster (with or without abstract) (Other academic)
National Category
Materials Chemistry Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-338360 (URN)
Conference
Swedish e-Science Academy 2017
Available from: 2018-01-08 Created: 2018-01-08 Last updated: 2019-02-19
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
Röckert, A., Pazoki, M. & Kullgren, J. (2017). Methylammonium lanthanide iodide perovskites as lead free alternatives for solar cell materials. In: : . Paper presented at Multiscale Modelling of Materials and Molecules.
Open this publication in new window or tab >>Methylammonium lanthanide iodide perovskites as lead free alternatives for solar cell materials
2017 (English)Conference paper, Poster (with or without abstract) (Other academic)
National Category
Materials Chemistry Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-338367 (URN)
Conference
Multiscale Modelling of Materials and Molecules
Available from: 2018-01-08 Created: 2018-01-08 Last updated: 2019-02-19
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ORCID iD: ORCID iD iconorcid.org/0000-0001-6776-5460

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