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Jain, Sagar Motilal
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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
Åpne denne publikasjonen i ny fane eller vindu >>The electronic structure and band interface of cesium bismuth iodide on a titania heterostructure using hard X-ray spectroscopy
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2018 (engelsk)Inngår i: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 6, nr 20, s. 9498-9505Artikkel i tidsskrift (Fagfellevurdert) 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.

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Identifikatorer
urn:nbn:se:uu:diva-357561 (URN)10.1039/c8ta00947c (DOI)000433427300020 ()
Forskningsfinansiär
Swedish Research Council, 2014-6019Swedish Research Council, 2016-4524Swedish Energy Agency, P43549-1Swedish Foundation for Strategic Research , 15-0130Wallenberg Foundations, 2012.0031StandUp
Tilgjengelig fra: 2018-08-20 Laget: 2018-08-20 Sist oppdatert: 2019-02-19bibliografisk kontrollert
Jain, S. M., Qiu, Z., Häggman, L., Mirmohades, M., Johansson, M. B., Edvinsson, T. & Boschloo, G. (2016). Frustrated Lewis pair-mediated recrystallization of CH3NH3PbI3 for improved optoelectronic quality and high voltage planar perovskite solar cells. Energy & Environmental Science, 9(12), 3770-3782
Åpne denne publikasjonen i ny fane eller vindu >>Frustrated Lewis pair-mediated recrystallization of CH3NH3PbI3 for improved optoelectronic quality and high voltage planar perovskite solar cells
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2016 (engelsk)Inngår i: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 9, nr 12, s. 3770-3782Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Films of the hybrid lead halide perovskite CH3NH3PbI3 were found to react with pyridine vapor at room temperature leading to complete bleaching of the film. In dry air or nitrogen atmosphere recrystallization takes place, leading to perovskite films with markedly improved optical and photovoltaic properties. The physical and chemical origin of the reversible bleaching and recrystallization mechanism was investigated using a variety of experimental techniques and quantum chemical calculations. The strong Lewis base pyridine attacks the CH3NH3PbI3. The mechanism can be understood from a frustrated Lewis pair formation with a partial electron donation of the lone-pair on nitrogen together with competitive bonding to other species as revealed by Raman spectroscopy and DFT calculations. The bleached phase consists of methylammonium iodide crystals and an amorphous phase of PbI2( pyridine)(2). After spontaneous recrystallization the CH3NH3PbI3 thin films have remarkably improved photoluminescence, and solar cell performance increased from 9.5% for as-deposited films to more than 18% power conversion efficiency for recrystallized films in solar cells with planar geometry under AM1.5G illumination. Hysteresis was negligible and open-circuit potential was remarkably high, 1.15 V. The results show that complete recrystallization can be achieved with a simple room temperature pyridine vapor treatment of CH3NH3PbI3 films leading to high quality crystallinity films with drastically improved photovoltaic performance.

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Forskningsprogram
Fysik med inriktning mot atom- molekyl- och kondenserande materiens fysik
Identifikatorer
urn:nbn:se:uu:diva-311577 (URN)10.1039/c6ee02544g (DOI)000392915500017 ()
Forskningsfinansiär
Swedish Energy AgencyStandUpSwedish Research CouncilGöran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of TechnologyKnut and Alice Wallenberg Foundation
Tilgjengelig fra: 2016-12-29 Laget: 2016-12-29 Sist oppdatert: 2017-11-29bibliografisk kontrollert
Jain, S. M., Philippe, B., Johansson, E. M. J., Park, B.-W., Rensmo, H., Edvinsson, T. & Boschloo, G. (2016). Vapor phase conversion of PbI2 to CH3NH3PbI3: spectroscopic evidence for formation of an intermediate phase. Journal of Materials Chemistry A, 4(7), 2630-2642
Åpne denne publikasjonen i ny fane eller vindu >>Vapor phase conversion of PbI2 to CH3NH3PbI3: spectroscopic evidence for formation of an intermediate phase
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2016 (engelsk)Inngår i: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 4, nr 7, s. 2630-2642Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The formation of CH3NH3PbI3 (MAPbI(3)) from its precursors is probably the most significant step in the control of the quality of this semiconductor perovskite material, which is highly promising for photovoltaic applications. Here we investigated the transformation of spin coated PbI2 films to MAPbI(3) using a reaction with MAI in vapor phase, referred to as vapor assisted solution process (VASP). The presence of a mesoporous TiO2 scaffold on the substrate was found to speed up reaction and led to complete conversion of PbI2, while reaction on glass substrates was slower, with some PbI2 remaining even after prolonged reaction time. Based on data from UV-visible spectroscopy, Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy, the formation of an X-ray amorphous intermediate phase is proposed, which is identified by an increasing absorption from 650 to 500 nm in the absorption spectrum. This feature disappears upon long reaction times for films on planar substrates, but persists for films on mesoporous TiO2. Poor solar cell performance of planar VASP prepared devices was ascribed to PbI2 remaining in the film, forming a barrier between the perovskite layer and the compact TiO2/FTO contact. Good performance, with efficiencies up to 13.3%, was obtained for VASP prepared devices on mesoporous TiO2.

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Identifikatorer
urn:nbn:se:uu:diva-279639 (URN)10.1039/c5ta08745g (DOI)000369665800029 ()
Tilgjengelig fra: 2016-03-08 Laget: 2016-03-02 Sist oppdatert: 2017-11-30bibliografisk kontrollert
Park, B.-w., Philippe, B., Jain, S. M., Zhang, X., Edvinsson, T., Rensmo, H., . . . Boschloo, G. (2015). Chemical engineering of methylammonium lead iodide/bromide perovskites: tuning of opto-electronic properties and photovoltaic performance. Journal of Materials Chemistry A, 3(43), 21760-21771
Åpne denne publikasjonen i ny fane eller vindu >>Chemical engineering of methylammonium lead iodide/bromide perovskites: tuning of opto-electronic properties and photovoltaic performance
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2015 (engelsk)Inngår i: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 3, nr 43, s. 21760-21771Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Hybrid (organic-inorganic) lead trihalide perovskites have attracted much attention in recent years due to their exceptionally promising potential for application in solar cells. Here a controlled one-step method is presented where PbCl2 is combined with three equivalents methylammonium halide (MAX, with X = land/or Br) in polar solvents to form MAPb(I-xBr(x))(3) perovskite films upon annealing in air at 145 degrees C. The procedure allows for a linear increment of the semiconductor bandgap from 1.60 eV to 2.33 eV by increasing the Br content. A transition from a tetragonal to a cubic structure is found when the Br fraction is larger than 0.3. X-ray photoelectron spectroscopy investigations shows that the increase of Br content is accompanied by a shift of the valence band edge to lower energy. Simultaneously, the conduction band moves to higher energy, but this shift is less pronounced. Time-resolved single-photon counting experiments of the perovskite materials on mesoporous TiO2 show faster decay kinetics for Br containing perovskites, indicative of improved electron injection into TiO2. Interestingly, kinetics of MAPb(12.7)Br(0.30)Cl(y) on TiO2 scaffold became faster after prolonged excitation during the measurement. In solar cell devices, MAPb(12.7)Br(0.30)), yielded best performance, giving more than 14% power conversion efficiency when used in combination with an n-type contact consisting of fluorine-doped tinoxide glass coated with dense TiO2 and a mesoporous Al2O3 scaffold, and a p-type contact, spiro-MeOTAD/Ag.

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Identifikatorer
urn:nbn:se:uu:diva-268726 (URN)10.1039/c5ta05470b (DOI)000364020400042 ()
Forskningsfinansiär
Swedish Energy AgencyStandUpSwedish Research CouncilGöran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of TechnologyKnut and Alice Wallenberg Foundation
Tilgjengelig fra: 2015-12-09 Laget: 2015-12-09 Sist oppdatert: 2017-12-01bibliografisk kontrollert
Park, B.-w., Jain, S. M., Zhang, X., Hagfeldt, A., Boschloo, G. & Edvinsson, T. (2015). Resonance Raman and Excitation Energy Dependent Charge Transfer Mechanism in Halide-Substituted Hybrid Perovskite Solar Cells. ACS Nano, 9(2), 2088-2101
Åpne denne publikasjonen i ny fane eller vindu >>Resonance Raman and Excitation Energy Dependent Charge Transfer Mechanism in Halide-Substituted Hybrid Perovskite Solar Cells
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2015 (engelsk)Inngår i: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 9, nr 2, s. 2088-2101Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Organo-metal halide perovskites (OMHPs) are materials with attractive properties for optoelectronics. They made a recent introduction in the photovoltaics world by methylammonium (MA) lead triiodide and show remarkably improved charge separation capabilities when chloride and bromide are added. Here we show how halide substitution in OMHPs with the nominal composition CH3NH3PbI2X, where X is I, Br, or Cl, influences the morphology, charge quantum yield, and local interaction with the organic MA cation. X-ray diffraction and photoluminescence data demonstrate that halide substitution affects the local structure in the OMHPs with separate MAPbI3 and MAPbCl(3) phases. Raman spectroscopies as well as theoretical vibration calculations reveal that this at the same time delocalizes the charge to the MA cation, which can liberate the vibrational movement of the MA cation, leading to a more adaptive organic phase. The resonance Raman effect together with quantum chemical calculations is utilized to analyze the change in charge transfer mechanism upon electronic excitation and gives important clues for the mechanism of the much improved photovoltage and photocurrent also seen in the solar cell performance for the materials when chloride compounds are included in the preparation.

Emneord
mixed halide perovskites, solution processing, solar cells, Raman spectroscopy, charge separation mechanism, density functional theory
HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-248950 (URN)10.1021/nn507345e (DOI)000349940500105 ()25668059 (PubMedID)
Tilgjengelig fra: 2015-04-09 Laget: 2015-04-09 Sist oppdatert: 2017-12-04bibliografisk kontrollert
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