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Svanstrom, S., Jacobsson, T. J., Boschloo, G., Johansson, E. M. J., Rensmo, H. & Cappel, U. B. (2020). Degradation Mechanism of Silver Metal Deposited on Lead Halide Perovskites. ACS Applied Materials and Interfaces, 12(6), 7212-7221
Open this publication in new window or tab >>Degradation Mechanism of Silver Metal Deposited on Lead Halide Perovskites
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2020 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 12, no 6, p. 7212-7221Article in journal (Refereed) Published
Abstract [en]

Lead halide perovskite solar cells have significantly increased in both efficiency and stability over the last decade. An important aspect of their longterm stability is the reaction between the perovskite and other materials in the solar cell. This includes the contact materials and their degradation if they can potentially come into contact through, e.g., pinholes or material diffusion and migration. Here, we explore the interactions of silver contacts with lead halide perovskites of different compositions by using a model system where thermally evaporated silver was deposited directly on the surface of the perovskites. Using X-ray photoelectron spectroscopy with support from scanning electron microscopy, X-ray diffraction, and UV-visible absorption spectroscopy, we studied the film formation and degradation of silver on perovskites with different compositions. The deposited silver does not form a continuous silver film but instead tends to form particles on a bare perovskite surface. These particles are initially metallic in character but degrade into AgI and AgBr over time. The degradation and migration appear unaffected by the replacement of methylammonium with cesium but are significantly slowed down by the complete replacement of iodide with bromide. The direct contact between silver and the perovskite also significantly accelerates the degradation of the perovskite, with a significant loss of organic cations and the possible formation of PbO, and, at the same time, changed the surface morphology of the iodide-rich perovskite interface. Our results further indicate that an important degradation pathway occurred through gas-phase perovskite degradation products. This highlights the importance of control over the interface materials and the use of completely hermetical barrier layers for the long-term stability and therefore the commercial viability of silver electrodes.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2020
Keywords
perovskite solar cells, electrode stability, X-ray photoelectron spectroscopy, interface chemistry, noble metal electrodes
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-269458 (URN)10.1021/acsami.9b20315 (DOI)000514256400040 ()31958007 (PubMedID)2-s2.0-85079341463 (Scopus ID)
Note

QC 20200310

Available from: 2020-03-10 Created: 2020-03-10 Last updated: 2020-03-10Bibliographically approved
Aung, S. H., Zhao, L., Nonomura, K., Oo, T. Z., Zakeeruddin, S. M., Vlachopoulos, N., . . . Grätzel, M. (2019). Toward an alternative approach for the preparation of low-temperature titanium dioxide blocking underlayers for perovskite solar cells. Journal of Materials Chemistry A, 7(17), 10729-10738
Open this publication in new window or tab >>Toward an alternative approach for the preparation of low-temperature titanium dioxide blocking underlayers for perovskite solar cells
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2019 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 7, no 17, p. 10729-10738Article in journal (Refereed) Published
Abstract [en]

The anodic electrodeposition method is investigated as an alternative technique for the preparation of a titanium oxide (TiO 2 ) blocking underlayer (UL) for perovskite solar cells (PSCs). Extremely thin Ti IV -based films are grown from aqueous acidic titanium(iii) chloride in an electrochemical cell at room temperature. This precursor layer is converted to the UL (ED-UL), in a suitable state for PSC applications, by undertaking a sintering step at 450 °C for half an hour. PSCs with the composition of the light-absorbing material FA 0.85 MA 0.10 Cs 0.05 Pb(I 0.87 Br 0.13 ) 3 (FA and MA denote the formamidinium and methylammonium cations, respectively) based on the ED-UL are compared with PSCs with the UL of a standard type prepared by the spray-pyrolysis method at 450 °C from titanium diisopropoxide bis(acetylacetonate) (SP-UL). We obtain power conversion efficiencies (PCEs) of over 20% for mesoscopic perovskite devices employing both ED-ULs and SP-ULs. Slightly higher fill factor values are observed for ED-UL-based devices. In addition, ED-ULs prepared by the same method have also been applied in planar PSCs, resulting in a PCE exceeding 17%, which is comparable to that for similar PSCs with an SP-UL. The preparation of ED-ULs with a lower sintering temperature, 150 °C, has also been examined. The efficiency of a planar PSC incorporating this underlayer was 14%. These results point out to the possibility of applying ED-ULs in flexible planar PSCs in the future.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2019
Keywords
Anodic oxidation, Chlorine compounds, Efficiency, Lead compounds, Perovskite, Sintering, Solar cells, Spray pyrolysis, Temperature, Titanium dioxide, Titanium oxides, Absorbing materials, Acetylacetonates, Anodic electrodeposition, Low temperatures, Lower sintering temperatures, Methylammonium cations, Power conversion efficiencies, Spray pyrolysis method, Perovskite solar cells
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-252234 (URN)10.1039/c8ta04246b (DOI)000472183200061 ()2-s2.0-85064966914 (Scopus ID)
Note

QC 20190612

Available from: 2019-06-12 Created: 2019-06-12 Last updated: 2020-01-29Bibliographically approved
Svanström, S., Jacobsson, T. J., Sloboda, T., Giangrisostomi, E., Ovsyannikov, R., Rensmo, H. & Cappel, U. B. (2018). Effect of halide ratio and Cs+ addition on the photochemical stability of lead halide perovskites. Journal of Materials Chemistry A, 6(44), 22134-22144
Open this publication in new window or tab >>Effect of halide ratio and Cs+ addition on the photochemical stability of lead halide perovskites
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2018 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 6, no 44, p. 22134-22144Article in journal (Refereed) Published
Abstract [en]

Lead halide perovskite solar cells with multi-cation/mixed halide materials now give power conversion efficiencies of more than 20%. The stability of these mixed materials has been significantly improved through the addition of Cs+ compared to the original methylammonium lead iodide. However, it remains one of the most significant challenges for commercialisation. In this study, we use photoelectron spectroscopy (PES) in combination with visible laser illumination to study the photo-stability of perovskite films with different compositions. These include Br : I ratios of 50 : 50 and 17 : 83 and compositions with and without Cs+. For the samples without Cs and the 50 : 50 samples, we found that the surface was enriched in Br and depleted in I during illumination and that some of the perovskite decomposed into Pb-0, organic halide salts, and iodine. After illumination, both of these reactions were partially reversible. Furthermore, the surfaces of the films were enriched in organic halide salts indicating that the cations were not degraded into volatile products. With the addition of Cs+ to the samples, photo-induced changes were significantly suppressed for a 50 : 50 bromide to iodide ratio and completely suppressed for perovskites with a 17 : 83 ratio at light intensities exceeding 1 sun equivalent.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2018
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-243971 (URN)10.1039/c8ta05795h (DOI)000456724800044 ()2-s2.0-85054176779 (Scopus ID)
Note

QC 20190301

Available from: 2019-03-01 Created: 2019-03-01 Last updated: 2020-01-29Bibliographically approved
Cappel, U. B., Liu, P., Johansson, F. O. L., Philippe, B., Giangrisostomi, E., Ovsyannikov, R., . . . Rensmo, H. (2018). Electronic Structure Characterization of Cross-Linked Sulfur Polymers. ChemPhysChem, 19(9), 1041-1047
Open this publication in new window or tab >>Electronic Structure Characterization of Cross-Linked Sulfur Polymers
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2018 (English)In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 19, no 9, p. 1041-1047Article in journal (Refereed) Published
Abstract [en]

Cross-linked polymers of elemental sulfur are of potential interest for electronic applications as they enable facile thin-film processing of an abundant and inexpensive starting material. Here, we characterize the electronic structure of a cross-linked sulfur/diisopropenyl benzene (DIB) polymer by a combination of soft and hard X-ray photoelectron spectroscopy (SOXPES and HAXPES). Two different approaches for enhancing the conductivity of the polymer are compared: the addition of selenium in the polymer synthesis and the addition of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) during film preparation. For the former, we observe the incorporation of Se into the polymer structure resulting in a changed valence-band structure. For the latter, a Fermi level shift in agreement with p-type doping of the polymer is observed and also the formation of a surface layer consisting mostly of TFSI anions.

Place, publisher, year, edition, pages
WILEY-V C H VERLAG GMBH, 2018
Keywords
cross-linking, hole-transporting material, solar cells, sulfur polymers, X-ray photoelectron spectroscopy
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-228264 (URN)10.1002/cphc.201800043 (DOI)000431492600005 ()29451358 (PubMedID)2-s2.0-85042538116 (Scopus ID)
Note

QC 20180523

Available from: 2018-05-23 Created: 2018-05-23 Last updated: 2020-01-29Bibliographically approved
Jacobsson, T. J., Svanström, S., Andrei, V., Rivett, J. P. H., Kornienko, N., Philippe, B., . . . Boschloo, G. (2018). Extending the Compositional Space of Mixed Lead Halide Perovskites by Cs, Rb, K, and Na Doping. The Journal of Physical Chemistry C, 122(25), 13548-13557
Open this publication in new window or tab >>Extending the Compositional Space of Mixed Lead Halide Perovskites by Cs, Rb, K, and Na Doping
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2018 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 25, p. 13548-13557Article in journal (Refereed) Published
Abstract [en]

A trend in high performing lead halide perovskite solar cell devices has been increasing compositional complexity by successively introducing more elements, dopants, and additives into the structure; and some of the latest top efficiencies have been achieved with a quadruple cation mixed halide perovskite Cs(x)FA(y)MA(z)Rb(1-x-y-z)PbBr(q)I(3-9). This paper continues this trend by exploring doping of mixed lead halide perovskites, FA(0.83)MA(0.17)PbBr(0.51)I(2.49), with an extended set of alkali cations, i.e., Cs+, Rb+, K+, and Na+, as well as combinations of them. The doped perovskites were investigated with X-ray diffraction, energy-dispersive X-ray spectroscopy, scanning electron microscopy, hard X-ray photoelectron spectroscopy, UV-vis, steady state fluorescence, and ultrafast transient absorption spectroscopy. Solar cell devices were made as well. Cs+ can replace the organic cations in the perovskite structure, but Rb+, K+, and Na+ do not appear to do that. Despite this, samples doped with K and Na have substantially longer fluorescence lifetimes, which potentially could be beneficial for device performance.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2018
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-232631 (URN)10.1021/acs.jpcc.7b12464 (DOI)000437811500039 ()2-s2.0-85048801160 (Scopus ID)
Funder
Swedish Energy Agency, P43294-1Swedish Foundation for Strategic Research , RMA15-0130StandUp
Note

QC 20180730

Available from: 2018-07-30 Created: 2018-07-30 Last updated: 2020-01-29Bibliographically approved
Johansson, F. O., Ivanovic, M., Svanstrom, S., Cappel, U. B., Peisert, H., Chasse, T. & Lindblad, A. (2018). Femtosecond and Attosecond Electron-Transfer Dynamics in PCPDTBT:PCBM Bulk Heterojunctions. The Journal of Physical Chemistry C, 122(24), 12605-12614
Open this publication in new window or tab >>Femtosecond and Attosecond Electron-Transfer Dynamics in PCPDTBT:PCBM Bulk Heterojunctions
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2018 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 24, p. 12605-12614Article in journal (Refereed) Published
Abstract [en]

Charge separation efficiency is a crucial parameter for photovoltaic devices-polymers consisting of alternating electron-rich and electron-deficient parts can achieve high such efficiencies, for instance, together with a fullerene electron acceptor. This offers a viable path toward solar cells with organic bulk heterojunctions. Here, we measured the charge-transfer times in the femtosecond and attosecond regimes via the decay of sulfur is X-ray core excited states (with the core-hole clock method) in blends of a low-band gap polymer {PCPDTBT [poly[2,6-(4,4-bis (2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4-1/1 dithiophene)-alt-4,7- (2,1,3-benzothiadiazole)]]} consisting of a cyclopentadithiophene electron-rich part and a benzothiadiazole electron-deficient part. The constituting parts of the bulk heterojunction were varied by adding the fullerene derivative PCBM ([6,6]-phenyl-C-61-butyric acid methyl ester) (weight ratio of polymer/PCBM as 1:0, 1:1, 1:2, and 1:3). For low-energy excitations, the charge-transfer time varies to the largest extent for the thiophene donor part. The charge-transfer time in the 1:2 blend is reduced by 86% compared to that of pristine PCPDTBT. At higher energy excitations, the charge-transfer time does not vary with the chemical environment, as this regime is dominated by intramolecular conduction that yields ultrafast charge-transfer times for all blends, approaching 170 as. We thus demonstrate that the core-hole clock method applied to a series with changing composition can give information about local electron dynamics (with chemical specificity) at interfaces between the constituting parts the crucial part of a bulk heterojunction where the initial charge separation occurs.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2018
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-232253 (URN)10.1021/acs.jpcc.8b02453 (DOI)000436381600004 ()2-s2.0-85047606902 (Scopus ID)
Note

QC 20180720

Available from: 2018-07-20 Created: 2018-07-20 Last updated: 2020-01-29Bibliographically approved
Schaefer, A., Lanzilotto, V., Cappel, U. B., Uvdal, P., Borg, A. & Sandell, A. (2018). First layer water phases on anatase TiO2(101). Surface Science, 674, 25-31
Open this publication in new window or tab >>First layer water phases on anatase TiO2(101)
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2018 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 674, p. 25-31Article in journal (Refereed) Published
Abstract [en]

The anatase TiO2(101) surface and its interaction with water is an important topic in oxide surface chemistry. Firstly, it benchmarks the properties of the majority facet of TiO2 nanoparticles and, secondly, there is a controversy as to whether the water molecule adsorbs intact or deprotonates. We have addressed the adsorption of water on anatase TiO2(101) by synchrotron radiation photoelectron spectroscopy. Three two-dimensional water structures are found during growth at different temperatures: at 100 K, a metastable structure forms with no hydrogen bonding between the water molecules. In accord with prior literature, we assign this phase to chains of disordered molecules. Growth 160 K results in a metastable structure with expressed hydrogen bonding between the water molecules. At 190 K, the water molecules become disordered as the thermal energy is too high and hence the hydrogen bonds break. The result is a structure with isolated monomers. Partial dissociation is observed for all three growths, with the molecular state only slightly favored in energy (20-40 meV) over the dissociated state. Heating of a thick film leads to more dissociation compared to a bilayer, when formed at 100 K. Thus, extending the water network facilitates proton transport and hence dissociation. The results reconcile apparent conflicting experimental results previously obtained by scanning tunneling microscopy (STM) and core level photoelectron spectroscopy.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2018
Keywords
Metal oxides, TiO2, Anatase, Water adsorption, Monolayer, Dissociation, Photoelectron spectroscopy
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-230395 (URN)10.1016/j.susc.2018.03.019 (DOI)000432759200005 ()
Note

QC 20180620

Available from: 2018-06-20 Created: 2018-06-20 Last updated: 2020-01-29Bibliographically approved
Saki, Z., Aitola, K., Sveinbjornsson, K., Yang, W., Svanstrom, S., Cappel, U. B., . . . Boschloo, G. (2018). The synergistic effect of dimethyl sulfoxide vapor treatment and C-60 electron transporting layer towards enhancing current collection in mixed-ion inverted perovskite solar cells. Journal of Power Sources, 405, 70-79
Open this publication in new window or tab >>The synergistic effect of dimethyl sulfoxide vapor treatment and C-60 electron transporting layer towards enhancing current collection in mixed-ion inverted perovskite solar cells
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2018 (English)In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 405, p. 70-79Article in journal (Refereed) Published
Abstract [en]

Inverted perovskite solar cells (PSCs) have been introduced as better candidate for roll-to-roll printing and scaleup than their conventional configuration counterparts, while their fabrication is technically more demanding. The common light absorbing layer in inverted PSCs is the single cation methylammonium lead iodide (MAPbI(3)) perovskite, whereas mixed-ion perovskites are chemically more stable. In mixed-ion perovskites, where FA (formamidinium) is the main replacement for MA, the electron affinity is larger than in MAPbI3 perovskites, leading to possible barriers against photoelectron collection by the electron transporting layer (ETL). In this paper we report on a mixed-ion (FAPbI(3))(0.83)(MAPbBr(3))(0.17) inverted PSC with improved photocurrent through using a dimethyl sulfoxide vapor treatment of perovskite layer and replacing the conventional [6,6]-phenyl-C-71 butyric acid methyl ester (PC70BM) with C-60/bathocuproine (BCP) as more effective ETL. The treatment of perovskite layer results in reduction of impurity phases of 8-FAPbI(3) and Pbl(2). Photoluminescence and open circuit voltage decay data demonstrate better charge carrier collection by the C-60/BCP compared to the PC70BM ETL, and an electron barrier for the back flow of electrons from ETL to perovskite. Our improvements in perovskite crystalization and electron transfer layer simultaneously lead to increasing the current density from 10 to 21 mA cm(-2).

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2018
Keywords
Mixed-ion perovskite, Dimethyl sulfoxide (DMSO) vapor treatment, Crystalline quality, Electron transporting layer (ETL)
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-239989 (URN)10.1016/j.jpowsour.2018.09.100 (DOI)000451102500009 ()2-s2.0-85054768009 (Scopus ID)
Note

QC 20181211

Available from: 2018-12-11 Created: 2018-12-11 Last updated: 2020-01-29Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-9432-3112

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