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Leandri, V., Gardner, J. M. & Jonsson, M. (2019). Coumarin as a Quantitative Probe for Hydroxyl Radical Formation in Heterogeneous Photocatalysis. The Journal of Physical Chemistry C, 123(11), 6667-6674
Open this publication in new window or tab >>Coumarin as a Quantitative Probe for Hydroxyl Radical Formation in Heterogeneous Photocatalysis
2019 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 11, p. 6667-6674Article in journal (Refereed) Published
Abstract [en]

In this work, we have assessed coumarin as a quantitative probe for hydroxyl radical formation in heterogeneous photocatalysis. Upon reaction with the hydroxyl radical, coumarin produces several hydroxylated products, of which one, 7-OH-coumarin, is strongly fluorescent. The fluorescence emission is strongly affected by inner filtering due to the presence of coumarin. Therefore, we performed a series of calibration experiments to correct for the coumarin concentration. From the calibration experiments, we could verify that the inner-filtering effect can be attributed to the competing absorption of the fluorescence excitation light between coumarin and 7-OH-coumarin. Through judicious calibration for the inner-filtering effects, the corrected results for the photocatalytic system show that the rate of hydroxyl scavenging is constant with time for initial coumarin concentrations of ≥50 μM under the conditions of our experiments. The rate increases linearly with coumarin concentration, as expected from the Langmuir–Hinshelwood model. Within the coumarin concentration range used here, the photocatalyst surface does not become saturated. Given the fact that the highest coumarin concentration used (1 mM) in this work is quite close to the solubility limit, we conclude that coumarin cannot be used to assess the full photocatalytic capacity of the system, i.e., surface saturation is never reached. The rate of hydroxyl radical scavenging will, to a large extent, depend on the affinity to the surface, and it is therefore not advisable to use coumarin as a probe for photocatalytic efficiency when comparing different photocatalysts.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-249493 (URN)10.1021/acs.jpcc.9b00337 (DOI)000462260700040 ()2-s2.0-85062883293 (Scopus ID)
Note

QC 20190426

Available from: 2019-04-12 Created: 2019-04-12 Last updated: 2019-04-26Bibliographically approved
Leandri, V., Liu, P., Sadollahkhani, A., Safdari, M., Kloo, L. & Gardner, J. M. (2019). Excited-State Dynamics of [Ru(bpy)(3)](2+) Thin Films on Sensitized TiO2 and ZrO2. ChemPhysChem, 20(4), 618-626
Open this publication in new window or tab >>Excited-State Dynamics of [Ru(bpy)(3)](2+) Thin Films on Sensitized TiO2 and ZrO2
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2019 (English)In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 20, no 4, p. 618-626Article in journal (Refereed) Published
Abstract [en]

The excited state dynamics of Tris(2,2 '-bipyridine)ruthenium(II) hexafluorophosphate, [Ru(bpy)(3)(PF6)(2)], was investigated on the surface of bare and sensitized TiO2 and ZrO2 films. The organic dyes LEG4 and MKA253 were selected as sensitizers. A Stern-Volmer plot of LEG4-sensitized TiO2 substrates with a spin-coated [Ru(bpy)(3)(PF6)(2)] layer on top shows considerable quenching of the emission of the latter. Interestingly, time-resolved emission spectroscopy reveals the presence of a fast-decay time component (25 +/- 5 ns), which is absent when the anatase TiO2 semiconductor is replaced by ZrO2. It should be specified that the positive redox potential of the ruthenium complex prevents electron transfer from the [Ru(bpy)(3)(PF6)(2)] ground state into the oxidized sensitizer. Therefore, we speculate that the fast-decay time component observed stems from excited-state electron transfer from [Ru(bpy)(3)(PF6)(2)] to the oxidized sensitizer. Solid-state dye sensitized solar cells (ssDSSCs) employing MKA253 and LEG4 dyes, with [Ru(bpy)(3)(PF6)(2)] as a hole-transporting material (HTM), exhibit 1.2 % and 1.1 % power conversion efficiency, respectively. This result illustrates the possibility of the hypothesized excited-state electron transfer.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2019
Keywords
Excited-state electron transfer, Ru(bpy)(3), DSSCs, Photochemistry, Solid state
National Category
Other Chemistry Topics
Identifiers
urn:nbn:se:kth:diva-245921 (URN)10.1002/cphc.201801010 (DOI)000458952600016 ()30623544 (PubMedID)2-s2.0-85061237720 (Scopus ID)
Note

QC 20190312

Available from: 2019-03-12 Created: 2019-03-12 Last updated: 2019-03-12Bibliographically approved
Leandri, V., Pizzichetti, A. R., Xu, B., Franchi, D., Zhang, W., Benesperi, I., . . . Gardner, J. M. (2019). Exploring the Optical and Electrochemical Properties of Homoleptic versus Heteroleptic Diimine Copper(I) Complexes. Inorganic Chemistry, 58(18), 12167-12177
Open this publication in new window or tab >>Exploring the Optical and Electrochemical Properties of Homoleptic versus Heteroleptic Diimine Copper(I) Complexes
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2019 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 58, no 18, p. 12167-12177Article in journal (Refereed) Published
Abstract [en]

Due to ligand scrambling, the synthesis and investigation of the properties of heteroleptic Cu(I) complexes can be a challenging task. In this work, we have studied the optical and electrochemical properties of a series of homoleptic complexes, such as [Cu(dbda)(2)](+), [Cu(dmp)(2)](+), [Cu(Br-dmp)(2)](+), [Cu(bcp)(2)](+), [Cu(dsbtmp)(2)](+), [Cu(biq)(2)](+), and [Cu(dap)(2)](+) in solution, and those of their heteroleptics [Cu(dbda)(dmp)](+), [Cu(dbda)(Br-dmp)](+), [Cu(dbda)(bcp)](+), [Cu(dbda)(dsbtmp))(+), [Cu(dbda)(biq)](+), [Cu(dbda)(dap)](+) adsorbed on the surface of anatase TiO2 (dbda = 6,6'-dimethyl-2,2'-bipyridine-4,4'-dibenzoic acid; dmp = 2,9-dimethyl-1,10-phenanthroline; Br-dmp = 5-bromo 2,9-dimethyl-1,10-phenanthroline; bcp = bathocuproine or 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline; dsbtmp = 2,9-di(sec-butyl)-3,4,7,8-tetramethyl-1,10-phenanthroline; biq = 2,2'-biquinoline; dap = 2,9-dianisyl-1,10-phenanthroline). We show that the maximum absorption wavelengths of the heteroleptic complexes on TiO2 can be reasonably predicted from those of the homoleptic complexes in solution through a simple linear relation, whereas the prediction of their redox properties is less trivial. In the latter case, two different linear patterns emerge: one including the ligands bcp, biq, and dap and another one including the ligands dmp, Br-dmp, and dsbtmp. We offer an interpretation of the data based on the chemical structure of the ligands. On one hand, ligands bcp, biq, and dap possess a more extended pi-conjugated system, which gives a more prominent contribution to the overall redox properties of the ligand dbda. On the other hand, the ligands dmp, Br-dmp, and dsbtmp are all phenanthroline-based containing alkyl substituents and contribute less than dbda to the overall redox properties.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2019
National Category
Inorganic Chemistry
Research subject
Chemistry
Identifiers
urn:nbn:se:kth:diva-261306 (URN)10.1021/acs.inorgchem.9b01487 (DOI)000486565600035 ()31483631 (PubMedID)2-s2.0-85072235085 (Scopus ID)
Note

QC 20191008

Available from: 2019-10-08 Created: 2019-10-08 Last updated: 2019-11-20Bibliographically approved
Zhang, W., Sadollahkhani, A., Li, Y., Leandri, V., Gardner, J. M. & Kloo, L. (2019). Mechanistic Insights from Functional Group Exchange Surface Passivation: A Combined Theoretical and Experimental Study. ACS APPLIED ENERGY MATERIALS, 2(4), 2723-2733
Open this publication in new window or tab >>Mechanistic Insights from Functional Group Exchange Surface Passivation: A Combined Theoretical and Experimental Study
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2019 (English)In: ACS APPLIED ENERGY MATERIALS, ISSN 2574-0962, Vol. 2, no 4, p. 2723-2733Article in journal (Refereed) Published
Abstract [en]

Four different functional groups including amino (-NH2), phosphine (-PH2), hydroxyl (-OH), and thiol (-SH) were combined with POSS (polyhedral oligomeric silsesquioxane) molecules to investigate how functional groups affect the surface passivation of POSS systems. Results from density-functional theory (DFT) calculations indicate that functional group amino (-NH2) with adsorption energy 86 (56) kJ mol(-1) is consistently better than that of thiol (-SH) with adsorption energy 68 (43) kJ mor(-1) for different passivation mechanisms. Theoretical studies on the analogous POSS-OH and POSS-PH2 systems show similar adsorption energies. Two of the systems were also investigated experimentally; aminopropyl isobutyl POSS (POSS-NH2) and mercaptopropyl isobutyl POSS (POSS-SH) were applied as passivation materials for MAPbI(3) (MA = methylammonium) perovskite and (FA)(0.85)(MA)(0.15)Pb(I-3)(0.85)(Br-3)(0)(.15)(FA = formamidinium) perovskite films. The same conclusion was drawn based on the results from contact angle studies, X-ray diffraction (XRD), and the stability of solar cells in ambient atmosphere, indicating the vital importance of choice of functional groups for passivation of the perovskite materials.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2019
Keywords
perovskite solar cells, polyhedral oligomeric silsesquioxane (POSS), passivation, DFT calculation, stability
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:kth:diva-251284 (URN)10.1021/acsaem.9b00050 (DOI)000465644600047 ()
Note

QC 20190517

Available from: 2019-05-17 Created: 2019-05-17 Last updated: 2019-05-17Bibliographically approved
Liu, J., Jia, D., Gardner, J. M., Johansson, E. M. J. & Zhang, X. (2019). Metal nanowire networks: Recent advances and challenges for new generation photovoltaics. MATERIALS TODAY ENERGY, 13, 152-185
Open this publication in new window or tab >>Metal nanowire networks: Recent advances and challenges for new generation photovoltaics
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2019 (English)In: MATERIALS TODAY ENERGY, ISSN 2468-6069, Vol. 13, p. 152-185Article, review/survey (Refereed) Published
Abstract [en]

Transparent conducting electrodes which allow photons passing through and simultaneously transfers the charge carriers are critical for the construction of high-performance photovoltaic cells. Electrodes based on metal oxides, such as indium-doped tin oxide (ITO) or fluorine-doped tin oxide (FTO), may have limited application in new generation flexible solar cells, which employ solution-processed roll-to-roll or ink-printing techniques toward large-area-fabrication approach, due to their brittleness and poor mechanical properties. Metal nanowire network (MNWN) emerges as a highly potential alternative candidate instead of ITO or FTO due to the high transparency, low sheet resistance, low cost, solution processable and compatibility with a flexible substrate for high throughput production. This feature article systematically summarizes the recent advances of the MNWNs, including new concepts and emerging strategies for the synthesis of metal nanowires (MNWs), various approaches for the preparation of MNWNs and comprehensively discusses the novel MNWN electrodes prepared on different substrates. The state-of-the-art new generation solar cell devices, such as transparent, flexible and light-weight solar cells, with MNWN as a transparent conductive electrode are emphasized. Finally, the opportunities and challenges for the development of MNWN electrodes toward application in the new generations of photovoltaic devices are discussed.

Place, publisher, year, edition, pages
ELSEVIER SCI LTD, 2019
Keywords
Metal nanowire network, Transparent electrode, New-generation photovoltaic, Solar cell, Conductivity
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-261327 (URN)10.1016/j.mtener.2019.05.007 (DOI)000486148000016 ()2-s2.0-85066819571 (Scopus ID)
Note

QC 20191007

Available from: 2019-10-07 Created: 2019-10-07 Last updated: 2019-10-07Bibliographically approved
Leandri, V., Gardner, J. M. & Jonsson, M. (2019). Reply to "Comment on 'Coumarin as a Quantitative Probe for Hydroxyl Radical Formation in Heterogeneous Photocatalysis'". The Journal of Physical Chemistry C, 123(33), 20685-20686
Open this publication in new window or tab >>Reply to "Comment on 'Coumarin as a Quantitative Probe for Hydroxyl Radical Formation in Heterogeneous Photocatalysis'"
2019 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 33, p. 20685-20686Article in journal, Editorial material (Other academic) Published
Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2019
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-259445 (URN)10.1021/acs.jpcc.9b06021 (DOI)000482545700067 ()2-s2.0-85071659297 (Scopus ID)
Note

QC 20190923

Available from: 2019-09-23 Created: 2019-09-23 Last updated: 2019-09-23Bibliographically approved
Zhang, W., Hua, Y., Wang, L., Zhang, B., Li, Y., Liu, P., . . . Kloo, L. (2019). The Central Role of Ligand Conjugation for Properties of Coordination Complexes as Hole-Transport Materials in Perovskite Solar Cells. ACS APPLIED ENERGY MATERIALS, 2(9), 6768-6779
Open this publication in new window or tab >>The Central Role of Ligand Conjugation for Properties of Coordination Complexes as Hole-Transport Materials in Perovskite Solar Cells
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2019 (English)In: ACS APPLIED ENERGY MATERIALS, ISSN 2574-0962, Vol. 2, no 9, p. 6768-6779Article in journal (Refereed) Published
Abstract [en]

Two zinc-based coordination complexes Y3 and Y4 have been synthesized and characterized, and their performance as hole-transport materials (HTMs) for perovskite solar cells (PSCs) has been investigated. The complex Y3 contains two separate ligands, and the molecular structure can be seen as a disconnected porphyrin ring. On the other hand, Y4 consists of a porphyrin core and therefore is a more extended conjugated system as compared to Y3. The optical and redox properties of the two different molecular complexes are comparable. However, the hole mobility and conductivity of Y4 as macroscopic material are remarkably higher than that of Y3. Furthermore, when employed as hole-transport materials in perovskite solar cells, cells containing Y4 show a power conversion efficiency (PCE) of 16.05%, comparable to the Spiro-OMeTAD-based solar cells with an efficiency around 17.08%. In contrast, solar cells based on Y3 show a negligible efficiency of about 0.01%. The difference in performance of Y3 and Y4 is analyzed and can be attributed to the difference in packing of the nonplanar and planar building blocks in the corresponding materials.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2019
Keywords
ligand conjugation, coordination complex, porphyrin, hole-transport material, perovskite
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-261967 (URN)10.1021/acsaem.9b01223 (DOI)000487770000073 ()
Note

QC 20191014

Available from: 2019-10-14 Created: 2019-10-14 Last updated: 2019-10-14Bibliographically 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: 2018-05-23Bibliographically approved
Phuyal, D., Safdari, M., Pazoki, M., Liu, P., Philippe, B., Kyashnina, K. O., . . . Gardner, J. M. (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.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-234611 (URN)10.1021/acs.chemmater.8b00909 (DOI)000442186500014 ()2-s2.0-85050821628 (Scopus ID)
Note

QC 20180914

Available from: 2018-09-14 Created: 2018-09-14 Last updated: 2018-09-14Bibliographically approved
Gao, J., El-Zohry, A. M., Trilaksana, H., Gabrielsson, E., Leandri, V., Ellis, H., . . . Kloo, L. (2018). Light-Induced Interfacial Dynamics Dramatically Improve the Photocurrent in Dye-Sensitized Solar Cells: An Electrolyte Effect. ACS Applied Materials and Interfaces, 10(31), 26241-26247
Open this publication in new window or tab >>Light-Induced Interfacial Dynamics Dramatically Improve the Photocurrent in Dye-Sensitized Solar Cells: An Electrolyte Effect
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2018 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, no 31, p. 26241-26247Article in journal (Refereed) Published
Abstract [en]

A significant increase in the photocurrent generation during light soaking for solar cells sensitized by the triphenylamine-based D-pi-A organic dyes (PD2 and LEG1) and mediated by cobalt bipyridine redox complexes has been observed and investigated. The crucial role of the electrolyte has been identified in the performance improvement. Control experiments based on a pretreatment strategy reveals TBP as the origin. The increase in the current and IPCE has been interpreted by the interfacial charge-transfer kinetics studies. A slow component in the injection kinetics was exposed for this system. This change explains the increase in the electron lifetime and collection efficiency. Photoelectron spectroscopic measurements show energy shifts at the dye/TiO2 interface, leading us to formulate a hypothesis with respect to an electrolyte induced dye reorganization at the surface.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2018
Keywords
dye-sensitized solar cells, electrolyte, interface, dynamics, light soaking
National Category
Other Chemistry Topics
Identifiers
urn:nbn:se:kth:diva-234184 (URN)10.1021/acsami.8b06897 (DOI)000441477800045 ()29996051 (PubMedID)2-s2.0-85049917640 (Scopus ID)
Note

QC 20181003

Available from: 2018-10-03 Created: 2018-10-03 Last updated: 2018-11-23Bibliographically approved
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