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Publications (10 of 30) Show all publications
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: 2019-12-09Bibliographically 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
Hua, Y., Liu, P., Li, Y., Sun, L. & Kloo, L. (2018). Composite Hole-Transport Materials Based on a Metal-Organic Copper Complex and Spiro-OMeTAD for Efficient Perovskite Solar Cells. SOLAR RRL, 2(5), Article ID UNSP 1700073.
Open this publication in new window or tab >>Composite Hole-Transport Materials Based on a Metal-Organic Copper Complex and Spiro-OMeTAD for Efficient Perovskite Solar Cells
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2018 (English)In: SOLAR RRL, ISSN 2367-198X, Vol. 2, no 5, article id UNSP 1700073Article in journal (Refereed) Published
Abstract [en]

Spiro-OMeTAD has been the most commonly used hole-transport material in perovskite solar cells. However, this material shows intrinisic drawbacks, such as low hole mobility and conductivity in its pristine form, as well as self-aggregation when deposited as thin film. These are not beneficial properties for efficient hole transport and extraction. In order to address these issues, we have designed a new type of composite hole-transport materials based on a new metal-organic copper complex (CuH) and Spiro-OMeTAD. The incorporation of the molecularly bulky HTM CuH into the Spiro-OMeTAD material efficiently improves the hole mobility and suppresses the aggregation in the Spiro-OMeTAD film. As a result, the conversion efficiencies obtained for perovskite solar cells based on the composite HTM system reached as high as 18.83%, which is superior to solar cells based on the individual hole-transport materials CuH (15.75%) or Spiro-OMeTAD (14.47%) under the same working conditions. These results show that composite HTM systems may constitute an effective strategy to further improve the efficiency of perovskite solar cells.

Place, publisher, year, edition, pages
WILEY-V C H VERLAG GMBH, 2018
Keywords
Hole transport materials, mobility, perovskite solar cells, small molecules
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-228439 (URN)10.1002/solr.201700073 (DOI)000432036200001 ()
Note

QC 20180529

Available from: 2018-05-29 Created: 2018-05-29 Last updated: 2018-05-29Bibliographically approved
Xu, P., Liu, P., Li, Y., Xu, B., Kloo, L., Sun, L. & Hua, Y. (2018). D-A-D-Typed Hole Transport Materials for Efficient Perovskite Solar Cells: Tuning Photovoltaic Properties via the Acceptor Group. ACS Applied Materials and Interfaces, 10(23), 19697-19703
Open this publication in new window or tab >>D-A-D-Typed Hole Transport Materials for Efficient Perovskite Solar Cells: Tuning Photovoltaic Properties via the Acceptor Group
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2018 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, no 23, p. 19697-19703Article in journal (Refereed) Published
Abstract [en]

Two D-A-D-structured hole-transport materials (YN1 and YN2) have been synthesized and used in perovskite solar cells. The two HTMs have low-lying HOMO levels and impressive mobility. Perovskite-based solar cells (PSCs) fabricated with YN2 showed a power conversion efficiency (PCE) value of 19.27% in ambient air, which is significantly higher than that of Spiro-OMeTAD (17.80%). PSCs based on YN1 showed an inferior PCE of 16.03%. We found that the incorporation of the stronger electron-withdrawing group in the HTM YN2 improves the PCE of PSCs. Furthermore, the YN2-based PSCs exhibit good long-term stability retaining 91.3% of its initial efficiency, whereas PSCs based on Spiro-OMeTAD retained only 42.2% after 1000 h lifetime (dark conditions). These promising results can provide a new strategy for the design of D-A-D HTMs for PSC applications in future.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2018
Keywords
acceptor, hole-transport material, mobility, perovskite solar cells, spiro-OMeTAD
National Category
Other Chemistry Topics
Identifiers
urn:nbn:se:kth:diva-238197 (URN)10.1021/acsami.8b04003 (DOI)000435525100045 ()29785846 (PubMedID)2-s2.0-85047487298 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationSwedish Energy Agency
Note

QC 20181119

Available from: 2018-11-19 Created: 2018-11-19 Last updated: 2018-11-19Bibliographically approved
Wang, L., Zhang, J., Liu, P., Xu, B., Zhang, B., Chen, H., . . . Sun, L. (2018). Design and synthesis of dopant-free organic hole-transport materials for perovskite solar cells. Chemical Communications, 54(69)
Open this publication in new window or tab >>Design and synthesis of dopant-free organic hole-transport materials for perovskite solar cells
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2018 (English)In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 54, no 69Article in journal (Refereed) Published
Abstract [en]

Two novel dopant-free hole-transport materials (HTMs) with spiro[dibenzo[c,h]xanthene-7,9-fluorene] (SDBXF) skeletons were prepared via facile synthesis routes. A power conversion efficiency of 15.9% in perovskite solar cells is attained by using one HTM without dopants, which is much higher than undoped Spiro-OMeTAD-based devices (10.8%). The crystal structures of both new HTMs were systematically investigated to reveal the reasons behind such differences in performance and to indicate the design principles of more advanced HTMs.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2018
National Category
Textile, Rubber and Polymeric Materials
Identifiers
urn:nbn:se:kth:diva-234569 (URN)10.1039/c8cc04026e (DOI)000442605100002 ()30043013 (PubMedID)2-s2.0-85052539543 (Scopus ID)
Funder
Swedish Energy Agency
Note

QC 20180917

Available from: 2018-09-17 Created: 2018-09-17 Last updated: 2019-08-20Bibliographically 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: 2019-12-09Bibliographically approved
Sharmoukh, W., Cong, J., Gao, J., Liu, P., Quentin, D. & Kloo, L. (2018). Molecular Engineering of D-D-pi-A-Based Organic Sensitizers for Enhanced Dye-Sensitized Solar Cell Performance. ACS OMEGA, 3(4), 3819-3829
Open this publication in new window or tab >>Molecular Engineering of D-D-pi-A-Based Organic Sensitizers for Enhanced Dye-Sensitized Solar Cell Performance
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2018 (English)In: ACS OMEGA, ISSN 2470-1343, Vol. 3, no 4, p. 3819-3829Article in journal (Refereed) Published
Abstract [en]

A series of molecularly engineered and novel dyes WS1, WS2, WS3, and WS4, based on the D35 donor, 1-(4-hexylphenyl)-2,5-di(thiophen-2-yl)-1H-pyrrole and 4-(4-hexylphenyl)-4H-dithieno[3,2-b: 2', 3'-d] pyrrole as pi-conjugating linkers, were synthesized and compared to the well-known LEG4 dye. The performance of the dyes was investigated in combination with an electrolyte based on Co(II/III) complexes as redox shuttles. The electron recombination between the redox mediators in the electrolyte and the TiO2 interface decreases upon the introduction of 4-hexylybenzene entities on the 2,5-di(thiophen-2-yl)-1H-pyrrole and 4H-dithieno[3,2-b: 2', 3'-d] pyrrole linker units, probably because of steric hindrance. The open circuit photovoltage of WS1-, WS2-, WS3-, and WS4-based devices in combination with the Co(II/III)-based electrolyte are consistently higher than those based on a I-/I-3(-) electrolyte by 105, 147, 167, and 75 mV, respectively. The WS3-based devices show the highest power conversion efficiency of 7.4% at AM 1.5 G 100 mW/cm(2) illumination mainly attributable to the high open-circuit voltage (V-OC).

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2018
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-227229 (URN)10.1021/acsomega.8b00271 (DOI)000430200300022 ()2-s2.0-85045042845 (Scopus ID)
Note

QC 20150514

Available from: 2018-05-14 Created: 2018-05-14 Last updated: 2019-10-08Bibliographically approved
Liu, P., Wang, L., Karlsson, K. M., Hao, Y., Gao, J., Xu, B., . . . Kloo, L. (2018). Molecular Engineering of D-pi-A Type of Blue-Colored Dyes for Highly Efficient Solid-State Dye-Sensitized Solar Cells through Co-Sensitization. ACS Applied Materials and Interfaces, 10(42), 35946-35952
Open this publication in new window or tab >>Molecular Engineering of D-pi-A Type of Blue-Colored Dyes for Highly Efficient Solid-State Dye-Sensitized Solar Cells through Co-Sensitization
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2018 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, no 42, p. 35946-35952Article in journal (Refereed) Published
Abstract [en]

A novel blue-colored organic donor-pi-acceptor sensitizer, the so-called MKA16 dye, has been employed to construct solid-state dye-sensitized solar cells (ssDSSCs). Using 2,2',7-,7'-tetrakis(N,N-di-p-methoxyphenyl-amine) 9,9'-spirobifuorene (Spiro-OMeTAD) as hole-transport material, a good conversion efficiency of 5.8% was recorded for cells based on the MKA16 dye and a high photovoltage of 840 mV in comparison with 5.6% efficiency using the known (Dyenamo Blue) dye. By co-sensitization using the orange-colored D35 dye and MKA16 together, the solid-state solar cells showed an excellent efficiency of 7.5%, with a high photocurrent of 12.41 mA cm(-2) and open-circuit voltage of 850 mV. The results show that the photocurrent of ssDSSCs can be significantly improved by co-sensitization mainly attributed to the wider light absorption range contributing to the photocurrent. In addition, results from photo-induced absorption spectroscopy show that the dye regeneration is efficient in co-sensitized solar cells. The current results possible routes of improving the design of aesthetic and highly efficient ssDSSCs.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2018
Keywords
solid-state dye-sensitized solar cell, blue-colored dye, co-sensitization, molecular engineering, D-pi-A dye
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-239097 (URN)10.1021/acsami.8b11405 (DOI)000448754500028 ()30260625 (PubMedID)2-s2.0-85054957061 (Scopus ID)
Note

QC 20181121

Available from: 2018-11-21 Created: 2018-11-21 Last updated: 2019-08-20Bibliographically approved
Chen, C., Zhang, W., Cong, J., Cheng, M., Zhang, B., Chen, H., . . . Sun, L. (2017). Cu(II) Complexes as p-Type Dopants in Efficient Perovskite Solar Cells. ACS ENERGY LETTERS, 2(2), 497-503
Open this publication in new window or tab >>Cu(II) Complexes as p-Type Dopants in Efficient Perovskite Solar Cells
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2017 (English)In: ACS ENERGY LETTERS, ISSN 2380-8195, Vol. 2, no 2, p. 497-503Article in journal (Refereed) Published
Abstract [en]

In this work, two Cu(II) complex compounds are designed and synthesized for applications as p-type dopants in solid-state perovskite solar cells (PSCs). Through the characterization of the optical and electrochemical properties, the complex Cu(bpcm)(2) is shown to be eligible for oxidization of the commonly used hole-transport material (HTM) SpiroOMeTAD. The reason is the electron-withdrawing effect of the chloride groups on the ligands. When the complex was applied as p-type dopant in PSCs containing Spiro-OMeTAD as HTM, an efficiency as high as 18.5% was achieved. This is the first time a Cu(II) pyridine complex has been used as p-type dopant in PSCs.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2017
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-204091 (URN)10.1021/acsenergylett.6b00691 (DOI)000394080000031 ()2-s2.0-85034060563 (Scopus ID)
Note

qc 20170329

Available from: 2017-03-29 Created: 2017-03-29 Last updated: 2019-12-09Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-5069-3245

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