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El-Zohry, Ahmed
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Publications (10 of 14) Show all publications
Abdelhamid, H. N., Wilk-Kozubek, M., El-Zohry, A., Gomez, A. B., Valiente, A., Martin-Matute, B., . . . Zou, X. (2019). Luminescence properties of a family of lanthanide metal-organic frameworks. Microporous and Mesoporous Materials, 279, 400-406
Open this publication in new window or tab >>Luminescence properties of a family of lanthanide metal-organic frameworks
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2019 (English)In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 279, p. 400-406Article in journal (Refereed) Published
Abstract [en]

Two isostructural series of lanthanide metal-organic frameworks denoted as SUMOF-7II (Ln) and SUMOF-7IIB (Ln) (Ln = La, Ce, Pr, Nd, Sm, Eu, and Gd) were synthesized using4,4',4 ''-(pyridine-2,4,6-triyl)tris(benzoic acid) (H(3)L2) and a mixture of H(3)L2 and 4,4',4 ''-(benzene-1,3,5-triyl)tris(benzoic acid) (H3BTB) as linkers, respectively. Both series were characterized using powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermal analysis (TGA), and photoluminescence spectroscopy. Photoluminescence measurements show that Eu-MOFs demonstrate a red emission while Pr- and Nd-MOFs display an emission in the near-infrared (NIR) range. On the other hand, La-, Ce-, Sm- and Gd-MOFs exhibit only a ligand-centered emission. The average luminescence lifetimes in the SUMOF-7IIB series are 1.3-1.4-fold longer than the corresponding ones in the SUMOF-7II series. SUMOF-7IIs show a good photo- and thermal stability. Altogether, the properties of SUMOF-7II and SUMOF-7IIB render them promising materials for applications including sensing, biosensing, and telecommunications.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2019
Keywords
Metal-organic frameworks, Lanthanide MOFs, Antenna effect, Luminescence, Photostability, Photophysical properties
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-380418 (URN)10.1016/j.micromeso.2019.01.024 (DOI)000460843500044 ()
Funder
Swedish Research CouncilVinnova
Available from: 2019-04-02 Created: 2019-04-02 Last updated: 2019-04-02Bibliographically approved
El-Zohry, A. M. (2019). The origin of slow electron injection rates for indoline dyes used in dye-sensitized solar cells. Dyes and pigments, 160, 671-674
Open this publication in new window or tab >>The origin of slow electron injection rates for indoline dyes used in dye-sensitized solar cells
2019 (English)In: Dyes and pigments, ISSN 0143-7208, E-ISSN 1873-3743, Vol. 160, p. 671-674Article in journal (Refereed) Published
Abstract [en]

This work highlights the direct impact of selecting acceptor moiety for organic dyes on the electron dynamics at faster time scales, in which overlooked photo-physical properties are present on semiconductor surfaces with specific acceptor moieties. Four top-performing dyes of indoline family (D131, D102, D149, and D205) sharing the same donor moiety, but through different acceptor groups, were selected and compared with respect of electron injection process, using ultrafast transient-infrared probe. The presence of rhodanine moiety at the acceptor unit in D102, D149 and D205, shows an additional slow electron injection process, of picosecond time-scale, on the low band-gap semiconductor, TiO2. This slow process is expected to be present due to a twisted intramolecular charge transfer/isomerized state of the excited dye prior to electron injection. This isomerized state reduces as well the detrimental electron recombination process rates, and results of high performance in solar cells based on these rhodanine dyes. Replacing the rhodanine moiety by a cyano-acrylic group in D131 dye shows faster electron injection and recombination processes, due to the lower dipole moment present in the excited state, hindering the formation of an isomerized state. These findings will aid to enhance the organic dyes design used in dye sensitized solar cells, in which designed photo-physical processes on semiconductor surfaces can increase the efficiencies of the solar cells.

Place, publisher, year, edition, pages
ELSEVIER SCI LTD, 2019
Keywords
Mid-IR, Electron dynamics, Semiconductors, Torsional motions, Acceptor moities, Rhodanine, Cyano-acrylic acid
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-369379 (URN)10.1016/j.dyepig.2018.09.002 (DOI)000447816700081 ()
Available from: 2019-01-15 Created: 2019-01-15 Last updated: 2019-01-15Bibliographically approved
El-Zohry, A. & Karlsson, M. (2018). Gigantic Relevance of Twisted Intramolecular Charge Transfer for Organic Dyes Used in Solar Cells. The Journal of Physical Chemistry C, 122(42), 23998-24003
Open this publication in new window or tab >>Gigantic Relevance of Twisted Intramolecular Charge Transfer for Organic Dyes Used in Solar Cells
2018 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 42, p. 23998-24003Article in journal (Refereed) Published
Abstract [en]

Within this work, we emphasis on the importance of twisted intramolecular charge transfer (TICT) process in organic dyes based on triphenyl amine moiety to achieve high performance in dye-sensitized solar cells. Through the comparison between two recent made dyes, Ll and L1Fc, on different semiconductors (TiO2, and ZrO2), we could spectrally and dynamically detect for the first time the formation of TICT state for Ll on ZrO2 after localized charge transfer (LCT) state population, and an electron injection process from TICT state on TiO2. However, for the excited L1Fc dye, the ultrafast electron transfer from ferrocene (Fc) moiety to the Ll unit quenched the formation of TICT state in L1Fc on semiconductors, leading instead to an electron injection process from the LCT state. The electron injection from TICT state in Ll associated with structural rearrangements on TiO2 leads to slow recombination process and an efficiency improvement of about 325%, compared to solar cells based on L1Fc dye, in which TICT state formation is hindered. Similar electron dynamics are obtained for Ll on TiO2 upon physically hindering the TICT process by adding polymer matrix. The presence of TICT state for Ll dye and similar triphenyl amine dyes aids to reconstruct the kinetic profile for these dyes on semiconductor surfaces, and to redesign organic dyes accordingly for higher efficiency in solar cells.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2018
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-369894 (URN)10.1021/acs.jpcc.8b08326 (DOI)000448754300020 ()
Available from: 2018-12-19 Created: 2018-12-19 Last updated: 2018-12-19Bibliographically approved
Gao, J., El-Zohry, A., 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
Materials Chemistry Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-362697 (URN)10.1021/acsami.8b06897 (DOI)000441477800045 ()29996051 (PubMedID)
Funder
Swedish Research CouncilSwedish Energy Agency
Available from: 2018-10-11 Created: 2018-10-11 Last updated: 2018-10-11Bibliographically approved
Abdelhamid, H. N., Huang, Z., El-Zohry, A., Zheng, H. & Zou, X. (2017). A Fast and Scalable Approach for Synthesis of Hierarchical Porous Zeolitic Imidazolate Frameworks and One-Pot Encapsulation of Target Molecules. Inorganic Chemistry, 56(15), 9139-9146
Open this publication in new window or tab >>A Fast and Scalable Approach for Synthesis of Hierarchical Porous Zeolitic Imidazolate Frameworks and One-Pot Encapsulation of Target Molecules
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2017 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 56, no 15, p. 9139-9146Article in journal (Refereed) Published
Abstract [en]

A trimethylamine (TEA)-assisted synthesis approach that combines the preparation of hierarchical porous zeolitic, imidazolate framework ZIF-8, nanoparticles and one-pot encapsulation of target molecules is presented. Two dye molecules, rhodamine B (RhB) and methylene blue (MB), and one protein (bovine serum albumin, BSA) were, tested as the target molecules. The addition of TEA into the solution of zinc nitrate promoted the formation of ZnO nanocrystals, which rapidly transformed to ZIF-8 nanoparticles after the addition of the linker 2-methylimidazole (Hmim): Hierarchical porous dye@ZIF-8 nanoparticles with high crystallinity, large BET surface areas (1300-2500 m(2)/g), and large pore Volatiles (0.5-1.0 cm(3)/g) could be synthesized. The synthesis procedure was fast (down to 2 min) and scalable. The Hmim/Zn ratio could be greatly reduced (down to 2:1) compared to previously reported ones. The surface areas, and the mesopore size, structure, and density could be modified by changing the TEA or dye concentrations, or by postsynthetic treatment using reflux in methanol. This synthesis and one-pot encapsulation approach is simple and can be readily scaled Up. The photophysical properties such as lifetime and photostability of the dyes could be tuned via encapsulation. The lifetimes of the encapsulated dyes were increased by 3-27-fold for RhB@ZIF-8 and by 20-fold for MB@ZIF-8, compared to those of the corresponding free dyes. The synthesis approach is general, which was successfully applied for encapsulation of protein BSA. It could also be extended for the synthesis of hierarchical porous cobalt-based ZIP (dye@ZIF-67).

National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-359807 (URN)10.1021/acs.inorgchem.7b01191 (DOI)000407405500060 ()28715176 (PubMedID)
Funder
Swedish Research CouncilVINNOVAKnut and Alice Wallenberg Foundation
Available from: 2018-09-24 Created: 2018-09-24 Last updated: 2018-09-24Bibliographically approved
El-Zohry, A. M., Cong, J., Karlsson, M., Kloo, L. & Zietz, B. (2016). Ferrocene as a rapid charge regenerator in dye-sensitized solar cells. Dyes and pigments, 132, 360-368
Open this publication in new window or tab >>Ferrocene as a rapid charge regenerator in dye-sensitized solar cells
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2016 (English)In: Dyes and pigments, ISSN 0143-7208, E-ISSN 1873-3743, Vol. 132, p. 360-368Article in journal (Refereed) Published
Abstract [en]

Using the reductive power of the ferrocene moiety (Fc), an ultrafast regeneration step via a covalent attachment of a Fc moiety to an organic triphenylamine-based dye (L1) when adsorbed on TiO2 is highlighted. Two modified dyes with one and two Fc moieties attached (L1Fc, and L1Fc2), respectively, were synthesized by addition to the L1 dye. These dyes have been studied spectroscopically using ultrafast transient absorption spectroscopy in the visible and the infrared (IR) regions. In acetonitrile, the results show an ultrafast excited state quenching of the modified dyes due to an expected electron transfer process from the Fc(s) to L1. Adsorbed onto TiO2, an electron transfer process is also detected from Fc to the oxidized dye (L1(+)). Despite the occurrence of an ultrafast regeneration step, the solar cell performance does not improve by the attachment of Fc(s) to the dye L1. Transient absorption measurements in the IR region revealed a fast electron recombination process to the Fc(+) moiety on an average time scale of ca. 300 ps, outcompeting the >12 ns process to L1(+). The reasons for the observed considerably faster recombination rate to Fc(+) than to L1(+) are discussed in detail. This study provides deep spectroscopic insights for such organic dyes utilized to afford ultrafast regeneration step without showing high performance in photovoltaic devices. In addition, this study will improve our understandings for the triangular relationship between the molecular design, electron kinetics, and the performance in photovoltaic devices.

Keywords
Electron dynamics, Charge transfer, Recombination, Transient absorption, Organic dyes
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-299825 (URN)10.1016/j.dyepig.2016.05.021 (DOI)000378456200043 ()
Funder
Swedish Research CouncilSwedish Energy AgencyKnut and Alice Wallenberg Foundation
Available from: 2016-07-29 Created: 2016-07-28 Last updated: 2017-11-28Bibliographically approved
Pavliuk, M. V., Fernandes, D. L. A., El-Zohry, A., Abdellah, M., Nedelcu, G., Kovalenko, M. V. & Sá, J. (2016). Magnetic Manipulation of Spontaneous Emission from Inorganic CsPbBr3 Perovskites Nanocrystals. ADVANCED OPTICAL MATERIALS, 4(12), 2004-2008
Open this publication in new window or tab >>Magnetic Manipulation of Spontaneous Emission from Inorganic CsPbBr3 Perovskites Nanocrystals
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2016 (English)In: ADVANCED OPTICAL MATERIALS, ISSN 2195-1071, Vol. 4, no 12, p. 2004-2008Article in journal (Refereed) Published
Abstract [en]

Metal halide perovskites have shown great potential for both light-absorbing and light-emitting devices. It is demonstrated that the presence of a low-magnetic field decreases dramatically the photoluminescence of CsPbBr3. This is found to be due to a decrease in charge separated state lifetime. The effect is fully reversible, and can be exploited for simple and remote modulation of the output of light-emitting devices.

National Category
Physical Chemistry Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-315916 (URN)10.1002/adom.201600611 (DOI)000392405100014 ()
Funder
Knut and Alice Wallenberg FoundationSwedish Research Council, 2015-03764EU, FP7, Seventh Framework Programme, 306733
Available from: 2017-02-23 Created: 2017-02-23 Last updated: 2018-12-17Bibliographically approved
El-Zohry, A. M., Roca-Sanjuán, D. & Zietz, B. (2015). Ultrafast Twisting of the Indoline Donor Unit Utilized in Solar Cell Dyes: Experimental and Theoretical Studies. The Journal of Physical Chemistry C, 119(5), 2249-2259
Open this publication in new window or tab >>Ultrafast Twisting of the Indoline Donor Unit Utilized in Solar Cell Dyes: Experimental and Theoretical Studies
2015 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 5, p. 2249-2259Article in journal (Refereed) Published
Abstract [en]

Previous time-resolved measurements on D149, the most-studied dye of the indoline family, had shown a fast time-component of 20–40 ps that had tentatively been attributed to structural relaxation. Using femtosecond transient absorption, we have investigated the isolated indoline donor unit (i.e., without acceptor group) and found an ultrafast decay characterized by two lifetimes of 3.5 and 23 ps. Density functional theory calculations show π-bonding and π*-antibonding character of the central ethylene group for the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO), respectively. The LUMO is localized on the flexible vinyl-diphenyl region of the donor unit and a twisting process is assumed to occur as a deactivation process for the excited molecule. This is confirmed by multireference second-order perturbation theory (CASSCF/CASPT2) calculations of the lowest-lying excited state, in which it is shown that torsion of the ethylene bond to 96° and pyramidalization to ca. 100° lead to a conical intersection with the ground state. Embedded in a plastic matrix, where double bond rotation is hindered, the decay is slowed down to nanoseconds. We have also investigated the dyes D102, D131, and D149, possessing the same indoline donor unit, by femtosecond transient absorption and found a similar decay component. The ca. 20 ps deactivation channel in D-family dyes is thus attributed to a twisting process of the donor unit. The fluorescence quantum yields of this unit and D149 were measured, and from comparison, the competition of the discovered twisting deactivation channel to the radiative decay of the excited indoline dyes could be confirmed. Blocking this deactivation channel is expected to further increase efficiency for the indoline dyes.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-263141 (URN)10.1021/jp505649s (DOI)
Available from: 2015-09-27 Created: 2015-09-27 Last updated: 2017-12-01Bibliographically approved
El-Zohry, A. M., Roca-Sanjuan, D. & Zietz, B. (2015). Ultrafast Twisting of the Indoline Donor Unit Utilized in Solar Cell Dyes: Experimental and Theoretical Studies. The Journal of Physical Chemistry C, 119(5), 2249-2259
Open this publication in new window or tab >>Ultrafast Twisting of the Indoline Donor Unit Utilized in Solar Cell Dyes: Experimental and Theoretical Studies
2015 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 5, p. 2249-2259Article in journal (Refereed) Published
Abstract [en]

Previous time-resolved measurements on D149, the most-studied dye of the indoline family, had shown a fast time-component of 20-40 ps that had tentatively been attributed to structural relaxation. Using femtosecond transient absorption, we have investigated the isolated indoline donor unit (i.e., without acceptor group) and found an ultrafast decay characterized by two lifetimes of 3.5 and 23 ps. Density functional theory calculations show p-bonding and p*-antibonding character of the central ethylene group for the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO), respectively. The LUMO is localized on the flexible vinyl-diphenyl region of the donor unit and a twisting process is assumed to occur as a deactivation process for the excited molecule. This is confirmed by multireference second-order perturbation theory (CASSCF/CASPT2) calculations of the lowest-lying excited state, in which it is shown that torsion of the ethylene bond to 96 degrees and pyramidalization to ca. 100 degrees lead to a conical intersection with the ground state. Embedded in a plastic matrix, where double bond rotation is hindered, the decay is slowed down to nanoseconds. We have also investigated the dyes D102, D131, and D149, possessing the same indoline donor unit, by femtosecond transient absorption and found a similar decay component. The ca. 20 ps deactivation channel in D-family dyes is thus attributed to a twisting process of the donor unit. The fluorescence quantum yields of this unit and D149 were measured, and from comparison, the competition of the discovered twisting deactivation channel to the radiative decay of the excited indoline dyes could be confirmed. Blocking this deactivation channel is expected to further increase efficiency for the indoline dyes.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-247391 (URN)10.1021/jp505649s (DOI)000349136400001 ()
Available from: 2015-03-20 Created: 2015-03-18 Last updated: 2017-12-04
Bi, D., El-Zohry, A. M., Hagfeldt, A. & Boschloo, G. (2015). Unraveling the Effect of PbI2 Concentration on Charge Recombination Kinetics in Perovskite Solar Cells. ACS Photonics, 2(5), 589-594
Open this publication in new window or tab >>Unraveling the Effect of PbI2 Concentration on Charge Recombination Kinetics in Perovskite Solar Cells
2015 (English)In: ACS Photonics, E-ISSN 2330-4022, Vol. 2, no 5, p. 589-594Article in journal (Refereed) Published
Abstract [en]

CH3NH3PbI3 perovskite solar cells have rapidly risen to the forefront of emerging photovoltaic technologies. A solution-based, two-step method was reported to enhance the reproducibility of these solar cells. In this method, first a coating of PbI2 is applied by spin-coating onto a TiO2-coated substrate, followed by a dip in a methylammonium iodide solution, leading to conversion to CH3NH3PbI3. The concentration of PbI2 in the spin-coating solution is a very important factor that affects the infiltration of the perovskite and the amount deposited. The best solar cell performance of 13.9% was obtained by devices prepared using 1.0 M of PbI2 in dimethylformamide. These devices also had the longest electron lifetime and shortest carrier transport time, yielding lowest recombination losses. Rapid quenching of the perovskite emission is found in device-like structures, suggesting reasonably good efficient carrier extraction at the TiO2 interface and quantitative extraction at the spiro-OMeTAD interface.

Keywords
CH3NH3PbI3, recombination, emission lifetime, hybrid photovoltaics
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-256848 (URN)10.1021/ph500255t (DOI)000355066900005 ()
Available from: 2015-06-26 Created: 2015-06-26 Last updated: 2018-06-14Bibliographically approved
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