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An arylene-vinylene based donor-acceptor-donor small molecule for the donor compound in high-voltage organic solar cells
Umeå University, Faculty of Science and Technology, Department of Chemistry. Department of Chemistry, University of Agriculture, Faisalabad 38040, Pakistan.
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.
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2016 (English)In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 155, p. 348-355Article in journal (Refereed) Published
Abstract [en]

A donor-acceptor-donor (D-A-D) molecule has been designed and synthesized for use as the electron donating material in solution-processed small-molecule organic solar cells (OSCs). The D-A-D molecule comprises a central electron-accepting (2Z,2'Z)-2,2'-(2,5-bis(octyloxy)-1,4-phenylene)bis(3-(thiophen-2-yl)acry lonitrile) (ZOPTAN) core, which is chemically connected to two peripheral and electron-donating triphenylamine (TPA) units. The ZOPTAN-TPA molecule features a low HOMO level of -5.2 eV and an optical energy gap of 2.1 eV. Champion OSCs based on a solution-processed and non-annealed active material blend of [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) and ZOPTAN-TPA in a mass ratio of 2:1 exhibits a power conversion efficiency of 1.9% and a high open-circuit voltage of 1.0 V. 

Place, publisher, year, edition, pages
2016. Vol. 155, p. 348-355
Keywords [en]
Organic solar cell, Small-molecule donor, Fullerene acceptor, Solution processing, High open-circuit ltage, Thermal stability
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:umu:diva-126290DOI: 10.1016/j.solmat.2016.06.018ISI: 000381529100040OAI: oai:DiVA.org:umu-126290DiVA, id: diva2:1045122
Projects
Wallenberg 2011.0055
Note

Originally included in Christian Larsens thesis with title [An Arylene-Vinylene Based Donor-Acceptor-Donor Small Molecule for the DonorCompound in High-Voltage Organic Solar Cells].

Available from: 2016-11-08 Created: 2016-10-03 Last updated: 2019-12-18Bibliographically approved
In thesis
1. Molecular design, synthesis and performance evaluation of phenothiazine-based small molecules for efficient organic solar cells
Open this publication in new window or tab >>Molecular design, synthesis and performance evaluation of phenothiazine-based small molecules for efficient organic solar cells
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Design, syntes och utvärdering av fenotiazin-innehållande små molekyler till effektiva organiska solceller
Abstract [en]

Photovoltaics offers one of the most promising routes to generate electricity in a clean way. As an emerging technology in photovoltaics, organic solar cells (OSC) have attracted a great deal of attention owing to their potential low-cost, lightweight, flexibility and solution processability. Although power conversion efficiencies above 12% have been achieved at this date, there is a great interest for new ideal materials to further improve the PCEs and address device durability, which are major concerns for the commercialization of this technology. The main objective of this thesis is to design and synthesize phenothiazine-based conjugate small molecules and explore their use as electron donor components in OSCs. Phenothiazine is a non-planar moiety with unusual “butterfly” type of geometry, which is known to reduce molecular aggregation and intermolecular excimer formation.

In the first study of this thesis, a small molecule based on a cyano-arylenevinylene building block with deep HOMO level was prepared. Although a high open-circuit voltage of 1.0 V was achieved, the tendency of the small molecule to crystallize in the active layer at a higher temperature and with time hindered the attainment of an optimal phase morphology required for the achievement of a higher efficiency. In the second and third studies, phenothiazine was used as a π-system bridge and as a core unit to construct small molecules based on symmetric and asymmetric frameworks with varying terminal electron-withdrawing groups. The electron-withdrawing property of the terminal units was found to have a significant influence on the optical absorption properties, electronic energy levels, molecular ordering, charge carrier mobility and morphology of the resulting active layers. In the fourth study, side-chain modification of the phenothiazine unit of symmetrically configured small molecules with an oxygen-containing (methoxyethoxy ethyl) side chain resulted in the enhancement of the dielectric constant. Although absorption properties were unchanged in solution, a dense π-π stacking was observed in the solid state.

In summary, it is demonstrated that phenothiazine is a promising candidate and worth exploring donor material for OSCs. Its versatility as a π-linker and as a central core unit in symmetric and asymmetric configurations has been explored. The use of nonplanar building blocks such as phenothiazine for the construction of donor materials is an interesting strategy for controlling molecular aggregation and difficult solution processability of small molecules if it is combined with a judiciously designed conjugate backbone.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2018. p. 90
Keywords
Organic solar cell, small molecule donors, phenothiazine, power conversion efficiency
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:umu:diva-144465 (URN)978-91-7601-835-4 (ISBN)
Public defence
2018-02-28, KBE301 - Lilla Hörsalen, KBC-huset, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2018-02-07 Created: 2018-02-04 Last updated: 2018-06-09Bibliographically approved
2. Structure and morphology control of organic semiconductors for functional optoelectronic applications
Open this publication in new window or tab >>Structure and morphology control of organic semiconductors for functional optoelectronic applications
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The functionality and application of organic semiconductors are largely dependent on their constituent structure and morphology. This thesis presents a number of functional and novel approaches for the control and tuning of structural and morphological features of a variety of organic semiconductor materials, and also demonstrates that these approaches can be utilized for improved device operation of field-effect transistors, organic solar cells and light-emitting electrochemical cells.

The fullerene family is a particular group of closed-cage organic semiconductors, which can be photochemically coupled into larger dimeric or polymeric structures through the excitation of the fullerene molecules by light emission. In Paper I, we perform a detailed experimental and analytical investigation, which demonstrates that this photochemical monomer-to-dimer transformation requires that both constituent fullerene molecules are photoexcited. The direct consequence is that the initial probability for the photochemical transformation is dependent on the square of the light-emission intensity.

The photochemical coupling of fullerene molecules commonly results in a distinctly lowered solubility in common hydrophobic solvents, which can be utilized for the direct patterning of fullerene films by resist-free lithography. In Paper II, we utilize this patterning opportunity for the fabrication of one-dimensional fullerene nano-stripes using two-beam laser interference lithography. A desired high contrast between the patterned and non-patterned fullerene regions is facilitated by the non-linear response of the photochemical transformation process, as predicted by the findings in Paper I. The patterned fullerene nano-stripes were utilized as the active material in field-effect transistors, which featured high electron mobility and large on-off ratio.

This patterning was in Paper III extended into easy tunable two-dimensional fullerene structures by the design and development of an exposure setup, essentially comprising a laser and a spatial light modulator featuring >8 millions of independently controlled mirrors. With this approach, we could fabricate well-defined fullerene microdots over a several square-millimeter sized area, which was utilized as an internal out-coupling layer in a light-emitting electrochemical cell with significantly enhanced light output.

Paper IV reports on the development of a new “spray-sintering” method for the cost-efficient solution-based deposition of the active material in light-emitting electrochemical cells. This carefully designed approach effectively resolves the issue with phase separation between the hydrophobic organic semiconductor and the hydrophilic electrolyte that results in a sub-par LEC performance, and also allows for the direct fabrication of LEC devices onto complex surfaces, including a stainless-steel fork.

Paper V finally reports on the design and synthesis of a soluble small molecule, featuring a donor-acceptor-donor configuration. It acts as the donor when combined with a soluble fullerene acceptor in the active material of organic solar cells, and such devices with optimized donor/acceptor nanomorphology feature a high open-circuit voltage of ~1.0 V during solar illumination.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2019. p. 65
Keywords
Organic electronics, organic photonics, patterning, fullerene, polymerization, dimerization, spray-deposition, morphology, small molecule donor, high open-circuit voltage
National Category
Polymer Technologies Nano Technology Other Physics Topics Condensed Matter Physics
Identifiers
urn:nbn:se:umu:diva-166407 (URN)978-91-7855-170-5 (ISBN)978-91-7855-169-9 (ISBN)
Public defence
2020-01-09, Bio.A.206, Biologihuset, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2019-12-19 Created: 2019-12-16 Last updated: 2019-12-17Bibliographically approved
3. Fabricating designed fullerene nanostructures for functional electronic devices
Open this publication in new window or tab >>Fabricating designed fullerene nanostructures for functional electronic devices
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A long-term goal within the field of organic electronics has been to developflexible and functional devices, which can be processed and patterned withlow-cost and energy-efficient solution-based methods. This thesis presents anumber of functional paths towards the attainment of this goal via thedevelopment and demonstration of novel fabrication and patterningmethods involving the important organic-semiconductor family termedfullerenes.Fullerenes are soccer-shaped small molecules, with two often-employedexamples being the symmetric C60 molecule and its more soluble derivative[6,6]-phenyl-C61-butyric acid methyl ester (PCBM). We show that PCBM canbe photochemically transformed into a dimeric state in a bi-excited reactionprocess, and that the exposed material features a significantly reducedsolubility in common solvents as well as an effectively retained electronmobility. This attractive combination of material properties allows for adirect and resist-free lithographic patterning of electronic PCBM films downto a smallest feature size of 1 µm, using a simple and scalable two-stepprocess constituting light exposure and solution development. In a furtherdevelopment, it was shown that the two-step method was useful also in thearea-selective transformation of fullerene/conjugated-polymer blend films,as demonstrated through the realization of a functional complementary logiccircuit comprising a 5-stage ring oscillator.In another project, we have synthesized highly flexible, single-crystal C60nanorods with a solution-based self-assembly process termed liquid-liquidinterfacial precipitation. The 1-dimensional nanorods can be deposited fromtheir synthesis solution and employed as the active material in field-effecttransistor devices. Here, it was revealed that the as-fabricated nanorods canfeature an impressive electron mobility of 1.0 cm2 V-1 s-1, which is on par withthe performance of a work horse in the transistor field, viz. vacuumdeposited amorphous Si. We further demonstrated that the processability ofthe nanorods can be improved by a tuned light-exposure treatment, duringwhich the nanorod shell is polymerized while the high-mobility interior bulkis left intact. This has the desired consequence that stabile nanoroddispersions can be prepared in a wide range of solvents, and we anticipatethat functional electronic devices based on solution-processable nanorodscan be realized in a near future.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2014. p. 71
Keywords
Organic electronics, Organic field-effect transistor, Organic photovoltaics, Fullerene C60, PCBM, Photochemical transformation, Resist-free lithography, C60 Nanorod, Solution processable
National Category
Physical Chemistry Nano Technology
Research subject
nanomaterials; Physical Chemistry; Physics; Materials Science
Identifiers
urn:nbn:se:umu:diva-97294 (URN)978-91-7601-187-4 (ISBN)
Public defence
2015-01-20, N300, Naturvetarhuset, Umeå universitet, Universitetsvägen, 901 87 Umeå, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2014-12-19 Created: 2014-12-12 Last updated: 2019-12-17Bibliographically approved

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Iqbal, JavedEnevold, JennyLarsen, ChristianWang, JiaRevoju, SrikanthBarzegar, Hamid RezaWågberg, ThomasEliasson, BertilEdman, Ludvig

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