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Abdalla, Hassan
Publications (7 of 7) Show all publications
Xu, K., Ruoko, T.-P., Shokrani, M., Scheunemann, D., Abdalla, H., Sun, H., . . . Fabiano, S. (2022). On the Origin of Seebeck Coefficient Inversion in Highly Doped Conducting Polymers. Advanced Functional Materials, 32(20), Article ID 2112276.
Open this publication in new window or tab >>On the Origin of Seebeck Coefficient Inversion in Highly Doped Conducting Polymers
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2022 (English)In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 32, no 20, article id 2112276Article in journal (Refereed) Published
Abstract [en]

A common way of determining the majority charge carriers of pristine and doped semiconducting polymers is to measure the sign of the Seebeck coefficient. However, a polarity change of the Seebeck coefficient has recently been observed to occur in highly doped polymers. Here, it is shown that the Seebeck coefficient inversion is the result of the density of states filling and opening of a hard Coulomb gap around the Fermi energy at high doping levels. Electrochemical n-doping is used to induce high carrier density (>1 charge/monomer) in the model system poly(benzimidazobenzophenanthroline) (BBL). By combining conductivity and Seebeck coefficient measurements with in situ electron paramagnetic resonance, UV-vis-NIR, Raman spectroelectrochemistry, density functional theory calculations, and kinetic Monte Carlo simulations, the formation of multiply charged species and the opening of a hard Coulomb gap in the density of states, which is responsible for the Seebeck coefficient inversion and drop in electrical conductivity, are uncovered. The findings provide a simple picture that clarifies the roles of energetic disorder and Coulomb interactions in highly doped polymers and have implications for the molecular design of next-generation conjugated polymers.

Place, publisher, year, edition, pages
Wiley-V C H Verlag GMBH, 2022
Keywords
conducting polymers; organic electrochemical transistor; Seebeck coefficient; thermoelectric application
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-182954 (URN)10.1002/adfm.202112276 (DOI)000751371400001 ()
Note

Funding Agencies|Swedish Research CouncilSwedish Research CouncilEuropean Commission [2020-03243]; Olle Engkvists Stiftelse [204-0256]; European CommissionEuropean CommissionEuropean Commission Joint Research Centre [GA-955837, GA-799477]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [SFO-Mat-LiU 2009-00971]; Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germanys Excellence Strategy via the Excellence Cluster 3D Matter Made to OrderGerman Research Foundation (DFG) [EXC-2082/1-390761711]; Carl Zeiss Foundation; Deutsche ForschungsgemeinschaftGerman Research Foundation (DFG) [FA 1502/1-1]; National Natural Science Foundation of ChinaNational Natural Science Foundation of China (NSFC) [52173156]; Swedish Foundation for Strategic ResearchSwedish Foundation for Strategic Research [ITM17-0316]

Available from: 2022-02-16 Created: 2022-02-16 Last updated: 2023-12-28Bibliographically approved
Abdalla, H. (2018). Charge and Energy Transport in Disordered Organic Semiconductors. (Doctoral dissertation). Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>Charge and Energy Transport in Disordered Organic Semiconductors
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Improvement of the performance of organic disordered semiconductors (OSC) is driven by the understanding   of the underlying charge transport mechanisms and systematic exploitation thereof. There exists a multitude of materials and material systems based on polymers and small molecules with promising performance for use in organic light emitting diodes, photovoltaics, organic field-effect transistors and thermoelectrics. However, universal understanding of many classes of these materials has eluded researchers, due to their broad   spectrum of morphologies, molecular structures and electrical properties. Building on the large body of existing models, this thesis deals with charge transport phenomena from the perspective of transport energetics, by studying the interplay between a few but important concepts commonly accepted to play a crucial role in all  OSC materials; energetic disorder, charge carrier hopping and Coulomb interactions. The influence of these concepts on the energetic landscape through which charge carriers move and how this translates to experimentally observed transport phenomena are studied by a combination of experimental work, kinetic Monte Carlo (MC) simulations and empirical and analytical models.

The universal scaling and collapse of the temperature and electric field dependence of the conductivity of PEDOT:PSS to a single curve is shown to be functionally equivalent to the scaling of the effective temperature, which describes the effect of field heating as a broadening of the charge carrier distribution. From numerical investigation of the energy relaxation, an empirical model is developed that relates the physical meaning   behind both concepts to the heat balance between Joule heating of the carrier distribution via the effective temperature and energy loss to the lattice. For this universal description to be applicable a strongly energy- dependent density of states (DOS) as well as Coulomb interactions and large carrier concentrations are needed.

Chemical doping is a common way of improving charge transport in OSC and is also beneficial for energy transport, which combined leads to an increased thermoelectric power factor. The ensuing thermoelectric investigations not only showed the potential of these materials for use in thermoelectric generators, but are  also helpful in unraveling charge transport mechanism as they give direct insight into the energetics of a material. Interestingly, doped OSC exhibit the same universal power-law relationship between thermopower and conductivity, independent of material system or doping method, pointing towards a common energy and charge transport mechanism. In this thesis an analytical model is presented, which reproduces said universal power-law behavior and is able to attribute it to Variable Range Hopping (VRH) or a transition between Nearest Neighbour Hopping (NNH) and VRH at higher concentrations. This model builds on an existing three- dimensional hopping formalism that includes the effect of the attractive Coulomb potential of ionized dopants that leads to a broadening of the DOS. Here, this model is extended by including the energy offset between   host and dopant material and is positively tested against MC simulations and a set of thermoelectric measurements covering different material groups and doping mechanisms.

Organic field effect transistors (OFETs) have become increasingly comparable in electrical mobility to their inorganic (silicon) counterparts. The spatial extent of charge transport in OFETs has been subject to debate since their inception with many experimental, numerical and analytical studies having been undertaken. Here it is shown that the common way of analyzing the dimensionality of charge transport in OFETs may be prone to misinterpretations. Instead, the results in this thesis suggest that charge transport in OFETs is, in fact, quasi- two-dimensional (2D) due to the confinement of the gate field in addition to a morphology-induced preferred in-plane direction of the transport. The inherently large charge carrier concentrations in OFETs in addition to   the quasi-2D confinement leads to increased Coulomb interaction between charge carriers as compared to bulk material, leading to a thermoelectric behavior that deviates from doped organic systems. At very large concentrations interesting charge transport phenomena are observed, including an unexpected simultaneous increase of the concentration dependence and the magnitude of the mobility, the appearance of a negative transconductance, indicating a transition to an insulating Mott-Hubbard phase. The experimental and   numerical results in this thesis relate these phenomena the intricacies of the interplay between Coulomb interactions, energetic disorder and charge carrier hopping.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2018. p. 100
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1909
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-145673 (URN)10.3384/diss.diva-145673 (DOI)9789176853528 (ISBN)
Public defence
2018-04-13, Sal Schrödinger, Fysikhuset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2018-03-14 Created: 2018-03-14 Last updated: 2019-09-26Bibliographically approved
Zuo, G., Andersson, O., Abdalla, H. & Kemerink, M. (2018). High thermoelectric power factor from multilayer solution-processed organic films. Applied Physics Letters, 112(8), Article ID 083303.
Open this publication in new window or tab >>High thermoelectric power factor from multilayer solution-processed organic films
2018 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 112, no 8, article id 083303Article in journal (Refereed) Published
Abstract [en]

We investigate the suitability of the "sequential doping" method of organic semiconductors for thermoelectric applications. The method consists of depositing a dopant (F4TCNQ) containing solution on a previously cast semiconductor (P3HT) thin film to achieve high conductivity, while preserving the morphology. For very thin films (similar to 25 nm), we achieve a high power factor around 8 mu W/mK(-2) with a conductivity over 500 S/m. For the increasing film thickness, conductivity and power factor show a decreasing trend, which we attribute to the inability to dope the deeper parts of the film. Since thick films are required to extract significant power from thermoelectric generators, we developed a simple additive technique that allows the deposition of an arbitrary number of layers without significant loss in conductivity or power factor that, for 5 subsequent layers, remain at similar to 300 S/m and similar to 5 mu W/mK(-2), respectively, whereas the power output increases almost one order of magnitude as compared to a single layer. The efficient doping in multilayers is further confirmed by an increased intensity of (bi)polaronic features in the UV-Vis spectra. Published by AIP Publishing.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2018
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-145764 (URN)10.1063/1.5016908 (DOI)000425977500021 ()
Note

Funding Agencies|China Scholarship Council (CSC); Knut och Alice Wallenbergs stiftelse (Project "Tail of the Sun")

Available from: 2018-03-22 Created: 2018-03-22 Last updated: 2018-05-14
Zuo, G., Abdalla, H. & Kemerink, M. (2016). Impact of doping on the density of states and the mobility in organic semiconductors. PHYSICAL REVIEW B, 93(23), 235203
Open this publication in new window or tab >>Impact of doping on the density of states and the mobility in organic semiconductors
2016 (English)In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 23, p. 235203-Article in journal (Refereed) Published
Abstract [en]

We experimentally investigated conductivity and mobility of poly(3-hexylthiophene) (P3HT) doped with tetrafluorotetracyanoquinodimethane (F(4)TCNQ) for various relative doping concentrations ranging from ultralow (10(-5)) to high (10(-1)) and various active layer thicknesses. Although the measured conductivity monotonously increases with increasing doping concentration, the mobilities decrease, in agreement with previously published work. Additionally, we developed a simple yet quantitative model to rationalize the results on basis of a modification of the density of states (DOS) by the Coulomb potentials of ionized dopants. The DOS was integrated in a three-dimensional (3D) hopping formalism in which parameters such as energetic disorder, intersite distance, energy level difference, and temperature were varied. We compared predictions of our model as well as those of a previously developed model to kinetic Monte Carlo (MC) modeling and found that only the former model accurately reproduces the mobility of MC modeling in a large part of the parameter space. Importantly, both our model and MC simulations are in good agreement with experiments; the crucial ingredient to both is the formation of a deep trap tail in the Gaussian DOS with increasing doping concentration.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2016
National Category
Other Physics Topics
Identifiers
urn:nbn:se:liu:diva-130276 (URN)10.1103/PhysRevB.93.235203 (DOI)000378813800009 ()
Note

Funding Agencies|Chinese Scholarship Council (CSC)

Available from: 2016-08-01 Created: 2016-07-28 Last updated: 2018-08-29
Booker, I. D., Abdalla, H., Hassan, J., Karhu, R., Lilja, L., Janzén, E. & Sveinbjörnsson, E. (2016). Oxidation-induced deep levels in n- and p-type 4H- and 6H-SiC and their influence on carrier lifetime. Physical Review Applied, 6(1), 1-15, Article ID 014010.
Open this publication in new window or tab >>Oxidation-induced deep levels in n- and p-type 4H- and 6H-SiC and their influence on carrier lifetime
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2016 (English)In: Physical Review Applied, ISSN 2331-7019, Vol. 6, no 1, p. 1-15, article id 014010Article in journal (Refereed) Published
Abstract [en]

We present a complete analysis of the electron- and hole-capture and -emission processes of the deep levels ON1, ON2a, and ON2b in 4H-SiC and their 6H-SiC counterparts OS1a and OS1b through OS3a and OS3b, which are produced by lifetime enhancement oxidation or implantation and annealing techniques. The modeling is based on a simultaneous numerical fitting of multiple high-resolution capacitance deep-level transient spectroscopy spectra measured with different filling-pulse lengths in n- and p-type material. All defects are found to be double-donor-type positive-U two-level defects with very small hole-capture cross sections, making them recombination centers of low efficiency, in accordance with minority-carrier-lifetime measurements. Their behavior as trapping and weak recombination centers, their large concentrations resulting from the lifetime enhancement oxidations, and their high thermal stability, however, make it advisable to minimize their presence in active regions of devices, for example, the base layer of bipolar junction transistors.

Place, publisher, year, edition, pages
American Physical Society, 2016
Keywords
Time-resolved photoluminescence, Deep level transient spectroscopy, Minority carrier transient spectroscopy, Lifetime enhancement, Oxidation; Recombination center, 4H-SiC, 6H-SiC
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-121546 (URN)10.1103/PhysRevApplied.6.014010 (DOI)000380125700001 ()
Funder
Swedish Foundation for Strategic Research Swedish Research Council
Note

At the time for thesis presentation publication was in status: Manuscript

Available from: 2015-09-24 Created: 2015-09-24 Last updated: 2018-09-01Bibliographically approved
Abdalla, H., van de Ruit, K. & Kemerink, M. (2015). Effective Temperature and Universal Conductivity Scaling in Organic Semiconductors. Scientific Reports, 5, Article ID 16870.
Open this publication in new window or tab >>Effective Temperature and Universal Conductivity Scaling in Organic Semiconductors
2015 (English)In: Scientific Reports, E-ISSN 2045-2322, Vol. 5, article id 16870Article in journal (Refereed) Published
Abstract [en]

We investigate the scalability of the temperature-and electric field-dependence of the conductivity of disordered organic semiconductors to universal curves by two different but commonly employed methods; by so-called universal scaling and by using the effective temperature concept. Experimentally both scaling methods were found to be equally applicable to the out-of-plane charge transport in PEDOT: PSS thin films of various compositions. Both methods are shown to be equivalent in terms of functional dependence and to have identical limiting behavior. The experimentally observed scaling behavior can be reproduced by a numerical nearest-neighbor hopping model, accounting for the Coulomb interaction, the high charge carrier concentration and the energetic disorder. The underlying physics can be captured in a simple empirical model, describing the effective temperature of the charge carrier distribution as the outcome of a heat balance between Joule heating and (effective) temperature-dependent energy loss to the lattice.

Place, publisher, year, edition, pages
Nature Publishing Group, 2015
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-123329 (URN)10.1038/srep16870 (DOI)000364933800002 ()26581975 (PubMedID)
Available from: 2015-12-14 Created: 2015-12-11 Last updated: 2022-09-15
Booker, I. D., Abdalla, H., Lilja, L., ul-Hassan, J., Bergman, P., Sveinbjörnsson, E. & Janzén, E. (2014). Oxidation induced ON1, ON2a/b defects in 4H-SiC characterized by DLTS. In: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2: . Paper presented at SILICON CARBIDE AND RELATED MATERIALS 2013 (pp. 281-284). Trans Tech Publications, 778-780
Open this publication in new window or tab >>Oxidation induced ON1, ON2a/b defects in 4H-SiC characterized by DLTS
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2014 (English)In: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2, Trans Tech Publications , 2014, Vol. 778-780, p. 281-284Conference paper, Published paper (Refereed)
Abstract [en]

The deep levels ON1 and ON2a/b introduced by oxidation into 4H-SiC are characterized via standard DLTS and via filling pulse dependent DLTS measurements. Separation of the closely spaced ON2a/b defect is achieved by using a higher resolution correlation function (Gaver-Stehfest 4) and apparent energy level, apparent electron capture cross section and filling pulse measurement derived capture cross sections are given.

Place, publisher, year, edition, pages
Trans Tech Publications, 2014
Series
Materials Science Forum, ISSN 1662-9752 ; 778-780
Keywords
4H-SiC; DLTS; oxidation; carrier lifetime; defect; deep level; trap; capture cross section
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-108196 (URN)10.4028/www.scientific.net/MSF.778-780.281 (DOI)000336634100066 ()
Conference
SILICON CARBIDE AND RELATED MATERIALS 2013
Available from: 2014-06-26 Created: 2014-06-26 Last updated: 2015-04-01
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