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Electronic Transport in Polymeric Solar Cells and Transistors
Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska högskolan.
2007 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

The main topic of this dissertation is electronic charge transport in polymeric and molecular organic materials and material blends intended for solar cell applications. Charge transport in polymers is a strange beast and carrier mobility is rarely a well-defined number. Measurements on different sample geometries and under different conditions tend to give different results and when everything is to be related to solar cell performance it is imperative that there is a way to correlate the results from different measurements. Polymer solar cells utilize composite materials for their function. This puts an additional twist on charge transport studies, as there will also be interaction between the different phases to take into account.

Several measurement techniques have been used and their interrelationships as well as information on their relevance for solar cells have been investigated. Field effect transistors (FET) with an organic active layer have proved to be one of the more versatile measurement geometries and are also an interesting topic in itself. FETs are discussed both as a route for material characterization and as components. A main result correlates bias stress in organic field effect transistors with the electronic structure of the material.

Power conversion efficiency in solar cells is discussed with respect to electrical properties. The interaction of different blend materials and the impact of stoichiometry on transport properties in the active layer have been investigated. Results indicate that charge transport properties frequently are a key determining factor for which material combinations and ratios that works best.

Some work on the conductive properties of nano-fibers coated with semiconducting polymers has also been done and is briefly discussed. The conductive properties of nano-fibers have been studied through potential imaging.

Ort, förlag, år, upplaga, sidor
Institutionen för fysik, kemi och biologi , 2007. , s. 70
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1142
Nationell ämneskategori
Fysik
Identifikatorer
URN: urn:nbn:se:liu:diva-10380ISBN: 978-91-85895-50-2 (tryckt)OAI: oai:DiVA.org:liu-10380DiVA, id: diva2:17130
Disputation
2007-11-20, Planck, Fysikhuset, Campus Valla, Linköpings Universitet, Linköping, 10:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2007-12-05 Skapad: 2007-12-05 Senast uppdaterad: 2017-01-11Bibliografiskt granskad
Delarbeten
1. Non-equilibrium effects on electronic transport in organic field effect transistors
Öppna denna publikation i ny flik eller fönster >>Non-equilibrium effects on electronic transport in organic field effect transistors
2007 (Engelska)Ingår i: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 8, nr 4, s. 423-430Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Non-ideal behavior in organic field effect transistors, in particular threshold voltage drift and light sensitivity, is argued to be due to intrinsic carrier dynamics. The discussion is based on the theory for hopping transport within a Gaussian density of states. Carrier concentration is shown to be of fundamental importance, and the time required to reach equilibrium at different bias is responsible for device behavior, with implications for mobility evaluation. Experimental results from various conjugated polymers in a field effect transistor illustrate the theory.

Nyckelord
Organic field-effect transistors (OFETs), Conjugated polymer, Hysteresis, Charge transport, Gaussian disorder model, Bias stress
Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:liu:diva-12822 (URN)10.1016/j.orgel.2007.02.001 (DOI)
Tillgänglig från: 2007-12-05 Skapad: 2007-12-05 Senast uppdaterad: 2017-12-14
2. Bipolar transport observed through extraction currents on organic photovoltaic blend materials
Öppna denna publikation i ny flik eller fönster >>Bipolar transport observed through extraction currents on organic photovoltaic blend materials
2006 (Engelska)Ingår i: Applied Physics Letters, ISSN 0003-6951, Vol. 89, s. 142111-Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Both electron and hole mobilities have been simultaneously measured through charge extraction by linearly increasing voltage on polymer heterojunction solar cells with varying stoichiometry of polymer and acceptor. The polymer is a low band gap copolymer of fluorene, thiophene, and electron accepting groups named APFO-Green 5, and the acceptor is [6,6]-phenyl-C61-butyric acid methylester. Results are correlated to field effect transistor measurements on the same material system. A monotonous increase in mobility for both carrier types is observed with increased acceptor loading.

Nyckelord
polymer blends, organic semiconductors, fullerene compounds, solar cells, electron mobility, hole mobility, stoichiometry, carrier density
Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:liu:diva-12823 (URN)10.1063/1.2360199 (DOI)
Tillgänglig från: 2007-12-05 Skapad: 2007-12-05
3. Stoichiometry, mobility, and performance in bulk heterojunction solar cells
Öppna denna publikation i ny flik eller fönster >>Stoichiometry, mobility, and performance in bulk heterojunction solar cells
2007 (Engelska)Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 91, nr 7, s. 071108-Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Bipolar transport in blends of a copolymer of fluorene, thiophene and electron accepting groups, and the substituted fullerene [6,6]-phenyl-C61-butyric acid methylester have been studied through charge extraction by linearly increasing voltage on solar cells and with field effect transistors. Between 10% and 90% polymer has been used and the results show a clear correlation to solar cell performance. Optimal solar cells comprise 20% polymer and have a power conversion efficiency of 3.5%. The electron mobility is increasing strongly with fullerene content, but is always lower than the hole mobility, thus explaining the low amount of polymer in optimized devices.

Nyckelord
electron mobility, field effect transistors, fullerenes, hole mobility, polymer blends, solar cells, stoichiometry
Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:liu:diva-12824 (URN)10.1063/1.2771524 (DOI)
Tillgänglig från: 2007-12-05 Skapad: 2007-12-05 Senast uppdaterad: 2017-12-14
4. Acceptor influence on hole mobility in fullerene blends with alternating copolymers of fluorene
Öppna denna publikation i ny flik eller fönster >>Acceptor influence on hole mobility in fullerene blends with alternating copolymers of fluorene
2006 (Engelska)Ingår i: Applied Physics Letters, ISSN 0003-6951, Vol. 88, s. 082103-Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Hole mobility in polyfluorene/fullerene blends has been studied with field effect transistors. Two different C60 derivatives and one C70 derivative have been investigated together with two different polyfluorenes. Mobility is presented as a function of acceptor loading at ratios suitable for photovoltaics and varies between 10–3 and 10–5  cm2  V–1  s–1 depending on the polymer/acceptor combination. The hole mobility is increased in blends with the commonly used acceptor [6-6]-phenyl-C61-butyric acid methylester (PCBM). With related C60 and C70 derivatives the hole mobility is decreased under the same circumstances.

Nyckelord
fullerenes, polymer blends, hole mobility, impurities, field effect transistors
Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:liu:diva-12825 (URN)10.1063/1.2177663 (DOI)
Tillgänglig från: 2007-12-05 Skapad: 2007-12-05
5. Intrinsic and extrinsic influences on the temperature dependence of mobility in conjugated polymers
Öppna denna publikation i ny flik eller fönster >>Intrinsic and extrinsic influences on the temperature dependence of mobility in conjugated polymers
Visa övriga...
2008 (Engelska)Ingår i: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 9, nr 5, s. 569-574Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The temperature dependence of charge carrier mobility in conjugated polymers and their blends with fullerenes is investigated with different electrical methods, through field effect transistor (FET), space charge limited current (SCLC) and charge extraction (CELIV) measurements. Simple models, such as the Gaussian disorder model (GDM), are shown to accurately predict the temperature behavior, and a good correlation between the different measurement methods is obtained. Inconsistent charge carrier concentrations in the modeling are explained through intrinsic non-equilibrium effects, and are responsible for the limited applicability of existing numerical models. A severe extrinsic influence from water in FETs with a hydrophilic insulator interface is also demonstrated. The presence of water leads to a significant overestimate of the disorder in the materials from measurements close to room temperature and erratic behavior in the 150-350 K range. To circumvent this problem it is shown to be necessary to measure under ultra high vacuum (UHV) conditions. © 2008 Elsevier B.V. All rights reserved.

Ort, förlag, år, upplaga, sidor
Elsevier, 2008
Nyckelord
Electrical transport, Field effect transistor, Fullerene, Mobility, Polymer, Temperature dependence
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
urn:nbn:se:liu:diva-50043 (URN)10.1016/j.orgel.2008.03.002 (DOI)
Anmärkning

The previous status of this article was Manuscript.

Tillgänglig från: 2009-10-11 Skapad: 2009-10-11 Senast uppdaterad: 2017-12-12Bibliografiskt granskad

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