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Charge transport modulation in organic electronic diodes
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology. (Organic Electronics)
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Since the discovery of conducting polymers three decades ago the field of organic electronics has evolved rapidly. Organic light emitting diodes have already reached the consumer market, while organic solar cells and transistors are rapidly maturing. One of the great benefits with this class of materials is that they can be processed from solution. This enables several very cheap production methods, such as printing and spin coating, and opens up the possibility to use unconventional substrates, such as flexible plastic foils and paper. Another great benefit is the possibility of tailoring the molecules through carefully controlled synthesis, resulting in a multitude of different functionalities.

This thesis reports how charge transport can be altered in solid-state organic electronic devices, with specific focus on memory applications. The first six chapters give a brief review of the field of solid-state organic electronics, with focus on electronic properties, resistance switch mechanisms and systems. Paper 1 and 3 treat Rose Bengal switch devices in detail – how to improve these devices for use in cross-point arrays as well as the origin of the switch effect. Paper 2 investigates how the work function of a conducting polymer can be modified to allow for better electron injection into an organic light emitting diode. The aim of the work in papers 4 and 5 is to understand the behavior of switchable charge trap devices based on blends of photochromic molecules and organic semiconductors. With this in mind, charge transport in the presence of traps is investigated in paper 4 and photochromic molecules is investigated using quantum chemical methods in paper 5.

Abstract [sv]

Elektroniska komponenter har traditionellt sett tillverkats av kisel ellerandra liknande inorganiska material. Denna teknologi har förfinats intillperfektion sedan mitten av 1900-talet och idag har kiselkretsar mycket högprestanda. Tillverkningen av dessas kretsar är dock komplicerad och är därförkostsam. Under 1970-talet upptäcktes att organiska polymerer (dvs plast) kanleda ström under vissa förutsättningar. Genom att välja lämplig polymer ochbehandla den med vissa kemikalier (så kallad dopning) kan man varieraledningsförmågan från isolerande till nästintill metallisk. Det öppnarmöjligheten för att skapa elektroniska komponenter där dessa organiskamaterial utgör den aktiva delen istället för kisel. En av de stora fördelarna medorganiska material är att de vanligtvis är lösliga i vanliga lösningsmedel. Det göratt komponenter kan tillverkas mycket enkelt och billigt genom att användakonventionell tryckteknik, där bläcket har ersatts med lösningen av detorganiska materialet. Det gör också att komponenterna kan tillverkas påokonventionella ytor såsom papper, plast eller textil. En annan spännandemöjlighet med organiska material är att dess funktioner kan skräddarsys genomvälkontrollerad kemisk syntes på molekylär nivå. Inom forskningsområdetOrganisk Elektronik studerar man de elektroniska egenskaperna i de organiskamaterialen och hur man kan använda dessa material i elektroniskakomponenter.

Vi omges idag av apparater och applikationer som kräver att data sparas,som till exempel digitala kameror, datorer och mobiltelefoner. Eftersom det finnsett stort intresse från konsumenter för nya smarta produkter ökar behovet avmobila lagringsmedia med stor lagringskapacitet i rasande fart. Detta harsporrat en intensiv utveckling av större och billigare fickminnen, hårddiskar ochminneskort. Många olika typer av minneskomponenter baserade på organiskamaterial har föreslagits de senaste åren. I vissa fall har dessa påståtts kunna erbjuda både billigare och större minnen än vad dagens kiselteknologi tillåter.En typ av organiska elektroniska minnen baseras på en reversibel ochkontrollerbar förändring av ledningsförmågan i komponenten. En informationsenhet – en så kallad bit – kan då lagras genom att till exempel koda en högledningsförmåga som en ”1” och en låg ledningsförmåga som en ”0”. Den härdoktorsavhandlingen är ett försök till att öka förståelsen för sådanaminneskomponenter.

Minneskomponenter bestående av det organiska materialet Rose Bengalmellan metallelektroder har undersökts. Egenskaper för system bestående avmånga sådana komponenter har beräknats. Vidare visas att minnesfenomenetinte härstammar i det organiska materialet utan i metallelektroderna.Tillsammans med studier av andra forskargrupper har det här resultatetbidragit till en debatt om huruvida minnesmekanismerna i andra typer avkomponenter verkligen beror på det organiska materialet.Olika sätt att ändra transporten av laddningar i organiska elektroniskasystem har undersökts. Det visas experimentellt hur överföringen av laddningarmellan metallelektroder och det organiska materialet kan förbättras genom attmodifiera metallelektroderna på molekylär nivå. Vidare har det studeratsteoretiskt hur laddningar kan fastna (så kallad trapping) i organiska materialoch därmed påverka ledningsförmågan i materialet.En speciell typ av organiska molekyler ändrar sin struktur, och därmedegenskaper, reversibelt när de belyses av ljus av en viss våglängd, så kalladefotokroma molekyler. Denna förändring kan användas till att ändraledningsförmågan genom en komponent och därmed skulle man kunna användamolekylerna i en minneskomponent. I den sista delen av avhandlingen användskvantkemiska metoder för att beräkna egenskaperna hos dessa molekyler för attöka förståelsen för hur de kan användas i minneskomponenter.

 

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2008. , 172 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1203
Keyword [en]
Organic electronics, switch device, memory, photochromic, trapping, resistance switching
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-14719ISBN: 978-91-7393-830-3 (print)OAI: oai:DiVA.org:liu-14718DiVA: diva2:24290
Public defence
2008-09-19, K2, Kåkenhus, Campus Norrköping, Linköpings universitet, Norrköping, 10:30 (English)
Opponent
Supervisors
Available from: 2008-09-25 Created: 2008-09-21 Last updated: 2017-02-03Bibliographically approved
List of papers
1.
The record could not be found. The reason may be that the record is no longer available or you may have typed in a wrong id in the address field.
2. Towards all-plastic flexible light emitting diodes
Open this publication in new window or tab >>Towards all-plastic flexible light emitting diodes
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2006 (English)In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 433, no 1-3, 110-114 p.Article in journal (Refereed) Published
Abstract [en]

All-plastic light emitting diodes require the design and fabrication of low work function plastic electrodes. Here, we show that the work function of poly(3,4-ethylenedioxythiophene)-polystyrenesulfonic acid (PEDOT-PSS) can be decreased from 4.8 eV to 3.9 eV by surface reaction with the strong electron-donor tetrakis(dimethylamino)ethylene (TDAE). The surface modification was characterized by photoelectron spectroscopy and optical spectroscopy. The low work function plastic electrode was used in a first prototype for all-plastic light emitting diodes.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-14831 (URN)10.1016/j.cplett.2006.11.007 (DOI)
Available from: 2008-11-12 Created: 2008-09-25 Last updated: 2017-12-13
3.
The record could not be found. The reason may be that the record is no longer available or you may have typed in a wrong id in the address field.
4. Prediction of the current versus voltage behavior of devices based on organic semiconductor host-guest systems
Open this publication in new window or tab >>Prediction of the current versus voltage behavior of devices based on organic semiconductor host-guest systems
2009 (English)In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 10, no 1, 95-106 p.Article in journal (Refereed) Published
Abstract [en]

Organic semiconductor blends are commonly used in organic based (opto-)electronic devices. They are composed of two types of (macro-) molecules, referredto as the guest and host. To achieve optimum device operation, the chemicalnature, electronic structure, molecular order and the relative concentration of theguests and host are crucial. Here, we present simulation results of the currentdensity versus the voltage (J-V) behavior of a two-terminal device based on avariable-range hopping model in which the electronic states of the guest and hostare represented by two Gaussian distributions. The J-V behavior is investigatedfor various energetic mismatches between guest and host states, widths of thedistribution as well as the guest concentration. Finally, a simple tool enablingeasy prediction of the J-V behavior of organic host-guest diodes is derived.

Keyword
Host–guest system, Diode, Trapping, Modeling, Hopping, Gaussian density of states
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-14837 (URN)10.1016/j.orgel.2008.10.006 (DOI)
Available from: 2008-11-12 Created: 2008-09-25 Last updated: 2017-12-13Bibliographically approved
5. Tuning the energy levels of photochromic diarylethene compounds for optoelectronic switch devices
Open this publication in new window or tab >>Tuning the energy levels of photochromic diarylethene compounds for optoelectronic switch devices
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(English)Manuscript (Other academic)
Abstract [en]

Photochromic diarylethene molecules (PC) is investigated for use in opticalwrite/electrical read memory applications. The frontier energy levels and dipolemoment is calculated using density functional theory. Good agreement is foundbetween calculated electronic structure and measured ultraviolet photoelectronspectra. The changes in frontier energy levels and dipole moment are scrutinizedupon two different approaches for chemical modification: (i) adding substituentsto the ethylene bridge; or (ii) changing the chemical nature of the aryl rings.Through the chemical modification the frontier energy levels can be tuned bymore than 2 eV. The calculated molecular properties are used in charge transportmodels to predict the behavior of devices based on these molecules. By using thePC in combination with an organic semiconductor (in bilayer or blend) goodswitching behavior can be achieved in a device. The switch effect is predicted tobe mainly due to switch in frontier energy levels rather than switch of dipolemoment. This is concluded since the dipole moment is either too small (< 5 D) orthe switch effect to small (less than a factor of two).

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-14838 (URN)
Available from: 2008-11-12 Created: 2008-09-25 Last updated: 2017-02-03

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Jakobsson, Fredrik Lars Emil

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