Please use this identifier to cite or link to this item: http://hdl.handle.net/2445/113723
Title: Carbazole-Based Materials for Organic Thin-Film Transistors and Organic Light-Emitting Diodes
Author: Reig Canyelles, Marta
Director: Velasco Castrillo, Dolores
Keywords: Semiconductors orgànics
Organic semiconductors
Issue Date: 7-Jul-2017
Publisher: Universitat de Barcelona
Abstract: [cat] El desenvolupament de nous semiconductors orgànics amb capacitat de transport de càrrega presenta un gran interès per a la seva aplicació en transistors orgànics de capa prima (OTFTs), díodes emissors de llum orgànics (OLEDs) i cel·les solars orgàniques, entre d’altres. L’objectiu d’aquesta tesi és la preparació i caracterització de nous semiconductors orgànics basats en l’heterocicle carbazole i el seu estudi com a components en OTFTs i en OLEDs. En primer terme, aquesta tesi està centrada en la preparació de nous derivats del carbazole amb propietats luminescents en la zona del blau de l’espectre electromagnètic. En concret, es pretén modular les propietats òptiques del carbazole mitjançant l’extensió de la conjugació del seu nucli aromàtic per introducció de grups donadors d’electrons en la seva estructura, així com per la introducció del triple enllaç com a espaiador entre el nucli carbazole i els grups donadors d’electrons. L’estudi dels materials preparats com a capes emissores en OLEDs ha donat lloc a dispositius amb emissió a la zona del blau que han presentat una elevada luminància de fins a 1.4 x 104 cd m–2. La segona part de la tesi està enfocada en el desenvolupament de nous semiconductors orgànics basats en l’heterocicle carbazole i l’estudi de les seves propietats de transport de càrrega. Per tal de preparar nous semiconductors orgànics de tipus n o ambipolars, es pretén modificar les propietats de transport de forats del nucli carbazole mitjançant la introducció de grups atractors d’electrons en la seva estructura. Per una altra banda, s’ha preparat una sèrie de materials basats en el carbazole en què s’ha variat progressivament l’extensió del seu sistema conjugat, per tal d’obtenir derivats amb propietats de transport de forats efectives. Les propietats de transport de càrrega dels materials preparats s’han avaluat mitjançant la tècnica “time of flight” (TOF) i la preparació i mesura de OTFTs. S’han obtingut alts valors de mobilitat de forats de fins a 0.1 cm2 V–1 s–1 a partir de OTFTs basats en derivats del triindole. Els resultats obtinguts s’han correlacionat amb l’estructura molecular, el tipus d’empaquetament molecular, i amb el grau d’ordre i disposició de les molècules a les capes dels dispositius mitjançant estudis de difracció de raigs X i càlculs teòrics.
[eng] This thesis deals with the preparation and characterization of novel organic semiconductors based on the carbazole heterocycle for electronic and optoelectronic applications, specifically to be studied as active layers in OTFTs and as emitting layers in OLEDs. Carbazole-based materials are recognised for their high thermal stability, high emission efficiencies and excellent hole-transporting properties associated to its electron-donating ability, which make of them promising candidates for OTFTs and OLEDs applications. OLEDs have been studied extensively due to their promising applications in flat panel displays and solid-state lighting. However, further improvement of power efficiency and colour purity are still required to produce more efficient industrial devices. Thus, the first part of this thesis deals with the preparation of a series of carbazole-based blue emitters for their application as emitting layers in blue and in particular in deep-blue OLEDs. The extension of the π-conjugated carbazole system by preparing bicarbazole and tricarbazole derivatives afforded materials with the sought deep-blue emission properties in the solid state, which were modulated by the insertion of the ethynylene linker. OLED devices exhibited very low turn-on voltages and a maximum luminance as high as 1.4 x 104 cd m–2. The second part of this thesis is focused on the development of new organic semiconductors with effective charge transport properties. In order to obtain new n-type or ambipolar materials, the hole-transporting behaviour of the electron-donating carbazole moiety was modified by the introduction of electron-withdrawing groups on its structure. As a first approach, the coupling of the carbazole heterocycle with the electron acceptor tris(2,4,6-trichlorophenyl)methyl radical (TTM) yielded ambipolar materials, whose charge-transporting properties were found to be dependent on the substitution patterns of the carbazole core. As a second approach, the introduction of the strong electron-withdrawing tricyanovinyl group on the carbazole core afforded a push-pull system with high electron affinity, resulting in materials with n-type or ambipolar behaviour as determined by TOF and OTFT measurements. The last part of this thesis is focused on the preparation of a series of p-type carbazole related derivatives, in which the extension of the π-conjugated core was progressively varied in order to study its effect on the charge-transporting properties. Indolo[3,2-b]carbazole and triindole derivatives showed enhanced OTFT device performance with hole mobilities in the range of 10–3 to 0.1 cm2 V–1 s–1. In particular, N-trimethyltriindole exhibits a face-to-face molecular packing with π–π interactions, and an optimal perpendicular molecular disposition to the substrate surface as determined by XRD, that can be related to a more favourable charge transport in the OTFT devices. The introduction of long hexyl chains in the triindole core contributes with additional C–H···π interactions to those of π–π type between the triindole cores, enhancing the degree of molecular order in the thin films as reflected in the determined hole mobility, which was found to be the highest value of all the series with a value of 0.1 cm2 V–1 s–1. The knowledge of the molecular packing and intermolecular interactions in the organic layers has been proved to be essential to rationalize the charge-transporting properties and it is shown here to be a useful tool to be considered on the design of new organic semiconductors.
URI: http://hdl.handle.net/2445/113723
Appears in Collections:Tesis Doctorals - Departament - Química Inorgànica i Orgànica

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