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dc.contributor.advisorPatil, Satish
dc.contributor.authorMukhopadhyay, Tushita
dc.date.accessioned2018-07-05T15:00:13Z
dc.date.accessioned2018-07-30T14:47:34Z
dc.date.available2018-07-05T15:00:13Z
dc.date.available2018-07-30T14:47:34Z
dc.date.issued2018-07-05
dc.date.submitted2017
dc.identifier.urihttp://etd.iisc.ac.in/handle/2005/3794
dc.identifier.abstracthttp://etd.iisc.ac.in/static/etd/abstracts/4665/G28572-Abs.pdfen_US
dc.description.abstractThe work carried out in this thesis systematically investigates the correlation between microstructures and electronic properties of organic semiconductors. The major directions that were pursued in this thesis are: (i) studies on structure-property relationship by rational design and synthesis of monodisperse oligomers with varying chain-lengths (ii) role of electronic properties and aggregation (microstructures) in governing singlet fission (SF). In the first part of the thesis, the optical, structural and charge transport properties of Diketopyrrolopyrrole (DPP)-based oligomers, as a function of the chain length, has been discussed. The energy bands became wider with an increase in chain length and a gain in backbone electron affinity was observed, with an offset in microstructural order. With an increase in chain length, the tendency to form intramolecular aggregates increased as compared to intermolecular aggregates due to the onset of backbone conformational defects and chain folding. An insight into the solid-state packing and microstructural order has been obtained by steady-state and transient spectroscopy, grazing incidence small angle x-ray scattering (GISAXS), atomic force microscopy (AFM) and transmission electron microscopy (TEM) studies. The charge-carrier mobilities varied in accordance with the degree of microstructural order as: dimer > trimer > pentamer. A library of DPP-DPP based trimers was also generated by modifying the donor chromophore (phenyl, thiophene and selenophene) in the oligomer backbone. Highest n-channel mobility of ~0.2 cm2V-1s-1 was obtained which validated that: (a) the effect of solid-state packing predominates the effect of backbone electronic structure on charge carrier mobility. Although oligomers possess lesser backbone defects than polymers in general, their charge carrier mobilities were not comparable to that of 2DPP-OD-TEG polymer, which forms highly oriented and isotropic edge-on crystallites/microstructures in the thin film, shows high n-channel mobility of 3 cm2V-1s-1 and band-like transport ;(b) although delocalized electronic states are achieved at greater chain lengths, the degree of solid-state microstructural order drastically reduces which leads to lower charge carrier mobilities; (c) conformational collapse resulted in lower electron mobilities and an increase in ambipolarity. The later part of the thesis debates on the relative contribution of electronic structure and aggregation (microstructures) in governing singlet fission (SF). Motivated by the recent SF model in carotenoid aggregates, a DPP-DPP based oligomer was synthesized by incorporating a vinylene bridge to imbue “polyene” character in the chromophore. Transient Spectroscopy (TA) measurements were carried out to monitor the formation of triplet states in the oligomer and to probe the occurrence of singlet fission. Although the oligomer exhibits “polyene” character like a typical “carotenoid aggregate”, it did not show singlet fission because of the additional stabilization of the singlet (S1) state which reduces the ∆EST. This study rationalized the importance of judicious control of band structures as well as microstructures to observe the SF phenomenon in this category of chromophores. The novel synthetic protocol provides the scope to tailor DPP-DPP based materials with desired effective conjugation lengths and side chains and can foreshow great prospects for future generation of organic electronics.en_US
dc.language.isoen_USen_US
dc.relation.ispartofseriesG28572en_US
dc.subjectOrganic Semiconductorsen_US
dc.subjectOrganic Electronicsen_US
dc.subjectDiketopyrrolopyrrole-based Copolymersen_US
dc.subjectDiketopyrrolopyrrole-based Oligomersen_US
dc.subjectDiketopyrrolopyrrole Based Chromophoresen_US
dc.subjectOrganic Field Effect Transistors (OFETs)en_US
dc.subjectOFET Measurementsen_US
dc.subjectCharge Transport Measurementsen_US
dc.subjectThin Film Transistors (TFTs)en_US
dc.subjectDiketopyrrolopyrrole-diketopyrrolopyrrole (DPP-DPP)en_US
dc.subject.classificationSolid State and Structural Chemistryen_US
dc.titleStudies on Correlation between Microstructures and Electronic Properties of Organic Semiconductorsen_US
dc.typeThesisen_US
dc.degree.namePhDen_US
dc.degree.levelDoctoralen_US
dc.degree.disciplineFaculty of Scienceen_US


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