The solvent effect on the electronic structure and charge transport properties of conjugated polymers

Hussin, Huda (2011) The solvent effect on the electronic structure and charge transport properties of conjugated polymers. Masters thesis, Memorial University of Newfoundland.

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Abstract

The solvent effect on optical and electronic properties of conjugated polymers has recently been paid much attention. Conjugated polymers have many potential industrial applications, for example, they are used in optoelectronic devices such as organic light emitting diodes, field effect transistors, solar cells, and many others. In some cases it was shown that the usage of an appropriate solvent can lead to higher efficiency in organic solar cells. In this work, we investigate the solvent effect on the electronic structure properties of some conjugated polymers, basically, fluorene and carbazole oligomers, and some benzodithiophene based co-monomers. Also solvent effect on some transport properties of benzodithiophene based co-monomers are investigated. The energy levels, band gaps, and dipole moments are obtained with density functional theory (DFT). The B3LYP, hybrid exchange-correlation functional, and the polarized split-valance basis set, 6-31G*, are used to determine optimized ground state structures of the above mentioned molecular systems. The time-dependant DFT is employed to calculate their excited state properties. For solvent effect we make use of the polarizable continuum model. Two solvents, chloroform and methanol are employed for fluorene and carbazole oligomers. Four solvents, chlorobenzene and o-dichlorobenzene, in addition to chloroform and methanol, are used for benzodithiophene based compounds. The results show that the presence of a solvent lowers the HOMO and LUMO energy levels, and increases or decreases the HOMO-LUMO energy gap depending on the chemical system, and decreases the lowest excitation energy. The magnitude of ground state electronic dipole moment of the systems is increased in solutions. The solvent effect on the reorganization energy depends on the system studied. The calculated values for the various quantities are compared with the experimental ones whenever possible.

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