Electronic properties of interfaces between domains in organic semiconductors
Elektronska svojstva organskih poluprovodnika na granicama domena
Author
Mladenović, MarkoMentor
Radovanović, JelenaCommittee members
Vukmirović, NenadMilanović, Vitomir
Balaž, Antun
Matavulj, Petar
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Show full item recordAbstract
The aim of this thesis is to provide a link between atomic and electronic structure
of different types of interfaces between domains in organic semiconductors.
In polycrystalline small-molecule organic semiconductors interfaces are formed between
single crystalline domains. We found that grain boundaries in polycrystalline
naphthalene introduce trap states within the band gap of the material. Trap states
are localized on closely spaced pairs of molecules from opposite sides of the boundary.
Realistic conjugated polymers, such as poly(3-hexylthiophene) (P3HT), contain
mixed crystalline and amorphous domains. We found that HOMO state of the interface
between crystalline and amorphous domain in P3HT belongs to crystalline
domains. States that belong to both domains and trap states were not found. Effects
of thermal disorder are important in realistic conjugated polymers. Our results
show that disorder in backbone chains of P3HT has strong effect on the electronic
structure and leads to th...e localization of the wave functions of the highest states
in the valence band, similar to the ones that occur in amorphous polymers. At the
interfaces between two materials in organic electronic devices, effects of spontaneous
polarization in one or both of them on electronic properties can be pronounced. We
show that ordered P3HT exhibits spontaneous polarization along the backbone direction,
which is caused by the lack of inversion symmetry due to head-to-tail side
chains arrangement. We additionally show that spontaneous polarization in ordered
P3HT keeps significant values even at room temperature when the effects of thermal
disorder are important.
Cilj ove disertacije da je pruži vezu izmedu atomske i elektronske strukture
različitih tipova granica izmedu domena u organskim poluprovodnicima. U polikristalnim organskim poluprovodnicima na bazi malih molekula granica se formira između homogenih kristalnih domena. Ustanovili smo da granica u polikristalnom naftalinu dovodi do pojave stanja zamki u energijskom procepu materijala, lokalizovanih na parovima molekula sa različitih strana granice izmedu kojih je rastojanje malo...