2012 Theses Doctoral

Single-crystal growth of organic semiconductors and organic electronic applications

Kim, Bumjung

This thesis describes single crystal growth of organic semiconductors and their applications in organic electronics.

In Chapter 2, a self-assembled monolayer of C60 derivatives with five carboxylic acids was employed to make C60 thin-film transistors. The highly-crystalline C60 monolayer enabled more ordered deposition of C60 thin film, which resulted in higher electrical characteristics when the thin film was used in field-effect transistors (FET). The C60 film with the monolayer was characterized by IR, XPS, and FET measurements.

In Chapter 3, organic single crystal FET of rubrene was studied. Graphene was used as an organic electrode instead of conventional gold film. Graphene is a sp2-hybridized carbon crystal which has high conductivity with negligible thickness. These factors are advantageous in organic FET as the graphene-organic interface has no Schottky barrier and structural contact resistance. The FET of rubrene showed much higher hole transport mobility compared to conventional FET using gold electrodes.

In Chapter 4, morphology dependence of dibenzotetrathienocoronene (DBTTC) crystal growth on different substrates was studied. Crystal growth of DBTTC on a single-layer graphene surface shows vertical growth of nanowire crystals not observed with other substrates. GIXD was measured to confirm this crystal morphology.

Chapter 5 discusses organic solar cells composed of hexabenzocoronene (HBC) and C60 and their improvement by utilizing the co-crystallization effect of these two molecules. In Chapter 6, HBC was fluorinated using two different ring-closing reactions, and their energy difference as well as conformation change was investigated.