The role of surface morphology in a performance of top-gate OFETs prepared from a solution processable derivative of perylene bisimide

A commercially available, soluble in chlorinated hydrocarbons perylene derivative, N,N-bis(1-ethylpropyl)-perylene-3,4:9,10-bis(dicarboximide) (PTCDI-C5(3)), was used to construct n-channel organic field effect transistors (OFETs). The transistors had the top-gate-bottom-contacts (TGBC) architecture, with a spin-coated layer of the active material. This material was subsequently coated with Parylene C gate dielectric layer which, together with a silver gate electrode deposited on the top of that layer, provided a protection of the device against the water and oxygen molecules. In order to investigate the effect of the morphology of semiconductor/gate dielectric interface on the device parameters, a series of OFETs with PTCDI-C5(3) layers spin-coated at different spinning rates were prepared. Three chlorinated hydrocarbon solvents with different boiling points were used: chloroform, chlorobenzene and 1,2-dichlorobenzene. The resulting polycrystalline layers of perylene derivative differed with regard to their thickness and to their roughness as well as exhibited different grains size and shape. Surprisingly however, no direct correlation between the transistor parameters and the thickness of the semiconductor layer or the roughness of the semiconductor/dielectric interface was found – in fact the worst performance was recorded for the OFETs with PTCDI-C5(3) layers of the lowest roughness, spin-coated from chloroform.