Band structures of organic thin-film transistor materials

Abstract

We report extended Hückel theory (EHT) band structure calculations for the high-temperature polymorph of α-6T (α-sexithiophene) and C60, two organic materials that have shown promising device characteristics, as the active element in thin-film transistors (TFTs). We also report calculations for α-3T and κ-(ET)2Cu(NCS)2[where ET = bis(ethylenedithio)tetrathiafulvalene] for comparison purposes. Both α-6T/HT and C60 show well developed band dispersions. Whereas C60 is an isotropic three-dimensional (3D) molecular solid, α-6T/HT shows a strongly 2D electronic structure, and the band structure is quite similar to that of the ET organic superconductors such as κ-(ET)2Cu(NCS)2. Factors important in determining the mobilities of organic semiconductors are reviewed.