Semiconducting Organic Molecular Materials

Abstract

This feature article gives an overview of recent advances in development of high performance molecular organic semiconductors for field-effect transistors with emphasis on the structure of molecular materials and requirements for highperformance.

Molecular orbital analysis of selected organic p-type and n-type conducting small molecules

“…5.1 eV below the vacuum level for Au. On the other hand, n-type dopants have a LUMO energy level between ca 3.0 and 4.0 eV (Filo and Putala, 2010). For selected small p-type molecules, the gas-phase HOMO energies ranged from -4.65 to -5.60 eV and the LUMO energy levels are between -1.12 and -3.57 eV (see Fig.…”

“…The efficient charge transport is mainly attributed to π-system extending with strong intermolecular overlaps. The optimal interval of energy level of the highest occupied orbitals for typical p-type semiconducting molecules is from 4.9 to 5.5 eV (Filo and Putala, 2010), because standard metallic hole injecting electrodes have comparable ionisation potentials, e.g. 5.1 eV below the vacuum level for Au.…”

“…Organic semiconductors can be divided accord-ing to the character of charge carriers into p-type (a positive charge or hole as the major carrier), n-type (a negative charge or electron as the major carrier) or ambipolar organic semiconductors (both electrons and holes are involved as charge carriers) (Cornill et al, 2007). The p-type conductivity was observed for the fused-ring arene compounds, including oligoacenes, and their derivatives (Filo and Putala, 2010). Special attention has been given to the pentacene molecule and its soluble derivatives.…”

“…Another interesting class of p-type semiconductors are oligothiophenes or aromatic heterocycles containing sulphur atoms. An effective approach for n-type organic semiconductors is to convert known p-type materials into the n-type ones by modifying them with strongly electronegative fluorine atoms (Filo and Putala, 2010). No matter the position or the type of electron-withdrawing substitution, perfluorarene and perfluoroalkyl both greatly affect the crystal structure and charge transport.…”

Quantum chemical study of electron structure and charge transport properties of symmetric acenequinones

“…Modern chemistry offers a wide range of possibilities to tune the electronic structure, such as Highest Occupied Molecular Orbital (HOMO) or Lowest Unoccupied Molecular Orbital (LUMO) energy levels of organic semiconducting materials (Brütting, 2005). Specifi cally, we can mention the introduction of strongly electronegative fl uorine atoms to lower the LUMOs (Filo and Putala, 2010). The measurements of Liang et al (Liang et al, 2010) showed that -defi cient fl uorinated 6,13-pentacenequinones and corresponding N-heteropentacenequinones can work as chemically stable n-type organic semiconductors in thin fi lm transistors with the electron mobility up to 0.1 cm 2 V -1 s −1 .…”