Materials For Organic Field-effect Transistors Research Articles

Structure, bonding, and growth at a metal–organic interface in the weak chemisorption regime: Perylene–Ag(111)

Organic semiconductors on single-crystalline metal surfaces are model systems for injection contacts in organic field-effect transistors (OFET) and light-emitting diodes. They allow us to classify possible metal–organic interaction scenarios and to elucidate general tendencies, which most likely will also be found at metal–organic interfaces in real devices. In this contribution, we report a comprehensive investigation of the interface of perylene, a promising material for OFETs, with the close-packed noble metal surface Ag(111), using high-resolution electron energy loss spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy as surface analytical techniques. The most important findings are: In the monolayer, molecules are oriented flat and form an incommensurate, most probably fluid overlayer. The molecules interact electronically with the substrate and become weakly metallic. Scanning tunneling microscopy reveals a propensity of perylene molecules toward a specific adsorption site on Ag(111), if the influence of intermolecular interactions is inhibited. Film growth at room temperature is similar to Stranski–Krastanov type. Finally, co-planar adsorption of perylene on Ag(111) is metastable, and annealing the monolayer at 420 K leads to a structural transformation of the film. The perylene–Ag(111) interface can therefore be classified as weakly interacting.

New Platform for Testing Candidate Materials for Organic Field-Effect Transistors

A field-effect transistor platform has been designed and fabricated from silicon that allows for the testing of organic semiconductors (OS) as potential materials for organic field-effect transistors (OFET) and as the gate conductor in chemically sensitive field-effect transistors (CHEMFET). Once the OS is deposited, the device can be operated in either mode. This platform should aid in the search for the semiconductor field effect in a variety of organic materials. The effects of contact resistance, surface conductivity, and gate leakage current have been demonstrated and analyzed. No semiconductor field effect has been observed in OFET mode using poly(phenylenesulfidephenyleneamine) as the organic semiconductor.

On the stability of organic field-effect transistor materials

Stability and degradation of transistor performance of devices based on pentacene and α-sexithiophene are investigated. In order to distinguish between effects at grain boundaries and material issues, macroscopic bicrystals were used, where transistors were prepared on a single grain as well as across a single grain boundary. The main reason for performance instabilities is the formation of oxygen-related trapping states at the grain boundary upon exposure to air. However, especially in the case of pentacene, stable hole transport properties are observed.