On the Air Stability of n-Channel Organic Field-Effect Transistors: A Theoretical Study of Adiabatic Electron Affinities of Organic Semiconductors

In an air-stable n-channel organic field-effect transistor (OFET), the charge carrier (i.e., the radical anion of an organic semiconductor (OSC)) has to be stable enough against ambient oxidants such as O-2 and H2O. It has been suggested that OSCs with large enough electron affinity (EA) will possess air-stable charge carriers, but extensive correlation between air stability and EA has not been established. We have studied 47 existing n-channel OSCs with different molecular core structures and device configurations. A correlation between calculated adiabatic EA and air stability was established, and the threshold value found at the B3LYP/6-31+G*//B3LYP/6-31G** level for air stability was ca. 2.8 eV. This information provides a foundation for theoretical screening of potential n-channel OFETs before their synthesis and facilitates the discussion of the complex device degradation mechanism. Analysis of EAs of derivatives of perylenetetracarboxylic diimide (PDI) and naphthalenetetracarboxylic diimide (NDI) also sheds light on the roles of various substituents.