Improving Bias-Stress Stability of p-Type Organic Field-Effect Transistors by Constructing an Electron Injection Barrier at the Drain Electrode/Semiconductor Interfaces

Bias-stress instability has been a challenging problem and a roadblock for developing stable p-type organic field-effect transistors (OFETs). This device instability is hypothesized because of electron-correlated charge carrier trapping, neutralization, and recombination at semiconductor/dielectric interfaces and in semiconductor channels. Here, in this paper, a strategy is demonstrated to improve the bias-stress stability by constructing a multilayered drain electrode with energy-level modification layers (ELMLs). Several organic small molecules with high lowest unoccupied molecular orbital (LUMO) energy levels are experimented as ELMLs. The energy-level offset between the Fermi level of the drain electrode and the LUMOs of the ELMLs is shown to construct the interfacial barrier, which suppresses electron injection from the drain electrode into the channel, leading to significantly improved bias-stress stability of OFETs. The mechanism of the ELMLs on the bias-stress stability is studied by quantitative modeling analysis of charge carrier dynamics. Of all injection models evaluated, it is found that Fowler-Nordheim tunneling describes best the observed experimental data. Both theory and experimental data show that, by using the ELMLs with higher LUMO levels, the electron injection can be suppressed effectively, and the bias-stress stability of p-type OFETs can thereby be improved significantly.