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

Abstract

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.

Doped Vertical Organic Field‐Effect Transistors Demonstrating Superior Bias‐Stress Stability

“…Since it is not direct to extract threshold voltage in VOFETs, we monitored their on‐state drain current as a function of stress time, that is, I DS (t). [ 18,53–55 ] Figure 5f shows the time‐dependent drain‐source current (normalized by I DS (t)/ I DS (0) with I DS (0) being the current at stressing time t = 0) of the three kinds of devices under bias‐stress conditions of V GS = −60 V and V DS = −10 V. The BGBC OFETs are observed to have the strongest decay with time while the doped VOFETs exhibit the least decay over time. The characteristic time (τ) indicating the decaying speed of I DS can be obtained by a stretched exponential equation: .…”

Influence of Polymer Gate Dielectric on Organic Field‐Effect Transistors: Interdependence of Molecular Weight, Solvent Polarity, and Surface Energy—A Case Study with PMMA and Pentacene

“…The magnitude of the bias‐stress instability is defined by the I DS decay ratio, [ I DS (0) − I DS ( t )] / I DS (0), where I DS (0) is the initial source/drain current established right after the OFET is on and I DS ( t )is the source/drain current during the bias stress. [ 47 ] After 1800 s bias stress, for low dipole moment solvent, the molecular weight does not play a significant role in decay. For toluene, it is almost the same for all molecular weight.…”

Eliminating Leakage Current in Thin‐Film Transistor of Solution‐Processed Organic Material Stack for Large‐Scale Low‐Power Integration

“…[ 22–24 ] The trapped electrons into the OSC layer or at the interfaces also resulted in performance instabilities. [ 25–27 ] Two types of strategies have been devoted to suppressing the adverse effects of minority carrier injection (electrons in p‐type OTFTs). [ 27–31 ] One is to introduce molecular additives as selective charge‐carrier electron traps in the channel, that prevents the injected electrons from contributing to the conduction process.…”

“…[ 25–27 ] Two types of strategies have been devoted to suppressing the adverse effects of minority carrier injection (electrons in p‐type OTFTs). [ 27–31 ] One is to introduce molecular additives as selective charge‐carrier electron traps in the channel, that prevents the injected electrons from contributing to the conduction process. [ 28,29 ] However, this method is difficult to be controlled in processes for full prevention of electrons while not disrupting the hole transport in the ON‐state.…”