Improving electron injection and transport in polymer field-effect transistors with guanidino-functionalized aromatic n-dopants

Abstract

The application of n-dopants in organic field-effect transistors (FETs) enables improvement of electron injection and transport. They can block hole injection and suppress ambipolar transport, thus creating purely n-type devices with large on/off current ratios. Here, we apply guanidino-functionalized aromatic (GFA) compounds such as 1,2,4,5-tetrakis(tetramethylguanidino)benzene (ttmgb) and 1,2,4,5-tetrakis(N,N′,-dimethyl-N,N′-ethyleneguanidino)benzene (tdmegb) as two-electron donors (n-dopants) with similar redox properties but different solubilities in bottom-contact/top-gate FETs with mostly electron-transporting but still somewhat ambipolar polymer semiconductors P(NDI2OD-T2) and DPPT-BT. The resulting n-type FETs show lower contact resistance and no hole transport while avoiding undesired onset voltage shifts and maintaining high electron mobilities, low hysteresis, and high stability under bias stress in ambient air. Various methods of integrating the GFA-dopants are explored (as injection layers on the electrodes, polymer-dopant blends and by deposition on top of the semiconducting layer) to identify the optimal process for the respective polymer-dopant combination.