The Factors Dominating the Effect of Electrode Modification Layer on the Work Function of the Electrode and Performances of Field-Effect Transistors

Abstract Organic field-effect transistors (OFETs) demonstrate promising applications in varied areas. Constructing a self-assembled monolayer (SAM) on metal electrodes is widely used to improve the performance of OFETs. However, the influence of SAM on the OFET performances and the behind mechanisms are rather complicated and yet to be learned. Herein, the factors determining the modification effect of pentafluorobenzenethiol (PFBT) SAM on the work function (Wf) of Au electrodes and performances of the p-type conjugated polymer OFETs were revealed through systematic investigations with density functional theory calculations and extensive experimental tests. The angle (θ) between the aromatic backbone of PFBT and the substrate plane is the decisive factor for the increment of Au Wf rather than the molecular density in SAM. Bigger θ leads to larger increment of Au Wf because more dipole moment of PFBT is projected to the out-of-plane direction. The enhancement of PFBT SAM on the device performance is more efficient when the energy gap between the Wf of bare Au and highest occupied molecular orbital (HOMO) of the p-type conjugated polymers is larger. The charge transport mechanism at the interface of the Au electrode and polymer film can be potentially changed by PFBT SAM. More importantly, our results disclose that the reliable injection barrier between the electrode and polymer film needs to be inferred from variable-temperature tests instead of estimating from the gap between the Au Wf and HOMO of the p-type conjugated polymers. The results are greatly helpful for developing efficient OFETs and related organic electronics.