Molecular contact doping in organic field-effect transistors (OFETs) has been proved to be a very efficient strategy to reduce the device contact resistance. It consists of inserting a dopant layer between the organic semiconductor (OSC) and the top gold contacts to reduce the energy barrier required to inject/ release charges. However, a main bottle-neck for its implementation is that the dopant diffuses toward the OFET channel with time, doping the OSC, and hampering the on/off switching device capability. In this work, we fabricated OFETs based on the benchmark OSC 2,7) by a solution shearing technique. First, we show that the OFET performance of these devices is significantly improved when a layer of the p-dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F 4 TCNQ) is inserted before the evaporation of the gold source/drain contacts. Remarkably, we demonstrate that the dopant diffusion can be controlled by blending the OSC with polystyrene (PS) of different molecular weights. In-depth electrical characterization combined with studies of surface and in-depth distribution of the dopant by time-of-flight secondary ion mass spectrometry (ToF-SIMS) unambiguously show that in thin films of OSC blends with high-molecular-weight PS, the dopant remained drastically confined into the contact areas, which was reflected by an enhanced long-term device stability.

Contact resistance and charge trapping are two key obstacles, often intertwined, that negatively impact on the performance of organic field-effect transistors (OFETs) by reducing the overall device mobility and provoking a nonideal behavior. Here, we expose organic semiconductor (OSC) thin films based on blends of 2,7-dioctyl[1]benzothieno [3,2-b][1]benzothiophene (C8-BTBT-C8) with polystyrene (PS) to (i) a CH 3 CN vapor annealing process, (ii) a doping I 2 /water procedure, and (iii) vapors of I 2 /CH 3 CN to simultaneously dope and anneal the films. After careful analysis of the OFET electrical characteristics and by performing local Kelvin probe force microscopy studies, we found that the vapor annealing process predominantly reduces interfacial shallow traps, while the chemical doping of the OSC film is responsible for the diminishment of deeper traps and promoting a significant reduction of the contact resistance. Remarkably, the devices treated with I 2 /CH 3 CN reveal ideal electrical characteristics with a low level of shallow/deep traps and a very high and almost gate-independent mobility. Hence, this work demonstrates the promising synergistic effects of performing simultaneously a solvent vapor annealing and doping procedure, which can lead to trapfree OSC films with negligible contact resistance problems.