Influence of moisture on device characteristics of polythiophene-based field-effect transistors

Abstract

We investigated a field-effect transistor (FET) based on a poly(3-n-hexylthiophene) (P3HT) to determine the influence of moisture on device characteristics and thus gain a deep understanding of the mechanism underlying the susceptibility to air of the operation of FETs of this kind. The fundamental output characteristics, which include effective field-effect modulation and saturation behavior in the output current, remained almost the same for every current–voltage profile in a vacuum, N2 and O2. By contrast, operation in N2 humidified with water resulted in enlarged off-state conduction and deterioration in the saturation behavior, in the same manner as that experienced with exposure to room air. We concluded that atmospheric water had a greater effect on the susceptibility of the device operation to air than O2, whose p-type doping activity as regards P3HT caused only a small increase in the conductivity of the active layer and a slight decrease in the field-effect mobility with exposure at ambient pressure. We discuss the mechanism of the significant distortion in the operation induced by moisture in terms of the difference between the influence of water and O2 on the device characteristics.

Reversibility of humidity effects in pentacene based organic thin-film transistor: Experimental data and electrical modeling

“…For these transistors the saturation of the drain current was not observed. This behavior is attributed to the diffusion of H 2 O molecules in the thin film of pentacene which increases the current I off and prevents the saturation of the output characteristics [20]. Moreover, we note that the drain current increases by increasing the gate voltage in all the measurement conditions.…”

Kinetics of occupancy of defect states in poly(3-hexylthiophene):fullerene solar cells

“…In order to further improve organic solar cell performance extracting information about defect states and their role as trapping or recombination centers seems to be crucial. It is well known that P3HT is a conjugated polymer that in exposure to oxygen [3], or moisture [4] results p-doped exhibiting relatively high levels of free carries ( 17 15 10 10  cm -3 ) [5]. Under such conditions, it has been suggested that the P3HT-metal contact forms a Schottky barrier behavior: band bending with a corresponding majority-carrier depletion zone made up at the cathode contact [6,7], due to the presence of acceptor defects (see Fig.…”

How the Charge-Neutrality Level of Interface States Controls Energy Level Alignment in Cathode Contacts of Organic Bulk-Heterojunction Solar Cells

“…16,17 Before contact is made, there exists an energy offset between the metal and the organic semiconductor work functions, φ c and φ s , respectively, as schematically illustrated in Figure 1B. Donor polymers as poly-(3-hexylthiophene), P3HT can easily undergo oxidation (p-doping) when exposed to the air or moisture, 18,19 producing a change in the hole conductivity. 20 Accordingly, we have proposed very recently that doping of the organic layer produces native mobile charges in the organic blend, which gives rise to the separate equilibration of each contact.…”