Henrik G.O. Sandberg

Current modulation of a hygroscopic insulator organic field-effect transistor

We have fabricated solution processable polymer transistors with high conductivity, requiring only a few volts for obtaining good current modulation. The devices can be fabricated and operated in air and the operation is greatly enhanced in humid atmosphere. Devices reach an On∕Off ratio of about 600 and a subthreshold swing of 500mV per decade operating on voltages less than 2V. In this letter the mechanism behind the current modulation is investigated, and we show that the current is modulated through ion-assisted oxidation and reduction of the semiconductor by ions moving vertically in the insulator material to the transistor channel.

Two-dimensional charge carrier mobility studies of regioregular P3HT

Charge carrier mobility of regioregular poly(3-hexylthiophene) (RR-P3HT) is studied within the temperature range 77 - 370 K using thin film field-effect transistors (FETs). The non-monotonic thickness dependence of the room temperature field-effect mobility (μ) has a maximum at ∼ 10 nm. The film thickness was varied both by changing the concentration of the solution of RR-P3HT in chloroform and by varying the spin coating speed. For films about 5-10 nm thick the maximum mobility is μ ∼ 10 -3 cm 2 V -1 s -1 and the maximum on-off ratio is > 10 5 . At low T, p(T) = μ 0 exp[-(T 0 /T) 0.33 ]. The results support Motts variable-range hopping model for two-dimensional systems.

Charge Carrier Mobility in Langmuir-Blodgett Films of Poly(3-hexylthiophene)

Abstract The tendency to saturation in the collected charge as a function of light intensity in Langmuir-Blodgett films of poly(3-hexylthiophene) (PHT) has been studied. The tendency to saturation can have two reasons; that the space charge limited current regime has been reached, or influence of very fast bimolecular recombination. We have studied these two cases, and we conclude that bimolecular recombination is a probable cause for the tendency to saturation. The hole mobility in PHT can therefore possibly be estimated as high as 1 cm 2 /Vs in the initial stage after photoexcitation.