Bart-Hendrik Huisman

Switch-on voltage in disordered organic field-effect transistors

The switch-on voltage for disordered organic field-effect transistors is defined as the flatband voltage, and is used as a characterization parameter. The transfer characteristics of the solution processed organic semiconductors pentacene, poly(2,5-thienylene vinylene) and poly(3-hexyl thiophene) are modeled as a function of temperature and gate voltage with a hopping model in an exponential density of states. The data can be described with reasonable values for the switch-on voltage, which is independent of temperature. This result also demonstrates that the large threshold voltage shifts as a function of temperature reported in the literature constitute a fit parameter without a clear physical basis.

Scaling behavior and parasitic series resistance in disordered organic field-effect transistors

The scaling behavior of the transfer characteristics of solution-processed disordered organic thin-film transistors with channel length is investigated. This is done for a variety of organic semiconductors in combination with gold injecting electrodes. From the channel-length dependence of the transistor resistance in the conducting ON-state, we determine the field-effect mobility and the parasitic series resistance. The extracted parasitic resistance, typically in the MΩ range, depends on the applied gate voltage, and we find experimentally that the parasitic resistance decreases with increasing field-effect mobility.

Photoconductivity enhancement of poly(3-hexylthiophene) by increasing inter- and intra-chain order

The transient conductivity of an organic thin film induced by the absorption of a nanosecond laser pulse can be probed by microwaves without the necessity of attaching electrodes to the sample. Poly(3-hexylthiophene), P3HT, samples of varying degrees of regioregularity and molecular weight were investigated. Films were produced by spin-coating or drop-casting in air or in a solvent-saturated atmosphere. We observed higher photoconductivity signals in films of higher regioregularity. Drop-casting as opposed to spin-coating yielded a further increase in the photoconductivity and also increased the lifetime of the mobile charge carriers. We conclude that the enhancement of the photoconductivity is due to a higher charge carrier mobility in films with increased intra- and inter-chain order in accordance with published results obtained from field-effect transistor studies.

Plastic transistors in active-matrix displays

An active-matrix display driven by a pixel circuit with polymer-based thin film transistors is demonstrated. The circuit contains 4096 solution-processed plastic transistors, which is among the largest organic circuits reported to date. The relation between the transistor parameters such as mobility and leakage current to the display performance is analyzed.

Polymeric integrated circuits: fabrication and first characterisation

A technology to fabricate polymeric integrated circuits on 150-mm foils is presented. The technology is demonstrated with functional code generators. The integration level is about 700 transistors. The yield of the circuits has been measured as function of the complexity and has been correlated with intrinsic noise margin of the logic gates.

Flash-photolysis time-resolved microwave conductivity of a poly(3-hexylthiophene) thin film

The transient conductivity of a spincoated poly(3-hexylthiophene) film upon laser excitation is probed using an electrodeless microwave conductivity technique which circumvents the drawbacks of electrode contacts, space charge and polarization in conventional DC methods. The dependence of the kinetics and the peak values of the conductivity transients is investigated as a function of excitation wavelength and intensity. From these results, insight into the mechanism of charge carrier generation, mobility and decay can be obtained.