We investigate the contact of bottom-contact pentacene-based thin-film transistors, with Au source/drain electrode. By separating the voltage drop at the contact from the source-drain voltage, the current-voltage characteristic of the injection contact is obtained. The contact characteristics are in a good agreement with a model of carrier injection from a metal electrode into a disordered hopping system.

We report on the experimental observation of large magnet field effect (MFE) on current and electroluminescence (EL) in polyfluorene organic light emitting diodes (OLEDs). We provide a comprehensive overview of the observed MFE. To the best of our knowledge, the mechanism causing these MFE is currently not known. Moreover, we show that these experiments do not allow determination whether the MFE acts on the carrier density or carrier mobility making any attempt of explaining it ambiguous. As a remedy, we performed magnetoresistance measurements in hole-only OLEDs and show that the MFE acts on the carrier mobility rather than carrier density.

Unlike many other conjugated polymers popular for use in LEDs, poly[p-(2,5-didodecylphenylene)ethynylene] (DPPE), shows less interchain interaction between polymer chains after annealing to an ordered film. Evidence of this decreased interchain interaction can be seen in the emission spectra of pristine and annealed films. Thin films of pristine DPPE show a broad featureless green emission, characteristic of an excimer-like state, whereas annealed films blue-shift and become structured, resembling dilute solution emission. DPPE packs into ordered domains after annealing, shown by birefringence, polarization anisotropy NSOM, and x-ray crystallography data. The lack of chromophore interaction in the ordered domains can be explained through a brick-wall-type packing motif, where the polymer backbone is insulated by the side chains of offset neighboring polymers. Electroluminescence spectra of pristine and annealed LEDs are nearly identical, both having green emission, unlike their different photoluminescence spectra. This is evidence that light emission in LEDs comes only from excimer sites within the film, which would indicate a decreased performance for the annealed devices compared to pristine devices. Preliminary data of pristine and annealed LEDs supports this theory, with most pristine devices having a slightly higher electroluminescence intensity compared to annealed devices.

Solution-processed bottom-gate organic field-effect transistors (OFET) with different dielectric materials were produced and characterized. As the active semiconductor layer, regioregular poly(3-hexylthiophene) (rr-P3HT) was used. In addition to the dielectrics which have been reported in literature, various other materials with simple processing conditions were used as gate-dielectrics. Also, the dielectric properties of the polymeric layers were investigated in metal-insulator-metal capacitor structures, where the thicknesses of the films were exactly the same as they were in the OFETs. The specific volume resistivity and dielectric constant values determined were then used to explain the electrical behavior of OFETs. The devices having BCB, SU-8 and NOA74 as the dielectric layers exhibited the desired transistor characteristics, whereas the transistors with Avatrel dielectric did not, due to higher gate-leakages. As a result, SU-8 and NOA74 resins were proven to be good candidates for gate-dielectric usage in solution-processed all-polymer OFETs.