From Ambi‐ to Unipolar Behavior in Discotic Dye Field‐Effect Transistors

Abstract

Ambipolar, solution-processed thin-film transistors based on a discotic dye turn into unipolar behavior after thermal annealing. No evidence for temperature-induced change in injection barrier or interface trapping can be found to explain this phenomenon. Instead, a variation in morphology is considered as the cause for the observed transition from ambipolar to unipolar charge transport.

Synthesis and thermotropic behavior of side chain polysiloxane bearing triphenylene moiety

“…The temperature difference, which accompanies this transition for (4) and (6) is %T = 1°C and a corresponding small change in enthalpy is observed (%H = 0.6 J/g). Transition to the isotropic phase (Iso) occurs at the temperature of 99°C and is identical for both monomer (4) and polymer (6). Upon cooling at the rate of 5°C/min, phase transitions from Iso to LC for both monomer (4) and polymer (6) occurs at 96°C (lack of a supercooling) and is accompanied by a enthalpy change %H = 6.9 J/g (Figure 2b).…”

“…The results from TOA for the triphenylene (4) correlate very well with the data obtained from the differential scanning calorimetry (DSC). TOA analysis of polymer (6) points that on heating of the layer the Cr-LC transition is observed changing the orientation of molecules [33]. This results in an increase in light intensity passing through the layer (red curve Figure 4a, image 1 and 2) at 58°C.…”

“…Upon cooling at the rate of 5°C/min, phase transitions from Iso to LC for both monomer (4) and polymer (6) occurs at 96°C (lack of a supercooling) and is accompanied by a enthalpy change %H = 6.9 J/g (Figure 2b). On the other hand, a small temperature difference of %T = 1°C between (4) and (6) is observed (Figure 2b) for the transition from the LC to Cr phase with 52°C for (4) and 51°C for (6). In addition to measurements obtained from differential scanning calorimetry (DSC) analysis, the phase transitions of (4) and (6) were independently studied by means of thermooptical analysis (TOA).…”

“…The columnar stacks are oriented along the fiber direction as evident from the small-angle equatorial reflections. From the position of these scattering intensities the intercolumnar arrangement is determined of a slightly oblique with dissimilar unit cell parameters a = 2.29 nm and b = 2.08 nm for (4) and a = 2.31 nm and b = 2.10 nm for (6). The disc-shaped triphenylenes pack in an orthogonal fashion in these stacks with a !-stacking distance of 0.36 nm in both cases as derived from the meridional wide-angle reflections (Figure 7f).…”

“…They have been extensively studied as a result of their electro-optical and semiconducting properties as well as expected applications in organic field effect transistor devices (OFET) and solar cells [4][5][6]. They can undergo an easy macroscopic alignment and can be processed in a simple way [7][8][9].…”