Time-of-flight mobility measurements in organic field-effect transistors

Abstract

We implement the “time-of-flight” (TOF) method for charge carrier mobility (μ) measurements in organic field-effect transistors (OFETs) by applying voltage steps, VS, to OFETs. We use the electric scheme for OFET-TOF introduced by Dunn et al. [Appl. Phys. Lett. 88, 063507 (2006)]. Our investigation of a series of low-threshold poly(triaryl amine) OFETs with different channel lengths, L, suggests that in the OFET-TOF setup, the effective voltage driving carriers across the channel, VTOF, is reduced from VS by a constant voltage that coincides with the OFET’s threshold voltage, VT: VTOF=VS−VT. Under this assumption, TOFs scale as expected from theory with both VS and channel length, L, and the extracted dynamically acquired μ agrees excellently between different samples, and experimental protocols (variation of VS / variation of L). However, “dynamic” μ is higher than the “static” μ conventionally extracted from saturated transfer characteristics, which is also less consistent between samples. Also, we observe that the TOF in OFETs switching from OFF→ON is longer than the TOF in the same OFET switching ON→OFF under the same VS. We rationalize this difference by trap filling in the populated OFET channel.

Computationally connecting organic photovoltaic performance to atomistic arrangements and bulk morphology

“…A discussion of the appropriate timescales and the justification of this assumption is given in the supplementary information (SI Section §2.1). This mobility calculation is more similar to time-of-flight experiments, where low excitation fluence, charge density, and active layer thickness are required [132,133], than field-effect transistor measurements on complete devices, which tend to report mobilities several orders of magnitude greater [134][135][136]. Figure 9.…”

Oscillator circuit based on a single organic transistor

“…GV D curves are more complex, but similar in shape to the transients observed when OFETs are driven with external, rectangular V S pulses. 8,9 We clearly observe V S switching between Ϯ3 V when GV D crosses V ref = 1.4 V. We explain the asymmetric duty cycle by the faster switching of the OFET from on to off, than vice versa, because traps in the channel are filled when the OFET is on and hence, mobility is higher. We have made similar observations when OFETs were driven with external V S pulses.…”

“…We have made similar observations when OFETs were driven with external V S pulses. 8 The nonperfect flanks indicate that the comparator's switching time is not negligible, despite the timescale in Fig. 2 being rather slow ͑10 ms/division͒.…”

The Charge Transport in Organic Field-Effect Transistor as an Interface Charge Propagation: The Maxwell–Wagner Effect Model and Transmission Line Approximation

“…It is assumed only that carrier transport is described as the drift in the average electric field V ds =L at a constant velocity v ¼ V ds =L. Later TOF study of Dost et al 13) suggested using the drain-source voltage reduced by the threshold (V ds À V th ) instead of V ds . This result was supported by the experiment, even though the detail explanation was not clear.…”