Dynamic character of charge transport parameters in disordered organic semiconductor field-effect transistors

Abstract

In this perspective article, we discuss the dynamic instability of charge carrier transport in a range of popular organic semiconductors. We observe that in many cases field-effect mobility, an important parameter used to characterize the performance of organic field-effect transistors (OFETs), strongly depends on the rate of the gate voltage sweep during the measurement. Some molecular systems are so dynamic that their nominal mobility can vary by more than one order of magnitude, depending on how fast the measurements are performed, making an assignment of a single mobility value to devices meaningless. It appears that dispersive transport in OFETs based on disordered semiconductors, those with a high density of localized trap states distributed over a wide energy range, is responsible for the gate voltage sweep rate dependence of nominal mobility. We compare such rate dependence in different materials and across different device architectures, including pristine and trap-dominated single-crystal OFETs, as well as solution-processed polycrystalline thin-film OFETs. The paramount significance given to a single mobility value in the organic electronics community and the practical importance of OFETs for applications thus suggest that such an issue, previously either overlooked or ignored, is in fact a very important point to consider when engaging in fundamental studies of charge carrier mobility in organic semiconductors or designing applied circuits with organic semiconductors.

Bulky End‐Capped [1]Benzothieno[3,2‐b]benzothiophenes: Reaching High‐Mobility Organic Semiconductors by Fine Tuning of the Crystalline Solid‐State Order

“…The gate‐voltage sweep‐rate dependence of the nominal mobility of our devices has also been investigated in order to avoid any over‐estimation of the extracted values. Chen et al have recently reported the influence of the gate‐voltage sweep‐rate in the case of trap dominated FETs exhibiting a dispersive transport . Our devices do not show any significant variation of the extracted mobility for gate‐voltage sweeping rates ranging from 0.5 to 19 V s −1 (see Figure S9, Supporting Information), confirming the good charge transport performances of ditBu‐BTBT .…”

Molecular Orientation‐Dependent Bias Stress Stability in Bottom‐Gate Organic Transistors Based on an n‐Type Semiconducting Polymer

“…The P(NDI2OD-T2) FETs exhibited an insignifi cant V GS sweep rate dependence for both face-on and edge-on orientations (see Figure S3 in the Supporting Information). According to the dispersive transport model , [ 36,44 ] OFETs prepared with Edgeon P(NDI2OD-T2) should have shown more signifi cant V GS sweep rate dependence than that of Face-on P(NDI2OD-T2). The measured results, however, were similar for both cases.…”

Solution‐Grown Organic Single‐Crystalline p‐n Junctions with Ambipolar Charge Transport

“…C8‐BTBT and C 60 were used to grow single‐crystalline p‐n junctions. C 60 is a typical electron transporting material with mobilities as high as 11 cm 2 V −1 s −1 , while C8‐BTBT is among the best hole transporting organic materials . Before growing crystals from their mixed solution, we examined crystallization from solutions with only one component (either C8‐BTBT or C 60 ).…”