The Influence of Isomer Purity on Trap States and Performance of Organic Thin‐Film Transistors

Abstract

Organic field-effect transistor (OFET) performance is dictated by its composition and geometry, as well as the quality of the organic semiconductor (OSC) film, which strongly depends on purity and microstructure. When present, impurities and defects give rise to trap states in the bandgap of the OSC, lowering device performance. Here, 2,8-difluoro-5,11-bis(triethylsilylethynyl)-anthradithiophene is used as a model system to study the mechanism responsible for performance degradation in OFETs due to isomer coexistence. The density of trapping states is evaluated through temperature dependent current-voltage measurements, and it is discovered that OFETs containing a mixture of syn- and anti-isomers exhibit a discrete trapping state detected as a peak located at ~ 0.4 eV above the valence-band edge, which is absent in the samples fabricated on single-isomer films. Ultraviolet photoelectron spectroscopy measurements and density functional theory calculations do not point to a significant difference in electronic band structure between individual isomers. Instead, it is proposed that the dipole moment of the syn-isomer present in the host crystal of the anti-isomer locally polarizes the neighboring molecules, inducing energetic disorder. The isomers can be separated by applying gentle mechanical vibrations during film crystallization, as confirmed by the suppression of the peak and improvement in device performance.

Crossover from band-like to thermally activated charge transport in organic transistors due to strain-induced traps

“…N T increases gradually as the channel length increases and mobility decreases. Although this would suggest that the interfacial trap density determines the mobility value, note that the estimation of N T from S does not allow access to the energy distribution of these traps, as we have shown in our earlier work using other methods (50)(51)(52), and it is likely that traps located at different energy levels will impact the mobility and its temperature dependence in a distinct way (53). Devices with channel lengths between 5 μm and 25 μm, consisting entirely of LG, showed similar changes in N T within the accuracy of our measurements.…”

Hybrid bilayer gate dielectric-based organic thin film transistors

“…In the case of rough dielectrics, interface trap density increases. As a result, more charges get trapped resulting in a large hysteresis width [54]. Nature of functional groups can influence the hysteresis width in the case of polymer dielectrics [52,55,56].…”

Effect of relative humidity and temperature on the stability of DNTT transistors: A density of states investigation

“…Another possible reason given for a peak in the DoS of organic semiconductors is a packing mismatch due to the presence of isomers. For example, in 2,8-difluoro-5,11bis(triethylsilylethynyl) anthradithiophene (diF-TES ADT), a mixture of sys-and anti-isomers gave rise to strong peaks in the DoS at ~0.4 eV above the valence band [39]. The molecular structure of DNTT does not allow for this possibility.…”