Organic field-effect transistor (OFET) performance is dictated by 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 band gap 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.
|Journal||Advanced Electronic Materials|
|State||Published - Jan 1 2017|
Bibliographical noteFunding Information:
The device studies were supported by NSF Grant ECCS-1254757. Semiconductor synthesis was supported by NSF Grant CMMI-1255494.
© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- charge trapping
- organic semiconductors
- organic thin-film transistors
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials