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Trapping States of Mixed-Isomer Organic Semiconductors within Organic Field-Effect Transistors

Published

Author(s)

Peter Diemer, Jacori Hayes, Evan Welchman, Rawad Hallani, Sujitra J. Pookpanratana, Christina A. Hacker, Curt A. Richter, Timo Thonhauser, Oana Jurchescu

Abstract

Organic field effect transistor (OFET) performance is dictated by the composition and geometry of the device, as well as the quality of the organic semiconductor (OSC) film, which strongly depends on the purity and structural defects. When present, these impurities and defects give rise to electronic states in the bandgap of the OSC, and these traps lower device performance. Here, 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene (diF-TES ADT) 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 (DOS) within the bandgap of the semiconductor is evaluated through temperature dependent current-voltage measurements, and it is discovered that OFETs containing a mixture of syn- and anti-isomers reveal a discrete trapping state detected as a peak located at ~ 0.4 eV above the valence-band edge, which vanishes in the samples fabricated on single-isomer films. Ultraviolet photoelectron spectroscopy (UPS) measurements and density functional theory (DFT) 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, thus inducing energetic disorder. Further, a method is proposed for separating the isomers during device processing by applying gentle mechanical vibrations of less than 100 Hz during film crystallization. This method is able to suppress the peak, lower the overall trap densities and, consequently, yield devices with better performance.
Citation
Advanced Functional Materials
Volume
3
Issue
1

Citation

Diemer, P. , Hayes, J. , Welchman, E. , Hallani, R. , Pookpanratana, S. , Hacker, C. , Richter, C. , Thonhauser, T. and Jurchescu, O. (2016), Trapping States of Mixed-Isomer Organic Semiconductors within Organic Field-Effect Transistors, Advanced Functional Materials, [online], https://doi.org/10.1002/aelm.201600294 (Accessed September 22, 2021)
Created December 14, 2016, Updated November 10, 2018