Solvent Vapor Annealing Improves Device Characteristics of Solution-Processable Triethylsilylethynyl Antradithiophene
Lynn Loo, Chemical Engineering, The University of Texas at Austin, CPE Building, C0400, Austin, TX 78712, Kimberly Dickey, Chemical Engineering, Chemical Engineering, The University of Texas at Austin, CPE Building, C0400, Austin, TX 78712, and John Anthony, Chemistry, University of Kentucky, KY.
The development of organic semiconductors is driven by the promise of low-cost device applications. To fully realize cost-effective organic electronics, solution-processable materials need to be developed. While several solution-processable materials have been demonstrated, these materials often suffer from significantly reduced carrier mobilities due to defects and grain boundaries introduced during the deposition process. We have been studying triethylsilylethynyl anthradithiophene (TES ADT), a solution-processable, p-type organic semiconductor. Transistors fabricated with spun-cast TES ADT exhibit low carrier mobilities (0.002 cm2/V-s), low on-off current ratios and significant current-voltage hysterisis. Subjecting the fabricated transistors to dichloroethane solvent vapor annealing, however, yields average carrier mobilities of 0.2 cm2/V-s, high on-off current ratios (104-5), and significantly reduces the current-voltage hysterisis. This dramatic improvement in transistor performance is solvent choice dependent, and can be directly correlated with morphological transformations in the thin films. Specifically, the solvent vapor is able to partition into the organic semiconductor thin film during the annealing process to induce structural rearrangment. TES ADT crystallizes as a consequence. The improvement in device characiteristics appear to be directly correlated with the grain size within the thin films. The polarity of the solvent, on the other hand, has a dramatic impact on the threshold voltage. In general, polar solvents can induce the presence of a dipole barrier at the organic semiconductor-dielectric interface, thereby increasing the threshold voltage. Annealing with non-polar solvents, like hexanes, results in a threshold voltage that is close to zero.