Effect of Surface Energy on Pentacene Growth and Characteristics of Organic Thin-Film Transistors

Abstract

Fluorinated hybrid materials were synthesized for a solution-processable gate insulator. The surface energy was modified by perfluoroalkyl chains contained in the hybrid gate insulator itself. We investigated the initial morphology and growth mode of pentacene and the characteristics of organic thin-film transistors ͑OTFTs͒ to determine how these characteristics depend on the surface energy. Pentacene growth was changed from a layer-by-layer mode to a three-dimensional ͑3D͒ island growth mode at low surface energy. Tightly and uniformly grown pentacene grains at 3D island mode induced good OTFT performance, but the carrier mobility was degraded at very low surface energy due to the large amount of grain boundaries.Organic thin-film transistors ͑OTFTs͒ attract great interest due to their ease of processing, low cost, and wide applicability. The characteristics of OTFTs are very dependent on the gate insulators because the majority of the charge carriers in the OTFTs are located close to the interface between the gate insulator and the organic semiconductor. 1-3 The surface energy of the gate insulator has an effect on the initial growth behavior, the morphology, and the crystallinity of the pentacene layer; these are critical performance factors for OTFTs. The hydrophobic surface of the gate insulator, which induces the pentacene crystallinity and the interconnection between pentacene grains, enhances OTFT performance. To this end, surface treatments on the gate insulator using hexamethyldisilazane, octadecyltrichlorosilane, and other self-assembled monolayers ͑SAMs͒ were employed. [4][5][6] In this study, we considered methacrylate siloxane hybrid materials ͑hybrimers͒ simply synthesized by a sol-gel process of organoalkoxysilane. The perfluoroalkyl chain was introduced in the design of the hybrimer to tune the surface energy of the gate insulator. Instead of using an additional surface treatment on the gate insulators, we added long perfluoroalkyl chains to the hybrimer gate insulator. These chains were concentrated on the insulator surface, leading to better growth of the pentacene. We added various amounts of perfluoroalkylsilane to the hybrimer to control the surface energy of the gate insulator. Next we observed the growth behavior of the pentacene on the hybrimer gate insulator. We investigated the electrical characteristics of the fabricated OTFT to determine how these characteristics depend on the content of perfluoroalkyl chains. ExperimentalWe synthesized fluorinated hybrid materials ͑hybrimers͒ via a sol-gel process using 3-͑trimethoxysilyl͒propyl methacrylate, titanium͑IV͒ butoxide, and 1H,1H,2H,2H-perfluorodecyltrimethoxysilane ͑PFAS͒. Instead of using an additional surface treatment, we added long perfluoroalkyl chains to the hybrimer gate insulator itself. These chains were concentrated on the insulator surface, leading to better growth of the pentacene. To control the surface energy of the gate insulator, the amounts of PFAS, which contained the hydrophobic perfluoroalkyl chain, were adjusted as f...

Ambient-atmosphere annealing effect on the carrier conduction behavior based on the linear-regime transfer characteristics of pentacene thin film transistors

“…Vollmer et al [40] found that O 2 and water do not react noticeably with pentacene, whereas singlet oxygen/ozone readily oxidizes the organic compound. We deduce that large pentacene grains lead to higher mobility than small grains [41,42]. However, Chou et al [21] found that the grain size did not show any significant relation to μ.…”

Low Cost Universal High‐k Dielectric for Solution Processing and Thermal Evaporation Organic Transistors

“…On the other hand, if W ad < 2 γ , the fi lm will grow in small islands (Volmer-Weber Mode) mode. [ 21 ] The growth mode of the thermal evaporated organic molecules would directly affect overall performance of the OFETs especially the carrier mobility. The layer-by-layer growth mode usually results in large and dendritic grains, while the island mode growth can provide a higher packing density in the fi rst few monolayers of organic semiconductors.…”

“…The layer-by-layer growth mode usually results in large and dendritic grains, while the island mode growth can provide a higher packing density in the fi rst few monolayers of organic semiconductors. [ 22 ] The work adhesion of the DNTT thin fi lm and the BST sample loaded into the evaporation chamber 5 h is evaluated by: [ 21 ] W Figure 2 (e,f) shows the AFM surface morphology of the thermal evaporated DNTT fi lm on BST thin fi lm stored in chamber for 5 h, both island and layer structure can be observed and the average grain size is around 500 nm. In the magnifi ed AFM image in Figure 2 .…”

Improving the performance of organic thin film transistors formed on a vacuum flash-evaporated acrylate insulator

“…[14][15][16][17][18] Large pentacene grains have been reported on dielectric surfaces with the total surface energy ranging widely from 25 to 55 mN/m. 14,17 In our experiment, the aliphatic ester-containing PMMA surface, with c total of 37 mN/m and c polar of 6.4 mN/m resulted in large pentacene grains (Fig. 2) and the highest XRD signal intensity (Table I).…”

“…Of course, the transistor performance is likely to be dominated by the pentacene order very close to the dielectric surface, which may be very different from the bulk and free-surface morphology, as suggested by the "layer þ island" crystal growth mode for the first few layers of pentacene. 16,17,19 In Table I and Fig. 3(a), we present the charge carrier mobility of OTFTs with different dielectric surface buffers and bare TPGDA.…”