Interfacial nucleation behavior of inkjet-printed 6,13 bis(tri-isopropylsilylethynyl) pentacene on dielectric surfaces

Abstract

The performance of organic thin film transistors (OTFTs) is heavily dependent on the interface property between the organic semiconductor and the dielectric substrate. Device fabrication with bottom-gate architecture by depositing the semiconductors with a solution method is highly recommended for cost-effectiveness. Surface modification of the dielectric layer is employed as an effective approach to control film growth. Here, we perform surface modification via a self-assembled monolayer of silanes, a spin-coated polymer layer or UV-ozone cleaning, to prepare surfaces with different surface polarities and morphologies. The semiconductor is inkjet-printed on the surface-treated substrates as single-line films with overlapping drop assignment. Surface morphologies of the dielectric before film deposition and film morphologies of the inkjet-printed semiconductor are characterized with polarized microscopy and AFM. Electrical properties of the films are studied through organic thin-film transistors with bottom-gate/bottom-contact structure. With reduced surface polarity and nanoscale aggregation of silane molecules on the substrates, semiconductor nucleates from the interior interface between the ink solution and the substrate, which contributes to film growth with higher crystal coverage and better film quality at the interface. Surface treatment with hydrophobic silanes is a promising approach to fabrication of high performance OTFTs with nonpolar conjugated molecules via solution methods.

Process optimization for inkjet printing of triisopropylsilylethynyl pentacene with single-solvent solutions

“…Secondly, the PVP-coating is intact and therefore a smooth interface with the semiconductor persists, which can reasonably lead to enhanced fieldeffect mobility, although the inferior steepness of the subthreshold slope still indicate a poor interface quality. A potential solution via interfacial nucleation on hydrophobic surfaces has been proposed recently [27].…”

Printed Thin-Film Transistors: Research from China

“…(c) AFM images of inkjet-printed TIPS-pentacene thin films on SiO 2 /Si substrates by PETS, PTS, PVP coating and UV-ozone treatment. Reprinted with permission from ref . Copyright 2015 AIP Publishing.…”

“…Organic small molecular semiconductor is normally processed by thermal deposition because of its insolubility, such as pentacene, phthalocyanine compounds. Recently, more and more soluble organic small molecular semiconductors have been synthesized via introducing suitable soluble groups for printed electronics, for example, 2,7-dioctyl[1]­benzothieno­[3,2- b ] benzothiophene (C8BTBT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), as shown in Figure b. , The group 6,13-bis­(triisopropyl-silylethynyl) (TIPS) is added into pentacene, it could form a excellently soluble, high-performance TIPS-pentacene. , For fabricating TIPS-pentacene thin film with homogeneity thickness and high-quality morphology via inkjet printing, surface energies were tuned via SAM, ultraviolet (UV)-ozone treatment and a polymeric dielectric (Figure c) . Wang et al demonstrated that the crystal growth of TIPS-pentacene could be controlled by inkjet printing, in which crystal orientation of TIPS-pentacene was adjusted by surface-modified Au because there is a slightly higher dispersive surface energy than the dielectric substrate .…”

“…Thus, it could produce high-quality TIPS-pentacene thin film with large grain size and more convergent crystalline microstructure. Furthermore, high-quality inkjet-printed TIPS-pentacene thin film and accordingly high-performance TFTs could be achieved via modifying the dielectric surface properties, in which inserting SAM, e.g., phenethyltrichlorosilane (PETS), phenyltrichlorosilane (PTS) and perfluorodecyltrichlorosilane (PDTS). , In addition, UV-ozone treatment on substrate could also control the morphology, crystallization behavior and device performance of TIPS-pentacene via inkjet printing. The UV irradiation accelerates the formation of uniform and large strip-like crystals (Figure c), leading to the mobility of TIPS-pentacene TFTs fabricated via inkjet printing up to 0.48 cm 2 V –1 s –1 .…”

“…100,101 For fabricating TIPS-pentacene thin film with homogeneity thickness and high-quality morphology via inkjet printing, surface energies were tuned via SAM, ultraviolet (UV)-ozone treatment and a polymeric dielectric (Figure 4c). 97 Wang et al demonstrated that the crystal growth of TIPS-pentacene could be controlled by inkjet printing, in which crystal orientation of TIPS-pentacene was adjusted by surface-modified Au because there is a slightly higher dispersive surface energy than the dielectric substrate. 102 Thus, it could produce high-quality TIPS-pentacene thin film with large grain size and more convergent crystalline microstructure.…”