Effect of the Phase States of Self-Assembled Monolayers on Pentacene Growth and Thin-Film Transistor Characteristics

Abstract

To investigate the effects of the phase state (ordered or disordered) of self-assembled monolayers (SAMs) on the growth mode of pentacene films and the performance of organic thin-film transistors (OTFTs), we deposited pentacene molecules on SAMs of octadecyltrichlorosilane (ODTS) with different alkyl-chain orientations at various substrate temperatures (30, 60, and 90 degrees C). We found that the SAM phase state played an important role in both cases. Pentacene films grown on relatively highly ordered SAMs were found to have a higher crystallinity and a better interconnectivity between the pentacene domains, which directly serves to enhance the field-effect mobility, than those grown on disordered SAMs. Furthermore, the differences in crystallinity and field-effect mobility between pentacene films grown on ordered and disordered substrates increased with increasing substrate temperature. These results can be possibly explained by (1) a quasi-epitaxy growth of the pentacene film on the ordered ODTS monolayer and (2) the temperature-dependent alkyl chain mobility of the ODTS monolayers.

Enhancing 2D growth of organic semiconductor thin films with macroporous structures via a small-molecule heterointerface

“…The soft and rubbery characteristics of the TSB3 surface facilitate the lateral diffusion of pentacene molecules 32,34 . Similarly, previous studies revealed higher D values for pentacene admolecules on disordered SAMs, which have mobile alkyl chains and soft surface, than on ordered SAMs 11,12 . This enhanced surface diffusion contributes to the self-ordering of pentacene with far fewer grain boundaries in the first seeding layer.…”

“…By adding an interfacial layer, such as self-assembled monolayers (SAMs) and polymeric materials, between the semiconductor and the underlying substrate, the interface properties can be controlled effectively for favourable mesoscale/nanoscale ordering of the organic semiconducting layer 5 . It is generally known that the surface of well-ordered SAMs promotes the two-dimensional (2D) growth of vacuum-deposited organic semiconductor thin films and improves the crystallinity; the surface of disordered SAMs is believed to degrade the film quality by reducing the interaction between the surface and admolecules, inducing the threedimensional growth rather than the 2D growth 11,12 .…”

Trap density of states in n-channel organic transistors: variable temperature characteristics and band transport

“…Silicon oxide surface was treated with self-assembled monolayers of octadecyltrichlorosilane (OTS) for Cy-NDI and octadecyltrimethoxysilane (OTMS) for DMDCNQI in prior to the evaporation of the materials. 45,46 Cy-NDI and DMDCNQI were thermally deposited on the substrates with a thickness of 50 nm, where the evaporation was carried out under 10 −4 Pa for Cy-NDI, but 10 −3 Pa for DMDCNQI due to the high vapor pressure. 41 In order to fabricate transistors with top-contact configuration, the sourcedrain electrode was patterned with shadow masks by thermal deposition of Au (channel length L = 100 μm and channel width W = 1000 μm) onto the organic thin films.…”

Effect of curing conditions of a poly(4-vinylphenol)gate dielectric on the performance of a pentacene-based thin film transistor

“…Many groups have reported field-effect mobilities greater than 1 cm 2 /Vs for OFETs in which pentacene is used as the active layer. [1][2][3][4] The surface characteristics of the gate dielectric strongly influence the quality of the gate dielectric-semiconductor interface hence the device performance. [5][6][7] In the last decade, considerable effort has been devoted to the fabrication of OTFTs using organic gate dielectrics [8][9][10][11][12] for use as switching devices for flexible displays.…”