Probing the Anisotropic Field‐Effect Mobility of Solution‐Deposited Dicyclohexyl‐α‐quaterthiophene Single Crystals

Abstract

Measuring the anisotropy of the field‐effect mobility provides insight into the correlation between molecular packing and charge transport in organic semiconductor materials. Single‐crystal field‐effect transistors are ideal tools to study intrinsic charge transport because of their high crystalline order and chemical purity. The anisotropy of the field effect mobility in organic single crystals has previously been studied by lamination of macroscopically large single crystals onto device substrates. Here, a technique is presented that allows probing of the mobility anisotropy even though only small crystals are available. Crystals of a soluble oligothiophene derivative are grown in bromobenzene and drop‐cast onto substrates containing arrays of bottom‐contact gold electrodes. Mobility anisotropy curves are recorded by measuring numerous single crystal transistor devices. Surprisingly, two mobility maxima occur at azimuths corresponding to both axes of the rectangular cyclohexyl‐substituted quaterthiophene (CH4T) in‐plane unit cell, in contrast to the expected tensorial behavior of the field effect mobility.

BODIPY derivatives as n-type organic semiconductors: Isomer effect on carrier mobility

“…Recently, they have reported a new acetylenic n-type organic semiconductor: fluoro-substituted phenyleneethynylenes with high performance [36]. Among intrinsic properties of organic semiconductors, the electrical anisotropy of organic materials has attracted much attention [9,[37][38][39][40][41][42][43][44][45][46][47]. The anisotropic effects in rubrene crystals were first observed by Sundar et al in 2004 [9].…”

Understanding electron-withdrawing substituent effect on structural, electronic and charge transport properties of perylene bisimide derivatives

“…Understanding the anisotropic mobility can assist in controlling the directions of transistor channel relative to reference direction of molecular crystal to obtain the highest charge mobility [50][51][52]. Figs.…”

Organic semiconductors for device applications: current trends and future prospects

“…In these experiments, flexible rubrene and pentacene devices showed mobilities as high as 0.9 and 0.1 cm 2 / Vs, respectively, besides showing no change in performance even with a 6-mm-diameter bend confirming the superior endurance of the patterned single-crystal devices to sufficiently large bending stress without performance degradation [323]. In further extended studies [354], it was noted that the stamped OTS films were particularly not as smooth as a self-assembled OTS monolayers, as the stamped domains were populated with large numbers of approx. 100-nm-tall OTS pillars that facilitated the selective nucleation [356,357].…”

“…100-nm-tall OTS pillars that facilitated the selective nucleation [356,357]. This, in fact, was further clarified by observing that nucleation started from the base of the rough OTS surface and the crystal grew on the surface of OTS pillars [354]. Having identified this mode of crystal growth, patterning of OS on other rough surfaces was subsequently realized, as expected.…”

“…On the contrary, unwanted deposition of smaller-sized debris during solution and/or solvent-based processing is equally troublesome. In order to mitigate these problems, a number of alternative schemes were developed including fabrication of free-standing single-crystal devices [18,352], electrostatic bonding of a single crystal onto prefabricated device electrodes [19,302,323,353], formation of single crystals by drop-casting from organic solutions [320,354], and solvent-grown organic single-crystal nanowires [355] as reported in the published literature. Keeping various types of the associated problems in view, several alternate strategies were developed to deposit organic single crystals directly onto the substrate: either using PVT or solution-based processing techniques [224].…”