Organic Field-Effect Transistor Using Oligoselenophene as an Active Layer

Abstract

Thiophene oligomers and polymers are promising compounds applicable to organic field-effect transistors 1 (OFETs), photodiodes, 2 light-emitting diodes, 3 and their integrated devices. 4 Selenophene is a homologue of the chalcogenophenes and the chemical and physical properties are similar to those of thiophene. To our knowledge, however, there has been no report on organic devices made with oligo-or polyselenophenes. This may be ascribable to the poor electrical properties of the polyselenophenes reported in early studies of the system. For example, the conductivities of doped polyselenophene films 5 are in the range of 10 -4 -10 -2 S cm -1 , which are fairly small compared with those (10-100 S cm -1 ) of doped polythiophenes. 6 Recently, we have synthesized structurally well-characterized oligoselenophenes and found that the iodine-doped oligoselenophenes exhibit the conductivities of 10 -2 S cm -1 , which are comparable with those of the analogous doped oligothiophenes. 7 This result encourages us in the studies of electronic devices based on organic functionality materials. The present work is the first report of an OFET made with oligoselenophene, showing good FET behavior.2,2′:5′,2′′:5′′,2′′′-Quaterselenophene (4S) was synthesized by the Stille coupling reaction between dibromobiselenophene and 2-fold of 2-tributylstanyl selenophene 7 and purified twice by sublimation prior to use. 8 OFETs were fabricated on heavily doped n + -Si (100) wafers with a 220-nm thermally grown SiO 2 ( Figure 1). The 4S film (50-nm thick) was vacuum-deposited onto the Si/SiO 2 substrate, and succeedingly Au films (100 nm) as drain and source electrodes were deposited on the organic layer through a shadow mask. For a typical device, the drain-source channel length and width are 50 µm and 2 mm, respectively. Characteristics of a drain current (i d ) versus drain voltage (V d ) of the OFET devices were measured under vacuum with an ADVANTEST R6245 power supply. The field-effect mobilities were calculated in the saturation regime of the i d as shown in a previous paper. 9 X-ray diffractions (Cu, λ KR ) 1.541 Å) of the organic thin films on Si/SiO 2 substrate were measured with a Maxscience M18XHF diffractometer. AFM images of the organic thin films were obtained by using a Shimadzu SPM-9500 microscope. All the measurements were conducted at room temperature (RT).The sublimed film of 4S is orange and shiny. X-ray diffraction of the 4S film on Si/SiO 2 shows a series of the peaks, indicating the order of the molecular repeat with 15.7 Å (Figure 2). This value was independent of the substrate temperature (T s ) and consistent with the b-axis of the single-crystal unit cell (a ) 7.94 Å, b ) (a) Berggren, M.; Inganas, O.; Gustafsson, G.; Rasmusson, J.; Andersson, M. R.; Hjertberg, T.; Wennerstrom, O. Nature 1994, 372, 444. (b) Geiger, F.; Stoldt, M.; Schweizer, H.; Bauerle, P.; Umbach, E. (8) Toxicities of the oligoselenophene compounds are not wellknown. The synthesis must be carefully performed in an efficient hood. Disposable vinyl or...

Oligo‐ and Polyselenophenes: A Theoretical Study

“…[11][12][13][14][15] Although the synthesis of several oligoselenophenes has been reported, oligoselenophenes in general have been scantly studied, especially when compared with at least one thousand papers on their oligothiophene analogues. [16,17] 2,2':5',2'':5'',2'''-Quaterselenophenes (4 Se) [17] have been used as active semiconductors in organic fieldeffect transistors (OFET). Selenophene-containing oligomers have attracted great interest as OFET materials [18,19] Abstract: Recently, a family of conducting polyselenophenes was synthesized, and they were shown to have a number of interesting properties.…”

Study of Hopping Transport in Long Oligothiophenes and Oligoselenophenes: Dependence of Reorganization Energy on Chain Length

“…[19] Other types of conjugated systems have also exhibited high mobilities in FET devices. [4,20] 2,2':5',2'':5'',2'''-Quaterselenophene (4Se) [21] and selenophene-containing oligomers [22,23] have been used as active semiconductors in OFETs. Selenium-containing oligomers have attracted great interest as OFET materials [23] since Takimiya et al [22] reported higher hole mobilities for selenium-containing compounds compared to the corresponding sulfur analogues.…”

Organic Semiconductors and Conductors with tert-Butyl Substituents

“…Compound 2 shows increasing performance with increasing the deposition temperature, and exhibits a mobility of 2.8 × 10 −3 cm 2 V −1 s −1 for a thin film deposited at 60 °C (Figure 5a,b). This is due to the increasing grain size and the decreasing number of grain boundaries [36,37], as observed in AFM and XRD. After 30 days, the device shows reduced carrier mobility by two orders of magnitude, though the unsubstituted pentacene does not show transistor properties at all after this period.…”