Solution-Processable Field-Effect Transistor Using a Fluorene- and Selenophene-Based Copolymer as an Active Layer

Abstract

We have synthesized a new p-type polymer, poly(9,9‘-n-dioctylfluorene-alt-biselenophene) (F8Se2), via the palladium-catalyzed Suzuki coupling reaction. The number-average molecular weight (M n) of F8Se2 was found to be 72 600. F8Se2 dissolves in common organic solvents such as chloroform and chlorobenzene. The PL emission peak of a film of F8Se2 is clearly red-shifted with respect to that of its sulfur analogue, poly(9,9‘-n-dioctylfluorene-alt-bithiophene) (F8T2), due to the electron-donating properties of selenium and the strong interactions between the biselenophene moieties in neighboring copolymer chains. We confirmed that F8Se2 is a thermotropic liquid crystalline polymer with an aligned structure by carrying out DSC, PLM, and XRD measurements. The introduction of the selenophene moiety into the liquid-crystalline polymer system results in better field-effect transistor (FET) performance than that of F8T2. A solution-processed F8Se2 FET device with a bottom contact geometry was found to exhibit a hole mobility of 0.012 cm2/(V s) and a low threshold voltage of −4 V, which is the one of the highest solution-processable FET performances.

Liquid crystalline conjugated polymers and their applications in organic electronics

“…28 The cast pristine film of the polymer did not exhibit birefringence because of its amorphous phase, whereas the film annealed to 270 C produced a clear birefringent image because of the LC domains, which is consistent with the phase transition characteristics revealed by the DSC analysis (as shown in Fig. 10).…”

“…Recently, LC conjugated polymers has attracted progressive attention for their self-organized nature to enhance their mobility, which opens a new trend to highperformance OTFTs. Several LC conjugated polymers have been studied for OFET application, for example, PFTT, PFT2, 104 fluorene-selenophene-based copolymer P6 (chemical structures are shown in previous section), 28 poly(9,9 0 -dioctylfluorene-alt-benzothiadiazole) (F8BT), 102 poly(3,3 000 -didodecylquaterthiophene) (PQT-12), 31 and some fluorene-thiophene copolymers P55-P57, as shown in Chart 24. These LC materials showed enhanced charge carrier mobility after aligning the polymer chains on the alignment layer under LC state.…”

Electronic structures of one-dimensional poly-fused selenophene radical cations: density functional theory study

“…This originates from the π-electron system delocalized widely along a one-dimensional polymer chain. Polyselenophene and its related compounds have attracted considerable attention over the past decade in view of their potential applications in electronic and optoelectronic devices [3,4]. 4 Present address: National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan.…”

“…Polyselenophenes are one-dimensional π-conjugated polymers that are utilized as conducting materials and field effect transistors [3,4]. Also, oligo-five-membered ring compounds have a possibility for application to high-performance molecular devices such as photocurrent multipliers and organic semiconductors [5].…”

Recent Progress of Semiconductors in Organic Thin-Film Transistors

“…Compound 3 [78] 1.95 ≈10 5 P(DPP-alt-DTBSe) [79] 1.5 10 6 F8T2 [80] 0.02 10 5 F8Se2 [81] 0.012 -Ts6T2 [82] 0.06 10 5 PCB-R [83] 10 -5 ～10 …”