Enhanced Performance of Cyclopentadithiophene-Based Donor-Acceptor-Type Semiconducting Copolymer Transistors Obtained by a Wire Bar-Coating Method

Abstract

Herein, we report the fabrications of high-performance polymer field-effect transistors (PFETs) with wire bar-coated semiconducting polymer film as an active layer. For an active semiconducting material of the PFETs, we employed cyclopentadithiophene-alt-benzothiadiazole (CDT-BTZ) that is a D-A-type-conjugated copolymer consisting of a repeated electron-donating unit and an electron-accepting unit, and the other two CDT-based D-A-type copolymer analogues are cyclopentadithiophene-alt-fluorinated-benzothiadiazole (CDT-FBTZ) and cyclopentadithiophene-alt-thiadiazolopyridine (CDT-PTZ). The linear field-effect mobility values obtained from the transfer curve of the PFETs fabricated with the spin-coating were 0.04 cm2/Vs, 0.16 cm2/Vs, and 0.31 cm2/Vs, for CDT-BTZ, CDT-FBTZ, and CDT-PTZ, respectively, while the mobility values measured from the PFETs with the wire bar-coated CDT-BTZ film, CDT-FBTZ film, and CDT-PTZ film were 0.16 cm2/Vs, 0.28 cm2/Vs, and 0.95 cm2/Vs, respectively, which are about 2 to 4 times higher values than those of the PFETs with spin-coated films. These results revealed that the aligned molecular chain is beneficial for the D-A-type semiconducting copolymer even though the charge transport in the D-A-type semiconducting copolymer is known to be less critical to the degree of disorder in film.

Analyzing Transfer Characteristics of Disordered Polymer Field-Effect Transistors for Intrinsic Device Parameter Extraction

“…Moreover, the contact resistance of the OTS-treated PFETs was also significantly decreased to ~10 5 Ω cm, which compared to that of the HMDS-treated PFETs of ~10 6 Ω cm. The enhanced ordering of the polymers leads to improved charge carrier injection from the source electrode to the π-electron orbitals of the polymers, decreasing the contact resistance of the PFETs [32,33]. The extraction plot and the output characteristics (I ds vs. V ds ) of the OTS-treated DPP-DTT PFETs are depicted in Figure S3.…”

Prominent processing techniques to manipulate semiconducting polymer microstructures

“…Because the wire-bar technique can be used with many polymer-based solution formulations, it can deliver large-area films of controlled microstructures for a variety of (conjugated) polymers 216–223 and polymer-based blends 224–228 that find applications in research fields such as thermal 228 and thermoelectric 221,224 management, sensors, 216 electrochromic displays, 223 OFETs 217,218,220,222 and other microelectronics. 219 Therefore, there is a large variety of interesting film microstructures that could be wire-bar coated.…”

“…221 Other film microstructures were developed by controlling the film thickness and some specific processing parameters and include well-organized interconnected fibril networks of the difluorobenzothiadiazole-dithienosilole (PDFDT) copolymer, 222 crystalline paraelectric α-phase of poly(vinylidenefluoride) (PVDF) 219 and uniaxially aligned macroscopic structures and nanofibrils with large grains made of cyclopentadithiophene- alt -benzothiadiazole (CDT-BTZ), cyclopentadithiophene- alt -fluorinated-benzothiadiazole (CDT-FBTZ) and cyclopentadithiophenealt-thiadiazolopyridine (CDT-PTZ) conjugated copolymers. 220…”

Crystallization of D-A Conjugated Polymers: A Review of Recent Research

“…In particular cases [123,124], conjugated polymers may adopt a "flat-on" orientation where the backbone is perpendicular to the substrate. Additionally, the backbones may form an ordered arrangement in the direction parallel to the substrate if an appropriate shear force is applied during the film formation process [125][126][127][128]. This situation will not be discussed here because the resulting structure belongs to film structure or texture structure.…”