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

Doyeon Kim,Jiyoul Lee,Minho Yoon

doi:10.3390/polym14010002

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.

Highlights

In recent decades, solution-processable polymer field-effect transistors (PFETs) based on conjugated copolymers with donor-acceptor (D-A)-type moieties, such as indacenodithiophene (IDT) [1,2], diketopyrrolopyrrole (DPP) [3,4], isoindigo (IDG) [5,6], naphthalenediimide (NDI) [7,8,9], and cyclopentadithiophene (CDT) [10,11,12], have received extensive attention due to their remarkably high field-effect mobilities exceeding 10 cm2 V−1 s−1 and low-energy bandgap characteristics
The enhanced molecular ordering of the bar-coated polymeric films was identified by UV/Vis absorption spectra analyses, of which additional peaks and red shifts definitely were exhibited in their intramolecular peaks. These improved structural characteristics were regarded to be attributed to the gradual drying from the edge to the center of the bar coating, and led to the high-performance PFETs
The electrical characteristics of the bar-coated PFETs were remarkably enhanced: The hole currents (Ids at Vgs = −60 V) increased by an order of magnitude, and the field-effect mobilities significantly increased by factors of 2~4 compared to those of the spin-coated PFETs

Summary

Introduction

Solution-processable polymer field-effect transistors (PFETs) based on conjugated copolymers with donor-acceptor (D-A)-type moieties, such as indacenodithiophene (IDT) [1,2], diketopyrrolopyrrole (DPP) [3,4], isoindigo (IDG) [5,6], naphthalenediimide (NDI) [7,8,9], and cyclopentadithiophene (CDT) [10,11,12], have received extensive attention due to their remarkably high field-effect mobilities exceeding 10 cm2 V−1 s−1 and low-energy bandgap characteristics. Since the disordered phase impedes the charge transport due to the trap sites, it is necessary to minimize the twisting or tangle of the polymer molecular chains present in the polymer thin film channel of the PFETs and to align them well to obtain the PFETs with higher performance.

Results

Conclusion