Bithiophene-Imide-Based Polymeric Semiconductors for Field-Effect Transistors: Synthesis, Structure−Property Correlations, Charge Carrier Polarity, and Device Stability

Abstract

Developing new high-mobility polymeric semiconductors with good processability and excellent device environmental stability is essential for organic electronics. We report the synthesis, characterization, manipulation of charge carrier polarity, and device air stability of a new series of bithiophene-imide (BTI)-based polymers for organic field-effect transistors (OFETs). By increasing the conjugation length of the donor comonomer unit from monothiophene (P1) to bithiophene (P2) to tetrathiophene (P3), the electron transport capacity decreases while the hole transport capacity increases. Compared to the BTI homopolymer P(BTimR) having an electron mobility of 10(-2) cm(2) V(-1) s(-1), copolymer P1 is ambipolar with balanced hole and electron mobilities of ∼10(-4) cm(2) V(-1) s(-1), while P2 and P3 exhibit hole mobilities of ∼10(-3) and ∼10(-2) cm(2) V(-1) s(-1), respectively. The influence of P(BTimR) homopolymer M(n) on film morphology and device performance was also investigated. The high M(n) batch P(BTimR)-H affords more crystalline film microstructures; hence, 3× increased electron mobility (0.038 cm(2) V(-1) s(-1)) over the low M(n) one P(BTimR)-L (0.011 cm(2) V(-1) s(-1)). In a top-gate/bottom-contact OFET architecture, P(BTimR)-H achieves a high electron mobility of 0.14 cm(2) V(-1) s(-1), only slightly lower than that of state-of-the-art n-type polymer semiconductors. However, the high-lying P(BTimR)-H LUMO results in minimal electron transport on exposure to ambient. Copolymer P3 exhibits a hole mobility approaching 0.1 cm(2) V(-1) s(-1) in top-gate OFETs, comparable to or slightly lower than current state-of-the-art p-type polymer semiconductors (0.1-0.6 cm(2) V(-1) s(-1)). Although BTI building block incorporation does not enable air-stable n-type OFET performance for P(BTimR) or P1, it significantly increases the OFET air stability for p-type P2 and P3. Bottom-gate/top-contact and top-gate/bottom-contact P2 and P3 OFETs exhibit excellent stability in the ambient. Thus, P2 and P3 OFET hole mobilities are almost unchanged after 200 days under ambient, which is attributed to their low-lying HOMOs (>0.2 eV lower than that of P3HT), induced by the strong BTI electron-withdrawing capacity. Complementary inverters were fabricated by inkjet patterning of P(BTimR)-H (n-type) and P3b (p-type).

Operational Stability of Organic Field‐Effect Transistors

“…Much progress has been made during the last decade in the development of environmentally stable p-type organic semiconductors with charge-carrier mobilities reaching up to 10 cm 2 /Vs, [4][5][6][7][8][9] while more recently stable high-mobility n-type organic semiconductors have become available. [10][11][12][13][14][15][16][17] However, high intrinsic stability of the semiconductor is not the only requirement for stable OFETs. Also the role of the gate dielectric needs to be considered.…”

Syntheses and Properties of Copolymers with N‐Alkyl‐2,2′‐bithiophene‐3,3′‐dicarboximide Unit for Polymer Solar Cells

“…3 The fact that the alkyl group on nitrogen atom of the imide is far away from the alkyl groups of the electron-pushing unit is another advantage of the BTI unit to provide better conjugation. [10][11][12] To improve the morphology of the bulk heterojunction (BHJ) using polymer and [6,6]-phenyl-C71-butyric acid methyl ester (PC 71 BM) of PSCs and expand the absorption range of the solar spectrum, copolymerization of the electron-rich and -deficient units with controlled ratios has been reported. 13,14 In this paper, we report push-pull type conjugated copolymers PBTIBDTs for PSC devices utilizing BTI as the electron-pulling unit and BDT as the electron-pushing unit (Scheme 1).…”

Thiepin‐Fused Heteroacenes: Simple Synthesis, Unusual Structure, and Semiconductors with Less Anisotropic Behavior

“…This new conjugated framework is interesting in terms of the following considerations: 1) thiepin is thermally unstable and thus thiepin-containing compounds are seldom reported; 2) the framework contains four sulfur atoms, which are beneficial for enhancing intermolecular interactions through S···S short contacts; 3) alkyl chains can be incorporated to improve the solubility in organic solvents; 4) in fact, seven-membered ring-fused conjugated structures have also attracted attentions recently for developing new optoelectronic materials. [7,8] For instance, both seven-membered cyclic diimide-and diketophosphepin-containing conjugated systems have been very recently designed and synthesized for new organic semiconductors. [8] In the following, we will firstly report the efficient synthesis of THA1 and THA6, followed by 1) discussions of HOMO/LUMO energies and electronic structures of THA1 and THA6 based on DFT (density functional theory) calculations, and 2) crystal structures and semiconducting properties.…”

“…[7,8] For instance, both seven-membered cyclic diimide-and diketophosphepin-containing conjugated systems have been very recently designed and synthesized for new organic semiconductors. [8] In the following, we will firstly report the efficient synthesis of THA1 and THA6, followed by 1) discussions of HOMO/LUMO energies and electronic structures of THA1 and THA6 based on DFT (density functional theory) calculations, and 2) crystal structures and semiconducting properties. The results reveal that both THA1 and THA6 show ptype semiconducting behavior.…”