Fused Bithiophene Imide Oligomer and Diketopyrrolopyrrole Copolymers for n‐Type Thin‐Film Transistors

Abstract

Polymer semiconductors have drawn much attention from both academia and industry due to their unique advantages for the fabrication of light-weight, largearea, low-cost, and flexible/stretchable electronic devices, such as organic thinfilm transistors (OTFTs) and organic solar cells (OSCs). [1][2][3][4][5][6][7][8][9] Recently, OTFTs have achieved promising device performance with charge carrier mobility exceeding that (0.1-1 cm 2 V −1 s −1 ) of amorphous silicon-based transistors. However, most of high-performance polymers exhibit p-type predominant or ambipolar transport characteristic in OTFT devices to date. [10][11][12][13][14][15] Due to the synthetic challenge and associated steric hindrance of highly electron-deficient building blocks, which are essential for n-type semiconductors, the development of n-type polymers far lagged behind the p-type or ambipolar analogues. [10,[16][17][18] Hence, in order to realize applications such as complementary metal-oxide-semiconductor (CMOS)-like logic circuits and all-polymer solar cells, [18][19][20] it is highly urgent to design and synthesize high-performance n-type polymer semiconductors with comparable device performance characteristics, such as charge carrier mobility and device stability.Benefiting from high electron deficiency, coplanar backbone conformation, and easy access, diketopyrrolo[3,4-c]pyrrole (DPP) is regarded as a remarkable electron-accepting building block and has been widely applied for constructing donor-acceptor (D-A) polymer semiconductors in the past decade, showing substantial charge carrier mobility in OTFT devices. [10,16,[21][22][23] The highest OTFT mobility based on DPP-incorporated polymer semiconductors has now surpassed 10 cm 2 V −1 s −1 (Figure 1a). [24] However, the electron-rich nature of the flanking thiophene moieties in DPP showed negative effects on the optimization of frontier molecular orbital (FMO) energy levels for n-type performance, resulting in a p-type dominating or ambipolar transport characteristic for most of the DPP-based copolymers (Figure 1a). [25][26][27] In this regard, copolymerizing DPP with another strong electron-acceptor co-unit should be an effective strategy for downshifting FMO energy levels, which is hence beneficial for achieving improved n-type performance due to Diketopyrrolopyrrole (DPP)-based copolymers have received considerable attention as promising semiconducting materials for high-performance organic thin-film transistors (OTFTs). However, these polymers typically exhibit p-type or ambipolar charge-transporting characteristics in OTFTs due to their high-lying highest occupied molecular orbital (HOMO) energy levels. In this work, a new series of DPP-based n-type polymers have been developed by incorporating fused bithiophene imide oligomers (BTIn) into DPP polymers. The resulting copolymers BTIn-DPP show narrow band gaps as low as 1.27 eV and gradually down-shifted frontier molecular orbital energy levels upon the increment of imide group number. Benefiting from the coplanar backbone conforma...

n-Type organic semiconducting polymers: stability limitations, design considerations and applications

“…10), whereby the BTI unit extends in length by fusing another BTI unit through the terminal thiophene. 119 With each additional BTI unit, the electron acceptor character increases, and the EA increases to 3.46 eV for BTI3-DPP, from 3.34 eV for BTI1-DPP, however backbone planarity is compromised, with the dihedral angle increasing from B31 to 101, as predicted by DFT calculations. 119 The highest electron mobility is observed for BTI2-DPP (0.48 cm 2 V À1 s À1 ; Table 5), where there is a careful balance between deepening the LUMO sufficiently to support electron injection and ensuring planarity of the backbone is maintained.…”

“…119 With each additional BTI unit, the electron acceptor character increases, and the EA increases to 3.46 eV for BTI3-DPP, from 3.34 eV for BTI1-DPP, however backbone planarity is compromised, with the dihedral angle increasing from B31 to 101, as predicted by DFT calculations. 119 The highest electron mobility is observed for BTI2-DPP (0.48 cm 2 V À1 s À1 ; Table 5), where there is a careful balance between deepening the LUMO sufficiently to support electron injection and ensuring planarity of the backbone is maintained. 119 To assess the influence of the comonomer, the sidechain length and the branching position on n-type performance, a series of four DPP polymers incorporating fluorine atoms were investigated, namely PPyDPP1-4FBT, PPyDPP2-4FBT, PPyDPP1-4FTVT and PPyDPP2-4FTVT (Fig.…”

“…119 The highest electron mobility is observed for BTI2-DPP (0.48 cm 2 V À1 s À1 ; Table 5), where there is a careful balance between deepening the LUMO sufficiently to support electron injection and ensuring planarity of the backbone is maintained. 119 To assess the influence of the comonomer, the sidechain length and the branching position on n-type performance, a series of four DPP polymers incorporating fluorine atoms were investigated, namely PPyDPP1-4FBT, PPyDPP2-4FBT, PPyDPP1-4FTVT and PPyDPP2-4FTVT (Fig. 10).…”

Synergistic Use of Pyridine and Selenophene in a Diketopyrrolopyrrole‐Based Conjugated Polymer Enhances the Electron Mobility in Organic Transistors

“…[2,3] Among the reported high-performance polymers, diketopyrrolopyrrole (DPP) has proven to be one of the most successful building blocks to construct semiconductors for applications in a wide range of electronic devices. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] In the community of organic field-effect transistors (OFETs), the semiconductors are classified as p-type, n-type, and ambipolar materials according to the polarity of the dominant charge carriers flowing along the conducting channel. [6] DPP-based polymers have made significant contributions to the advancement of all types of semiconducting materials.…”

Recent progress in lactam‐based polymer semiconductors for organic electronic devices

“…The polymers were synthesized by tuning the electronic properties and conjugation length of BTI. 150 By integrating BTI into the DPP backbone, the FMO energy level was effectively lowered. As a result, the maximum electron mobility was recorded for P353 (0.48 cm 2 V À1 s À1 ).…”