n-Channel Polymers by Design: Optimizing the Interplay of Solubilizing Substituents, Crystal Packing, and Field-Effect Transistor Characteristics in Polymeric Bithiophene-Imide Semiconductors

Abstract

Electron transporting (n-channel) polymer semiconductors for field-effect transistors are rare. In this investigation, the synthesis and characterization of new electron-depleted N-alkyl-2,2'-bithiophene-3,3'-dicarboximide-based pi-conjugated homopolymers and copolymers containing the 2,2'-bithiophene unit are reported. A novel design approach is employed using computational modeling to identify favorable monomer properties such as core planarity, solubilizing substituent tailorability, and appropriate electron affinity with gratifying results. Monomeric model compounds are synthesized to confirm these properties, and a crystal structure reveals a short 3.43 A pi-pi stacking distance with favorable solubilizing substituent orientations. A family of 10 homopolymers and bithiophene copolymers is then synthesized via Yamamoto and Stille polymerizations, respectively. Two of these polymers are processable in common organic solvents: the homopolymer poly(N-(2-octyldodecyl)-2,2'-bithiophene-3,3'-dicarboximide) (P1) exhibits n-channel FET activity, and the copolymer poly(N-(2-octyldodecyl)-2,2':5',2'':5'',2'''-quaterthiophene-3,3'-dicarboximide) (P2) exhibits air-stable p-channel FET operation. After annealing, P1 films exhibit a very high degree of crystallinity and an electron mobility > 0.01 cm (2) V(-1) s(-1) with a current on-off ratio of 10 (7), which is remarkably independent of film-deposition conditions. Extraordinarily, P1 films also exhibit terracing in AFM images with a step height matching the X-ray diffraction d spacing, a rare phenomenon for polymeric organic semiconductors. Another fascinating property of these materials is the air-stable p-channel FET performance of annealed P2 films, which exhibit a hole mobility of approximately 0.01 cm(2) V(-1) s(-1) and a current on-off ratio of 10(7).

Trends in molecular design strategies for ambient stable n-channel organic field effect transistors

“…This goal has not been achieved yet because apart from computing the intrinsic electronic properties of the material this requires predicting the crystal structures, 89,90 accounting for anisotropy, 91 including molecular vibrations, 92 and correctly assessing the amount of structural and dynamic disorder. Research on disorder is picking up momentum [93][94][95][96][97] but the majority of studies are concerned with the intrinsic electronic properties [98][99][100][101][102] of idealized materials. Coherent transport in highly ordered materials can be calculated by applying the Landauer formula 103 or various other flavors of scattering theory.…”

Molecular Self‐Assembled Monolayers and Multilayers for Organic and Unconventional Inorganic Thin‐Film Transistor Applications

“…[1][2][3] While much of the attention of the organic TFT community has been focused on the search for high-mobility, [4][5][6] ambient stable, [7][8][9] and solution-processable small molecule [10][11][12][13][14][15][16][17] and polymeric [18][19][20] semiconductor materials, [21][22][23][24][25][26][27][28][29][30] it is now clear that substantial improvements in TFT performance can also be achieved by replacing and/or modifying the gate dielectric. [1,[31][32][33][34][35][36] As will be discussed here, self-assembled monolayers (SAMs) and multilayers (SAMTs), such as self-assembled nanodielectrics (SANDs), [37] are gaining significant attention as gate dielectrics due to their robust insulating properties, tunable thicknesses, and efficient solution processability.…”

Emerging N‐Type Redox‐Active Radical Polymer for a Totally Organic Polymer‐Based Rechargeable Battery

“…[1,2] Not many, but some n-type redox polymers bearing quinone, quinoline, and oxadiazole derivatives and n-dopable polythiophenes have been reported as an electron-accepting and -transporting material in the organic light-emitting diodes, [2,3] organic thin-film transistors, [4,5] and photovoltaics. [6,7] However, the use of such n-type redox activity of the polymers has been limited for transient (short time-scale) charge-separation and -transport, and its use for charge-storage (in a long term) has not been examined except for a few reports on capacitors based on n-dopable polythiophenes.…”