High‐Mobility Naphthalene Diimide and Selenophene‐Vinylene‐Selenophene‐Based Conjugated Polymer: n‐Channel Organic Field‐Effect Transistors and Structure–Property Relationship

Abstract

Interdependence of chemical structure, thin-film morphology, and transport properties is a key, yet often elusive aspect characterizing the design and development of high-mobility, solution-processed polymers for large-area and flexible electronics applications. There is a specific need to achieve >1 cm 2 V −1 s −1 field-effect mobilities (μ) at low processing temperatures in combination with environmental stability, especially in the case of electron-transporting polymers, which are still lagging behind hole transporting materials. Here, the synthesis of a naphthalene-diimide based donor-acceptor copolymer characterized by a selenophene vinylene selenophene donor moiety is reported. Optimized field-effect transistors show maximum μ of 2.4 cm 2 V −1 s −1 and promising ambient stability. A very marked film structural evolution is revealed with increasing annealing temperature, with evidence of a remarkable 3D crystallinity above 180 °C. Conversely, transport properties are found to be substantially optimized at 150 °C, with limited gain at higher temperature. This discrepancy is rationalized by the presence of a surface-segregated prevalently edge-on packed polymer phase, dominating the device accumulated channel. This study therefore serves the purpose of presenting a promising, high-electron-mobility copolymer that is processable at relatively low temperatures, and of clearly highlighting the necessity of specifically investigating channel morphology in assessing the structure-property nexus in semiconducting polymer thin films.

Diffractive X-ray waveguiding reveals orthogonal crystalline stratification in conjugated polymer thin films

“…Electron-yield NEXAFS spectroscopy, which is sensitive to the first few nanometers of the film, confirms a more edge-on (though not necessarily crystalline -NEXAFS measures both crystalline and amorphous material) surface alignment in all spin-coated films even without annealing, while bulk-sensitive fluorescenceyield NEXAFS spectroscopy confirms face-on molecular orientation in the majority of the films. 23 Thus the very surface layer which is consistently edge-on at all temperatures is only able to start to template orientational propagation through the film at 210 °C. And similarly, the bulk of the film which is overwhelmingly face-on at lower temperatures is only able to reorient isolated pockets of edge-on crystals at 210 °C, resulting in a clean stratification.…”

“…The results of this process is shown in Fig. 3, and the effects of slight variations are shown in Although independent atomic-force microscopy (AFM) measurements of film thickness and roughness were taken (see previous work 23 and Supporting Information) we can also narrow down the parameter space using only the diffraction data, as shown in Fig. 4.…”

“…The synthesis and full device properties of PNDI-SVS are reported elsewhere. 23 The batch of PNDI-SVS used here had a molecular weight (Mw) of 168.0 kg/mol, with a polydispersity index of 2.1.1 PNDI-SVS films for GIWAXS analysis were prepared by spin-coating onto silicon wafers with a natural oxide layer. PNDI-SVS was dissolved in anhydrous chlorobenzene solvent with a solution concentration of 12 mg/ml.…”

Imide‐Functionalized Polymer Semiconductors

“…Owing to its low‐lying LUMO of −3.98 eV, the OTFT device based on this polymer showed a promising air stability. The μ e,OTFT as high as 2.4 cm 2 V −1 s −1 was achieved after thermal annealing at 150 °C for 20 min . Li and co‐workers reported another furan‐containing NDI‐based polymer 27 , incorporating a vinylene linkage.…”

“…The m e,OTFT as high as 2.4 cm 2 V À1 s À1 was achieved after thermala nnealing at 150 8C for 20 min. [38] Li and co-workers reported another furan-con-tainingN DI-based polymer 27,i ncorporating av inylene linkage. The polymerf eaturing am ore planar backbone afforded a redshifted absorption and stronger aggregation (versus 23).…”