Solvent Vapor-Assisted Magnetic Manipulation of Molecular Orientation and Carrier Transport of Semiconducting Polymers

Abstract

Effective control of the molecular orientation and the degree of ordering in organic semiconductors is important to achieve high-performance organic electronics. Herein, we have successfully achieved highly oriented films in centimeter scale for a naphthalenedicarboximide-based semiconducting polymer (P­(NDI2OD-T2)) by solvent vapor annealing (SVA) of precast films under a high magnetic field (HMF). As revealed by the microstructural studies, the SVA-HMF films exhibit a remarkably higher degree of chain alignment and high morphological uniformity compared to the HMF-guided drop-cast films. Based on the structural evolution of the films with the SVA time, a mechanism is proposed to elucidate the alignment process, which emphasizes that the chain aggregates re-formed in the swollen films trigger magnetic alignment and determine the film order. Compared with the unaligned films, field-effect transistors of the magnetic aligned P­(NDI2OD-T2) films have exhibited a 19-fold enhancement of electron mobility and an extraordinarily large mobility anisotropy of 125. Furthermore, a significantly reduced energetic barrier for activated transport is observed on the aligned devices from temperature-variable measurements. The improved performance achieved by the HMF-SVA process has indicated its potential for high-performance organic electronic applications.

The synergistic effect of processing solvents on magnetic manipulation of orientational order and carrier transport of semiconducting polymers

“…The weaken chain aggregation indicates that some amounts of the crystallinities within the as-spun dry film are partially destructed and broken into smaller-size chain aggregates, which also leads to reduced chain entanglement and viscosity of the CF-swollen film. Thus, it further evidences the aggregate-triggered alignment mechanism for the SVA-HMF process proposed previously, 21 via which the alignment process of the P(NDI2OD-T2) films is schematically shown in Fig. 6c.…”

“…1c, revealing the high alignment of the P(NDI2OD-T2) chains. Notably, in contrast to the “wet” polymer films as-spun from the high- T b DCB as reported previously, 21 the “dry films” spun from low- T b solutions were employed in the SVA-HMF process in present cases. This indicates that the high vapor pressure of the lower- T b solvents ( e.g.…”

“…In this work, the dynamics of magnetic alignment of polymer films has been investigated during the SVA process employing two processing solvents with different boiling points ( T b ) and solubility to P(NDI2OD-T2): chloroform (CF) and toluene (TL), instead of the previously used dichlorobenzene (DCB). 21 The comprehensive microstructural studies reveal the critical role of the nature of processing solvents on the degree of alignment and the order of chain packing of SVA-HMF films. It is found that the formation of a highly oriented film structure is facilitated drastically via the SVA-HMF process by chloroform vapor, which leads to an enhanced degree of molecular orientation with an extraordinarily large dichroic ratio, compared to the films annealed by TL and DCB vapors.…”

Out-of-Plane Alignment of Conjugated Semiconducting Polymers by Horizontal Rotation in a High Magnetic Field

“…To determine the crystallinity and molecular packing properties of the highly textured films in the out-of-plane direction, synchrotron radiation X-ray diffraction under specular reflection conditions (SR-XRD) was performed. The SR-XRD curves (Figure b) of films prepared without magnetic alignment and those prepared with static magnetic alignment show obvious (200) and (010) peaks in the out-of-plane direction, which correspond to d -spacing values of 2.44 and 0.39 nm for lamellar stacking and π–π stacking, respectively. ,,− These results confirm that face-on and edge-on crystalline domains were mixed in the solid film, which is consistent with previous reports. ,, Notably, the intensity of (010) diffraction peaks of the two films are nearly identical, suggesting the static magnetic field did not obviously affect the molecular planar alignment in the out-of-plane direction. However, for the HR-HMF alignment films, the (200) diffraction peak disappears, accompanied by a gradual increase in intensity of the (010) diffraction peaks, indicating that the HR-HMF alignment process inhibited the edge-on packing and promoted the face-on packing in the P­(NDI2OD-T2) films; that is, the process can effectively enhance the degree of face-on molecular packing.…”

Molecular single crystals induce chain alignment in a semiconducting polymer

“…To address the above challenges, extensive efforts have been devoted to constructing oriented conjugated polymer lms with strengthening intermolecular interactions through a variety of alignment processes, such as capillary action [12], nanogroove-guided [13], magnetic force-induced [14], directed self-assembly [15][16][17] and others [18,19]. Despite high charge mobility of polymer-based transistors have been obtained through above processing methods, they all need the external directional force guidance to achieve aligned crystalline thin lms, rendering the process more complicated.…”