Oriented Conjugated Copolymer Films with Controlled Crystal Forms and Molecular Stacking Modes for Enhanced Charge Transport and Photoresponsivity

Abstract

Most of conjugated copolymers are semicrystalline. The crystal modification and crystalline morphology have an obvious effect on their charge transport. Therefore, controlling the crystal structures of conjugated copolymers is necessary for optimizing charge transport. Herein, large-area oriented poly [2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT) crystalline films are produced by the epitaxial crystallization on oriented polyethylene (PE) substrates based on perfect two-dimensional lattice matching. Furthermore, the stacking modes of PCPDTBT crystals has been successfully controlled by epitaxy combined with chlorobenzene (CB) annealing or addition of 1,8-diiodooctane (DIO). PCPDTBT films spin-coated from CB solution on a PE substrate exist in both edge-on and face-on molecular chain orientations. The amount of edge-on stacking in CB-annealed PCPDTBT/PE films is much higher than that in the DIO-processed films. Moreover, the oriented PCPDTBT films exposed to CB vapor are confirmed to adopt the dimer crystal form. The addition of DIO can significantly improve the orientation extent of PCPDTBT main chains with a π-stacked form. The highly oriented films with a πstacked form demonstrate excellent carrier mobility (2.1 × 10 −2 cm 2 V −1 s −1 ) measured along the direction of PCPDTBT chains. The carrier mobility of DIO-processed PCPDTBT films along molecular chains is 76 times higher than that measured in the perpendicular direction of molecular chains. As a result, the ratio of anisotropic photoresponsivity of DIO-processed oriented PCPDTBT films can reach to 100. This work demonstrates a facile method to fabricate large-area and highly oriented PCPDTBT crystalline films with controlled crystal forms, which have potential applications in phototransistors.

Alignment of Organic Conjugated Molecules for High‐Performance Device Applications

“…[ 79 ] The DIO was previously employed as a morphological and crystallinity modifier in organic electronics to achieve high charge transport properties. [ 32 ] DBrO, on the other hand, has been considered a new and effective solvent additive to improve charge transport characteristics and stability. The authors investigated the role of solvent additives in defining polymer thin film morphologies, finding that DIO‐processed films had huge aggregations separated by a significant distance.…”

“…[ 89 ] A number of researchers have demonstrated high‐performance phototransistor devices through traditional fabrication methods such as spin‐coating method. [ 32, 71i,j,73d ] However, only a few reports that demonstrate high‐performance OPTs fabricated through alignment strategies have been reported. Among them, Singh and coworkers reported the fabrication of highly aligned PFO‐DBT polymer thin prepared by unidirectional film transfer methods (UFTM).…”

“…Very recently, Yan and coworkers also demonstrated the photosensitive performance of PCPDTBT aligned thin films using epitaxial crystallization and an additive approach. [ 32 ] It was observed that DIO as a solvent additive significantly improved the degree of polymer backbone alignment. These aligned structures led to anisotropic charge transport and photoresponsivity.…”

Structure and Mechanical Property of Melt-Drawn Oriented PLA Ultrathin Films

“…Highly oriented PLLA and PDLA thin films were prepared according to the melt-draw technique, which has been frequently used for getting highly oriented ultrathin films. − During the melt-draw procedure, a small amount of 0.6 wt % polymer solution in DMF was first poured on a preheated glass plate at specified temperatures ranging from 152 to 180 °C and spread uniformly by a glass rod. After evaporation of the DMF solvent, the thin molten polymer layer was then picked up by a motor-driven cylinder with a draw speed ranging from 5 to 45 cm/s.…”

Gaining control over conjugated polymer morphology to improve the performance of organic electronics

“…[1][2][3] As a result, developing functional semiconducting CPs is at the forefront of organic electronics research due to their superior mechanical characteristics compared to small molecules and suitability for solution casting fabrication methods. [4][5][6][7][8] Furthermore, the unique ability of certain CPs to uptake electrolyte solution and conduct ions alongside electrons/holes enables their application in organic electrochemical transistors (OECTs), which is useful in various bioelectronic devices, such as tissue monitoring, molecular and ionic sensing. [9][10][11] Last but not least, considerable advancements have been demonstrated in the development of stretchable and conformable CPs toward implementation in biomedical devices, wearable consumer electronics, and large-area mechanically soft OPVs, OLEDs, and OFETs.…”