Photoinduced Anisotropic Assembly of Conjugated Polymers in Insulating Polymer Blends

Abstract

Low-dose UV irradiation of poly(3-hexylthiophene) (P3HT)-insulating polymer (polystyrene (PS) or polyisobutylene (PIB)) blend solutions led to the formation of highly ordered P3HT nanofibrillar structures in solidified thin films. The P3HT nanofibers were effectively interconnected through P3HT islands phase-separated from insulating polymer regions in blend films comprising a relatively low fraction of P3HT. Films prepared with a P3HT content as low as 5 wt % exhibited excellent macroscopic charge transport characteristics. The impact of PS on P3HT intramolecular and intermolecular interactions was systematically investigated. The presence of PS chains appeared to assist in the UV irradiation process of the blend solutions to facilitate molecular interactions of the semiconductor component, and to enhance P3HT chain interactions during spin coating because of relatively unfavorable P3HT-PS chain interactions. However, P3HT lamellar packing was hindered in the presence of PS chains, because of favorable hydrophobic interactions between the P3HT hexyl substituents and the PS chains. As a result, the lamellar packing d-spacing increased, and the coherence length corresponding to the lamellar packing decreased, as the amount of PS in the blend films increased.

Macroscopic Alignment of One-Dimensional Conjugated Polymer Nanocrystallites for High-Mobility Organic Field-Effect Transistors

“…24,32 This isotropic morphology or lack of anisotropy is consistent with the AFM images (Figure 2A,B). In contrast, both randomly oriented and shear-aligned P3HT 24,32 However, the birefringent textures of shearaligned P3HT NWs display higher brightness compared to the randomly oriented P3HT NWs, which is primarily due to enhancement in the anisotropy. The birefringent brightness of shear-aligned P3HT NWs increases as a function of the shearing speed in the following order: 4.0 mm/s < 0.5 mm/s < 2.0 mm/s < 1.0 mm/s.…”

“…The slow shearing speed presumably allows for the slow evaporation rate of the solvent and provides polymer chains and NWs to reach an equilibrium rate. 7,21,32,35 Quantitative modeling of the absorption spectra was employed to probe the intramolecular ordering and effective conjugation length of the polymer chains. [22][23][24]36 Two phases are observed in the P3HT absorption spectrum that correlate with a crystalline phase and an amorphous phase.…”

“…13,18,23,24 Furthermore, the shearaligned P3HT NWs are oriented parallel to the source-drain electrodes, which provide an efficient pathway for charge transport due to bridging chains compared to randomly oriented P3HT NWs, where the grain boundaries are randomly oriented. 13,28,32 We evaulated the impact of the shearing speed on the electrical properties of aligned P3HT NWs at different shearing speeds of 0.5, 1.0, 2.0, and 4.0 mm/s (Figures 5E and S4). The average mobility along the shearing direction increased up to 0.20 cm 2 V −1 s −1 for films obtained from P3HT NWs dispersion as the shearing speed increased from 0.5 to 2.0 mm/s.…”

Effective Use of Electrically Insulating Units in Organic Semiconductor Thin Films for High‐Performance Organic Transistors

“…[246] The chain-like nanowires were observed to be distributed homogenously in the PS/CH 2 Cl 2 solution and did not further aggregate during solvent evaporation and subsequent vitrification of PS. [275] The authors suggested that the presence of PS chains facilitated the formation of molecular interactions between P3HTs in the UV irradiation process, and enhanced interactions between P3HT chains during spin coating, because of the relatively unfavorable P3HT−PS chain interactions. The P3HT nanofibrilar network kept the connection of charge pathways at the channel so effectively that the percolation threshold of the blend was below 1 wt% P3HT.…”

“…With such an approach, the nozzle clog problem, which frequently occurs during inkjet printing of long-chain polymers with high viscoelasticity, can be avoided. [275] Copyright 2015, American Chemical Society. Wang and coworkers showed the ability to control the crosslinking density and thus solubility of the pre-deposited PS layer by adjusting the UV irradiation time.…”