Orientation Control of Semiconducting Polymers Using Microchannel Molds

Abstract

The molecular orientation of organic semiconductors (OSCs) is of fundamental importance to anisotropic electrical behavior as well as superior properties in practical applications. Here, a simple and effective method is demonstrated to fabricate highly oriented semiconducting polymers, poly­(3-hexylthiophene) (P3HT) and poly­{[N,N′-bis­(2-octyldodecyl)-1,4,5,8-naphthalenediimide-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (P­(NDI2OD-T2)), by mass transfer effect under microchannel molds by diffusion and convection. Furthermore, parallel or perpendicular molecular arrangements relative to the channel direction were achieved by varying the widths of the microchannels, which are directly observed using polarized optical microscopy and two-dimensional grazing-incidence X-ray diffraction experiments. The method could enable the fabrication of organic field-effect transistors that exhibit anisotropic electrical properties indicating inter- or intrachain charge transport. The resulting platform will provide a simple approach for multidirectional orientations of anisotropic OSCs.

Chiral Optoelectronic Functionalities via DNA–Organic Semiconductor Complex

“…The synergistic effect of hydrodynamic effects and compression/ accumulation phenomena results in the DNA−PDI complex orientation differently depending on the DNA concentration and the pulling speed (Figure 4 and Figure S4), as had been previously reported. 28,30,42 As the concentration of DNA increases at a fixed concentration of PDI, a more condensed DNA−PDI complex is compressed and accumulates near the contact line, which is in line with the common phenomenon of the high thickness of deposited films. 48 Therefore, the degree of compression/ accumulation increases for the PDI (83.3%) + DNA (16.7%) condition, but the hydrodynamic effect decreases compared with PDI (90.9%) + DNA (9.1%), exhibiting the distinct perpendicular orientation of the average aggregates axis to the shearing direction.…”

“…Note that DNA and PDI molecules assemble perpendicularly to the resultant aggregates' optic axis, n DNA and n PDI , indicating negative birefringent materials. 28 When n DNA is parallel or perpendicular to the slow axis of the λ plate, yellowish or blueish coloration appears, respectively. 29,30 Therefore, from the POM measurement, we could suggest that the DNA molecules within the DNA−PDI complex orient along the shearing direction.…”

“…In addition to the elastic free-energy consideration, as shown in the previously reported lyotropic LC (LLC) orthogonal orientation phenomena, ,, the Ericksen number ( E r ) (the viscosity ( i.e. , shear) ratio to elastic terms) can be introduced to reveal the underlying alignment mechanism.…”

“…For example, the perpendicular or parallel alignment generates if the hydrodynamic effect or elasticity is dominant, respectively. Namely, the competition between the hydrodynamic effect and the elastic energy minimization modulates the LLC alignment. ,, For the DNA–PDI complex system, there are limitations to examining the exact viscoelastic relaxation dynamics because of the changing solution concentration with resultant different viscous drag effects and viscoelastic relaxations of the DNA chains during processing.…”

“…In general, it is well known that the inter- and intramolecular organization of OSCs directly governs the charge-carrier transport to minimize the domain boundaries and defect generation while ensuring in-plane π–π stacking to avoid the undesired charge scattering or trapping . Thus, various solution-processable methods have been suggested to induce the ordered and oriented structures by facilitating meniscus-guided shearing, off-center spin-coating, mechanical rubbing methods, and utilizing the confined fluid flow on prepatterned substrates. , In particular, liquid-crystalline (LC) materials are considered for the fabrication of long-range orientation and zigzag-like chiral morphologies with added functionalities under controlled shearing conditions, − which can be critical in the scaffold to fabricate the large-area, well-ordered, and oriented OSCs.…”