Dynamic-template-directed multiscale assembly for large-area coating of highly-aligned conjugated polymer thin films

Abstract

Solution processable semiconducting polymers have been under intense investigations due to their diverse applications from printed electronics to biomedical devices. However, controlling the macromolecular assembly across length scales during solution coating remains a key challenge, largely due to the disparity in timescales of polymer assembly and high-throughput printing/coating. Herein we propose the concept of dynamic templating to expedite polymer nucleation and the ensuing assembly process, inspired by biomineralization templates capable of surface reconfiguration. Molecular dynamic simulations reveal that surface reconfigurability is key to promoting template–polymer interactions, thereby lowering polymer nucleation barrier. Employing ionic-liquid-based dynamic template during meniscus-guided coating results in highly aligned, highly crystalline donor–acceptor polymer thin films over large area (>1 cm2) and promoted charge transport along both the polymer backbone and the π–π stacking direction in field-effect transistors. We further demonstrate that the charge transport anisotropy can be reversed by tuning the degree of polymer backbone alignment.

Printing 2D Conjugated Polymer Monolayers and Their Distinct Electronic Properties

“…Therefore, we chose substrates with higher surface energies as reference static substrates—plasma treated (γ = 67.2 × 10 −3 m m −1 )13 and phenyltrichlorosilane (PTS) (γ = 36.0 × 10 −3 n m −1 )13 functionalized SiO 2 (Figure S1, Supporting Information). We note that the surface energy of the IL used is comparable (γ = 36.2 × 10 −3 n m −1 )9 to that of PTS and thus rule out the effect of surface energy when comparing polymer films coated on IL versus PTS.…”

“…In the Landau–Levich regime where viscous drag‐out dominates over solvent evaporation, film thickness increases with increasing printing speed. For 5 mg mL −1 DPP2T‐TT/chloroform solution coated on IL at 25 °C, we have previously determined that the transition from evaporation regime to Landau–Levich regime occurs at ≈10 mm s −1 9. With decrease in solution concentration, the viscosity of the solution decreases, hence we expect the transition speed to increase at lower solution concentration 16.…”

“…To incorporate the dynamic template on the MGC setup, a nanoporous matrix, anodized aluminum oxide (AAO) was infiltrated with an ionic liquid (IL), 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM]‐[TFSI]), such that the thin layer of IL surfacing on top of AAO can be used as the substrate during the printing process. During the short time frame of printing, the capillary force imposed by the AAO nanopores retain the IL in place and the polymer ink solution is immiscible with IL 9. The molecular structure of the IL as well as the two D–A polymers used in this study‐ DPP2T‐TT and PII‐2T are shown in Figure 1.…”

“…The molecular structure of the IL as well as the two D–A polymers used in this study‐ DPP2T‐TT and PII‐2T are shown in Figure 1. We chose imidazolium‐based IL as our previous study has shown strong interactions between the IL and polymer backbone via molecular dynamics and NMR 9. The ink solution of DPP2T‐TT and PII‐2T was prepared in chloroform and chlorobenzene, respectively.…”

“…This technique of 2D film fabrication is compatible with a wide variety of substrates, as demonstrated in this work. We have shown in our previous work that using dynamic template such as ionic‐liquid‐infiltrated nanoporous media, conjugated polymer films printed atop exhibit high degree of alignment and crystallinity owing to strong, template–polymer interactions and template reconfigurability 9. In this work, we adapt this approach to fabricate 2D monolayers of two different donor–acceptor (D–A) conjugated polymers, DPP2T‐TT with diketopyrrolopyrrole acceptor copolymerized with thienothiophene donor and PII‐2T with isoindigo acceptor and bithiophene donor.…”