Achieving High Alignment of Conjugated Polymers by Controlled Dip‐Coating

Abstract

Realizing high polymer chain orientation and ordered thin‐film microstructures is beneficial for efficient charge transport of conjugated polymers. However, achieving a high alignment degree remains a challenge due to the sensitive nature of polymers to the processing conditions. By simply varying concentrations during a dip‐coating method, the component of polymer aggregates that adopt the planar backbones is enlarged and the ensuing assembly process is promoted. Herein, highly oriented polymer thin films of an isoindigo‐based conjugated polymer (PII‐2T) are prepared to enhance polymer orientation resulting in a drastic booming in carrier mobilities of organic field‐effect‐transistors (OFETs). The maximum mobility from aligned polymer films increases by up to 8.3 cm2 V−1 s−1, which is tenfold beyond the value evaluated from the unaligned direction or traditional spin‐coated samples. The enhanced orientation can also reduce the adverse effects of the contact resistance and facilitate charge transport in transistors. This work demonstrates that the highly aligned conjugated polymer films can be approached by the dip‐coating method while offers a latent cornerstone toward understanding the critical role of processing‐related parameters in determining morphology of solution‐coated thin films.

Temperature Induced Aggregation of Organic Semiconductors

“…Taking OPV as an example, the presence of π–π stacking at the molecular level and the locally ordered phase is of great importance to exciton diffusion, dissociation and charge transport within the photoactive layer [18–20] . For OFETs, efficient charge injection and transport rely on the ordered structure at both molecular and device‐size scales [21–23] . A typical characteristic of solution‐processed organic semiconductors is that the aggregation and ordering process can occur at various conditions.…”

Recent progress in lactam‐based polymer semiconductors for organic electronic devices

“…In 2020, Pei et al reported the fabrication of P308-based OFET's fabricated using the dip-coating method. 131 The fast coating speed and the short relaxation time of the transition region facilitated the planarization of the polymer backbone. A high mobility of 8.31 cm 2 V À1 s À1 was recorded when the coating speed was 15 μm s À1 .…”

Recent advances in the application of isoindigo derivatives in materials chemistry

“…According to the available data, the most studied polymeric isoindigos are dithienyl derivatives, in which two thiophene fragments can be linked to each other [74][75][76][77][78][79][80][81][82][83][84][85][86] or be separated by spacers of different structures [87][88][89][90][91]. Structures containing a 2,2'-dithienyl fragment can be divided into three types: 1) not containing substituents in the benzo and thienyl fragments; 2) containing fluorine atoms in the thienyl fragment; and 3) containing fluorine atoms in positions 7,7' and in thienyl fragments (Scheme 24).…”

“…In contrast to the traditional spin-coating technique, the authors succeeded in obtaining a thin film by immersing a substrate in a polymer solution, followed by slow extraction, accompanied by slow evaporation of the solvent. The device thus obtained showed one of the highest values of hole conductivity of μ e = 8.3 cm 2 ⋅V −1 ⋅s −1 [ 78 ]. It was also found that a device based on compound 45 (R = 2-decyltetradecyl) with the addition of iron phthalocyanine showed slightly better mobility.…”