In addition, their chemical tunability, and potential for coating large areas make these materials attractive for roll-to-roll processing. [2,3] Further, the charge transport in SCPs is highly anisotropic because of the presence of three possible directions with different magnitudes of orbital overlap, which decrease in the following order: along the π-conjugated main chain, along the π−stacking direction, and through the insulating side chains. As a result, control over the alignment of SCPs in films can significantly modulate their electronic properties. [4] Further, the controlled orientation of SCPs is beneficial for improving charge transport and understanding their anisotropic properties to optimize the chemical structure. In particular, the uniaxial alignment of SCPs parallel to the channel direction of organic field-effect transistors (OFET) promotes in-plane charge transport, resulting in a high fieldeffect mobility (µ), [4] and several excellent reviews concerning alignment methods for SCPs for application in OFETs have been published. [4][5][6][7] Recently, there has been considerable interest in fabricating active-layer films on liquid substrates (both of SCPs and small molecules) that can, thus, be transferred to arbitrary substrates. [8][9][10] Importantly, compared to conventional solution processing methods, this strategy offers better control of the film morphology because of the use of a liquid substrate; specifically, in conventional methods, the morphology of the resultant film is strongly affected by the interfacial properties of the device substrate. In contrast, when using a liquid substrate, the films are transferred to the device substrate after solvent evaporation, and the morphology of any underlying film is unaffected, thus facilitating the development of layer-by-layer structures without the need for orthogonal solvents. [11][12][13] Morita et al. [14] first reported the floating film transfer method (FTM), and they demonstrated that the preparation of thin floating films of poly(3-hexylthiophene) on a hydrophilic liquid substrate resulted in better optoelectronic properties than those prepared by spin-coating method. Subsequently, FTM has been applied for the preparation of various SCPs. [8,12,13,[15][16][17][18][19] The orientational control of semiconducting polymers (SCPs) in floating films offers several advantages over conventional solution-processing methods for device fabrication, and the unidirectional floating film transfer method (UFTM) has been applied to fabricate large-area oriented p-type SCP films. Here, UFTM can be used to prepare high-performance n-type SCP films of P(NDI2OD-T2) is reported. A strong correlation between the degree of polymer orientation and the solvent used for the preparation of P(NDI2OD-T2) floating films is observed. In particular, the size of the nanofibers aligned along the orientation direction prepared using chloroform is dramatically increased by adding a small amount of chlorobenzene. Microstructural characterization reveals that the P(NDI2O...
