The synergistic effect of processing solvents on magnetic manipulation of orientational order and carrier transport of semiconducting polymers

This work demonstrates the achievement of employing highly aligned films of semiconducting polymers via solvent vapor annealing (SVA) treatment of the pre-deposited films under a high magnetic field (HMF). Detailed investigations are performed for understanding the effect of processing solvents on magnetic alignment dynamics and the resultant orientational order of a naphthalenedicarboximide-based polymer P(NDI2OD-T2) via such a process. As revealed from the microstructural characterization studies, magnetic alignment is remarkably promoted and the highest degree of alignment (with a large dichroic ratio of 19.7) is achieved via chloroform-vapor annealing, compared to annealing in toluene or dichlorobenzene vapor. These observations can be assigned to the low boiling point of chloroform as well as its favorable solubility to P(NDI2OD-T2). Our results also present substantial evidence on the alignment mechanism based on magnetically guided assembly of chain aggregates reformed in the solvent-vapor swollen films. The field-effect transistors (FETs) with these aligned P(NDI2OD-T2) films via SVA-HMF in chloroform vapor exhibit a 5-fold enhancement of electron mobility compared to those with isotropic films, as well as an extraordinarily large mobility anisotropy of 59 in a top gate/bottom contact device. Furthermore, the toluene vapor-annealed films show a higher mobility on FET devices, in spite of a slightly lower mobility anisotropy.