Influence of Different Polymorphs on the Electrical and Mechanical Properties of F4TCNQ-Doped Regioregular P3BT Films

In this work, we prepared poly­(3-butylthiophene) (P3BT) samples with different polymorphs by spin-coating a P3BT solution to form P3BT films and then carbon disulfide (CS₂) vapor annealing and thermal annealing these P3BT films. Combining UV–visible (UV–vis) spectroscopy, grazing-incidence wide-angle X-ray diffraction (GIXRD), and Fourier transform infrared (FTIR) spectroscopy, we found that both form I and form I′ of P3BT can be doped with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano­quinodimethane (F4TCNQ), wherein the higher disorder of butyl side chains and the larger lamella distance of form I made the doping level of form I higher than that of form I′; in addition, form II of P3BT can hardly be doped with F4TCNQ due to the tighter interdigitation of butyl side chains. In accordance with the doping level, the P3BT film with form I can obtain the highest conductivity among the three doped P3BT films with different polymorphs. Intriguingly, doping with F4TCNQ is observed to improve the stretchability and decrease the elastic modulus (E_f) of P3BT films by decreasing the crystallinity and altering the interactions between molecular chains. By doping with the same F4TCNQ solution, the crack onset strain (COS) of doped P3BT film with form I is higher than that of P3BT with form I′. Our work suggests that modulating polymorphs is a new method to prepare doped CP films with simultaneous improvement in both electrical and stretchability performance and may offer a new direction of research on stretchable semiconductors to facilitate future practical applications.