KCS

In the case of conjugated polymers with donor-acceptor repeating units featuring long polymer chains, chain disorders, and various undesirable impurities, it is difficult to grow single crystalline (SC) structures and study their charge-transport properties on the micro- and nanoscopic scales. Many scientists have recognized the importance of the orientation and packing of the polymer chains in the solid state, but few have investigated these properties and the resulting electronic properties using nanoscaled objects. In our previous work, we had demonstrated that SC polymer NWs (SC-PNWs) could be fabricated, but this polymer showed a relatively poor ability to form NWs, which were limited to short lengths. These phenomena could have resulted from the large polydispersity index (PDI = 7.0) of the polymer and from the particular arrangement of the donating unit in the repeating group in the SC structure, which could interfere with the longitudinal growth of the NWs. Therefore, it might be useful to control the molecular weight (MW) or the PDI of polymers and to introduce a properly designed donating unit in the polymer backbone to allow for the longitudinal growth of NWs of the polymer. In this study, a diketopyrrolopyrrole (DPP)-based polymer (DPPBTSPE) was synthesized. MW fractionation of the synthesized polymer was carried out to yield high- and low-MW DPPBTSPE by Soxhlet extraction. The low-MW polymer formed well-isolated SC-PNWs with relatively higher aspect ratio, in which the direction of π-π stacking was perpendicular to the direction of the long axis of the PNWs. Field-effect transistor (FET) devices fabricated from individual SC-PNWs of low-MW DPPBTSPE exhibited a maximum hole mobility of 24.0 cm² V^-1 s^-1. In addition to remarkable charge-transport behavior, intriguing photo-induced exciton generation and dissociated charge transport could be investigated in phototransistors (PTs) elaborated with SC-PNW. The highly ordered SC-PNWs displayed much better electronic and optoelectronic device performance compared with thin-film-based corresponding devices.