For drop-on-demand (DOD) inkjet printing, stable and single ink droplet formation without satellite dots is the key to improve the print quality. The formation of stable and single droplet is influenced by filament break up and the polymer chain's coil-stretch transition behavior. In this paper, the droplet formation behaviors of polyfluorene (PFO) ink at various driving voltages (V), polymer chain's coil-stretch transition mechanism and its effects on single ink droplet formation are investigated. It indicates that when 58 ＜V≤ 63 V, a single and stable droplet is formed with a pulse time of 38.5 μs. At this stage, the Weissenberg number (Wi) ＜ 0.5, the PFO molecular chain is coiled to guarantee stable and single droplets. When V ＞63 V, Wi ＞ 0.5, the PFO molecular chain is stretched because of the high hydrodynamic forces, resulting unwanted satellite droplets. When 55 ＜ V≤ 58 V, the droplet shrinks into the nozzle, which indicates that the kinetic energy supplied by the deformation of the piezoelectric transducer isn't enough to force the droplet to be jetted from the nozzle.