Charge carrier mobility in blue-green emitting fluorenyl-substituted poly(p-phenylene vinylene)s

Abstract

The charge carrier mobility in three blue-green emitting conjugated polymers, poly[2-(9′,9′-dihexylfluorenyl)-1,4-phenylene vinylene] (DHF-PPV), poly[2-(7′-methoxy-9′,9′ -dihexylfluorenyl)-1,4-phenylene vinylene] (MDHF-PPV), and poly[2-(7′-cyano-9′,9′ -dihexylfluorenyl)-1,4-phenylene vinylene] (CNDHF-PPV) was measured using the time-of-flight technique. We observed dispersive charge carrier transport in DHF-PPV with a room-temperature hole mobility of 4.5×10−4 cm2/Vs at an electric field of 2.5×105 V/cm. This mobility is two orders of magnitude higher than that of poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene] at the same electric field. The introduction of an electron donating or an electron withdrawing group to fluorene unit in DHF-PPVs resulted in a decrease in the hole mobilities to 1.1×10−4 cm2/Vs for MDHF-PPV and 4.1×10−7 cm2/Vs for CNDHF-PPV at 298 K and an electric field of 2.5×105 V/cm, respectively. These results demonstrate that both the PPV backbone and the fluorene side unit in DHF-PPVs act as carrier hopping sites.