New charge-transport materials for OLED applications
Novel fluorene-1 ,3,4-oxadiazole and spirobifluorene-1 ,3,4-oxadiazole compounds 202 and 211, respectively, have been synthesised. Compound 202 was blended with MEHPPV in various ratios and incorporated into organic light-emitting diodes (OLEDs).The devices were found to emit light purely from MEH-PPV up to very high doping levels. When the device architecture ITO/PEDOT:PSS/MEH-PPV :202/Ca:Al was used it was found that increasing the amount of202 increases the lifetime of the device. Novel bipolar fluorene- I ,3 ,4-oxadiazole-triphenylamine molecules 237 and 240 were synthesised using silicon protecting groups. When incorporated into devices with architecture ITO/PEDOT:PSS/237 or 240/Ca:Al it was found that the materials facilitated the transport of electrons and holes as well as acting as blue-green emitters with efficiencies of up to 0.26%/0.6 cd A-1. Compound 237 also performed well when blended with MEH-PPV giving rise to efficiencies two orders of magnitude greater than for pure MEH -PPV devices.