Organic light-emitting diodes with p-doped alpha-sexithiophene hole transport and n-doped phenyldipyrenylphosphine oxide electron transport layers are fabricated. In the doped diodes, we demonstrate an extremely low driving voltage of 2.9 V at a current density of 100 mA/cm2 and very high luminance at a low driving voltage: 1 000 cd/m2 at 2.4 V, 10 000 cd/m2 at 2.8 V, and 920 000 cd/m2 at 4.5 V. Such lowered driving voltages and enhanced luminance characteristics are attributed to formation of charge-transfer complexes in the doped layers, resulting in an increase in electrical conductivities and formation of ohmic contacts at metal/organic interfaces.
By doping bis-styrylbenzene derivatives (BSBs) into a wide energy gap 4,4’-bis(9-carbazole)-2,2’- biphenyl (CBP) host, we demonstrate an extremely low ASE threshold. In particular, the lowest threshold of Eth=0.11±0.05 microJ/cm2 was obtained with 2,7-bis[4-(N-carbazole)phenylvinyl]- 9,9’-spirobifluorene (spiro-SBCz) which is the lowest ASE threshold ever reported. We demonstrate that the BSB thin film functions as an active light emitting layer in organic light-emitting diode (OLED) and a field-effect transistor (FET). Based on the EL characteristics, we discuss prospect of organic laser diodes.
