Carrier mobilities in organic electron transport materials determined from space charge limited current

We report the mobility in organic electron transport materials determined from current-voltage characteristics in the regime of space charge limited current. The electron mobilities obtained are highly dependent on applied electric field, similar to the cases using a conventional time-of-flight method. The electron mobilities of phenanthroline derivatives are high and comparable to hole mobilities of conventional hole transport materials. Two parameters. zero-field mobility and electric field activation parameter are discussed from the viewpoint of oxidation and reduction reactions. The electric field activation parameter increases gradually with the increase of ionization potential. These facts suggest that there is a good possibility for realizing low driving voltage in organic light-emitting diodes (OLEDs).