Efficient electroluminescence (EL) was obtained in organic light-emitting devices using 8-quinolinolate complexes of scandium (Scq3) and yttrium (Yq3) as emitters. Compared to the device based on the analogous Alq3 complex, no notable difference in the EL performances of the Yq3 device can be found; however, the EL characteristics of device with Scq3 were significantly enhanced. The device with the configuration of indium tin oxide/ N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine/Scq3/Yb exhibits a maximum current efficiency of 4.6 cd/A and a maximum power efficiency of 2.6 lm/W at a luminance of 300 cd/m2. The improvement of the performance of this device should be attributed to the higher hole mobility of the Scq3 as compared to Alq3 or a smaller barrier for hole injection into Scq3 compared to Alq3.

Hole transport in a blue emitting polyspirobifluorene polymer and in a white emitting polymer consisting of a polyspirobifluorene backbone and two dyes ͑green and red͒ was studied. The hole mobility was measured using the time-of-flight method as a function of the electric field and temperature in the range 10 5 −10 6 V / cm and 285− 335 K, respectively. The observed temperature and electric field dependence of the hole mobility was analyzed in the framework of the Bässler disorder model. Also, steady-state current-voltage characteristics were measured over a wide range of electric fields and temperatures and the hole mobility was determined. Our measurements have shown that the hole mobility in the white emitting polymer is the same as in the blue emitting polymer. The performed disorder model analysis gives the same values for the effective energetic disorder ͑115 meV͒ and for the positional disorder ͑1.85͒ for both polymers. Therefore, we have concluded that the added green and red dyes do not act as hole traps as they have no influence on the hole mobility. It can therefore be concluded that their highest occupied molecular orbital ͑HOMO͒ levels are aligned with the HOMO level of the polyspirobifluorene backbone.

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