measurements of the devices. Luminescence maxima of 12 500,
12 100, 9900, 10 500, and 8200 cd mꢀ2 were recorded for devices
DDP1–DDP5 respectively. The maximum current efficiencies of
the devices were 29.4, 19.6, 17.1, 21.0, and 34.7 cd Aꢀ1 under
operating potentials of 16, 15, 15, 15, and 17 V, respectively.
Relative to that of the standard device S2 (12.9 cd Aꢀ1), the
device DDP5 exhibited a significantly improved current effi-
ciency of 34.7 cd Aꢀ1 as a result of the presence of P5 as the
hole-transporting layer. The DDP1 device also displayed a higher
current efficiency (29.4 cd Aꢀ1 at 16 V) than that of the standard
device S2 (21.8 cd Aꢀ1 at 15 V).
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This study was supported by the Ministry of Economic Affairs
(grant no. 93-EC-17-A-08-S1-0015), the National Science
Council of Taiwan, and the Advanced Polymer Nanotechnology
Research Center.
This journal is ª The Royal Society of Chemistry 2008
J. Mater. Chem., 2008, 18, 1296–1301 | 1301