Photoluminescence and electroluminescence of vacuum-deposited poly(p-phenylene) thin film

We have studied the photoluminescence (PL) and electroluminescence (EL) pro perties of vacuum-deposited poly(p-phenylene) (PPP) thin film. The film sho ws the blue PL and EL emission at about 450 nm with well-resolved vibronic structures. The current-voltage-light (I-V-L) characteristics are systemati cally studied in the temperature range between 12 and 300 K in light-emitti ng devices of ITO/PPP/Al, and the devices with a hole transporting layer of N,N'-diphenyl-N,N'-bis(3-methylphenyl)-[1,1'-biphenyl]-4,4'-diamine (TPD), ITO/TPD/PPP/Al. The I-V dependence appears to follow the power law, 1 prop ortional to V-m/1, characteristics of a space-charge-limited current. The E L quantum efficiency increases with the decreasing temperature in ITO/TPD/P PP/Al. From the time delay between the EL emission and the onset of the bia s voltage pulse in ITO/PPP/Al, we estimated the hole mobility of similar to 4 x 10(-6) cm(2)/V s in the vacuum-deposited PPP film. (C) 2001 Elsevier Sc ience B.V. All rights reserved.