Effect of dye concentrations in blended-layer white organic light-emitting devices based on phosphorescent dyes

Pearson, C; Cadd, DH; Petty, MC; Hua, YL

Abstract

The electronic and optoelectronic behavior of white organic light-emitting devices (OLEDs) based on blue (FIrpic) and red [Ir(piq)(2)(acac)] phosphorescent dyes doped into the same layer of a polyvinylcarbazole (PVK) host are reported. The conductivity of all the OLEDs studied appeared to be dominated by space-charge injection effects, exhibiting a current I versus voltage V dependence of the form I alpha V-n, with n approximate to 7 at applied voltages at which electroluminescence was observed. Systematic studies of the current versus voltage and light-emitting behavior of the OLEDs have identified different excitation processes for the two dyes. It is suggested that electroluminescence from the FIrpic molecules originates by direct transfer of the exciton energy from the PVK to the dye molecules, while the process of light emission from the Ir(piq)(2)(acac) molecules involves carrier trapping. The efficiency of the devices can be tuned, to some extent, by varying the thickness of the organic film. Luminous efficiencies and luminous power efficiencies of 8 cd A(-1) and 3 lm W-1 were measured for these blended-layer OLEDs, with Commission Internationale de l'Eclairage coordinates of 0.35, 0.35.

Citation

Pearson, C., Cadd, D., Petty, M., & Hua, Y. (2009). Effect of dye concentrations in blended-layer white organic light-emitting devices based on phosphorescent dyes. Journal of Applied Physics, 106(6), https://doi.org/10.1063/1.3226780

• Journal Article Type: Article
• Publication Date: Sep 1, 2009
• Deposit Date: Oct 17, 2011
• Publicly Available Date: Nov 3, 2011
• Journal: Journal of Applied Physics
• Print ISSN: 0021-8979
• Electronic ISSN: 1089-7550
• Publisher: American Institute of Physics
• Peer Reviewed: Peer Reviewed
• Volume: 106
• Issue: 6
• DOI: https://doi.org/10.1063/1.3226780
• Keywords: Dyes, Electrical conductivity, Electroluminescence, Electron traps, Excitons, Organic light emitting diodes, Phosphorescence, Polymer blends, Space-charge-limited conduction, Electron transporting material, P-Phenylene-vinylene, Limited conduction, Diodes
• Public URL: https://durham-repository.worktribe.com/output/1524891