Title: Modelling and simulation of electronic relaxation processes in phosphorescent molecules in organic light emitting diodes

Authors: Nadeer Aljaroudi, Taiju Tsuboi

Addresses: Faculty of Engineering, Kyoto Sangyo University, Kamigamo, Kyoto 603-8555, Japan. ' Faculty of Engineering, Kyoto Sangyo University, Kamigamo, Kyoto 603-8555, Japan

Abstract: Simulation is made for the temperature dependences of emission intensity of phosphorescent tris(2-phenylpyridine) iridium [Ir ppy)₃] molecules doped in fluorescent N,N|-bis(3-methylphenyl)-N,N|-bis(phenyl)-benzidine (TPD) molecules from numerical calculation and compared them with the experimental result. Rate equations are constructed for the three zero-field splitting substates in the spin-triplet state T1 of the Ir(ppy)₃ guest and for the TT₁ state of the TPD host. It is concluded that (1) the increase of emission intensity above 100 K is due to the endothermic energy transfer from host to guest and (2) the decrease of PL intensity observed above 200 K is due to the energy transfer from the excited host to the neighbouring unexcited host. Calculation is extended to the case of Ir(ppy)₃ doped in aluminium tris 8-hydroxyquinoline (Alq₃) where the T₁ state of Alq₃ lies at much deeper energy than the case of TPD host.

Keywords: simulation; electronic relaxation processes; rate equations; organic light emitting diodes; OLEDs; LED; photoluminescence; phosphorescence; endothermic energy transfer; nanotechnology; nanoscale technology; temperature dependences; emission intensity; modelling.

DOI: 10.1504/IJCSE.2006.012773

International Journal of Computational Science and Engineering, 2006 Vol.2 No.3/4, pp.196 - 204

Published online: 14 Mar 2007 *

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