Comparison of device performance using various metal quinolates as the host for a guest-host active layer

Abstract

ABSTRACT We present a study that focuses on a comparison of the absolute photoluminescence quantum efficiency (P) withthe electroluminescence quantum efficiency (Tiel) using a guest-host active layer. We also report the luminous powerefficiency of devices based on this same emissive layer. The active layer consists of a series of metal quinolates used as thehost for the dopant rubrene. We find that rubrene doping enhances the i of the metal qumolate host materials, tris(8- hydroxyquinolinato) gallium III (Gaq3), tris(8-hydroxyquinolinato) aluminum III (A1q3), and tris(4-methyl-8- hydroxyquinolinato) aluminum III (Almq3), from 0.13, 0.25, and 0.42, respectively, to — 1.0 for all metal quinolates. This isachieved by efficient Forster energy transfer from host to guest molecules. We also find that doping enhances the flel ofdevices using Gaq3 or A1q3 as the active layer from 0.6 % and 1 .0 %, respectively, to 2.2 % for both hosts when measured ata current density of 100 AIm2. The 1e1 of devices based on Almq3 increases from 1.6% to 2.9% upon doping with rubrene.At a brightness of 100 cd/rn2, the luminous power efficiency of devices based on the metal quinolates increases from 1.0lm!W, 0.99 lniIW, and 2. 1 lm!W to 3.6 lm/W, 4.0 lm/W, and 3.8 lm/W for Gaq3, Alq3, and Almq3, respectively, when dopedwith an optimized concentration of rubrene. These enhancements are attributed to carrier trapping followed by directrecombination on the rubrene dopant as well as efficient energy transfer from the host to rubrene.Keywords: Organic light emitting diodes, A1q3, Almq3, Gaq3, rubrene, dopant, guest-host system, photoluminescencequantum efficiency, electroluminescence quantum efficiency, luminous power efficiency.