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

We present a study that focuses on a comparison of the absolute photoluminescence quantum efficiency (phi(pl)) with the electroluminescence quantum efficiency (eta(el)) using a guest-host active layer. We also report the luminous power efficiency of devices based on this same emissive layer. The active layer consists of a series of metal quinolates used as the host for the dopant rubrene. We find that rubrene doping enhances the phi(pl) of the metal quinolate host materials, tris(8-hydroxyquinolinato) gallium III (Gaq(3)), tris(8-hydroxyquinolinato) aluminum III (Alq(3)), and tris(4-methyl-8-hydroxyquinolinato) aluminum III (Almq(3)), from 0.13, 0.25, and 0.42, respectively, to similar to 1.0 for all metal quinolates. This is achieved by efficient Forster energy transfer from host to guest molecules. We also find that doping enhances the eta(el) Of devices using Gaq(3) or Alq(3) as the active layer from 0.6 % and 1.0 %, respectively, to 2.2 % for both hosts when measured at a current density of 100 A/m(2). The eta(el) of devices based on Almq(3) increases from 1.6% to 2-9% upon doping with rubrene. At a brightness of 100 cd/m(2), the luminous power efficiency of devices based on the metal quinolates increases from 1.0 lm/W, 0.99 lm/W, and 2.1 lm/W to 3.6 lm/W, 4.0 lm/W, and 3.8 lm/W for Gaq(3), Alq(3), and Almq(3), respectively, when doped with an optimized concentration of rubrene. These enhancements are attributed to carrier trapping followed by direct recombination on the rubrene dopant as well as efficient energy transfer from the host to rubrene.