Phosphorescence Quantum Efficiency and Intermolecular Interaction of Iridium(III) Complexes in Co-Deposited Films with Organic Semiconducting Hosts

<jats:title>ABSTRACT</jats:title><jats:p>We accurately measured the absolute photoluminescence (PL) quantum efficiency (η<jats:sub>PL</jats:sub>) of organic solid-state thin films by using an integrating sphere. We measured the η<jats:sub>PL</jats:sub> of conventional organic materials used in organic light emitting diodes, such as a tris (8-quinolionolato)aluminum(III) complex (Alq<jats:sub>3</jats:sub>), and a phosphorescent 1.5mol%-<jats:italic>fac</jats:italic>-tris(2-phenylpyridyl)iridium(III):4, 4'-bis(carbazol-9-yl)-2, 2'-biphenyl [Ir(ppy)<jats:sub>3</jats:sub>:CBP] co-deposited film. Alq<jats:sub>3</jats:sub> and Ir(ppy)<jats:sub>3</jats:sub>:CBP showed a η<jats:sub>PL</jats:sub> = 20 ± 1% and 97 ± 2%, which corresponded well to external electroluminescence efficiency using these materials. We also measured red emitting bis[2-(2'-benzothienyl)pyridinato-<jats:italic>N</jats:italic>, <jats:italic>C</jats:italic><jats:sup>3</jats:sup>'] (acetylacetonato) iridium(III) [Btp<jats:sub>2</jats:sub>Ir(acac)] with CBP, and the blue complex, bis[(4, 6-difluorophenyl)pyridinato-<jats:italic>N, C</jats:italic><jats:sup>2</jats:sup>](picolinato)iridium(III) [FIrpic], with <jats:italic>m</jats:italic>-bis(<jats:italic>N</jats:italic> -carbazolyl)benzene. The maximum η<jats:sub>PL</jats:sub> values for Btp<jats:sub>2</jats:sub>Ir(acac), and FIrpic were 51±1% (at 1.4mol%), and 99±1% (1.2mol%), respectively. These results suggest that the η<jats:sub>EL</jats:sub> of red phosphorescent OLEDs using Btp<jats:sub>2</jats:sub>Ir(acac) as the dopant can be as high as 10%, and blue devices using FIrpic can reach the theoretical limit of 20%.</jats:p>