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Kim, Sei‐,Yong,Jeong, Won‐,Ik,Mayr, Christian,Park, Young‐,Seo,Kim, Kwon‐,Hyeon,Lee, Jeong‐,Hwan,Moon, Chang‐,Ki,Brü,tting, Wolfgang,Kim, Jang‐,Joo WILEY‐VCH Verlag 2013 Advanced Functional Materials Vol.23 No.31
<P><B>Abstract</B></P><P>High‐efficiency phosphorescent organic light‐emitting diodes (OLEDs) doped with Ir(ppy)<SUB>2</SUB>(acac) [bis(2‐phenylpyridine)iridium(III)‐acetylacetonate] in an exciplex forming co‐host have been optically analyzed. This emitter has a preferred orientation with the horizontal to vertical dipole ratio of 0.77:0.23 as compared to 0.67:0.33 in the isotropic case. Theoretical analysis based on the orientation factor (<I>Θ</I>, the ratio of the horizontal dipoles to total dipoles) and the photoluminescence quantum yield (<I>q</I><SUB>PL</SUB>) of the emitter predicts that the maximum external quantum efficiency (EQE) of the OLEDs with this emitter is about 30%, which matches very well with the experimental data, indicating that the electrical loss of the OLEDs is negligible and the device structure can be utilized as a platform to demonstrate the validity of optical modeling. Based on the results, the maximum EQE achievable for a certain emitting dye in a host can be predicted by just measuring <I>q</I><SUB>PL</SUB> and <I>Θ</I> in a neat film on glass without the need to fabricate devices, which offers a universal plot of the maximum EQE as a function of <I>q</I><SUB>PL</SUB> and <I>Θ</I>.</P>