Optimization of the luminescence efficiencies in solution-processed phosphorescent dendrimers

We demonstrate that photoluminescence (PL) quantum yield and PL lifetime of fac-tris(2-phenylpyridyl) iridium(III) [Ir(ppy)₃]-cored dendrimers in neat film and dispersed into a 4,4′-bis(]V-carbazoly])bipheny] host can be significantly improved by a simple adjustment of the solution preparation. Quenching of the PL in these materials is due to an energy transfer of the triplet excitons to less-emissive sites and can be reduced by blending the phosphorescent molecules into a suitable wide energy gap host or by increasing the number of attached dendrons. We show here that the concentration of these quenchers can also be controlled by changing the time spent by the dendrimer solution under illumination prior to spin-coating. By optimizing the film preparation procedure, the external efficiency of devices made from neat dendrimer films was increased from 2% to 10%.