A phosphorescent poly(dendrimer) with increased viscosity for solution-processed OLED devices

We describe a phosphorescent green solution-processable iridium(III) complex containing poly(dendrimer), where the polymer character enhances compatibility with ink-jet printing techniques while the dendritic structure improves solid-state performance. The poly(dendrimer) shows an increased viscosity in chlorobenzene solutions of 1.1 mPa s at 25 mg/ml concentration relative to a simple first generation dendrimer. The poly(dendrimer) has a photoluminescence quantum yield of 15% in a neat film which increases to 52%, accompanied by an increase in radiative rate, when the material is blended with 4,4′-bis(N-carbazolyl)-2,2′-biphenyl (CBP). Blending with poly(styrene) results in a slightly decreased efficiency of 13%, showing the importance of choosing compatible materials when blending the poly(dendrimer). Organic light emitting diodes were fabricated containing the poly(dendrimer) and these had a 5.1% external quantum efficiency.