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High efficiency, solid-state light-emitting devices have been fabricated from a water soluble, polymeric ruthenium (II) complex, Ru(bpy) 3 2+ polyester, via the use of a layer-by-layer processing scheme. Spin-coated devices of this material were found to produce maximum luminance levels of 250−300 cd/m 2 with an external quantum efficiency of 0.2% photons/electron. Devices based on sequentially adsorbed layers of the Ru(bpy) 3 2+ polyester and poly(acrylic acid), on the other hand, exhibit external quantum efficiencies in the 1−3% range with a maximum light output of 40−50 cd/m 2 . These high device efficiencies were obtained by optimizing the relative amounts of Ru(bpy) 3 2+ polyester and poly(acrylic acid) incorporated into the film via a layer-by-layer molecular-level blending approach. Through this type of control, it was also possible to create compositionally graded heterostructures and to produce devices that emit light only in the forward or reverse bias or that were completely symmetrical (similar light output, current flow, and efficiency in both forward and reverse bias).
Wu et al. (Sat,) studied this question.