Solid-state light-emitting devices based on the tris-chelated ruthenium(II) complex: 3. High efficiency devices via a layer-by-layer molecular-level blending approach

High efficiency, solid-state light-emitting devices have been fabricated fr om a water soluble, polymeric ruthenium (II) complex, Ru(bpy)(3)(2+) polyes ter, 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. Devi ces based on sequentially adsorbed layers of the RU(bpy)(3)(2+) polyester a nd poly(acrylic acid), on the other hand, exhibit external quantum efficien cies in the 1-3% range with a maximum light output of 30-50 cd/m(2). These high device efficiencies were obtained by optimizing the relative amounts o f Ru(bpy)(3)(2+) polyester and poly(acrylic acid) incorporated into the fil m via a layer-by-layer molecular-level blending approach. Through this type of control, it was also possible to create compositionally graded heterost ructures and to produce devices that emit light only in the forward or reve rse bias or that were completely symmetrical (similar light output, current flow, and efficiency in both forward and reverse bias).