Sequentially adsorbed layer-by-layer self assembled films: light-emitting devices based on Evans blue

Abstract

We have shown that small organic molecules can be incorporated in thin films via layer-by-layer self-assembly method. Poly(allylamine hydrochloride) with electrostatically attached evans blue molecules have been used as a polycation, while poly(acrylic acid) has been used as a polyanion. Alternate deposition of the polycation and the polyanion resulted in stable and homogeneous films of evans blue. Concentration of evans blue in the polymeric cation has been varied to deposit different layer-by-layer self-assembled films. The light-emitting devices have been fabricated based on such films. Charge injection mechanism has been studied in these devices and the barrier height of hole injection has been calculated. Luminance-current characteristics have been studied and compared with those based on spin-cast films of evans blue. Beyond the turn-on current, the luminance at a current density was two to three orders of magnitude higher in the devices based on self-assembled films as compared to the spin-cast counter parts.