Light Emitting thin Film Devices Based on Self-assembled Multilayer Heterostructures of PPV

Abstract

PPV based light emitting thin film devices were fabricated using a layer-by-layer deposition technique involving the alternate spontaneous adsorption of a PPV precursor polymer and either poly(styrene-4-sulfonate) (SPS) or poly(methacrylic acid) (PMA). It was demonstrated that the polyanion used to self-assemble the PPV precursor strongly influences the characteristics and performance of the resulting LEDs. Devices fabricated with PPV created in the presence of SPS exhibited symmetric I–V curves, low luminance levels and very high current densities while PPV/PMA devices exhibited luminance levels in the range of 10–60 cd/m2 and classical rectifying behavior. These dramatic differences are primarily due to a low level of p-type doping activated during the thermal conversion of PPV and/or during device operation that confers excellent hole carrier transport capabilities to the PPV/SPS combination. Fabrication of a multi-slab type heterostructure device comprised of a PPV/SPS block (hole transporting block) and a PPV/PMA block (emitting block) resulted in improved performance with luminance levels significantly higher than previously obtained for a single slab PPV/PMA device (typically > 100 cd/m2). It was also demonstrated that the presence of very thin (about 20–30 Å thick) insulating layers at the Al/polymer interface improves device efficiency by a factor of 2–4.

Self-Assembled Heterostructures of Electroactive Polymers: New Opportunities for Thin-Film Devices

“…This is a very interesting observation considering that PMA behaves as an insulating material and is therefore not expected to improve carrier injection into the device. In order to understand the origin of this interesting effect, we have recently fabricated ITO/(PPV/SPS)io/(PPV/PMA)20/Al heterostructure devices with extra insulating layers of PMA/PAH at the top of the heterostructure (9). Each PMA/PAH bilayer, in Sus case, contributes about 16 Â of insulating material to the total multilayer thickness.…”

“…This approach, which involves the alternate deposition of oppositely charged polymers from dilute aqueous solutions, makes it possible to process conjugated polymers in a layer-by-layer manner with nanometer level control over the thickness of the individual layers. To date, our group has demonstrated that this process can be used to manipulate a wide variety of materials into multilayer thin films including, conjugated polyions (3,4), electrically conducting polymers (5,6), light emitting polymers (7)(8)(9)(10), derivatized fullerenes (7,8), precursor polymers (77), and molecular dyes (72). This paper reviews some of our more recent developments in this area.…”

Formation and Characterization of Anionic Dye–Polycation Molecular Films by Layer-by-Layer Adsorption Process

“…These systems are believed to have technological applications in both optical and molecular electronic devices [8,9]. The growing interest in these films among researchers throughout the world is due to their potential applications in wetting, lubrication, high-resolution lithography, adhesion [10], electroluminescent devices [11,12], and second harmonic generation [13]. Recent investigations suggest that the sequential adsorption process can be exploited to manipulate various kinds of materials, including conducting polymers [14], light emitting materials [15], nonlinear optical polymers [16], inorganic nanoparticles [17], biomaterials [18], dyes [19], and many other organic and inorganic polymeric systems [20,21].…”

Spectroscopic Characterization of Niagara Blue Dye in the Restricted Geometry of Layer-by-Layer Self-Assembled Films

“…1 LbL method has several advantages over other techniques for fabricating thin lms such as: the assembly based on spontaneous adsorption, the¯lm deposited on any type of charged substrate regardless of size, shape, topography and topology. The nanoscale¯lms prepared by this simple, relatively fast, and potentially economical process are the subject of interest because of their potential utility in such applications as wetting, adhesion, lubrication, high resolution lithography, 2,3 molecular electronic devices, 4,5 electroluminescent devices 6 and second harmonic generation. 7 This novel lm fabrication process involving LbL deposition of oppositely charged polyions has been utilized in the fabrication of a wide variety of materials including conducting polymers, 8 light emitting materials, 9 nonlinear optical polymers, 10 inorganic nanoparticles, 11 biomaterials, 12 dyes 13 and various other organic, inorganic and polymeric systems.…”