Abstract
The paper describes the development of a novel thick film top emission electroluminescent (EL) lamp which displays excellent performance and is fabricated without an ITO film and is encapsulated for safe use. The conductive adhesive laminate can be applied to low cost opaque substrates such as paper. The development utilises a commercial contact adhesive which has been blended with a PEDOT:PSS solution to form a liquid which can be coated onto a conductively micro-structured PET film. This PET film can then be applied under minimal pressure to the EL lamp, to provide a laminated top electrode. An optimization of the material formulation and deposition thickness was required in to order the balance the primary requirements of the coating; namely adhesive tack, conductivity (lateral and through film) and optical transparency. For example, a pure adhesive layer would achieve excellent adhesion but would not be conductive while a pure PEDOT: PSS layer would provide the necessary conductivity but lack any adhesive properties. Nonoptimised light output achieved 88% of that of conventional glass devices and this could be further optimised through manipulation of the PEDOT: PSS concentration and film thickness to create devices with an output of 96% of that of conventional devices. The optimum balance was found to be a 15 mu m film with a 1.25% concentration of PEDOT: PSS in the adhesive. This material and specification is screen printable, thus the entire material stack can be manufactured using a common single low cost printing process. In order to examine whether silver could be replaced in the manufacture, lamps were manufactured on an aluminium substrate. These achieved 87% of the light output of conventional lamps although they showed a variability which was associated with the fragility of the substrate and its subsequent variation in flatness during lamp manufacture. The work has shown that EL lamps can be printed that are self-encapsulating and possess a performance close to that of conventional bottom emission lamps.