Abstract: The invention provides a solution comprising a proton-doped polyaniline in combination with a protonic acid which is a solvent thereof, and an article coated with an optically-transparent, electrically-conductive layer, formed from the solution, and comprising a proton-doped poiyaniline. The invention also provides a method for preparing a processable solution of a proton-doped polyaniline for use in the preparation of electrically-conductive and optically-transparent coatings, comprising oxidatively polymerizing aniline in the presence of a second protonic acid to yield a solid polyaniline; and dissolving the solid polyaniline in the first protonic acid.