TECHNOLOGY FOCUS - POLYMERS - Preferred Method: The first region is prepared by forming a solution of a first doped polymer; and forming a layer of a first doped polymer. The second region is an organic material doped with an immobile dopant. It is prepared by forming a solution of a second doped polymer; and forming a layer of a second doped polymer. Forming the region comprising organic material doped with an immobile dopant involves a process selected from spin coating, dip coating, spray coating, curtain coating, doctor blading, screen printing, roll printing, flexographic printing, offset printing, ink jet printing, spray painting, stamping, or brush painting. The first and second regions are brought into contact by laminating the first layer with the second region. Each of the first and second doped polymers comprises the same polymer, forming homojunction; or different conjugated polymer, forming heterojunction. The first doped polymer film is formed over an electrode (21, 23, 25), which is a transparent electrode. The method includes forming a layer of the second doped polymer over or partially over the first doped polymer layer. The first region is prepared by dissolving first undoped polymer in a solvent; reacting the first undoped polymer with a doping agent to produce a doped polymer and by-products such that the doped polymer remains in solution or precipitates from solution and the by-products precipitate or remain in the solution; filtering the solution to remove the by-products; redissolving the first doped polymer in a second solvent to form a first doped polymer solution; and forming a layer of the first doped polymer from the filtered solution of the first doped polymer. The second region is prepared by dissolving a second undoped polymer in a solvent; reacting the second undoped polymer with a second doping agent to produce a second doped polymer and by-products such that the second doped polymer remains in solution or precipitates from solution and the by-products precipitate or remain in the solution; filtering the solution to remove the by-products; redissolving the second doped polymer in a second solvent; and forming a layer of the second doped polymer from the filtered solution of the second doped polymer. The first and/or second undoped polymers are ionic; and the corresponding doped polymer is a self-doped polymer.