Visualization of electrochemical doping and light-emitting junction formation in conjugated polymer films

In situ electrochemical doping and light-emitting junction formation in conjugated polymer films have been visualized by direct imaging of a massive planar device structure under UV illumination. Both p- and n-doping of conjugated polymers have been observed. When the p- and n-doped regions meet, a light-emitting p–n junction forms and significant current flow begins. The reversal of applied bias creates many tiny and transient light-emitting p–n junctions in the previously n-doped region by the uneven growth of new p-doped areas. Eventually a stable emission zone is formed closer to the new cathode, from a polymer film that shows almost no photoluminescence due to doping.