Shaping Electroluminescence with a Large, Printed Bipolar Electrode Array: Solid Polymer Electrochemical Cells with Over a Thousand Light-Emitting p-n Junctions

The electroluminescence from a solid polymer light-emitting electrochemical cell typically originates from a single, narrow p-n or p-i-n junction. The bulk of the active material is non-emitting and must be doped before an emitting junction is formed. Here, we show that the doping and emission profiles of a planar cell can be drastically altered with the introduction of a large printed array of ink-jet-printed bipolar electrodes. Redox doping reactions induced at the wireless bipolar electrodes led to the simultaneous formation of over a thousand highly emissive p-n junctions uniformly distributed throughout the active layer of the large planar cell. The multi-junction cell achieved an eightfold increase in light-emitting area, a 14-fold increase in peak current and ten times faster response speed compared to a single-junction cell. Moreover, a giant open-circuit voltage of approximately 35 V was observed when the doped cell was allowed to discharge. Here, bipolar electrochemistry offers a simple and yet elegant solution to engineer a better light-emitting electrochemical cell.