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