A linear array of aluminum discs is deposited between the driving electrodes of an extremely large planar polymer light-emitting electrochemical cell (PLEC). The planar PLEC is then operated at a constant bias voltage of 100 V. This promotes in situ electrochemical doping of the luminescent polymer from both the driving electrodes and the aluminum discs. These aluminum discs function as discrete bipolar electrodes (BPEs) that can drive redox reactions at their extremities. Time-lapse fluorescence imaging reveals that p- and n-doping that originated from neighboring BPEs can interact to form multiple light-emitting p-n junctions in series. This provides direct evidence of the working principle of bulk homojunction PLECs. The propagation of p-doping is faster from the BPEs than from the positive driving electrode due to electric field enhancement at the extremities of BPEs. The effect of field enhancement and the fact that the doping fronts only need to travel the distance between the neighboring BPEs to form a light-emitting junction greatly reduce the response time for electroluminescence in the region containing the BPE array. The near simultaneous formation of multiple light-emitting p-n junctions in series causes a measurable increase in cell current. This indicates that the region containing a BPE is much more conductive than the rest of the planar cell despite the latter's greater width. The p- and n-doping originating from the BPEs is initially highly confined. Significant expansion and divergence of doping occurred when the region containing the BPE array became more conductive. The shape and direction of expanded doping strongly suggest that the multiple light-emitting p-n junctions, formed between and connected by the array of metal BPEs, have functioned as a single rod-shaped BPE. This represents a new type of BPE that is formed in situ and as a combination of metal, doped polymers, and forward-biased p-n junctions connected in series.

We present solid‐state, polymer‐based, light‐emitting electrochemical cells incorporating bipolar electrodes (BPEs) positioned between the driving electrodes. The dominant processes in these planar electrochemical cells are in situ electrochemical p and n doping of the luminescent conjugated polymer when a sufficient voltage bias is applied between the feeder anode and cathode. The inclusion of floating BPEs causes additional doping at the extremities of the BPE, which has been visualized through in situ fluorescence imaging. We investigate how the applied voltage bias and the BPE size affect electrochemical doping from the BPE. We observe an interesting delay in the appearance of doping from the BPE if the applied voltage bias was initially insufficient. Doping eventually occurs when the potential difference across the BPE/polymer interface becomes sufficient, as doping from the driving electrodes propagates. The inclusion of BPEs can lead to more efficient polymer light‐emitting and photovoltaic cells when a large number of active junctions are formed.

We use a micro-manipulated vacuum probe station to generate and visualize bipolar electrochemical redox reactions in a solid-state polymer light-emitting electrochemical cell (PLEC). In situ electrochemical p-and n-doping of a luminescent polymer is initially induced via a pair of biased metallic probes in direct contact with the luminescent polymer. Subsequently, the biased probes are moved to contact the planar aluminum driving electrodes of the PLEC to activate the device. By analyzing the complex doping patterns generated, we conclude that the doped polymers have functioned as bipolar electrodes (BPEs), from which electrochemical p-or n-doping are induced wirelessly. The potential energy barrier between the polymer BPE and the undoped polymer have played a major role in doping initiation. In a separate planar cell of a smaller gap size, a pair of planar aluminum electrodes was driven in such a way that they functioned as long BPEs to create five coupled and strongly emitting polymer p-n junctions. These results offer vivid visualization of the intriguing bipolar electrochemical phenomena in a solid-state polymer blend. The ability to form a BPE in situ, and in the form of a heavily doped polymer offer innovative ways to modify the doping profiles in molecular devices. The all-polymer BPE also expands the realm of bipolar electrochemistry to beyond that of a conventional liquid cell containing metal or carbon electrodes.

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Do me a solid: Solid‐state light‐emitting electrochemical cells incorporating bipolar electrodes are reported. Multiple p–n junctions are formed in situ by electrochemical doping of the luminescent conjugated polymer. More information can be found in the Full Paper by J. Gao and co‐workers on page 392 in Issue 3, 2016 (DOI: 10.1002/celc.201500373).