Bipolar Electrode Array Embedded in a Polymer Light-Emitting Electrochemical Cell

Abstract

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.

Optical analysis of light-emitting electrochemical cells

“…It is firmly established that the electrochemical doping is highly attractive from an electrical point-of-view, since it effectuates efficient and balanced injection of electrons and holes at low voltage. It is also practical from a fabrication viewpoint, since it renders the LEC tolerant to variations of the active-layer thickness ( d al ) and the selection of the electrode materials 20–25 . The influence of this doping on the optical performance is, however, less understood, although recent reports indicate that an appropriate optical design is paramount if a good LEC performance is to be attained 26–30 .…”

Remote Actuation of a Light‐Emitting Device Based on Magnetic Stirring and Wireless Electrochemistry

“…To date, an increasing number of applications in analytical chemistry and materials science were already proposed . For example, the design of tailored surface gradients or particles, single cell‐capture devices, polymer light‐emitting electrochemical cells and various analytical platforms were reported . Analytical approaches based on BPE very often involve metal electrodes (like Pt, Au, or Ag) that are screen‐printed on glass and integrated inside a microchannel .…”

Wireless Coupling of Conducting Polymer Actuators with Light Emission

“…[15] Recently, we were able to use polypyrrole (PPy) to generate mechanical output upon electrochemical stimulation without any direct connection to a power supply, thus the actuation is truly wireless. [19][20][21] However, a major challenge in this context is to obtain both light and actuation simultaneously to increase the application potential and the smartness of conducting polymers. The electric field polarizes the polymer in such a way that one extremity participates in an oxidation reaction, while the other one is undergoing a reduction process.…”

“…Either color change or light emission induced by bipolar electrochemistry has already been reported with different conducting polymers. [19][20][21] However, a major challenge in this context is to obtain both light and actuation simultaneously to increase the application potential and the smartness of conducting polymers.…”