Exploring the interactions between electrons, ions and photons
Solid-state bipolar electrochemistry-ChemElectroChem cover image (Chen, 2016)
A polymer LED with a structure of ITO/Polymer/Ca under a DC voltage bias-a simple device made to test the quality of the ITO substrate, the light-emitting polymer and the cleaning procedures (Gao, 2006).
Two planar LECs turned on in series with a 800 V DC bias-the two cells had a combined gap size of 3 mm, 100 times that of any previously reported planar LECs (Gao, 2003).
A planar LEC with 52 aluminum bipolar electrodes coated on top of the polymer and between the driving electrodes-the emission looks uniform because it is from 53 closely spaced light-emitting p-n junctions. The cell is actually 60% covered with opaque aluminum between the driving electrodes (Tracy, 2005).
Electrochemical doping induced with a pair of biased probes-no evaporated electrodes are needed (Hu, 2009).
Time lapse images and cell current of a planar LEC under a 20 V DC bias under UV illumination-a flat junction at last. This cell was cooled to 170 K after activation on which optical scanning was carried out. The junction width was found to be only 0.2% of the interelectrode gap of 700 microns (AlTal, 2016).
A sandwich LEC activated with a reverse bias. The active layer consists of only a light-emitting polymer and a lithium salt. The removal of polyethylene oxide makes the cell much harder to activate. But once turned on to emit light, the activated state is stable for hundreds of hours, even at room temperature (Gautier, 2016).
Long-term, intermittent testing of a sandwich LEC showing unexpected recovery in luminance after storage. The size, not the number of the black spots increased with time (Li, 2013).
Turn on a frozen p-n junction to emit light-one area at a time (Hu, 2011).
RGB bulk homojunction planar LECs-not poor quality sandwich LECs, but planar LECs with thousands of tiny light-emitting p-n junctions formed via bipolar electrochemistry (Tracy, 2006).
A polymer bulk homojunction LEC-thousands of light-emitting p-n junctions are formed by the introduction of tiny conductive particles to the LEC film which served as bipolar electrodes under bias. A new way to visualize the electric field lines (Tracy, 2005).
An organic light-emitting diode (OLED) is a semiconductor device with an active layer that is an organic light emitter. The light emitter can take the form of either a small molecule or a polymer. Photons are emitted when electronic charges are injected into the light emitter with the application of a voltage bias. The opposite of an OLED is an organic photovoltaic (OPV) cell. In an OPV cell, photons are absorbed by the organic layer and electricity is generated that can be used to power an electric load.
Both OLEDs and OPV cells are called photonic devices since photons play an important role in their operation. Introducing mobile ions into the organic layer of an OLED creates a new class of devices called the light-emitting electrochemical cells (LECs or LEECs). The effect of ions can be very dramatic on the performance of these organic photonic devices. The operation of a polymer LEC, for example, involves in situ electrochemical doping of the luminescent polymer and the formation of a dynamic p-n junction. Because of doping, the LEC’s performance is no longer highly sensitive to the thickness of the active layer and the type of electrode used. A polymer LEC can also function as an OPV cell when the p-n junction is fixed.
Our goal is to understand the physics and electrochemistry of mixed ionic/electronic conductors by studying the interactions between ions, electronic charges and photons.
Recent Publications
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AlTal, F.. and Gao, J. (2018) Laser-Induced Bipolar Electrochemistry—On-Demand Formation of Bipolar Electrodes in a Solid Polymer Light-Emitting Electrochemical Cell, Journal of the American Chemical Society, 140 (30):9737-9742.
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Hu, S. and Gao, J. (2018) Wireless Electroluminescence: Polymer Light-Emitting Electrochemical Cells with Ink-jet Printed 1D and 2D Bipolar Electrode Arrays, Journal of Physical Chemistry C, 122 (16): 9054-9061
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Gao, J. (2017) Strategies toward long lasting light-emitting electrochemical cells, ChemPlusChem, 82:1-15. Invited review article
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Gao, J., Chen, S., AlTal, F., Hu, S., Bouffier, L. and Wantz, G. (2017) Bipolar Electrode Array Embedded in a Polymer Light-Emitting Electrochemical Cell, ACS Applied Materials and Interfaces, 9(37):32405-32410
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Hu, S., Chi, K., Chen, S., AlTal, F. and Gao, J. (2017) Visualizing the Bipolar Electrochemistry of Electrochemically Doped Luminescent Conjugated Polymers Journal of Physical Chemistry C 121:8409-8415
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AlTal, F. and Gao, J. (2017) High resolution scanning optical imaging of a frozen planar polymer light-emitting electrochemical cell: an experimental and modeling study Science China Chemistry 60: 497-503. Invited article
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AlTal, F. and Gao, J. (2016) High resolution scanning optical imaging of a frozen polymer p-n junction Journal of Applied Physics 120:115501
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AlTal, F. and Gao, J. (2016) Charging and discharging a planar polymer light-emitting electrochemical cell Electrochimica Acta 220: 529-535
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Chen, S., Wantz, G., Bouffier, B., and Gao, J. (2016) Solid-state bipolar electrochemistry:polymer light-emitting electrochemical cells ChemElectroChem 3:392-398. Invited article
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Gautier, B., Wu, X., AlTal, F., Chen, S., and Gao, J. (2016) Reverse bias activation of salt-doped polymer light-emitting devices Organic Electronics 28:47-52
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AlTal, F. and Gao, J. (2015) Long-term testing of polymer light-emitting electrochemical cells: Reversible doping and black spots, Organic Electronics 18:1-7
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AlTal, F. and Gao, J. (2015) Scanning photocurrent and PL imaging of a frozen polymer p–i–n junction Physical Status Solidi-Rapid Research Letters 9(1): 77–81