How do electrons, ions and photons interact in organic semiconductors?
An organic light-emitting diode (OLED), in its simplest form, is a layer of organic luminescent material sandwiched between two dissimilar electrodes. Under a forward voltage bias, electrons and holes are injected into the organic layer, where they recombine to emit photons. OLEDs, especially the variety based on evaporated stacks of organic small molecules, have found applications in high-end flat panel displays.
Introducing mobile ions into OLEDs creates the light-emitting electrochemical cells (LECs), a fascinating device full of unknowns and drastically different from both a OLED and a conventional LED. The operation of an LEC involves in situ electrochemical doping of the organic semiconductor and the formation of a molecular p-n junction.The LEC technology is a prime candidate for low-cost, printable organic photonic devices.
Our research on organic photonics and iontronics straddles the boundaries of condensed matter physics, device physics, optics, and solid polymer electrolytes. We pioneered the interdisciplinary field of solid-state bipolar electrochemistry and demonstrated many novel device structures such as the world's largest planar LECs. We explore the sciences and applications of mixed organic semiconductors in which electrons, ions and photons interact in many unexpected ways.
Recent Publications
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Birdee, K., Hu, S., and Gao, J. (2020) Strong Doping and Electroluminescence Realized by Fast IonTransport through a Planar Polymer/Polymer Interface in Bilayer Light-Emitting Electrochemical Cells ACS Applied Materials & Interfaces. 12: 46381-46389
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Hu, S. and Gao, J. (2020). Shaping Electroluminescence with a Large, Printed Bipolar Electrode Array: Solid Polymer Electrochemical Cells with Over a Thousand Light-Emitting p–n Junctions. ChemElectroChem. 7: 1748-1751.
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Hu, S. and Gao, J. (2020). Polymer Light-Emitting Electrochemical Cells with Bipolar Electrode-Dynamic Doping and Wireless Electroluminescence. Advanced Functional Materials. 30 (33): 1907003. Invited review article.
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Hu, S. and, Gao, J. (2019). The Dynamic Bipolar Electrode in Polymer Light-Emitting Electrochemical Cells. Electrochimica Acta. 304: 184-191.
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Wang, D., Desroche, E., and Gao, J. (2019). Decoding the Polymer p-n Junction: Controlled De-doping and Reverse Bias Electroluminescence. Advanced Materials Interfaces. 7(1): 1901216.
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Hu, S. and Gao, J. (2019). Dynamic Bipolar Electrode Array for Visualized Screening of Electrode Materials in Light-Emitting Electrochemical Cells. ACS Applied Materials & Interfaces. 11: 1117-1124.
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Gao, J. (2018) Polymer Light-Emitting Electrochemical Cells—Recent Advances and Future Trends. Current Opinion in Electrochemistry 7: 87-94. Invited review article.
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Hu, S. and Gao, J. (2018) Stress Testing Polymer Light-Emitting Electrochemical Cells: Suppression of Voltage Drift and Black Spot Formation Advanced Materials Technologies, 3(11): 1800229
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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. (2016) High Resolution Scanning Optical Imaging of a Frozen Polymer P-N Junction Journal of Applied Physics 120:115501.