Laboratory of Organic Photonics and Iontronics

Laboratory of Organic Photonics and Iontronics
Laboratory of Organic Photonics and Iontronics

How do electrons, ions and photons interact in organic semiconductors?

  • Solid-state bipolar electrochemistry

    Solid-state bipolar electrochemistry-ChemElectroChem cover image (Chen, 2016)

  • A Sandwich Polymer LED

    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

    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 multiple coated bipolar electrodes

    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 of a light-emitting polymer with a pair of biased probes

    Electrochemical doping induced with a pair of biased probes-no evaporated electrodes are needed (Hu, 2009).

  • Time lapse image and cell current of a planar LEC under a 20 V DC bias under UV illumination

    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

    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 test

    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). 

  • Probing a frozen LEC junction

    Turn on a frozen p-n junction to emit light-one area at a time (Hu, 2011). 

  • RGB bulk homojunction planar LECs

    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

    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), 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

  • 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

  • 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.

  • 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.

  • Hu, S. and, Gao, J. (2019). The Dynamic Bipolar Electrode in Polymer Light-Emitting Electrochemical Cells. Electrochimica Acta. 304: 184-191.

  • 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.

  • 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.

  • Gao, J. (2018) Polymer Light-Emitting Electrochemical Cells—Recent Advances and Future Trends. Current Opinion in Electrochemistry 7: 87-94. Invited review article.

  • 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

  • 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.

  • 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.

  • Gao, J. (2017) Strategies Toward Long Lasting Light-Emitting Electrochemical Cells, ChemPlusChem, 82:1-15. Invited review article.

  • 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.

  • 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.

  • AlTal, F. and Gao, J. (2016) High Resolution Scanning Optical Imaging of a Frozen Polymer P-N Junction Journal of Applied Physics 120:115501.