Light-Emitting Electrochemical Cell

The light-emitting electrochemical cell ( LEC or abbreviated LEEC ) is an electronic thin film device which, similar to the OLED, an electric voltage is generated by light.

Design and operation

LEC consists of three layers (anode, cathode active layer ) which are formed on a transparent substrate. Its structure is thus similar to an OLED. However, in contrast to this, the LEC has only a single organic active layer containing the free ions.

Applying a DC voltage to the electrodes ( anode and cathode), holes are emitted into the active layer from the cathode and the anode. The ions present in the active layer are drawn to each to opposite pole. Here, the ions combine with the respective oppositely charged electrons or electron holes. In the active layer is formed between the positively and negatively charged particles of a pn junction to which a light emission takes place. For operation under ambient conditions, the LEC must be encapsulated to protect the organic material from oxygen and moisture.

Pros and Cons

In principle, the LEC has similar advantages and disadvantages as the OLED, but also some specific advantages and disadvantages. As the OLED to have a small thickness together with a small heat generation for the human eye and a pleasant, diffused light.

With respect to the OLED is an advantage of the non- LEC depending on the work function of the electrodes. Thus, both electrodes can be made ​​of the same material, and it is thus possible to produce a completely metal-free LEC. This allows operation of the LEC with very low voltages. Another technical advantage is production in the layer thickness tolerance of the LEC. This is substantially greater than that of the OLED, which can find application for the production, less accurate process, such as printing or coating method. Furthermore, the LEC can be produced under ambient conditions.

Main disadvantage of the LEC compared to the OLED are the values ​​achieved so far in terms of efficiency and service life. The achieved maximum light yield is about 10 lm / W at a lifespan of up to 5000 hours. Here they have achieved with OLEDs and LEDs values ​​are much higher.

History

The operation of the LEC is based on electroluminescence, also known as Destriau effect. This is emitted from a solid state after application of an electric voltage or an electric field light. This effect is, among other things, based on the LED and OLED. For the first time it was announced the LEC in 1995 by the research of Qibing Pei, Alan J. Heeger and others at the University of California at Los Angeles and the UNIAX Corporation.

One of the more remarkable step forward was made a research team led by Ludvig Edman at Umeå University in 2012. They managed the production of the LEC with the help of slot die coating under ambient conditions. This can serve as a basis for possible future production on a larger scale.