Light emitting electrochemical cell

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A light-emitting electrochemical cell , also English light-emitting electrochemical cell ( LEC or LEEC ), is an electronic thin-film component , which - similar to the OLED - after applying an electric voltage light generated.

history

The LEC's mode of action is based on electroluminescence , also known as the Destriau effect . Here, light is emitted from a solid body after an electrical voltage or an electrical field has been applied. This effect is also the basis for LED and OLED , among other things . The LEC first became known in 1995 through research by Qibing Pei, Alan J. Heeger and others at the University of California in Los Angeles and the UNIAX Corporation.

Another noteworthy progress was made by a research team led by Ludvig Edman at Umeå University in 2012. They succeeded in producing the LEC using the slot nozzle coating under ambient conditions. This can serve as a basis for possible subsequent production on a larger scale.

Structure and functionality

The LEC consists of three layers ( anode , cathode , active layer) which are built up on a transparent substrate. Their structure is therefore similar to an OLED. In contrast to this, however, the LEC only has a single organic active layer which contains free ions.

If a direct voltage is applied to the electrodes (anode and cathode), electrons are emitted from the cathode and defect electrons from the anode into the active layer. The ions in the active layer are drawn to the opposite pole. The ions combine with the oppositely charged electrons or defect electrons. In the active layer, a pn junction forms between the positively and negatively charged particles , at which light emission takes place. For operation under ambient conditions, the LEC must be encapsulated to protect the organic material from oxygen and moisture.

Advantages and disadvantages

In principle, the LEC has similar advantages and disadvantages as the OLED, but also some special advantages and disadvantages. Like the OLED, it has a small thickness, together with low heat generation and a diffuse light that is pleasant to the human eye.

An advantage of the LEC over the OLED is that it is not dependent on the work function of the electrodes. Both electrodes can thus be made from the same material, and it is also possible to manufacture a completely metal-free LEC. This enables the LEC to be operated with very low voltages. Another advantage in terms of production technology is the layer thickness tolerance of the LEC. This is much larger than that of the OLED, which means that less precise processes, for example printing or coating processes, can also be used for production. Furthermore, the LEC can be produced under ambient conditions.

Because of their simple construction, they are also easier to recycle than other lighting technologies.

The main disadvantage of the LEC compared to the OLED are the values ​​achieved so far in terms of efficiency and service life. The maximum light output achieved is around 10 lm / W with a service life of up to 5000 hours. The values ​​achieved with OLEDs and LEDs are much higher here.

In contrast, luminous efficacies of almost 40 lm / W have already been achieved in the laboratory.

literature

  • Qibing Pei, Gang Yu, Chi Zhang, Yang Yang, Alan J. Heeger: Polymer Light-Emitting Electrochemical Cells . In: Science . tape 269 , no. 5227 , August 25, 1995, p. 1086-1088 , doi : 10.1126 / science.269.5227.1086 , PMID 17755530 .
  • Andreas Sandström, Henrik F. Dam, Frederik C. Krebs, Ludvig Edman: Ambient fabrication of flexible and large-area organic light-emitting devices using slot-die coating . In: Nature Communications . tape 3 , no. 1002 , August 14, 2012, doi : 10.1038 / ncomms2002 .
  • Liquid light - For Next Generation Packaging, Illumination, And Signage. LUNALEC, 2012 (LEC product brochure).

Individual evidence

  1. ^ A b Ruben D. Costa, Enrique Ort, Henk J. Bolink, Filippo Monti, Gianluca Accorsi, Nicola Armaroli , Luminescent Ionic Transition-Metal Complexes for Light-Emitting Electrochemical Cells . In: Angewandte Chemie International Edition . 51, No. 33, 2012, 8178–8211, doi: 10.1002 / anie.201201471 .