Tunneling electroluminescence devices

Kim, Y.E., H. Park, and J.J. Kim. 1996. Enhanced quantum efficiency in polymer electroluminescence devices by inserting a tunneling barrier formed by Langmuir-Blodgett films. AppZ Phys Lett 69 599-601. 

As shown above, the short circuit current, reaches 0.5 mA/cm under 20 mW/ cm illumination, corresponding to a collection efficiency of rjc = lA% electrons per incident photon. This value is approximately two orders of magnitude higher than that of pure MEH-PPV tunnel diodes as well as of the non-optimized MEH-PPV/Ceo heterojunction device as described in the previous section. The electroluminescence quantum efficiency of this blend device was 10 —10 times less than in pure MEH-PPV devices, consistent with the ultrafast photoinduced charge separation, which quenches the emission of the donor. The efficiencies are nearly independent of the incident illumination intensity as shown in Figure 15-28. Furthermore, the internal efficiencies are even higher when corrected for the small thickness of the film, which absorbs only 60% of the incident photons. 

As explained previously for polymer LEDs, a semiconducting polymer with asymmetric contacts (a low-work-function metal on one side and a high-work-function metal on the opposite side) functions as a tunneling injection diode [1262]. In forward bias, tunneling injection diodes exhibit relatively high efficiency electroluminescence. In reverse bias, Yu et al. (1265,1266] reported that the devices exhibit a strong photoresponse with a quantum yield larger than 20% (electron/photon at 10-V reverse bias), which comparable to UV-sensitized Si photodiodes. 

---