Microcavities enable high-efficiency OLEDs

Increasing the efficiency of organic light-emitting diodes (OLEDs) is a continuing focus in efforts aimed at reducing the cost of energy-efficient lighting and “solving the global energy crisis.

Increasing the efficiency of organic light-emitting diodes (OLEDs) is a continuing focus in efforts aimed at reducing the cost of energy-efficient lighting and “solving the global energy crisis.” To that end, a team at the Technical University of Dresden (Germany) has reported on outcoupling enhancements by way of a microcavity design in bottom-emission OLEDs. To explore outcoupling improvements, the group used monochrome red, green, and blue devices with p-i-n-doped structures that had layers of silver added to the indium tin oxide (ITO) anode. The thicknesses of the p and n layers were optimized in terms of constructive interference to maximize light output. The team also introduced a microcavity between the highly reflective cathode and a semitransparent metallic ground contact, which enhances the conversion of trapped photons into free external ones. The improvements enabled the OLEDs to reach efficiencies of 81 lm/W for red, 101 lm/W for green, and 4.0 lm/W for blue—a factor of 2.3 times better than standard ITO devices. The team attributes the improvements largely to amplification of light in the microcavity between the cathode and the silver layer. Contact Rico Meerheim at rico.meerheim@iapp.de.

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