Electroluminescence from light-emitting polymer/ZnO nanoparticle heterojunctions at sub-bandgap voltages

SummaryThe turn-on voltage of a light-emitting diode is generally equal to or greater than its bandgap voltage (or the bandgap energy divided by the electron charge). In contrast, we have found that electroluminescence at sub-bandgap voltages can be observed in polymer light-emitting devices with a heterojunction based on ZnO nanoparticles (NPs). This sub-bandgap electroluminescence is attributed to an Auger-assisted energy up-conversion process at the polymer/ZnO NPs interface, the observation of which depends strongly on the size of the nanoparticles.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (149 K)Download as PowerPoint slideResearch highlights▶ Light emission from polymer light emitting devices (PLEDs) was observed at energies less than the photon energy. ▶ Energy up-conversion Auger process resulted in photon emission at sub-bandgap energy (driving voltages). ▶ A layer of <5 nm diameter ZnO nanoparticles was necessary to observe sub-bandgap emission.