All-inorganic light emitting devices based on semiconducting nanoparticles
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1260-T09-02
All-inorganic light emitting devices based on semiconducting nanoparticles Ekaterina Neshataeva1, Tilmar Kümmell1, André Ebbers2 and Gerd Bacher1 1 Werkstoffe der Elektrotechnik and CeNIDE, University Duisburg-Essen, Bismarckstr. 81, D-47057 Duisburg, Germany 2 Evonik Degussa GmbH, Creavis, Paul-Baumann-Str. 1, D-45764 Marl, Germany ABSTRACT We demonstrate light emitting devices based on ZnO nanoparticles and realized without any additional organic support layers. Pure ZnO devices showed electroluminescence in the visible and the UV spectral range at voltages below 10 V. In order to facilitate hole injection and to stabilize device operation, additional p-type inorganic support layers were introduced. Sputtered NiO layers are shown to improve the stability of the device and its I/V behavior. First bilayer devices consisting of a layer sequence of p-doped Si and naturally n-doped ZnO nanoparticles revealed promising electro-luminescence results with a high contribution in the UV spectral range at reduced current densities. INTRODUCTION Nanoparticles are very attractive candidates for future large-area light emitting applications that are both robust and cost-effective. However, light emission at low operation voltages is mostly achieved by organic layers which support injection and transport of the charge carriers into the vicinity of the nanoparticles.1-3 These organic layers are susceptible to atmospheric conditions, humidity, electrochemical and thermal degradation which limits the lifetime of such organic/inorganic hybrid light emitting devices under ambient conditions. In this contribution, we demonstrate nanoparticle light emitting devices (LEDs) realized without any organic support layers. We introduce ZnO nanoparticles as a promising active light emitting material, since this material system is expected to be non-toxic, robust against oxidation and can be produced at low costs, which makes it suitable for large area applications under ambient air conditions. Another advantage of ZnO is its direct wide band gap and high exciton binding energy at room temperature, which allows efficient emission in the ultra violet (UV) and visible spectral range.4,5 Only few all-inorganic ZnO nanoparticle LEDs were demonstrated so far. Some concepts used ZnO nanopowder pressed between indium tin oxide (ITO) coated glass and Al electrode. Electroluminescence (EL) was observed at voltages in the order of several hundred volts.6 A significant reduction of the operation voltage could be achieved by reducing the thickness of the nanoparticle layer from 0.3 mm6 down to 500 nm7. In both cases, however, purely defect related emission in the visible range was obtained. A distinctive contribution of the near band gap emission to the EL spectrum was demonstrated by using the fluorine doped tin oxide (FTO) coated glass as a transparent conductive substrate instead of ITO8 and by thermal treatment of the nanoparticle layers9. Still, an efficient carrier injection, in particular of the holes, into the active ZnO material remain
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