Self assembly of CdSe/ZnS quantum dots for organic/inorganic light emitting devices for the next generation display technology

Abstract

We have investigated the effect of quantum dot (QD) concentrations, spin speed and temperature on the self assembly of CdSe/ZnS QDs on substrate for the optimisation of QDs used in organic light-emitting devices (OLEDs) applications. The atomic force microscopy (AFM) results showed that surface morphology and coverage are varied with different process parameters. There is also a tendency for the formation of aggregates/islands on a smooth substrate that could be caused by spinodal phase separation. The uniform distribution of QDs with controllable density was achieved using the conventional spin-coating method. We fabricated and investigated the effect of CdSe/ZnS QD concentrations on the self-assembly hybrid organic/inorganic light emitting diodes (QD-OLEDs) for the tuning of performance. There was a QD threshold concentration below which there was no emission from the QDs. The estimated QD concentration was around 9 × 1011 cm−2 for the best performance of QD-OLED. The annealing of QD-OLED increased the QD emission about three times. No wavelength shift was observed in the electroluminescence spectra from the QD before and after the annealing of QD-OLEDs. The mechanism of this emission improvement is discussed.