The synthesis and characterization of  semiconductor nanorods as active materials  for light emitting diodes

This Master’s thesis describes the preparation of nanorod semiconductors and its application in light emitting diodes (LEDs). The synthsis was carried out by the hot injection method and the closely packaged nanorods layers were obtained for the LED devices. The assemblies provide a realistic path to incorporate these materials into devices. The technique of fabrication of LED was undertaken by synthesis of II-VI semiconductor nanorods, assembling them using electrophoretic deposition. Typically, the supercrystal films consisting of highly ordered and vertically aligned CdSe1-xSx nanorod, CdSe nanorod and CdS nanorod were prepared as the emitters which are regarded as one of the most promising. LED materials due to their tunable and directional emission spectra, high damage threshold and low energy formation processes. In addition, preparation of highly monodisperse CdSe/CdS core/shell nanorods with tunable aspect ratios is described. The optical properties are compositionally tunable with the size of the CdSe core. Importantly, the influence of reaction time on shape/size control of the CdSe core is explored to achieved the desired nanorod Photoluminescence (PL). The synthetic protocol is reliable to allow good control over the PL of nanorod from green (535nm) to red (621nm), suited for the application in the LEDs with vertical superstructures.

The electrophoretic deposition (EPD) is employed to the fabrication of the emission layer. The green and red NR-LEDs show a peak external quantum efficiency (EQE) of 0.041 % and 0.0003% respectively. This performance is lower, the performance can be enhanced by the formation of vertically aligned NRs made by EPD, which can reduce the resistance of the carrier transport and balance the carrier injection.