Table of Contents

Abstract

Thin-film light-emitting diodes ͑LEDs͒ containing solution-processed ZnO nanocrystals ͑NCs͒ were prepared as printed electronics. The electroluminescent ͑EL͒ properties of thin-film LEDs were investigated along with the structural and photoluminescence ͑PL͒ properties of the ZnO NCs. Scanning electron microscope and x-ray diffraction studies revealed that the crystal sizes D were ranged from 5-11 nm, and can be controlled by varying growth time t G in the Zn 2+ / OH − solution at 40°C. The time evolution of D was analyzed using Lifshitz-Slyozov-Wagner theory, showing that growth is limited by diffusion. The results of PL studies indicated that increases in the peak energies in the ultraviolet ͑UV͒ region could be attributed to the quantum-size effects on the exciton emission in the NCs with a small D, the ZnO surfaces became sufficiently passivated as D increases. Printed layers containing well-passivated ZnO NCs with different D of 8-11 nm were used as emission layers in thin-film LEDs together with pentacene hole transport layers. The current-voltage characteristics were analyzed using the trapped-charge-limited current mechanism. EL spectral measurements revealed the presence of weak UV emission that increased slightly as D decreased.