New Type of Core-Shell Nanocrystal Quantum Dots for Applications in Light Emitting Diodes (LEDs)

We demonstrate a proof of principle for LEDs based on giant nanocrystal quantum dots (g-NQDs). These dots consist of a CdSe core overcoated with a thick CdS shell built one monolayer at a time. Our device structure is composed only of a PEDOT:PSS coated indium-tin oxide (ITO) anode and a LiF-Al cathode. These simple devices exhibit a maximum external quantum efficiency (EQE) and luminance of 0.12{\%} and 1000 Cd/m2 respectively when 16 shell g-NQDs are used for the active layer. This performance is already comparable to that of more sophisticated all-inorganic NQD LEDs. Thick shell ($>$13 monolayer) g-NQD devices show EQEs about one order of magnitude higher than those of thin-shell (4 monolayer) NQD devices, as well as much greater stability for operation under ambient conditions. Although current g-NQD devices do not set any new performance records, this work demonstrates a significant potential of g-NQDs for LED applications.