Non-radiative energy-transfer-driven quantum dot LEDs

Semiconductor nanocrystal quantum dots with their tunable optical properties, narrow photoluminescence, and high photostability have generated great interest in light-emitting device applications. [1, 2] Such colloidal quantum dots that are directly electrically driven in light-emitting diode (LED) structures have been extensively studied in the last decade. However, these LEDs unfortunately suffer from the fundamental problem of poor charge injection into these nanocrystals, which have high potential barriers due to their ligands surrounding them. This problem has been investigated and attempted to be minimized through various optimization methods. [3, 4] As a result, although today the device external quantum efficiencies can now reach ca 2.7 % [5], the main problem with charge injection still exists. On the other hand, conjugated conductive polymers are being used for organic based LEDs for several decades. These LEDs can reach higher quantum efficiencies over 20 % [6]. But these devices suffer in most of the cases from instabilities and degradation of the polymer active layers. To combine the advantages of each material system, hybrid organic-inorganic structures have also previously been investigated to obtain more ingenious devices. However, in all of these hybrid devices, the basic operation has mainly been based on the same mechanism of conventional charge injection into the nanocrystal active material.