The influence of the electron transport and emission layers on the morphological instability of QDLEDs

The exceptional luminescence properties of colloidal quantum dots (QDs) make them advantageous for use as an electroluminescent material in light emitting devices (QDLEDs). Drastic improvements in the performance of QDLEDs have been achieved through the use of inorganic electron transport layers and organic hole transport layers (HTLs), yet the electroluminescence stability of QDLEDs remains insufficient for commercial applications. To address the issue of QDLED stability, significant work has been done to reduce charge imbalance and Auger recombination in the QDs which arises from the large energy level mismatch between the valence band of the QD and the highest occupied molecular orbital (HOMO) of the HTL. This work identifies morphological stability within QDLEDs as an additional degradation mechanism limiting device stability. Interaction between the HTL and surface roughness of the underlying layers appears to be a critical parameter to address in QDLED design. Studies of QDLEDs using electrical measurements and electroluminescence imaging elucidate upon the role that morphological stability plays in the degradation of electroluminescent QDLEDs.