Observation and Suppression of Stacking Interface States in Sandwich-Structured Quantum Dot Light-Emitting Diodes

Abstract

Interfacial quality of functional layers plays an important role in the carrier transport of sandwich-structured devices. Although the suppression of interface states is crucial to the overall device performance, our understanding on their formation and annihilation mechanism via direct characterization is still quite limited. Here, we present a thorough study on the interface states present in the electron transport layer (ETL) of blue quantum dot (QD) light-emitting diodes (QLEDs). A ZnO/ZnMgO bilayer ETL is adopted to enhance the electron injection into blue QDs. By probing the ETL band structure with photoelectron spectroscopy, we discover that substantial band bending exists at the ZnO/ZnMgO interface, elucidating the presence of a high density of interface states which hinder electron transport. By inserting a ZnO@ZMO interlayer composed of mixed ZnO and ZnMgO nanoparticles, the band bending and thus the interface states are observed to reduce significantly. We attribute this to the hybrid surface properties of ZnO@ZMO, which can annihilate the surface states of both the ZnO and ZnMgO layers. The introduction of a bridging layer has led to ∼40% enhancement in the power efficiency of blue QLEDs and noticeable performance boosts in green and red QLEDs. The findings here demonstrate a direct observation of interface states via detailed band structure studies and outline a potential pathway for eliminating these states for better performances in sandwich-structured devices.

Phenethylammonium bromide interlayer for high-performance red quantum-dot light emitting diodes

“…In order to address these aforementioned issues related to ZnO, researchers have developed several strategies, including the passivation and chemical doping of the ZnO-based ETL, interfacial modification, device engineering, and ligand modification of QDs. 15–20 Among these strategies, interfacial modification is one of the most cost-effective methods and widely employed in optoelectronic devices, such as organic light-emitting diodes (OLEDs), organic solar cells (OSCs), perovskite light emitting diodes (PeLEDs), and perovskite solar cells (PSCs). 9,21–24 For example, Tang et al modified the interface between the perovskite EML and the ZnMgO ETL with the amino-based compound, which not only interacted with ZnMgO and thereby modified the growth of perovskite film, but also passivated the perovskite defects.…”