Atomic Layer Deposition Strategies for Quantum Dot Displays—From Photolithographic Passivation Layers to Charge Transport Engineering

In this presentation, we will discuss research on applying Atomic Layer Deposition (ALD) techniques to quantum dot electroluminescent displays. Initially, we demonstrated the feasibility of fabricating light-emitting diodes (LEDs) using a solution process by applying ALD to Cs-based inorganic perovskite materials. Traditional perovskites, which involve ionic bonding and organic ligands, face processing challenges as subsequent functional layers must be deposited in a vacuum environment. To address this issue, we treated the perovskite surface with ALD oxides, discovering that the reaction between ALD precursors and the perovskite surface is a complex vapor-phase reaction with the surface ligands, rather than a simple deposition. We optimized this reaction pathway to minimize the precipitation of Pb metal, which can reduce emission efficiency.<br/>We also applied ALD ZnO to the surface of quantum dot materials for a very limited number of cycles, significantly improving their resistance to solvents. This enabled us to apply traditional photolithography with photoresist coating to achieve high-resolution patterning of over 3,600 PPI, suitable for AR/VR/XR applications.<br/>Furthermore, we extended the application of ALD beyond interlayers to charge transport layers by doping Al2O3 and MgO in ultrathin cycles, forming Al-doped ZnMgO alloy thin films. These were applied in QD-LED devices, resulting in high-efficiency, long-lifetime, and high-brightness QD electroluminescent devices. This ALD-based process suggests that such techniques can be utilized not only for the encapsulation or semiconductor processes of conventional display devices but also within the active layers of displays, offering diverse functionality for emissive materials.