Printing and In Situ Assembly of CdSe/CdS Nanoplatelets as Uniform Films with Unity In-Plane Transition Dipole Moment

Abstract

Distribution of the transition dipole moments (TDMs) of light emitters can intrinsically affect the light out-coupling efficiency of planar light-emitting diodes (LEDs). Lacking the control of TDM distribution has limited the efficiency of nanocrystal-based LEDs to 20%. Here, we present a method that deposits uniform nanocrystal films with unity in-plane TDM distribution. Combining an inkjet printing technique and colloidal nanocrystal self-assembly, we achieved direct printing and in situ assembly of colloidal CdSe/CdS nanoplatelets to all orient “face-down” on various substrates. With motorized translation stages, pattern printing is realized, which demonstrates the potential for integration in industrial-scale fabrication. The method is applied to achieve uniform nanoplatelet films with unity in-plane TDM distribution on zinc-oxide films, a commonly used electron-transport layer. Thus, our work paves the way to break the light out-coupling efficiency limitation of 20% in state-of-the-art nanocrystal-based LEDs, which exclusively possess an isotropic TDM distribution.

Spectrally Wide-Range-Tunable, Efficient, and Bright Colloidal Light-Emitting Diodes of Quasi-2D Nanoplatelets Enabled by Engineered Alloyed Heterostructures

“…However, NPLs offers a possible solution to enhance light extraction efficiency by their in-plane orientation due to their geometrically anisotropic nature . Unity in-plane orientation and transition dipole moment distribution have been recently reported using core/shell NPLs. The theoretical EQE of the NPL-LED device is predicted as ∼40%. , Therefore, there is a definite need for further research to demonstrate spectrally wide color spanning and efficient NPL-LED devices to break the light outcoupling efficiency limitation of 20% for NC-based LEDs using the opportunity of unity in-plane orientation of the NPLs.…”

Manipulation of the Optical Properties of Colloidal 2D CdSe Nanoplatelets

“…[ 142,145 ] Figure 9c displays TEM images of these twisted CdSe NPL ribbons. Motivated by the groundbreaking properties of NPL superstructures, other self‐assembly approaches such as the traditional Langmuir technique, [ 146 ] solvent‐evaporation‐mediated inkjet printing technique, [ 147 ] stretching‐controlled copolymer composites, [ 148–150 ] external electric field–adjusted self‐assembly, [ 151 ] and liquid–liquid interfacial assembly [ 50,152 ] have also been reported and the fundamental physical properties of these ordered assemblies have been investigated in recent years. Among all these self‐assembly methods, liquid–liquid interfacial assembly is the most powerful strategy to achieve both face‐down‐ and edge‐up‐oriented CdSe NPL stacks by controlling the interaction strength between adjacent NPLs and the NPL‐polar subphase at the liquid–liquid interface.…”

Green CdSe/CdSeS Core/Alloyed‐Crown Nanoplatelets Achieve Unity Photoluminescence Quantum Yield over a Broad Emission Range

“…[1][2][3] Cadmium-based nanoplatelets, in particular, exhibit narrow emission linewidths, anisotropic transition-dipole distributions, giant modal gain coefficients, and ultra-low lasing thresholds. [4][5][6][7][8][9][10] Compared to other colloidal emitters, like quantum dots, nanorods, and perovskites nanocrystals, cadmium-based nanoplatelets have narrower linewidths, higher color purity, and can thus fulfill the nextgeneration display criterion of the Rec. 2020 (refs.…”