Electrohydrodynamic Inkjet Printing of Three-Dimensional Perovskite Nanocrystal Arrays for Full-Color Micro-LED Displays

Perovskite nanocrystal (PeNC) arrays are showing a promising future in the next generation of micro-light-emitting-diode (micro-LED) displays due to the narrow emission linewidth and adjustable peak wavelength. Electrohydrodynamic (EHD) inkjet printing, with merits of high resolution, uniformity, versatility, and cost-effectiveness, is among the competent candidates for constructing PeNC arrays. However, the fabrication of red light-emitting CsPbBrxI(3-x) nanocrystal arrays for micro-LED displays still faces challenges, such as low brightness and poor stability. This work proposes a design for a red PeNC colloidal ink that is specialized for the EHD inkjet printing of three-dimensional PeNC arrays with enhanced luminescence and stability as well as being adaptable to both rigid and flexible substrates. Made of a mixture of PeNCs, polymer polystyrene (PS), and a nonpolar xylene solvent, the PeNC colloidal ink enables precise control of array sizes and shapes, which facilitates on-demand micropillar construction. Additionally, the inclusion of PS significantly increases the brightness and environmental stability. By adopting this ink, the EHD printer successfully fabricated full-color 3D PeNC arrays with a spatial resolution over 2500 ppi. It shows the potential of the EHD inkjet printing strategy for high-resolution and robust PeNC color conversion layers for micro-LED displays.

Ligand-Enhanced Neodymium Doping of Perovskite Quantum Dots for Superior Exciton Confinement

In this study, all-inorganic perovskite quantum dots (QDs) for pure blue emission are explored for full-color displays. We prepared CsPbBr3 and Cs3NdCl6 QDs via hot injection methods and mixed in various ratios at room temperature for color blending. Nd-doped CsPb(Cl/Br)3 QDs showed a blueshift in emission, and the photoluminescence quantum yields (PLQY, ΦPL) were lower in the 460-470 nm range due to surface halogen and Cs vacancies. To address this, we introduced a silane molecule, APTMS, via a ligand exchange process, effectively repairing these vacancies and enhancing Nd doping into the lattice. This modification promotes the PLQY to 94% at 466 nm. Furthermore, combining these QDs with [1]Benzothieno[3,2-b][1]benzothiophene (BTBT), a conjugated small-molecule semiconductor, in a composite film reduced PLQY loss caused by FRET in solid-state QD films. This approach achieved a wide color gamut of 124% National Television System Committee (NTSC), using a UV LED backlight and RGB perovskite QDs in a BTBT-based organic matrix as the color conversion layer. Significantly, the photostability of this composite was enhanced when used as a color conversion layer (CCL) under blue-LED excitation.

Lanthanide and Ladder-Structured Polysilsesquioxane Composites for Transparent Color Conversion Layers

Ladder-type polysilsesquioxanes (LPSQs) containing phenyl as a high refractive index unit and cyclic epoxy as a curable unit were found to be excellent candidates for a transparent color conversion layer for displays due to being miscible with organic solvents and amenable to transparent film formation. Therefore, the LPSQs were combined with luminescent lanthanide metals, europium Eu(III), and terbium Tb(III), to fabricate transparent films with various emission colors, including red, orange, yellow, and green. The high luminescence and transmittance properties of the LPSQs-lanthanide composite films after thermal curing were attributed to chelating properties of hydroxyl and polyether side chains of LPSQs to lanthanide ions, as well as a light sensitizing effect of phenyl side chains of the LPSQs. Furthermore, Fourier-transform infrared (FT-IR) and X-ray photoelectron spectroscopy and nanoindentation tests indicated that the addition of the nanoparticles to the LPSQs moderately enhanced the epoxy conversion rate and substantially improved the wear resistance, including hardness, adhesion, and insusceptibility to atmospheric corrosion in a saline environment. Thus, the achieved LPGSG-lanthanide hybrid organic-inorganic material could effectively serve as a color conversion layer for displays.

Optimization and performance of nitrogen-doped carbon dots as a color conversion layer for white-LED applications

In this study, green-emitting nitrogen-doped carbon dots (N-CDots) were synthesized and incorporated into drop-cast composite films for use as color conversion layers in a white-LED configuration to generate white light. In order to resolve the red deficiency of this configuration, a commercial red phosphor was integrated into the system. Moreover, the N-CDots were also processed into polymer/N-CDot composite fibers, for which we determined the amount of N-CDots that yielded adequate white-light properties. Finally, we showed that white light with excellent properties could be generated by employing both of the fabricated N-CDot composites either as drop-cast films or composite fibers. Hence, N-CDots provide a promising alternative to inorganic phosphors that are commonly employed in white-LED configurations.