In recent years, Micro-LED technology has garnered significant attention due to its outstanding characteristics such as high brightness, high contrast, wide color gamut, fast response time, and high energy efficiency. However, achieving full-color Micro-LED displays remains a challenge. The color conversion layer is considered the most effective solution to address this challenge. While traditional phosphors and perovskite materials have been explored for full-colorization, they are encumbered by inherent limitations. Quantum dot (QD) has been introduced as the material for the color conversion layer in this field. As excellent semiconductor nanomaterials, QD holds promise in addressing issues of low color purity and brightness in traditional display technologies. Inkjet printing (IJP) technology, with its precision, cost-effectiveness, and rapid prototyping capabilities, offers a novel approach for fabricating quantum dot color conversion (QDCC) layer on high-resolution Micro-LED displays. However, literature on the fabrication of ultra-thick (>10 μm) QDCC layer using IJP is relatively limited. Therefore, we propose a method for fabricating ultra-thick QDCC layer using high-concentration green QD ink via IJP, without the incorporation of any filtering layer. The resulting color conversion layer devices demonstrate exceptional brightness and color saturation. These findings underscore the significant potential of ultra-thick color conversion layers prepared with high-concentration QD ink for Micro-LED displays, offering cost-effectiveness and paving the way for further advancements in Micro-LED technology.

We utilize Tracepro optical simulation software to analyze the optical crosstalk of the QDCC layer, facilitating the determination of the optimal distance between the LED and the black matrix (BM), as well as the line width of the BM. Through research and optimization of lithography and IJP processes, a uniform and repeatable QD film is successfully achieved. A green CdSe/ZnS QD ink, with a solid content of 20% (mass fraction), is utilized to print green QD film with sub-pixel sizes of 40 μm×40 μm and line width of 5 μm on the BM with a thickness of 14 μm, which is treated by reactive ion etching (RIE) using a piezoelectric inkjet printer. An integrating sphere photochromatic electric integrated test system is employed to analyze the photoluminescence (PL) spectrum, external quantum efficiency (EQE), and color coordinates of the QDCC layer integrated with blue Micro-LED. Additionally, the luminance of the green QD device is measured by employing an imaging luminance meter.

The simulation results indicate that when the LED is positioned far from the BM, optical crosstalk significantly exerts a substantial impact on the brightness and contrast of central sub-pixels. Conversely, reducing the distance between the LED and the BM to 3 μm effectively mitigates the optical crosstalk (Fig. 5). Moreover, varying the line width of the BM reveals that optical crosstalk is minimized at a line width of 5 μm. Overall, considering LED to BM distance is 3 μm, BM height is 14 μm, and line width is 5 μm, optical crosstalk could be minimized to enhance image clarity and color accuracy (Fig. 6). Additionally, the EQE of the green QDCC layer device is 3.59% for a thickness of 5 μm and 3.11% for a thickness of 14 μm. Brightness testing reveals that the device with a thickness of 14 μm reaches a maximum brightness of 159120.4 cd/cm² at a current of 90 mA. PL spectral analysis of devices with varying thicknesses of the color conversion layer at different currents demonstrates that the device with a thickness of 14 μm could completely block blue light and emit green light. Furthermore, changes in CIE color coordinates indicate a transition from cyan to highly saturated green (Fig. 9).

We successfully achieve the fabrication of an ultra-thick green QDCC layer using high-concentration QD ink via IJP without the incorporation of an additional filtering layer, following meticulous process optimization. The printed QD film, with sub-pixel dimensions of 40 μm×40 μm and a line width of 5 μm, is deposited on an RIE-treated BM. The green QDCC layer, with a thickness of 14 μm, exhibits outstanding performance metrics, including a maximum luminance of 159120.4 cd/cm², a correlated color temperature of 5844.463 K, and an EQE of 3.11%. Its CIE (x, y) coordinates are (0.2234, 0.7252), with no observable blue light leakage on the device surface. Our findings underscore the significant potential of an ultra-thick color conversion layer prepared using high-concentration QD ink for Micro-LED displays. This approach not only offers potential cost-effectiveness but also paves the way for new avenues in advancing Micro-LED technology, particularly in enhancing display performance and color fidelity.