Ultra-High Resolution Environmentally-Friendly Full-Colour Quantum Dot Display Fabricated via Cracking Assisted Transfer Printing

The increasing need for immersive displays in Augmented Reality (AR) / Virtual Reality (VR) technologies has heightened the demand for displays that offer high resolution, brightness, and a wide colour gamut, along with extended lifetimes. Quantum dots (QDs) have emerged as a leading emissive material in the in this application, with the properties of tuneable bandgap controlled by the QD size and composition, high photoluminescence quantum yield (PLQY), high colour purity with narrow emission spectra, and superior stability. Recent advancements in quantum dot light-emitting diodes (QD-LEDs), including improvements in brightness, lifetime, and efficiency, have fuelled research into their integration within future display application for AR/VR. In particular, the emergence of cadmium-free QDs, prompted by environmental considerations, has achieved performance levels on par with traditional cadmium-based alternatives. Despite advancements in the performance of cadmium-free QD-LEDs, their full integration remains challenged by the limitations of current integration technologies. Current technologies do not provide a comprehensive solution that simultaneously meets several crucial criteria: 1) achieving high resolution while ensuring consistent reproducibility, 2) offering high throughput capability in large area, 3) enabling scalability over large areas with good uniformity, 4) minimizing colour cross-contamination or damage to maintain high performance, and 5) ensuring compatibility with quantum dot materials produced through generic colloidal synthesis methods. This underscores the need for thorough research from QD material, QD-LED device architecture, patterning process, and integration of QD-LEDs into display technologies to concurrently satisfy these requirements. To meet these needs, a comprehensive study of the Cd-free EL QD-LED display system, an in-depth investigation was conducted, encompassing the synthesis and analysis of cadmium-free quantum dots, the design and fabrication of QD-LED unit devices, and the technology for patterning quantum dot EL structures, along with its implementation on various surface pixel structures. Additionally, simulations were carried out to validate the underlying physics of the QD-LEDs, including charge transport and electro-optical properties. As a result, the first Cd-free colour QD-LED was examined from the material level, device physics level, process for precision patterning, device fabrication, and system integration on thin-film transistor arrays. At the material level, synthesized Cd-free QDs showed PLQY of 83%, 85%, 42%, and 45% for InP-based red, green, blue, and ZnTeSe blue, respectively. At the QD-LED device level, the charge transport model and its extension through ABC model simulations was developed analyse the electro-optical characteristics of QD-LED. The simulation model was utilized to optimize device architecture controlling parameters of the charge transport layers. As for the pixelation process level, a unique pixelization process known as cracking assisted transfer printing was specially designed and developed for pixel sizes ranging from micrometre scale to nanometre scale. This method demonstrated superior and unique processability for large-area, ultrahigh-resolution patterning of RGB QD pixels down to nanometre size for future AR/VR applications. This technology achieved maximum luminance values of 37,499 cd/m², 22,210 cd/m², and 11,480 cd/m², and maximum external quantum efficiencies (EQE) of 4.24%, 1.63%, and 3.43%, showing superior performance compared to its spin-coated counterparts. In addition, the cracking assisted transfer printing technique allows for the preparation of RGB cadmium-free QD pixels of 600 nm × 900 nm size, corresponding to a resolution of 16,900 pixels per inch. Finally, this cracking assisted transfer printing technique is utilized for pixelization of Cd-free RGB QD layer on the nonplanar p-type low-temperature polycrystalline silicon (LTPS) thin-film transistor (TFT) backplanes, to fabricate a cadmium-free active matrix (AM) QD-LED display. The 1.41-inch diagonal with display, with its impressive resolution of 341 PPI, demonstrates exceptional colour performance with overlapping 135.3% with sRGB and 99.7% with DCI-P3 in colour chart.

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2024

Author dc:creator

• Kim, Yoonwoo

Advisor dc:contributor.advisor

• Kim, Jong

• cracking assisted transfer printing
• quantum dot

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/23b39c68-4f82-4267-ae20-886e8e69bd82/download
• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.114632

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/378080