Quantum dots (QDs) are now on the verge of widespread adoption in display applications, after 25 years of scientific research and over a decade of commercialization efforts. This is the result of a combination of industry trends such as liquid crystal displays (LCDs) and light emitting diode (LED) backlight units (BLUs), combined with improvements in QD performance and manufacturing that have taken place across the growing QD ecosystem of Universities, National Labs, and private and public companies. As QDs emerge as a viable choice as downconversion materials in LED backlit LCD displays, they have the potential to be employed in several geometries within these otherwise similar display systems. In all geometries, QD LCDs will provide the broadest available color gamut to the user, in addition to potential benefits in power efficiency, brightness, and contrast. This work will summarize QD properties and advantages in such LED backlit LCDs relative to other competitive downconversion materials, as well as compare and contrast the three primary geometries that will likely be explored during the pursuit of a potentially dominant design.

http://ma.ecsdl.org/content/MA2013-02/49/2729.full.pdf

Quantum Dots for LED Downconversion in Display Applications

https://onlinelibrary.wiley.com/doi/pdf/10.1002/adom.201901429

High‐Resolution Inkjet Printing of Quantum Dot Light‐Emitting Microdiode Arrays

Material composition engineering and device fabrication of perovskite nanocrystals (PNCs) in solution can introduce organic contamination and entail several synthetic, processing, and stabilization steps. We report three-dimensional (3D) direct lithography of PNCs with tunable composition and bandgap in glass. The halide ion distribution was controlled at the nanoscale with ultrafast laser–induced liquid nanophase separation. The PNCs exhibit notable stability against ultraviolet irradiation, organic solution, and high temperatures (up to 250°C). Printed 3D structures in glass were used for optical storage, micro–light emitting diodes, and holographic displays. The proposed mechanisms of both PNC formation and composition tunability were verified. Description Perovskite nanocrystals under glass Perovskite nanocrystals (PNCs) such as cesium lead triiodide (CsPbI3) can display bright photoemission with narrow linewidths for display applications, but their long-term stability requires passivation and encapsulation steps after synthesis in solution. Sun et al. created three-dimensional arrays of PNCs in doped metal oxide glasses using ultrafast laser pulses that caused local melting and subsequent crystallization. They tuned the bandgap of PNCs and their photoluminescence between 480- and 700-nanometer wavelengths by transforming the composition from CsPb(Cl1-xBrx)3 to CsPbI3. These encapsulated PNCs exhibited long-term stability after prolonged heating or organic solvent and ultraviolet light exposure. —PDS Melting of a doped metal oxide glass with ultrafast laser pulses created perovskite nanocrystal arrays for optoelectronics.

Three-dimensional direct lithography of stable perovskite nanocrystals in glass

Metal halide perovskites are emerging as attractive materials for light-emitting diode (LED) applications. The external quantum efficiency (EQE) has experienced a rapid progress and reached over 21%, comparable to the state of the art organic and quantum dot LEDs. For metal halide perovskites, their simple solution-processing preparation, facile band gap tunability, and narrow emission line width provide another attractive route to harness their superior optoelectronic properties for multicolor display applications. In this work, we demonstrate a high-resolution, large-scale photolithographic method to pattern multicolor perovskite films. This approach is based on a dry lift-off process which involves the use of parylene as an intermediary and the easy mechanical peeling-off of parylene films on various substrates. Using this approach, we successfully fabricated multicolor patterns with red and green perovskite pixels on a single substrate, which could be further applied in liquid crystal displays (LCDs) with blue backlight. Besides, a prototype green perovskite micro-LED display under current driving has been demonstrated.

Photolithographic Patterning of Perovskite Thin Films for Multicolor Display Applications.

Quantum-dot light-emitting diodes (QLEDs) with high brightness have potential application in lighting and display. The high brightness is realized at high current density (J). However, at high J, the efficiency drops significantly, thereby limiting the achievable brightness. This notorious phenomenon has been known as efficiency roll-off, which is likely caused by the Auger- and/or thermal-induced emission quenching. In this work, we show that the Joule heat generated during device operation significantly affects the roll-off characteristics of QLEDs. To realize ultrabright and efficient QLEDs, the thermal stability of QDs is improved by replacing the conventional oleic acid ligands with 1-dodecanethiol. By further using a substrate with high thermal conductivity, the Joule heat generated at high J is effectively dissipated. Because of the effective thermal management, thermal-induced emission quenching is significantly suppressed, and consequently, the QLEDs exhibit a high external quantum efficiency (EQE) of 16.6%, which is virtually droop-free over a wide range of brightness (e.g., EQE = 16.1% @ 105 cd/m2 and 140 mA/cm2). Moreover, due to the reduced efficiency roll-off and enhanced heat dissipation, the demonstrated QLEDs can be operated at a very high J up to 3885 mA/cm2, thus enabling the devices to exhibit a record-high brightness of 1.6 × 106 cd/m2 and a lumen density of 500 lm/cm2. Our work demonstrates the significance of thermal management for the development of droop-free and ultrabright QLED devices for a wide variety of applications including lighting, transparent display, projection display, outdoor digital signage, and phototherapy.

Investigation on Thermally Induced Efficiency Roll-Off: Toward Efficient and Ultrabright Quantum-Dot Light-Emitting Diodes

In Situ Inkjet Printing Strategy for Fabricating Perovskite Quantum Dot Patterns

Highly Stable and Spectrally Tunable Gamma Phase RbxCs1–xPbI3 Gradient‐Alloyed Quantum Dots in PMMA Matrix through A Sites Engineering

One‐Step Polymeric Melt Encapsulation Method to Prepare CsPbBr3 Perovskite Quantum Dots/Polymethyl Methacrylate Composite with High Performance

Reducing the Chromaticity Shifts of Light-Emitting Diodes Using Gradient-Alloyed CdxZn1−xSeyS1−y@ZnS Core Shell Quantum Dots with Enhanced High-Temperature Photoluminescence

Photolithography has shown great potential in patterning solution-processed nanomaterials for integration into advanced optoelectronic devices. However, photolithography of perovskite quantum dots (PQDs) has so far been hindered by the incompatibility of perovskite with traditional optical lithography processes where lots of solvents and high-energy ultraviolet (UV) light exposure are required. Herein, we report a direct in situ photolithography technique to pattern PQDs based on the photopolymerization catalyzed by lead bromide complexes. By combining direct photolithography with in situ fabrication of PQDs, this method allows to directly photolithograph perovskite precursors, avoiding the complicated lift-off processes and the destruction of PQDs by solvents or high-energy UV light, as PQDs are produced after lithography exposure. We further demonstrate that the thiol-ene free-radical photopolymerization is catalyzed by lead bromide complexes in the perovskite precursor solution, while no external initiators or catalysts are needed. Using direct in situ photolithography, PQD patterns with high resolution up to 2450 pixels per inch (PPI), excellent fluorescence uniformity, and good stability, are successfully demonstrated. This work opens an avenue for non-destructive direct photolithography of high-efficiency light-emitting PQDs, and potentially expands their application in various integrated optoelectronic devices. 

/pdf/direct-in-situ-photolithography-of-perovskite-quantum-dots-1uwvr1pr.pdf

Fei Li

Papers

In Situ Inkjet Printing Strategy for Fabricating Perovskite Quantum Dot Patterns

Highly Stable and Spectrally Tunable Gamma Phase RbxCs1–xPbI3 Gradient‐Alloyed Quantum Dots in PMMA Matrix through A Sites Engineering

One‐Step Polymeric Melt Encapsulation Method to Prepare CsPbBr3 Perovskite Quantum Dots/Polymethyl Methacrylate Composite with High Performance

Reducing the Chromaticity Shifts of Light-Emitting Diodes Using Gradient-Alloyed CdxZn1−xSeyS1−y@ZnS Core Shell Quantum Dots with Enhanced High-Temperature Photoluminescence

Direct in situ photolithography of perovskite quantum dots based on photocatalysis of lead bromide complexes