Micro light-emitting diodes (μ-LEDs) coupled to color conversion phosphors are among the most promising technologies for future display and artificial light sources. However, current emitters suffer from excessively large particle sizes, preventing micron-scale processability, and/or low stability that hampers the device lifetime. Here, we demonstrate down-conversion μ-LED phosphors based on CsPbBr3 perovskite nanocrystals directly grown inside perfectly sealed mesoporous silica nanospheres (NSs). Key for this advancement is a high-throughput calcination procedure in the presence of K2CO3 as selective pore sealing agent, which simultaneously produces the CsPbBr3 nanocrystals, boosts their emission efficiency to >87%, and perfectly isolates them from the outer environment without causing inter-particle cross-linking or aggregation. This results in size-homogeneous, finely solution-dispersible, ultra-stable, and highly emissive CsPbBr3-SiO2 NSs that fit the technological requirements of photolithographic inks for highly uniform μ-LED color conversion patterns with pixels smaller than 20 μm. 

https://pubs.acs.org/doi/pdf/10.1021/acsenergylett.2c02062

Ultra-stable, Solution-Processable CsPbBr3-SiO2 Nanospheres for Highly Efficient Color Conversion in Micro Light-Emitting Diodes

MoS2‐based transparent electronics can revolutionize the state‐of‐the‐art display technology. The low‐temperature synthesis of MoS2 below the softening temperature of inexpensive glasses is an essential requirement, although it has remained a long persisting challenge. In this study, plasma‐enhanced chemical vapor deposition is utilized to grow large‐area MoS2 on a regular microscopic glass (area ≈27 cm2). To benefit from uniform MoS2, 7 × 7 arrays of top‐gated transparent (≈93% transparent at 550 nm) thin film transistors (TFTs) with Al2O3 dielectric that can operate between −15 and 15 V are fabricated. Additionally, the performance of TFTs is assessed under irradiation of visible light and estimated static performance parameters, such as photoresponsivity is found to be 27 A W−1 (at λ = 405 nm and an incident power density of 0.42 mW cm−2). The stable and uniform photoresponse of transparent MoS2 TFTs can facilitate the fabrication of transparent image sensors in the field of optoelectronics.

Low‐Temperature Plasma‐Assisted Growth of Large‐Area MoS2 for Transparent Phototransistors

The implementation of high efficiency and high-resolution displays has been the focus of considerable research interest. Recently, micro-LEDs, which are inorganic light-emitting diodes of size less than 100 μm2 , have emerged as a promising display technology owing to their superior features and advantages over other displays like liquid crystal displays and organic light-emitting diodes. Although many companies have introduced micro-LED displays since 2012, obstacles to mass production still exist. Three major challenges, i.e., low quantum efficiency, time consuming transfer, and complex color conversion, have been overcome with technological breakthroughs to realize cost-effective micro-LED displays. In the review, methods for improving the degraded quantum efficiency of GaN based micro-LEDs induced by the size effect are examined, including wet chemical treatment, passivation layer adoption, LED structure design, and growing LEDs in self-passivated structures. Novel transfer technologies, including pick-up transfer and self-assembly methods, for developing large-area micro-LED displays with high yield and reliability are discussed in depth. Quantum dots as color conversion materials for high color purity, and deposition methods such as electrohydrodynamic jet printing or contact printing on micro-LEDs have also been addressed. This review presents current status and critical challenges of micro-LED technology and promising technical breakthroughs for commercialization of high performance displays. This article is protected by copyright. All rights reserved.

Technological breakthroughs in chip fabrication, transfer, and color conversion for high performance micro-LED display.

Dual-wavelength multiple quantum wells (MQWs) have great potential in realizing high quality illumination, monolithic micro light-emitting diode (LED) displays and other related fields. Here, we demonstrate a single chip white light indium gallium nitride (InGaN) LED via the manipulation of the dual-wavelength MQWs. The MQWs contain four pairs of blue light-emitting MQWs and one pair of green light-emitting QW. The fabricated LED chips with nickel/gold (Ni/Au) as the current spreading layer emit white light with the injection current changing from 0.5 mA to 80 mA. The chromaticity coordinates of (0.3152, 0.329) closing to the white light location in the Commission International de I’Eclairage (CIE) 1931 chromaticity diagram are obtained under a 1 mA current injection with a color rendering index (CRI) Ra of 60 and correlated color temperature (CCT) of 6246 K. This strategy provides a promising route to realize high quality white light in a single chip, which will significantly simplify the production process of incumbent white light LEDs and promote the progress of high-quality illumination.

/pdf/realizing-single-chip-white-light-ingan-led-via-dual-vm6w2fez.pdf

Realizing Single Chip White Light InGaN LED via Dual-Wavelength Multiple Quantum Wells

Synthesis of large‐area patterned MoS2 is considered the principle base for realizing high‐performance MoS2‐based flexible electronic devices. Patterning and transferring MoS2 films to target flexible substrates, however, require conventional multi‐step photolithography patterning and transferring process, despite tremendous progress in the facilitation of practical applications. Herein, an approach to directly synthesize large‐scale MoS2 patterns that combines inkjet printing and thermal annealing is reported. An optimal precursor ink is prepared that can deposit arbitrary patterns on polyimide films. By introducing a gas atmosphere of argon/hydrogen (Ar/H2), thermal treatment at 350 °C enables an in situ decomposition and crystallization in the patterned precursors and, consequently, results in the formation of MoS2. Without complicated processes, patterned MoS2 is obtained directly on polymer substrate, exhibiting superior mechanical flexibility and durability (≈2% variation in resistance over 10,000 bending cycles), as well as excellent chemical stability, which is attributed to the generated continuous and thin microstructures, as well as their strong adhesion with the substrate. As a step further, this approach is employed to manufacture various flexible sensing devices that are insensitive to body motions and moisture, including temperature sensors and biopotential sensing systems for real‐time, continuously monitoring skin temperature, electrocardiography, and electromyography signals.

Large‐Scale Ultra‐Robust MoS2 Patterns Directly Synthesized on Polymer Substrate for Flexible Sensing Electronics

Wafer-scale monolithic integration of full-colour micro-LED display using MoS2 transistor

Abstract A flexible full-color micro-LED display with high mechanical robustness was fabricated by printing quantum dots (QDs) on a blue micro-LED array using standard photolithography. The red and green colors yielded from QDs exhibit a better color gamut than conventional color filters. The light conversion efficiency was enhanced by adding TiO 2 nanoparticles to the QD-photoresist composite. This full-color micro-LED display was successfully mounted on various unusual substrates such as curved glass, fabrics, and human skin, enabling diverse optoelectronic applications. In addition, wireless multi-channel visible light communication (VLC) based on the wavelength-division-multiplexing orthogonal-frequency-division-multiplexing (WDM-OFDM) technique was demonstrated using a QD-based color micro-LED panel. A high data transmission rate of 1.9 Gbps was successfully obtained owing to the high electrical–optical modulation bandwidth of the QD-based micro-LED panel. 

https://www.nature.com/articles/s41528-022-00234-z.pdf

Sumin Hwangbo

Papers

Wafer-scale monolithic integration of full-colour micro-LED display using MoS2 transistor

Flexible micro-LED display and its application in Gbps multi-channel visible light communication