Metal halide perovskites (MHPs) have been a hot research topic due to their facile synthesis, excellent optical and optoelectronic properties, and record-breaking efficiency of corresponding optoelectronic devices. Nowadays, the development of miniaturized high-performance photodetectors (PDs) has been fueling the demand for novel photoactive materials, among which low-dimensional MHPs have attracted burgeoning research interest. In this report, the synthesis, properties, photodetection performance, and stability of low-dimensional MHPs, including 0D, 1D, 2D layered and nonlayered nanostructures, as well as their heterostructures are reviewed. Recent advances in the synthesis approaches of low-dimensional MHPs are summarized and the key concepts for understanding the optical and optoelectronic properties related to the PD applications of low-dimensional MHPs are introduced. More importantly, recent progress in novel PDs based on low-dimensional MHPs is presented, and strategies for improving the performance and stability of perovskite PDs are highlighted. By discussing recent advances, strategies, and existing challenges, this progress report provides perspectives on low-dimensional MHP-based PDs in the future.

Low-Dimensional Metal Halide Perovskite Photodetectors.

With rapid advances in high-speed communication and computation, augmented reality (AR) and virtual reality (VR) are emerging as next-generation display platforms for deeper human-digital interactions. Nonetheless, to simultaneously match the exceptional performance of human vision and keep the near-eye display module compact and lightweight imposes unprecedented challenges on optical engineering. Fortunately, recent progress in holographic optical elements (HOEs) and lithography-enabled devices provide innovative ways to tackle these obstacles in AR and VR that are otherwise difficult with traditional optics. In this review, we begin with introducing the basic structures of AR and VR headsets, and then describing the operation principles of various HOEs and lithography-enabled devices. Their properties are analyzed in detail, including strong selectivity on wavelength and incident angle, and multiplexing ability of volume HOEs, polarization dependency and active switching of liquid crystal HOEs, device fabrication, and properties of micro-LEDs (light-emitting diodes), and large design freedoms of metasurfaces. Afterwards, we discuss how these devices help enhance the AR and VR performance, with detailed description and analysis of some state-of-the-art architectures. Finally, we cast a perspective on potential developments and research directions of these photonic devices for future AR and VR displays.

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Augmented reality and virtual reality displays: emerging technologies and future perspectives.

J Soc Inf Display. 2019;27:387–401. Abstract We review the emerging mini/micro–light‐emitting diode (LED) displays featuring high dynamic range and good sunlight readability. For mini‐LED backlit liquid crystal displays (LCDs), we quantitatively evaluate how the device contrast ratio, local dimming zone number, and local light profile affect the image quality. For the emissive mini/micro‐LED displays, the challenges of ambient contrast ratio and size‐dependent power efficiency are analyzed. Two figure‐of‐merits are proposed for optimizing the optical and electrical performances of mini/micro‐LED displays.

Prospects and challenges of mini-LED and micro-LED displays

Lead halide perovskite quantum dots (LHP QDs) exhibit great potential in the backlighting display of light-emitting diode applications. Light-emitting backlighting with high brightness, low cost, a...

Perovskite Quantum Dots for Application in High Color Gamut Backlighting Display of Light-Emitting Diodes

This review traces nanocrystal quantum dot (QD) research from the early discoveries to the present day and into the future. We describe the extensive body of theoretical and experimental knowledge that comprises the modern science of QDs. Indeed, the spatial confinement of electrons, holes, and excitons in nanocrystals, coupled with the ability of modern chemical synthesis to make complex designed structures, is today enabling multiple applications of QD size-tunable electronic and optical properties.

Nanocrystal Quantum Dots: From Discovery to Modern Development.

Micro-light-emitting diodes (μ-LEDs) are regarded as the cornerstone of next-generation display technology to meet the personalised demands of advanced applications, such as mobile phones, wearable watches, virtual/augmented reality, micro-projectors and ultrahigh-definition TVs. However, as the LED chip size shrinks to below 20 μm, conventional phosphor colour conversion cannot present sufficient luminance and yield to support high-resolution displays due to the low absorption cross-section. The emergence of quantum dot (QD) materials is expected to fill this gap due to their remarkable photoluminescence, narrow bandwidth emission, colour tuneability, high quantum yield and nanoscale size, providing a powerful full-colour solution for μ-LED displays. Here, we comprehensively review the latest progress concerning the implementation of μ-LEDs and QDs in display technology, including μ-LED design and fabrication, large-scale μ-LED transfer and QD full-colour strategy. Outlooks on QD stability, patterning and deposition and challenges of μ-LED displays are also provided. Finally, we discuss the advanced applications of QD-based μ-LED displays, showing the bright future of this technology. Micrometre-sized light-emitting diodes (LEDs) based on quantum dots (QDs) will propel the next generation of display technologies, a review by leading researchers shows. Conventional LED designs, with phosphor coatings that convert light to different colours, are difficult to make smaller than 20 micrometres. Jr-Hau He at City University of Hong Kong and co-workers explain how this problem can be tackled using QDs, tiny particles whose optical properties can be tuned by varying their size, providing brighter and more precise colours. Ultra-high-resolution displays based on phospholuminescent QD-LEDs are now being released to the market thanks to finely-controlled methods for synthesising QDs and depositing them onto films. Further research should focus on the best ways to stabilise and protect QD films within LEDs, and to continue developing electroluminescent QD-LEDs, which could potentially outperform their phospholuminescent cousins.

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Micro-light-emitting diodes with quantum dots in display technology

This report investigated underwater wireless optical communication (UWOC) links in the presence of surface currents and tides. The scenario of surface currents and tides was generated by a sea water tank, a water pipe, and a water pump of different flow rates. It built the oceanic channel of UWOC varied with the salinity and flow rate in the UWOC transmission. The data rate of UWOC links based on a 520-nm laser diode and none-return-to-zero on-off keying (NRZ-OOK) modulation can achieve 3.4 Gb/s at a bit error rate (BER) of 3.78 $\times 10^{-4}$ in 1.8 m long sea water tank when a flow rate reached 1.08 m/s. The BER, eye-diagrams, and received signal optical power measurements showed that both the increasing salinity and flow rate cause the UWOC channel attenuation, thus degrade the performance of UWOC links.

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Investigation of Underwater Wireless Optical Communications Links With Surface Currents and Tides for Oceanic Signal Transmission

Underwater wireless optical communications (UWOC) are considered an emerging high-speed wireless network for underwater applications and compete with underwater radio frequency (RF) communications and underwater acoustic communications (UAC). Even though the utilization of laser diodes (LDs) enhances the -3dB modulation bandwidth extraordinarily from a few tens of MHz to GHz, LDs have the features of high collimation and narrow spectrum. Without the point-to-point optical alignment, the performance of the LD-based UWOC system drops exponentially because the received optical power determines the signal-to-noise ratio (SNR) of the UWOC system. To achieve a high-performance and reliable UWOC link based on LDs requires focusing optics and an alignment system. In this paper, we demonstrated a CMOS monolithic photodetector with a built-in 2-dimensional light direction sensor for the UWOC link by using a 450 nm LD and none-return-to-zero on-off keying (NRZ-OOK) modulation method. Employing this innovative technique, the field of view (FOV) was enlarged to 120°, and data rates up to 110 Mb/s at a bit error rate (BER) of 2.3×10−10 were obtained. The establishment of a proposed UWOC physical link showed enhanced communication performance for more practical and robust wireless communication applications.

CMOS monolithic photodetector with a built-in 2-dimensional light direction sensor for laser diode based underwater wireless optical communications.

We realize signal transmission with a miniature light source fabricated by a $4\; {\rm mm}^2 $4mm2 red-emissive CdSe/ZnS quantum-dot light-emitting diode (QLED) in visible light communication (VLC). The light emitted from the 60°-designed QLED transmits in free space with a data rate of 4 Mb/s at a 3 m transmission distance by using a simple modulation scheme of non-return-to-zero on-off keying. The maximum data rate of 2.5 Mb/s with a bit error rate below the forward-error-correction (FEC) limit is achieved with the optical angles of ${\rm \pm 20}^\circ $±20∘. The influences caused by the voltage, distance, and optical angle of emitting light are taken into consideration during communication. The performance of the QLED-based light source compares favorably with other solution-processed devices in efficiency, luminance, bandwidth, transmission speed, and distance. Additionally, to the best of our knowledge, this is the first report of an investigation on the application of QLED in VLC. Our results should be instructive for further investigation on QLED communication.

Zhijian Lv

Papers

Micro-light-emitting diodes with quantum dots in display technology

Investigation of Underwater Wireless Optical Communications Links With Surface Currents and Tides for Oceanic Signal Transmission

CMOS monolithic photodetector with a built-in 2-dimensional light direction sensor for laser diode based underwater wireless optical communications.

4 Mb/s under a 3 m transmission distance using a quantum dot light-emitting diode and NRZ-OOK modulation.

Performance Evaluation of 520nm Laser Diode Underwater Wireless Optical Communication Systems in the Presence of Oceanic Turbulence