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We report a photolithography‐based technology for patterning quantum dot color converters for micro‐LED displays. A patterning resolution of ~1 µm is achieved. The method can be applied to any color converter materials. Integration of perovskite quantum dots and CdSe/ZnS quantum dots is demonstrated to show the versatility of the technology. [ABSTRACT FROM AUTHOR]

Abstract: All‐inorganic perovskite quantum dots (IPQDs) are a promising material for use in various optoelectronic devices due to their excellent optoelectronic properties and high environmental stability. Here, a high‐performance phototransistor based on a layered heterojunction composed of CsPbI3 QDs and a narrow‐bandgap conjugated polymer DPP‐DTT is reported, which shows a high responsivity of 110 A W−1, a specific detectivity of 2.9 × 1013 Jones and a light to dark current ratio up to 6 × 103. The heterojunction phototransistor exhibits unipolar p‐type and gate bias modulated behaviors. In addition, the device exhibits a broad spectral detection range from ultraviolet to near infrared. The high sensitivity of the device is attributed to the layered heterojunction and the gate bias modulation property. The work overcomes the existing limitations in sensitivity of IPQD photodetectors due to the poor charge transport between QDs. The convenient solution‐processed fabrication and excellent device performance especially suggest the IPQD/narrow‐bandgap conjugate polymer heterojunction as a promising structure for potential applications of ultrasensitive broadband photodetectors compatible with a wide variety of substrates. [ABSTRACT FROM AUTHOR]

A critical event during kidney organogenesis is the differentiation of podocytes, specialized epithelial cells that filter blood plasma to form urine. Podocytes derived from human pluripotent stem cells (hPSC-podocytes) have recently been generated in nephron-like kidney organoids, but the developmental stage of these cells and their capacity to reveal disease mechanisms remains unclear. Here, we show that hPSC-podocytes phenocopy mammalian podocytes at the capillary loop stage (CLS), recapitulating key features of ultrastructure, gene expression, and mutant phenotype. hPSC-podocytes in vitro progressively establish junction-rich basal membranes (nephrin+podocin+ZO-1+) and microvillus-rich apical membranes (podocalyxin+), similar to CLS podocytes in vivo. Ultrastructural, biophysical, and transcriptomic analysis of podocalyxin-knockout hPSCs and derived podocytes, generated using CRISPR/Cas9, reveals defects in the assembly of microvilli and lateral spaces between developing podocytes, resulting in failed junctional migration. These defects are phenocopied in CLS glomeruli of podocalyxin-deficient mice, which cannot produce urine, thereby demonstrating that podocalyxin has a conserved and essential role in mammalian podocyte maturation. Defining the maturity of hPSC-podocytes and their capacity to reveal and recapitulate pathophysiological mechanisms establishes a powerful framework for studying human kidney disease and regeneration. S tem C ells 2017;35:2366-2378 [ABSTRACT FROM AUTHOR]

Photodetectors with ultrafast response are explored using inorganic/organic hybrid perovskites. High responsivity and fast optoelectronic response are achieved due to the exceptional semiconducting properties of perovskite materials. However, most of the perovskite-based photodetectors exploited to date are centered on Pb-based perovskites, which only afford spectral response across the visible spectrum. This study demonstrates a high-performance near-IR (NIR) photodetector using a stable low-bandgap Sn-containing perovskite, (CH3NH3)0.5(NH2CHNH2)0.5Pb0.5Sn0.5I3 (MA0.5FA0.5Pb0.5Sn0.5I3), which is processed with an antioxidant additive, ascorbic acid (AA). The addition of AA effectively strengthens the stability of Sn-containing perovskite against oxygen, thereby significantly inhibiting the leakage current. Consequently, the derived photodetector shows high responsivity with a detectivity of over 1012 Jones ranging from 800 to 970 nm. Such low-cost, solution processable NIR photodetectors with high performance show promising potential for future optoelectronic applications. [ABSTRACT FROM AUTHOR]

We proposed and experimentally demonstrated a cost-efficient and easy-to-fabricate flexible thin-film nanocrystal quantum dot (NCQD) photodetector, by sandwiching a piece of NCQD-soaked tracing paper between two PEDOT:PSS electrodes. The highly conductive and transparent multilayer polymer electrodes are printed with an office inkjet printer without further patterning on commercial unmodified transparency films. The tracing paper is able to act as both the bed for NCQD attachment and the interspacing layer to prevent short-circuiting in vertical devices. Consistent increase in device performance is observed when the bending radius becomes smaller. Linear I-V characteristics are obtained, which show our device structure works as a photoconductor. [ABSTRACT FROM PUBLISHER]

We propose a compact and low-cost design for a variable wave plate using tunable form-birefringent grating structures in polydimethylsiloxane (PDMS). The described device operates through PDMS deformation via electrostatically actuated transparent electrodes. The optical and mechanical properties of tunable form-birefringent structures are modeled using birefringence, rigorous coupled-wave analysis, and simple structural mechanics theory. The device is fabricated by a form of soft nanoimprint lithography. The optical properties are characterized for different structure geometries. Operating principles were verified through testing of the completed device. The experimental results and theoretical study show that an irregular grating structure performs better than a periodic subwavelength structure. [ABSTRACT FROM AUTHOR]

We demonstrate hybrid colloidal silicon quantum dot (SiQD)-organic light-emitting diodes with electroluminescence (EL) in the visible wavelengths. The device using blue photoluminescence (PL) SiQDs as emitters shows multiple EL peaks which are attributed to carrier recombination in the core quantum confinement states, the hole-transport-layer and the surface trap states, respectively. However, the red PL SiQD device shows a single EL peak consistent with the PL peak. These findings are in agreement with the previous report that large Stokes shift were observed for oxidized blue emission SiQDs due to oxide states while red emission SiQDs show negligible PL shift after oxidation. [ABSTRACT FROM AUTHOR]

Self-assembled colloidal plasmonic silver nanoparticles monolayers were integrated into solution-processed colloidal quantum dot (QD) photodetectors. We observed plasmon enhancement of photodetector responsivity over a board spectrum range (400-600 nm), with a 1.2-1.6 fold enhancement for a 440-nm-thick QD film device and a 2.4-3.3 fold enhancement for a 100-nm-thick QD device. The enhancement behavior was wavelength dependent with higher enhancement factor at longer wavelengths. The origins of responsivity enhancement were discussed. [ABSTRACT FROM AUTHOR]

We report high-performance nanoscale photodetectors utilizing annealed nanocrystal quantum dots (QDs) within a nanoscale metal electrode gap. By optimizing the nanogap size and fabrication process, the device demonstrates a significantly better sensitivity (noise equivalent power=7.76×10-14 W/Hz1/2) and bandwidth (≥125 kHz) than previously reported nanoscale photodetectors. Furthermore, by utilizing a lateral photoconduction structure and a self-assembled layer of QDs, the detector fabrication is highly compatible with many substrates and device architectures. [ABSTRACT FROM AUTHOR]

We demonstrate high-performance photodetectors from multilayers of CdTe quantum dots (QDs). The QDs are synthesized and dispersed in aqueous solution with either 2-mercaptoethylamine (positively charged) or thioglycolic acid (negatively charged) as capping stabilizers. By electrostatic attraction, the charged QDs are self-assembled layer by layer on an indium tin oxide substrate modified with (3-aminopropyl)triethoxysilane. This process allows control of active layer thickness by self-assembly, and can in principle be applied to a wide range of substrates. The photodetector exhibits high responsivity (0.18 A/W) under 0.1 V bias due to extremely short capping ligands of QDs, which have high internal quantum efficiency, and the densely packed multilayer structure. [ABSTRACT FROM AUTHOR]

We present an optical microfluidic mixing approach via thermally induced convective flow sustained by localized surface plasmon (LSP) energy. The phonon energy associated with the nonradiative damping of LSP from a Au nanoparticle (NP) array under optical excitation creates a thermal gradient which initiates a convective fluidic flow. Experimental evidence and modeling results both show that LSP from the Au NPs is crucial in establishing a temperature gradient with sufficient magnitude to induce the convective flow with low input optical intensity. [ABSTRACT FROM AUTHOR]

The high transmission speed of optical signals and their application in optical computation have created a growing demand for photon‐programmed memory devices. Rather than using electrical pulses to store data in one of two states, the photomemory (PM) devices exploit the optical stimulation to store the light information. In this work, the application of a nonvolatile rewritable PM array using the photochromic inorganic perovskite CsPbIBr2 grown by a vapor‐deposition process is demonstrated. Reversible phase transitions between orthorhombic (δ) and cubic (α) phases are achieved in CsPbIBr2 films through laser‐induced heat and moisture exposure. The PM pixels in an optically absorbing perovskite phase exhibit ≈50‐fold photoresponsivity as large as those in a transparent‐colored non‐perovskite phase. Storing optical data are achieved by heating pixels through a near‐infrared laser, while moisture exposure is used to erase the stored information. The nonvolatile PM array exhibits great write‐read‐erase cycle endurance and data retention capability without obvious performance degradation after storage in air for one week. This work demonstrates the promising application of vapor‐deposited inorganic perovskite for optical information storage and the unique potential of them for use in optical switches, tunable metasurfaces, and many other applications. [ABSTRACT FROM AUTHOR]

Recently, metal halide perovskites have been widely used and considered as an alternative to oxides or chalcogenides in memory devices due to the high on–off ratio and low operating voltage, as well as ease of fabrication. However, most of the perovskite thin films in previous studies have been deposited by lab‐scale solution‐processed methods. They are not directly applicable to larger‐scale and volume manufacturing, hindering the commercialization of this technology. Herein, the performance of memory devices based on vacuum‐deposited inorganic perovskite (VDIP) is investigated for the first time. The optimized VDIP‐based memory devices exhibit reliable and reproducible resistive switching (RS) behaviors with a high on–off ratio (>100), low set/reset voltage (<2 V), and reversible RS by fast pulse‐voltage operations. Furthermore, the devices show an excellent ambient stability, and no obvious degradation is observed after storage in an ambient condition for 30 days. The memory devices on flexible substrates also show a good mechanical flexibility under a bending stress. In addition, a VDIP memory array with 16 × 16 memory cells on a large‐scale substrate is demonstrated, suggesting the strong potential of the VDIP for high‐density, large‐area storage devices. [ABSTRACT FROM AUTHOR]

Conventional approaches to flexible optoelectronic devices typically require depositing the active materials on external substrates. This is mostly due to the weak bonding between individual molecules or nanocrystals in the active materials, which prevents sustaining a freestanding thin film. Herein we demonstrate an ultrathin freestanding ZnO quantum dot (QD) active layer with nanocellulose structuring, and its corresponding device fabrication method to achieve substrate-free flexible optoelectronic devices. The ultrathin ZnO QD-nanocellulose composite is obtained by hydrogel transfer printing and solvent-exchange processes to overcome the water capillary force which is detrimental to achieving freestanding thin films. We achieved an active nanocellulose paper with ~550 nm thickness, and >91% transparency in the visible wavelength range. The film retains the photoconductive and photoluminescent properties of ZnO QDs and is applied towards substrate-free Schottky photodetector applications. The device has an overall thickness of ~670 nm, which is the thinnest freestanding optoelectronic device to date, to the best of our knowledge, and functions as a self-powered visible-blind ultraviolet photodetector. This platform can be readily applied to other nano materials as well as other optoelectronic device applications. [ABSTRACT FROM AUTHOR]

The article introduces a series of reports on optical microelectromechanical systems (MEMS) and nanophotonics published within the issue.

A correction to the article "High Efficiency Photodetectors Fabricated by Electrostatic Layer-by-Layer Self-Assembly of CdTe Quantum Dots" that was published in the online issue on May 26, 2009 is presented.