Perovskite Quantum Dot-Reduced Graphene Oxide Superstructure for Efficient Photodetection.

High-performance photodetectors require efficient photogeneration and charge transport. Perovskite quantum dots (PQDs) have received enormous interest for applications in optoelectronics due to their high photogeneration efficiency. However, they offer meager carrier transport. Reduced graphene oxide (RGO) exhibits inferior photoresponse compared to materials such as quantum dots. An effective synthesis protocol to grow PQDs from the RGO lattice may facilitate direct charge transfers from PQDs to RGO, which could not be accomplished by mixing individual PQDs with RGO or making a bilayer. At ambient condition, the photodetector fabricated with the PQD-RGO superstructure showed high responsivity of 1.07 × 103 A/W, detectivity of 1 × 1013 Jones as well as sharp switching in the visible wavelength. After 3 months in an unencapsulated sample, the photocurrent was decreased ∼10% of its initial value while preserving speed and cycle stability at ambient condition.

Synthesis of air-stable two-dimensional nanoplatelets of Ruddlesden-Popper organic-inorganic hybrid perovskites.

We present a simple and facile method to synthesize nanoplatelets of 2D Ruddlesden-Popper (RP) perovskites of the type (CH3(CH2)3NH3)2(CH3NH3)Pb2I7 where n = 2. The 2D RP nanoplatelets are synthesized from bulk 2D RP crystals via a reflux pre-treatment mediated-ultrasonication method. The as-synthesized 2D RP nanoplatelets are highly air-stable even after two months of storage under an ambient atmosphere. The bulk 2D RP crystals and 2D RP nanoplatelets are characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Kelvin probe force microscopy, UV-visible spectroscopy, X-ray photoelectron spectroscopy (XPS), photoluminescence, time correlated single photon counting measurement, etc. A significant blue shift in the ultraviolet-visible absorption spectrum, high photoluminescence in the UV region, and the modified work function of the nanoplatelets indicate a strong quantum confinement effect. The quantum confinement in the nanoplatelets is further confirmed using XPS. A photodetector fabricated using these 2D RP nanoplatelets exhibits a high photodetectivity of 3.09 × 1010 Jones.

Ultrasensitive and ultrathin phototransistors and photonic synapses using perovskite quantum dots grown from graphene lattice.

Organic-inorganic halide perovskite quantum dots (PQDs) constitute an attractive class of materials for many optoelectronic applications. However, their charge transport properties are inferior to materials like graphene. On the other hand, the charge generation efficiency of graphene is too low to be used in many optoelectronic applications. Here, we demonstrate the development of ultrathin phototransistors and photonic synapses using a graphene-PQD (G-PQD) superstructure prepared by growing PQDs directly from a graphene lattice. We show that the G-PQDs superstructure synchronizes efficient charge generation and transport on a single platform. G-PQD phototransistors exhibit excellent responsivity of 1.4 × 108 AW-1 and specific detectivity of 4.72 × 1015 Jones at 430 nm. Moreover, the light-assisted memory effect of these superstructures enables photonic synaptic behavior, where neuromorphic computing is demonstrated by facial recognition with the assistance of machine learning. We anticipate that the G-PQD superstructures will bolster new directions in the development of highly efficient optoelectronic devices.

Ligand assisted swelling-deswelling microencapsulation (LASDM) for stable, color tunable perovskite-polymer composites.

Metal halide perovskite nanocrystals (PNCs), with excellent electronic and optical properties, are promising for a variety of optoelectronic and photonic applications. However, the instability issue still impedes their practical applications. Here a ligand-assisted swelling-deswelling microencapsulation (LASDM) strategy is proposed and evaluated for improving the stability and photoluminescence (PL) performance of PNCs. With ligand assistance, well dispersed and intimately passivated PNCs in polymer matrices are obtained. Compared with the previously reported swelling-deswelling microencapsulation (SDM) strategy, the proposed method can provide better nanocrystal size control and surface coordination. Thus, full-color perovskite-polymer composites (PPCs) with unprecedented environmental stability can be achieved and concentration quenching can be avoided in polymer matrices. The excellent color purity, color tunability, optical density variability and environmental stability make PPCs highly promising for a range of PL applications, such as tailored lighting and transparent projection displays. Moreover, the simple, low cost, scalable process and the compatibility of this method with a group of polymer matrices should pave the way for PPCs to meet the requirements for practical use.

In situ synthesis and macroscale alignment of CsPbBr3 perovskite nanorods in a polymer matrix.

We report an in situ catalyst-free strategy to synthesize inorganic CsPbBr3 perovskite nanorods in a polymer matrix (NRs-PM) with good dimensional control, outstanding optical properties and ultrahigh environmental stability. Polarization photoluminescence (PL) imaging with high spatial resolution was carried out for the first time on single nanorod (NR) and shows a relatively high local polarization ratio (∼0.4) consistent with theoretical predictions based on a dielectric contrast model. We further demonstrate that macroscale alignment of the CsPbBr3 nanorods can be achieved through mechanically stretching the NRs-PM films at elevated temperature, without deteriorating the optical quality of the NRs. A polarization ratio of 0.23 is observed for these aligned NRs-PM films, suggesting their potential as polarized down-converters to increase the light efficiency in liquid crystal display (LCD) backlights.

Ultrastable, Highly Luminescent Organic-Inorganic Perovskite-Polymer Composite Films.

A simple yet general swelling-deswelling microencapsulation strategy has been developed to achieve well dispersed and intimately passivated crystalline organic-inorganic perovskites nanoparticles within polymer matrixes and results in a series of highly luminescent CH3 NH3 PbBr3 (MAPbBr3 )-polymer composite films with unprecedented water and thermal stabilities and superior color purity.

Factors affecting perceived quality of life of older persons with self-reported visual disability.

PURPOSE: The purpose of this paper was to determine the extent to which factors thought to be related to quality of life (QoL) among older persons with a visual disability impact on their perceived QoL (PQol). METHOD: Analysis was conducted on responses from the second wave of a large population-based longitudinal study of those aged 57-72 years (i.e., HWR Study). The sample was split between those who identified as having difficulty seeing newsprint (n = 265) and those who did not (n = 1987). The groups were compared on 11 variables thought to affect QoL plus their response to a single-item measure of PQoL. Variables found to differ across the groups were entered into a standard multiple regression to determine the extent to which they predicted PQoL among those who had difficulty seeing. RESULTS AND CONCLUSIONS: Significant differences were found between the groups on PQoL and seven of the other variables assessed. Of those, three were found to make a significant and unique contribution to the prediction of PQoL. These were satisfaction with life, ability to get around, and number of diagnosed health conditions reported in that order. Together, they accounted for 64% of the observed variance in PQoL.