Cong Chen

Highly Efficient LiYF4:Yb3+, Er3+ Upconversion Single Crystal under Solar Cell Spectrum Excitation and Photovoltaic Application

Luminescent upconversion is a promising way to harvest near-infrared (NIR) sunlight and transforms it into visible light that can be directly absorbed by active materials of solar cells and improve their power conversion efficiency (PCE). However, it is still a great challenge to effectively improve the PCE of solar cells with the assistance of upconversion. In this work, we demonstrate the application of the transparent LiYF4:Yb(3+), Er(3+) single crystal as an independent luminescent upconverter to improve the PCE of perovskite solar cells. The LiYF4:Yb(3+), Er(3+) single crystal is prepared by an improved Bridgman method, and its internal quantum efficiency approached to 5.72% under 6.2 W cm(-2) 980 nm excitation. The power-dependent upconversion luminescence indicated that under the excitation of simulated sunlight the (4)F(9/2)-(4)I(15/2) red emission originally results from the cooperation of a 1540 nm photon and a 980 nm photon. Furthermore, when the single crystal is placed in front of the perovskite solar cells, the PCE is enhanced by 7.9% under the irradiation of simulated sunlight by 7-8 solar constants. This work implies the upconverter not only can serve as proof of principle for improving PCE of solar cells but also is helpful to practical application.

Optical gain at 1535nm in LaF3:Er,Yb nanoparticle-doped organic-inorganic hybrid material waveguide

LaF3:Er,Yb nanoparticle-doped organic-inorganic hybrid material waveguides were demonstrated using reactive ion etching technology. The absorption and photoluminescence spectra were observed on a 140μm thick film of the nanoparticle-doped hybrid material. Under excitation at 976nm, the fluorescence was obtained at 1535nm, and its full width at half maximum was about 83nm. A relative optical gain of about 5dB was measured at 1535nm in a 22-mm-long waveguide.

Solution-processable erbium–ytterbium complex for potential planar optical amplifier application

Novel erbium and erbium–ytterbium complexes based on 4-pentylbenzoate (PBa) groups and 1,10-phenanthroline (Phen) ligands have been synthesized and structurally characterized. The X-ray single crystal structure of the erbium–ytterbium complex indicates that it is a binuclear complex model with a short metal-to-metal distance (4.269 A), which facilitates the intramolecular Yb–Er energy-transfer process in the erbium–ytterbium complex. The optical properties for solid state films of the erbium–ytterbium complex prepared by spin-coating technique were studied in detail. The NIR PL spectrum of the film shows considerable room temperature emission at 1.53 µm with a large bandwidth (full width at half maximum) of 72 nm. The planar waveguide of the complex is capable of guiding 1550 nm light with low loss. The mechanism for the formation of high-quality films is also proposed according to the structural investigation. Our results show that the erbium–ytterbium complex film has promising potential for the planar optical amplifier application.

Engineered IrO2@NiO Core–Shell Nanowires for Sensitive Non-enzymatic Detection of Trace Glucose in Saliva

Hierarchical core-shell IrO2@NiO nanowires (NWs) have been designed through two simple steps, which combined electrospinning of IrO2 conductive core and chemical bath deposition growth of ultracontinuous NiO nanoflakes. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy-dispersive X-ray spectrometry mapping, and X-ray photoelectron spectroscopy were employed to characterize the morphologies and structures of the as-prepared samples, and the results were also carefully compared with that of pure NiO nanoflowers and IrO2 NWs. Electrochemical studies indicate that the as-prepared core-shell IrO2@NiO NWs exhibited excellent nonenzymatic detection ability to glucose. At 0.35 V, it offered a sensitivity of 1439.4 μA mM-1 cm-2 (one order higher than pure NiO) with a wider linear range from 0.5 μM to 2.5 mM, a low detection limit of 0.31 μM (signal-to-noise ratio = 3, and moreover, good resolution in low glucose concentration, reproducibility, and long-term performance stability. Owing to the high sensitivity and performance, application of the proposed sensor in monitoring saliva glucose was also demonstrated; the results indicated that the sensor can effectively distinguish the diabetes from the healthy people and even the varying degrees of diabetic.

Enhanced Performance and Photostability of Perovskite Solar Cells by Introduction of Fluorescent Carbon Dots

Perovskite solar cells (PSCs) with high efficiency have recently received tremendous attention, but the stability under light irradiation, namely, photostability, of PSCs still represents a major obstacle that must be overcome before their practical applications can be used. The degeneration of perovskite under ultraviolet irradiation from sunlight is a major impacting factor. To solve this problem, in this work we introduce fluorescent carbon dots (CDs), which could effectively convert ultraviolet to blue light in the mesoporous TiO2 (m-TiO2) layer of the traditional PSCs. As a result, CD-based devices exhibit an improved power conversion efficiency (PCE) of 16.4% on average compared to 14.6% for bare devices, and the light stability of CD-based devices is highly enhanced. These devices can maintain nearly 70% of the initial efficiency after 12 h of full sunlight illumination, while the bare devices maintain only 20% of the initial efficiency. This work indicates that fluorescent down conversion based on CDs is a novel and effective approach to improve the performance and photostability of PSCs.

Enhanced Performance of Perovskite Solar Cells with Zinc Chloride Additives

Perovskite solar cells (PSCs) have attracted extensive attention due to their impressive photovoltaic performance. The quality of the perovskite layer is very critical to achieve high device performance. Here, we explore the partial substitution of PbI2 by ZnCl2 in the preparation of CH3NH3PbI3 and its effects on perovskite morphology, optical properties, and photovoltaic performance. Consequently, the device with 3% ZnCl2 shows great improvement in power conversion efficiency (PCE) from 16.4 to 18.2% compared to that of the control device. Moreover, the device is more stable than the control device, with only 7% degradation after aging for 30 days. These results are attributed to the increased grain size, improved film morphology, and reduced recombination loss after the partial substitution of PbI2 by ZnCl2 in the perovskite film. This work develops a new approach for morphology control through rational additives in the perovskite film, and paves the way toward further enhancing the device performances of PSCs including PCE and stability.

Considerably enhanced perovskite solar cells via the introduction of metallic nanostructures

Currently, perovskite solar cells (PSCs) are attracting extensive interest due to their potential for overcoming the energy crisis. However, increasing the power conversion efficiency (PCE) of PSCs to realize outdoor applications is still one of the crucial issues in PSC research. In this study, metallic nanostructures including Au, Ag and Au–Ag nanoalloy with different sizes and morphology were synthesized via a chemical solution method and embedded into an electron collecting TiO2 layer in PSCs based on the physical deposition method, which allows control over the incorporation of the metallic-nanostructures. The best improvement in the PCE was obtained using the Au–Ag nanoalloy, exhibiting an efficiency of 14.8%, which increases 17.5% compared to the bare PSCs. We believe that the increased device performance originates from increased light harvesting due to the increased optical path length caused by the light scattering of the metallic nanostructures. This strategy demonstrates a novel way to enhance the performance of photovoltaic devices.

Fast polymer thermo-optic switch with silica under-cladding

A polymer/silica hybrid 2 × 2 multimode-interference Mach-Zehnder interferometer thermo-optic (TO) switch is designed and fabricated. Silica is adopted as the under-cladding to accelerate heat release for its large thermal conductivity. The fabricated switch exhibits low power consumption of 6.2 mW, low crosstalk of -28 dB, and fast speed. The rise and fall times of this hybrid switch are 103 and 91 μs, respectively. Comparing with the fabricated TO switch (174 and 191 μs) using polymer as both upper-cladding and under-cladding, response times of this hybrid one are shortened by 40.8% and 52.4%, respectively.

APTES-functionalized thin-walled porous WO3 nanotubes for highly selective sensing of NO2 in a polluted environment

High sensitivity and reliable selectivity are the main requirements for gas sensors to be applied in portable devices, especially for semiconducting metal oxide (SMO)-based gas sensors. However, SMO-based sensors suffer from insufficient selectivity, which limits their practical applications. In this work, a high-performance NO2 sensor based on a self-assembled monolayer-modified semiconducting metal oxide is presented. Controllable porous WO3 nanotubes with an ultrathin wall thickness are prepared through a new and simple method by using electrospun fibres as a sacrificial template followed by a facile soaking process, providing a large surface area and fast transport pathway for gas molecules. Through the introduction of 3-aminopropyltriethoxysilane (APTES), which acts as an electron acceptor on the surface, the as-designed sensor exhibited a highly improved response compared to that based on bare WO3 nanotubes due to the specific interaction between APTES and NO2. Importantly, the detection limit of the as-prepared sensor approaches 10 ppb, which is the lowest detection limit of all WO3-based NO2 sensors to date. In addition, it shows a very fast response and recovery time with a high response value, maintaining 80% of the initial response, even in a saturated humid environment, due to the hydrophobic group of APTES. The optimized sensor was successfully used for the real-time detection of NO2 in the daytime under different air quality conditions, even in a heavily polluted environment. These results provide a model platform to achieve a simple, inexpensive sensor design with a high recognition capability.