Interactions between nonfullerene acceptors lead to unstable ternary organic photovoltaic cells.

For organic photovoltaic (OPV) devices to achieve consistent performance and long operational lifetimes, organic semiconductors must be processed with precise control over their purity, composition, and structure. This is particularly important for high volume solar cell manufacturing where control of materials quality has a direct impact on yield and cost. Ternary-blend OPVs containing two acceptor-donor-acceptor (A-D-A)-type nonfullerene acceptors (NFAs) and a donor have proven to be an effective strategy to improve solar spectral coverage and reduce energy losses beyond that of binary-blend OPVs. Here, we show that the purity of such a ternary is compromised during blending to form a homogeneously mixed bulk heterojunction thin film. We find that the impurities originate from end-capping C=C/C=C exchange reactions of A-D-A-type NFAs, and that their presence influences both device reproducibility and long-term reliability. The end-capping exchange results in generation of up to four impurity constituents with strong dipolar character that interfere with the photoinduced charge transfer process, leading to reduced charge generation efficiency, morphological instabilities, and an increased vulnerability to photodegradation. As a consequence, the OPV efficiency falls to less than 65% of its initial value within 265 h when exposed to up to 10 suns intensity illumination. We propose potential molecular design strategies critical to enhancing the reproducibility as well as reliability of ternary OPVs by avoiding end-capping reactions.

Ferrocene-Based Artificial Interfacial Layer for High-Performance Lithium Metal Anodes: Continuous Regulation of Li+ Diffusion Behavior.

The diversified design of hybrid artificial layers is a promising method for suppressing the Li dendrite growth and maintaining high Colombic efficiency of lithium (Li) metal anode. Previously, various kinds of organic/inorganic hybrid artificial layers were constructed on the Li metal anode and possessed a positive effect on electrochemical performance. However, the tunable synthesis of artificial layers to continuously regulate the Li diffusion behavior remains a challenge. In this work, the Li diffusion behavior could be tuned by modulating the proportion of components (LiClO4, PMMA and ferrocene (Fc)) in the hybrid artificial layer (LF layer). After optimizing the proportion of each component, the resultant artificial SEI layer exhibits a high Li+ transference number (tLi+ = 0.66) and a high Young's modulus (4.8 GPa). Based on the excellent properties of the as-constructed Fc-based artificial SEI layer, a high-performance lithium anode with no volume effect and dendrite growth is achieved. The Li||Li symmetric cells with a Fc-based artificial SEI layer yielded a stable cycle performance for 1500 h with a high current density of 10 mA cm-2. The pouch cell with LF@Li anode coupled with high-loading LiFePO4 cathode (12.8 mg cm-2) exhibits excellent cyclic stability for 250 cycles with a capacity retention of 75% at 0.5C rate.

Spontaneous Folding Growth of Graphene on h-BN.

Graphene has been the subject of much research, with structural engineering frequently used to harness its various properties. In particular, the concepts of graphene origami and kirigami have inspired the design of quasi-three-dimensional graphene structures, which possess intriguing mechanical, electronic, and optical properties. However, accurate controlling the folding process remains a big challenge. Here, we report the discovery of spontaneous folding growth of graphene on the h-BN substrate via adopting a simple chemical vapor deposition method. Folded edges are formed when two stacked graphene layers share a joint edge at a growth temperature up to 1300 °C. Using first-principles density functional theory calculations, the bilayer graphene with folded edges is demonstrated to be more stable than that with open edges. Utilizing this novel growth mode, hexagram bilayer graphene containing entirely sealed edges is eventually realized. Our findings provide a route for designing graphene devices with a new folding dimension.

Enhanced Light Utilization in Semitransparent Organic Photovoltaics Using an Optical Outcoupling Architecture.

Building-integrated photovoltaics employing transparent photovoltaic cells on window panes provide an opportunity to convert solar energy to electricity rather than generating waste heat. Semitransparent organic photovoltaic cells (ST-OPVs) that utilize a nonfullerene acceptor-based near-infrared (NIR) absorbing ternary cell combined with a thin, semitransparent, high conductivity Cu-Ag alloy electrode are demonstrated. A combination of optical outcoupling and antireflection coatings leads to enhanced visible transmission, while reflecting the NIR back into the cell where it is absorbed. This combination of coatings results in doubling of the light utilization efficiency (LUE), which is equal to the product of the power conversion efficiency (PCE) and the average photopic transparency, compared with a conventional semitransparent cell lacking these coatings. A maximum LUE = 3.56 ± 0.11% is achieved for an ST-OPV with a PCE = 8.0 ± 0.2% at 1 sun, reference AM1.5G spectrum. Moreover, neutral colored ST-OPVs are also demonstrated, with LUE = 2.56 ± 0.2%, along with Commission Internationale d'Eclairage chromaticity coordinates of CIE = (0.337, 0.349) and a color rendering index of CRI = 87.

Citric Juice-mediated Synthesis of Tellurium Nanoparticles with Antimicrobial and Anticancer Properties.

Bacterial infections and cancer are two of the most significant concerns that the current healthcare system should tackle nowadays. Green nanotechnology is presented as a feasible solution that is able to produce materials with significant anticancer and antibacterial activity, while overcoming the main limitations of traditional synthesis. In the present work, orange, lemon and lime extracts were used as both reducing and capping agents for the green synthesis of tellurium nanoparticles (TeNPs) using a microwave-assisted reaction. TeNPs showed a uniform size distribution, and rod- and cubic-shapes, and were extensively characterized in terms of morphology, structure and composition using TEM, SEM, XPS, XRD, FTIR and EDX analysis. TeNPs showed an important antibacterial activity against both Gram-negative and -positive bacteria in a range concentrations from 5 to 50 µg/mL over a 24-hour time period. Besides, nanoparticles showed anticancer effect towards human melanoma cells over 48 hours at concentrations up to 50 µg/mL. Moreover, the Te nanostructures showed no significant cytotoxic effect towards human dermal fibroblast at concentrations up to 50 µg/mL. Therefore, we present an environmentally-friendly and cost-effective synthesis of TeNPs using only fruit juices and showing enhanced and desirable biomedical properties towards both infectious diseases and cancer.

Low cost, high performance white-light fiber-optic hydrophone system with a trackable working point.

A working-point trackable fiber-optic hydrophone with high acoustic resolution is proposed and experimentally demonstrated. The sensor is based on a polydimethylsiloxane (PDMS) cavity molded at the end of a single-mode fiber, acting as a low-finesse Fabry-Perot (FP) interferometer. The working point tracking is achieved by using a low cost white-light interferometric system with a simple tunable FP filter. By real-time adjusting the optical path difference of the FP filter, the sensor working point can be kept at its highest sensitivity point. This helps address the sensor working point drift due to hydrostatic pressure, water absorption, and/or temperature changes. It is demonstrated that the sensor system has a high resolution with a minimum detectable acoustic pressure of 148 Pa and superior stability compared to a system using a tunable laser.