Improving the Efficiency and Stability of MAPbI3 Perovskite Solar Cells by Dipeptide Molecules.

Passivating the electronic defects of metal halide perovskite is regarded as an effective way to improve the power conversion efficiency (PCE) of perovskite solar cells (PVSCs). Here, a series of dipeptide molecules with abundant ─C═O, ─O─ and ─NH functional groups as defects passivators for perovskite films are employed. These dipeptide molecules are utilized to treat the surface of prototype methyl ammonium lead iodide (MAPbI3 ) films and the corresponding PVSCs exhibit enhanced photovoltaic performance and ambient stability, which can be ascribed to: 1) the ─C═O and ─O─ can interact with the undercoordinated Pb2+ ions and the ─NH groups can form hydrogen bonds with the I- ions, passivating the defects in perovskite film and reducing charge recombination in PVSCs; 2) the long alkyl chain of dipeptide molecules increases the hydrophobicity of the perovskite surface and thus enhance the stability of PVSCs. The passivated MAPbI3 -based PVSCs exhibit a champion PCE of 20.3% and retain 60% of the initial PCE after 1000 h. It is believed that the defects passivation engineering using polypeptide moleculars can be applied in other perovskite compositions for high device efficiency and stability.

Phosphorescent [3 + 2 + 1] coordinated Ir(iii) cyano complexes for achieving efficient phosphors and their application in OLED devices.

A series of neutral [3 + 2 + 1] coordinated iridium complexes bearing tridentate bis-NHC carbene chelates (2,6-bisimidazolylidene benzene), bidentate chelates (C^N ligands, e.g. derivatives of 2-phenylpridine), and monodentate ions (halides and pseudo-halides, such as Br, I, OCN and CN ions) have been systematically designed and synthesized. X-ray single crystal structure characterization revealed that the nitrogen atom in C^N ligands is located trans to the carbon atom in the benzene ring in tridentate chelates, while the coordinating carbon atom in C^N ligands is located trans to the monodentate ligands. Photophysical studies reveal that the C^N ligands play a vital role in tuning the UV absorption and emission properties, while the tridentate bis-NHC carbene chelates influence the lowest absorption band and emission energy when compared to heteroleptic Ir(ppy)2(acac) [i.e. molar absorptivities at ∼450 nm for ppy-OCN and Ir(ppy)2(acac) are 350 M-1 cm-1 and 1520 M-1 cm-1 and emission maximum peaks are at 465 nm and 515 nm respectively]. Among monodentate ligands that the complexes bear, the group containing the cyanide ligand displays higher emission energy, higher photophysical quantum yields, longer triplet lifetimes and better electrochemical and thermal stabilities than those of cyanate and bromide. Particularly, a blue organic light-emitting diode (OLED) based on dfppy-CN exhibited a maximum external quantum efficiency of 22.94% with CIE coordinates of (0.14, 0.24). Furthermore, a small efficiency roll-off of 5.7% was observed for this device at 1000 cd m-2.

Serine peptidase inhibitor Kazal type III (SPINK3) promotes BRL-3A cell proliferation by targeting the PI3K-AKT signaling pathway.

The serine protease inhibitor, Kazal type III (SPINK3), is a trypsin inhibitor associated with liver disease, which highly overexpresses in a variety of cancers. In one of our previous studies of our laboratory, Spink3 was observed to be significantly upregulated in rat liver regeneration (LR) via a gene expression profile. For the current study, rat hepatocyte BRL-3A cells were treated by gene addition/interference, and the addition of the exogenous rat recombinant protein SPINK3. It was revealed that both the overexpression of endogenous Spink3 and addition of exogenous rat recombinant SPINK3 (rrSPINK3) significantly promoted the cell proliferation of BRL-3A cells, whereas cell proliferation was inhibited when Spink3 was interfered. Furthermore, quantitative reverse transcription polymerase chain reaction and western blot results revealed that three signaling pathways, including extracellular-signal-regulated kinase 1/2 (ERK1/2), Janus kinase (JAK)-signal transducer and activator of transcription (STAT), and phosphatidylinositol-3-kinase (PI3K)-protein kinase B (AKT), as well as their related genes, were altered following endogenous Spink3 addition/interference. Also, the PI3K-AKT and SRC-p38 pathways and their related genes were modified following exogenous SPINK3 treatment. Among them, the common signaling pathway was PI3K-AKT pathway. We concluded that SPINK3 could activate the PI3K-AKT pathway by enhancing the expression of AKT1 to regulate the proliferation of BRL-3A cells. This study may contribute to shedding light on the potential mechanisms of SPINK3 that regulate the proliferation of BRL-3A cells.

Evidence of Delocalization in Charge-Transfer State Manifold for Donor:Acceptor Organic Photovoltaics.

How charge-transfer states (CTSs) assist charge separation of a Coulombically bound exciton in organic photovoltaics has been a hot topic. It is believed that the delocalization feature of a CTS plays a crucial role in the charge separation process. However, the delocalization of the "hot" and the "relaxed" CTSs is still under debate. Here, with a novel frequency dependent charge-modulated electroabsorption spectroscopy (CMEAS) technique, we elucidate clearly that both "hot" and "relaxed" CTSs are loosely bound and delocalized states. This is confirmed by comparing the CMEAS results of CTSs with those of localized polaron states. Our results reveal the role of CTS delocalization on charge separation and indicate that no substantial delocalization gradient exists in CTSs.

Probing the Energy Level Alignment and the Correlation with Open-Circuit Voltage in Solution-Processed Polymeric Bulk Heterojunction Photovoltaic Devices.

Energy level alignment at the organic donor and acceptor interface is a key to determine the photovoltaic performance in organic solar cells, but direct probing of such energy alignment is still challenging especially for solution-processed bulk heterojunction (BHJ) thin films. Here we report a systematic investigation on probing the energy level alignment with different approaches in five commonly used polymer:[6,6]-phenyl-C71-butyric acid methyl ester (PCBM) BHJ systems. We find that by tuning the weight ratio of polymer to PCBM the electronic features from both polymer and PCBM can be obtained by photoemission spectroscopy. Using this approach, we find that some of the BHJ blends simply follow vacuum level alignment, but others show strong energy level shifting as a result of Fermi level pinning. Independently, by measuring the temperature-dependent open-circuit voltage (VOC), we find that the effective energy gap (Eeff), the energy difference between the highest occupied molecular orbital of the polymer donor (EHOMO-D) and lowest unoccupied molecular orbital of the PCBM acceptor (ELUMO-A), obtained by photoemission spectroscopy in all polymer:PCBM blends has an excellent agreement with the extrapolated VOC at 0 K. Consequently, the photovoltage loss of various organic BHJ photovoltaic devices at room temperature is in a range of 0.3-0.6 V. It is believed that the demonstrated direct measurement approach of the energy level alignment in solution-processed organic BHJ will bring deeper insight into the origin of the VOC and the corresponding photovoltage loss mechanism in organic photovoltaic cells.

Decomposition of Organometal Halide Perovskite Films on Zinc Oxide Nanoparticles.

Solution processed zinc oxide (ZnO) nanoparticles (NPs) with excellent electron transport properties and a low-temperature process is a viable candidate to replace titanium dioxide (TiO2) as electron transport layer to develop high-efficiency perovskite solar cells on flexible substrates. However, the number of reported high-performance perovskite solar cells using ZnO-NPs is still limited. Here we report a detailed investigation on the chemistry and crystal growth of CH3NH3PbI3 perovskite on ZnO-NP thin films. We find that the perovskite films would severely decompose into PbI2 upon thermal annealing on the bare ZnO-NP surface. X-ray photoelectron spectroscopy (XPS) results show that the hydroxide groups on the ZnO-NP surface accelerate the decomposition of the perovskite films. To reduce the decomposition, we introduce a buffer layer in between the ZnO-NPs and perovskite layers. We find that a commonly used buffer layer with small molecule [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) can slow down but cannot completely avoid the decomposition. On the other hand, a polymeric buffer layer using poly(ethylenimine) (PEI) can effectively separate the ZnO-NPs and perovskite, which allows larger crystal formation with thermal annealing. The power conversion efficiencies of perovskite photovoltaic cells are significantly increased from 6.4% to 10.2% by replacing PC61BM with PEI as the buffer layer.

Controllable Synthesis of Bandgap-Tunable CuSx Se(1-x) Nanoplate Alloys.

Composition engineering is an important approach for modulating the physical properties of alloyed semiconductors. In this work, ternary CuS(x)Se(1-x) nanoplates over the entire composition range of 0≤x≤1 have been controllably synthesized by means of a simple aqueous solution method at low temperature (90 °C). Reaction of Cu(2+) cations with polysulfide/-selenide ((S(n)Se(m))(2-)) anions rather than independent S(n)(2-) and Se(m)(2-) anions is responsible for the low-temperature and rapid synthesis of CuS(x)Se(1-x) alloys, and leads to higher S/Se ratios in the alloys than that in reactants owing to different dissociation energies of the Se-Se and the S-S bonds. The lattice parameters 'a' and 'c' of the hexagonal CuS(x)Se(1-x) alloys decrease linearly, whereas the direct bandgaps increase quadratically along with the S content. Direct bandgaps of the alloys can be tuned over a wide range from 1.64 to 2.19 eV. Raman peaks of the S-Se stretching mode are observed, thus further confirming formation of the alloyed CuS(x)Se(1-x) phase.

High interfacial storage capability of porous NiMn2O4/C hierarchical tremella-like nanostructures as the lithium ion battery anode.

Porous hierarchical NiMn2O4/C tremella-like nanostructures are obtained through a simple solvothermal and calcination method. As the anode of lithium ion batteries (LIBs), porous NiMn2O4/C nanostructures exhibit a superior specific capacity and an excellent long-term cycling performance even at a high current density. The discharge capacity can stabilize at 2130 mA h g(-1) within 350 cycles at a current density of 1000 mA g(-1). After a long-term cycling of 1500 cycles, the capacity is still as high as 1773 mA h g(-1) at a high current density of 4000 mA g(-1), which is almost five times higher than the theoretical capacity of graphite. The porous NiMn2O4/C hierarchical nanostructure provides sufficient contact with the electrolyte and fast three-dimensional Li(+) diffusion channels, and dramatically improves the capacity of NiMn2O4/C via interfacial storage.

A recyclable carbon nanoparticle-based fluorescent probe for highly selective and sensitive detection of mercapto biomolecules.

Carbon nanoparticles (CNPs) with strong blue emission are synthesized using a microwave-assisted hydrothermal method. The fluorescence of the CNPs can be completely quenched by Hg2+ through an effective electron or energy transfer process due to the synergetic strong electrostatic interaction and metal-ligand coordination. Based on this, a system containing Hg2+-quenched CNPs (CNP-Hg2+) is designed to be a sensitive and selective turn-on fluorescent probe towards cysteine (a type of mercapto biomolecule) with a detection limit of 15 nM. The fluorescence of CNP-Hg2+ aqueous solution can be repeatedly turned on and off for over 10 times by alternative addition of cysteine and Hg2+, respectively. After 10 cycles, the fluorescence intensity could be recovered to as high as 85% of the original value of CNPs. Remarkably, the sensing process is able to be observed by the naked eye under UV irradiation. Furthermore, the sensing is specific to biothiols and the sensor is able to work in living cells.

A bipolar transporter as an efficient green fluorescent emitter and host for red phosphors in multi- and single-layer organic light-emitting diodes.

Multifunctional donor-acceptor compound 4,4'-bis(dibenzothiophene-S,S-dioxide-2-yl)triphenylamine (DSTPA) was obtained by linking a strongly electron-withdrawing core and a strongly electron-donating core with a biphenyl bridge in linear spatial alignment. DSTPA not only has suitable HOMO and LUMO levels for easily accepting both holes and electrons, it was also demonstrated to have a high fluorescence quantum yield of 0.98 and a high triplet energy level of 2.39 eV. Versatile applications of DSTPA for bipolar transport, green fluorescent emission, and sensitizing a red phosphor were systematically investigated in a series of multi- and single-layer organic light-emitting devices. In traditional multilayer devices, it shows excellent performance both in an undoped fluorescent device (used as a green emitter and achieving maximum current and power efficiencies (CE and PE) of 12.6 cd A(-1) and 9.4 Lm W(-1) , respectively) and in a red phosphorescent device (used as a host and achieving maximum CE and PE of 26.4 cd A(-1) and 26.3 Lm W(-1) , respectively). Furthermore, DSTPA was also simultaneously used as an emitter, a hole transporter, and an electron transporter in a single-layer device showing CE and PE of 5.1 cd A(-1) and 4.7 Lm W(-1) , respectively. A single-layer red phosphorescent device with efficiencies of 11.7 cd A(-1) and 12.6 Lm W(-1) was obtained by doping DSTPA with a red phosphor. The performances of all of the devices in this work are comparable to the best of their corresponding classes in the literature.

Phase conversion from hexagonal CuS(y)Se(1-y) to cubic Cu(2-x)S(y)Se(1-y): composition variation, morphology evolution, optical tuning, and solar cell applications.

In this work, we report a simple and low-temperature approach for the controllable synthesis of ternary Cu-S-Se alloys featuring tunable crystal structures, compositions, morphologies, and optical properties. Hexagonal CuS(y)Se(1-y) nanoplates and face centered cubic (fcc) Cu(2-x)S(y)Se(1-y) single-crystal-like stacked nanoplate assemblies are synthesized, and their phase conversion mechanism is well investigated. It is found that both copper content and chalcogen composition (S/Se atomic ratio) of the Cu-S-Se alloys are tunable during the phase conversion process. Formation of the unique single-crystal-like stacked nanoplate assemblies is resulted from oriented stacking coupled with the Ostwald ripening effect. Remarkably, optical tuning for continuous red shifts of both the band-gap absorption and the near-infrared localized surface plasmon resonance are achieved. Furthermore, the novel Cu-S-Se alloys are utilized for the first time as highly efficient counter electrodes (CEs) in quantum dot sensitized solar cells (QDSSCs), showing outstanding electrocatalytic activity for polysulfide electrolyte regeneration and yielding a 135% enhancement in power conversion efficiency (PCE) as compared to the noble metal Pt counter electrode.

Synthesis of In2O3-In2S3 core-shell nanorods with inverted type-I structure for photocatalytic H2 generation.

In2O3-In2S3 core-shell nanostructures were prepared via a simple hydrothermal process at low temperatures. Ultraviolet photoelectron spectroscopy (UPS) shows that the In2O3-In2S3 nanorod is an inverted type I nanostructure. The energy potential in this structure would drive both the photo-generated holes and electrons towards the shell to facilitate photocatalytic H2 generation. Such inverted type-I nanostructure is firstly used for hydrogen generation. Comparing with reported indium-based photocatalysts upon UV-Vis illumination, the core-shell In2O3-In2S3 nanostructure obtained here exhibits a good H2 evolution rate of 61.4 µmol h(-1) g(-1).

Thermal evaporation-induced anhydrous synthesis of Fe3O4-graphene composite with enhanced rate performance and cyclic stability for lithium ion batteries.

We present a high-yield and low cost thermal evaporation-induced anhydrous strategy to prepare hybrid materials of Fe3O4 nanoparticles and graphene as an advanced anode for high-performance lithium ion batteries. The ~10-20 nm Fe3O4 nanoparticles are densely anchored on conducting graphene sheets and act as spacers to keep the adjacent sheets separated. The Fe3O4-graphene composite displays a superior battery performance with high retained capacity of 868 mA h g(-1) up to 100 cycles at a current density of 200 mA g(-1), and 539 mA h g(-1) up to 200 cycles when cycling at 1000 mA g(-1), high Coulombic efficiency (above 99% after 200 cycles), good rate capability, and excellent cyclic stability. The simple approach offers a promising route to prepare anode materials for practical fabrication of lithium ion batteries.

The effects of oxygen on controlling the number of carbon layers in the chemical vapor deposition of graphene on a nickel substrate.

While oxygen is typically considered undesirable during the chemical vapor deposition (CVD) of graphene on metal substrates, we demonstrate that suitable amounts of oxygen in the CVD system can in fact improve the uniformity and thickness control of the graphene film. The role of oxygen on the CVD of graphene on a nickel substrate using a propylene precursor was investigated with various surface analytical techniques. It was found that the number of carbon layers in the deposited graphene sample decreases as the concentration of oxygen increases. In particular, single-layer graphene can be easily obtained with an oxygen/propylene ratio of 1/9. In the presence of oxygen, a thin layer of nickel oxide will form on the substrate. The oxide layer decreases the concentration of carbon atoms dissolved in the nickel substrate and results in graphene samples with a decreasing number of carbon layers.

A versatile triphenylamine/fluoranthene-based derivative as a nondoped green-emitting, hole-transporting interlayer for electroluminescent devices.

A new triphenylamine-bridged fluoranthene derivative, 4-(7,10-diphenylfluoranthen-8-yl)-N-[4-(7,10-diphenylfluoranthen-8-yl)phenyl]-N-phenylaniline (BDPFPA), with a high glass transition temperature of 220 °C has been synthesized and characterized. BDPFPA is a highly fluorescent and versatile material that can be used as a nondoped green emitter and as a hole transporter. BDPFPA was used in a standard trilayer device as the emitting layer, which showed a low turn-on voltage (<3 V) and a high efficiency of 11.6 cd A(-1). The device also shows little efficiency roll-off at high brightness. For example, the efficiency can still be maintained at 11.4 cd A(-1) (5.4 lm W(-1)) at a brightness of 10,000 cd m(-2). These results are among the best reported for nondoped fluorescent green organic light-emitting diodes. A simple bilayer device, in which BDPFPA serves as a hole-transporting layer, has a maximum power efficiency of 3.3 lm W(-1) and the performance is nearly 40 % higher than that of an N,N'-bis(1-naphthyl)-N,N'- diphenyl-1,1'-biphenyl-4,4'-diamine (NPB)-based standard device.

Highly active and enhanced photocatalytic silicon nanowire arrays.

Nanoporous and nonporous three-dimensional silicon nanowire arrays (SiNWAs) prepared with metal-assisted chemical etching method were investigated as photocatalysts in dye photodegradation systematically. In comparison with nonporous SiNWAs, nanoporous SiNWAs have higher surface area, larger pore volume, stronger light absorption and better photocatalytic activity. After the HF-treatment, the photocatalytic activity of all kinds of SiNWAs increased significantly and the nanoporous SiNWAs showed excellent stability. The photocatalytic activity of different types of SiNWAs with hydrogen surface termination can be recovered by HF treatment. This study also reveal that the hydrogen terminated surfaces on silicon nanowires (SiNWs) enhance the performance of SiNWAs by increasing their photocatalytic activity.

[Studies on the chemical constituents of Lithocarpus polystachyus].

OBJECTIVE: To study the chemical constituents from Lithocarpus polystachyus. METHODS: Compounds were isolated and purified with silica gel, and there structures were identified by chemical property and spectral data. RESULTS: Nine compounds were isolated as phloridzin (I), phloretin (II), dihydrochalcone-2'-beta-D-glucopyranoside (III), daucossterol (IV), beta-sitosterol (V), quercetin (VI), luteolin (VII), quercitrin (VI), oleanolic acid (IX). CONCLUSION: Compounds II, IV - IX are isolated from this plant for the first time.