Graphene Oxide alpha Bi2O3 Composites for Visible Light Photocatalysis, Chemical Catalysis and Solar Energy Conversion

The growing challenges of environmental purification by solar photocatalysis, precious metal free catalysis and photocurrent generation in photovoltaic cells are receiving the utmost global attention. Here we demonstrate the one pot green chemical synthesis of a new stable heterostructured, eco friendly, multifunctional micro composite consisting of amp; 945; Bi2O3 micro needles intercalated with anchored graphene oxide GO micro sheets 1.0 wt for the above mentioned applications in a large economical scale. The bare amp; 945; Bi2O3 micro needles display twice as better photocatalytic activities than commercial TiO2 Degussa P25 while the GO hybridized composite exhibit 4 6 times enhanced photocatalytic activities than neat TiO2 photocatalyst in the degradation of colored aromatic organic dyes crystal violet and rhodamine 6G under visible light irradiation 300 W tungsten lamp . The highly efficient activity is associated with the strong surface adsorption ability of GO for aromatic dye molecules, the high carrier acceptability and efficient electron hole pair separation in Bi2O3 by individual adjoining GO sheets. Introduction of Ag nanoparticles 2.0 wt further enhances the photocatalytic performance of the composite over 8 folds due to a plasmon induced electron transfer process from Ag nanoparticles via GO sheets into the conduction band of Bi2O3. The new composites are also catalytically active. They catalyze the reduction of 4 nitrophenol to 4 aminophenol in presence of borohydride ions. Photoanodes assembled from GO amp; 945; Bi2O3 and Ag GO amp; 945; Bi2O3 composites display an improved photocurrent response power conversion efficiency 20 higher over those prepared without GO in dye sensitized solar cells DSSCs

Perovskite Solar Cells with Large Area CVD Graphene for Tandem Solar Cells

Perovskite solar cells with transparent contacts may be used to compensate for thermalization losses of silicon solar cells in tandem devices. This offers a way to outreach stagnating efficiencies. However, perovskite top cells in tandem structures require contact layers with high electrical conductivity and optimal transparency. We address this challenge by implementing large area graphene grown by chemical vapor deposition as a highly transparent electrode in perovskite solar cells, leading to identical charge collection efficiencies. Electrical performance of solar cells with a graphene based contact reached those of solar cells with standard gold contacts. The optical transmission by far exceeds that of reference devices and amounts to 64.3 below the perovskite band gap. Finally, we demonstrate a four terminal tandem device combining a high band gap graphene contacted perovskite top solar cell Eg 1.6 eV with an amorphous crystalline silicon bottom solar cell Eg 1.12 e

Multi timescale infrared quantum cascade laser ellipsometry

We recently introduced a versatile infrared laser ellipsometer for sub decisecond spectroscopy and 0.03 mm2 spot sized hyperspectral imaging. Here we report on the next device generation for thin film sensitive simultaneous single shot amplitude and phase measurements. The multitimescale ellipsometer achieves 10 amp; 956;s time resolution and long term stability over hours at high spectral resolution 0.2 cm amp; 8722;1 . We investigate the temporal stages from minutes to milliseconds of fatty acid thin film formation upon solvent evaporation from acetone diluted microliter droplets. Optical thickness variations, structure modifications, and molecular interactions are probed during the liquid to solid phase transition. Multi timescale ellipsometry could greatly impact fields like in situ biosensing, microfluidics, and polymer analytics, but also operando applications in membrane research, catalysis, and studies of interface processes and surface reaction

Fast IR laser mapping ellipsometry for the study of functional organic thin films

Fast infrared mapping with sub millimeter lateral resolution as well as time resolved infrared studies of kinetic processes of functional organic thin films require a new generation of infrared ellipsometers. We present a novel laboratory based infrared IR laser mapping ellipsometer, in which a laser is coupled to a variableangle rotating analyzer ellipsometer. Compared to conventional Fourier transform infrared FT IR ellipsometers, the IR laser ellipsometer provides ten to hundredfold shorter measurement times down to 80 ms per measured spot, as well as about tenfold increased lateral resolution of 120 amp; 956;m, thus enabling mapping of small sample areas with thin film sensitivity. The ellipsometer, equipped with a HeNe laser emitting at about 2949 cm amp; 8722;1, was applied for the optical characterization of inhomogeneous poly 3 hexylthiophene [P3HT] and poly N isopropylacrylamide [PNIPAAm] organic thin films used for opto electronics and bioapplications. With the constant development of tunable IR laser sources, laser based infrared ellipsometry is a promising technique for fast in depth mapping characterization of thin films and blend

Combined first principles statistical mechanics approach to sulfur structure in organic cathode hosts for polymer based lithium sulfur Li S batteries

Polymer based batteries that utilize organic electrode materials are considered viable candidates to overcome the common drawbacks of lithium sulfur Li S batteries. A promising cathode can be developed using a conductive, flexible, and free standing polymer, poly 4 thiophen 3 yl benzenethiol PTBT , as the sulfur host material. By a vulcanization process, sulfur is embedded into this polymer. Here, we present a combination of electronic structure theory and statistical mechanics to characterize the structure of the initial state of the charged cathode on an atomic level. We perform a stability analysis of differently sulfurized TBT dimers as the basic polymer unit calculated within density functional theory DFT and combine this with a statistical binding model for the binding probability distributions of the vulcanization process. From this, we deduce sulfur chain length rank distributions and calculate the average sulfur rank depending on the sulfur concentration and temperature. This multi scale approach allows us to bridge the gap between the local description of the covalent bonding process and the derivation of the macroscopic properties of the cathode. Our calculations show that the main reaction of the vulcanization process leads to high probability states of sulfur chains cross linking TBT units belonging to different polymer backbones, with a dominant rank around n 5. In contrast, the connection of adjacent TBT units of the same polymer backbone by a sulfur chain is the side reaction. These results are experimentally supported by Raman spectroscop

Unravelling the low temperature metastable state in perovskite solar cells by noise spectroscopy

The hybrid perovskite methylammonium lead iodide CH3NH3PbI3 recently revealed its potential for the manufacturing of low cost and efficient photovoltaic cells. However, many questions remain unanswered regarding the physics of the charge carrier conduction. In this respect, it is known that two structural phase transitions, occurring at temperatures near 160 and 310 K, could profoundly change the electronic properties of the photovoltaic material, but, up to now, a clear experimental evidence has not been reported. In order to shed light on this topic, the low temperature phase transition of perovskite solar cells has been thoroughly investigated by using electric noise spectroscopy. Here it is shown that the dynamics of fluctuations detect the existence of a metastable state in a crossover region between the room temperature tetragonal and the low temperature orthorhombic phases of the perovskite compound. Besides the presence of a noise peak at this transition, a saturation of the fluctuation amplitudes is observed induced by the external DC current or, equivalently, by light exposure. This noise saturation effect is independent on temperature, and may represent an important aspect to consider for a detailed explanation of the mechanisms of operation in perovskite solar cell