Total scattering measurements at the Australian Synchrotron Powder Diffraction beamline: capabilities and limitations.

This study describes the capabilities and limitations of carrying out total scattering experiments on the Powder Diffraction (PD) beamline at the Australian Synchrotron, ANSTO. A maximum instrument momentum transfer of 19 Å-1 can be achieved if the data are collected at 21 keV. The results detail how the pair distribution function (PDF) is affected by Qmax, absorption and counting time duration at the PD beamline, and refined structural parameters exemplify how the PDF is affected by these parameters. There are considerations when performing total scattering experiments at the PD beamline, including (1) samples need to be stable during data collection, (2) highly absorbing samples with a µR > 1 always require dilution and (3) only correlation length differences >0.35 Šmay be resolved. A case study comparing the PDF atom-atom correlation lengths with EXAFS-derived radial distances of Ni and Pt nanocrystals is also presented, which shows good agreement between the two techniques. The results here can be used as a guide for researchers considering total scattering experiments at the PD beamline or similarly setup beamlines.

Specific Ion Effects at the Vapor-Formamide Interface: A Reverse Hofmeister Series in Ion Concentration Depth Profiles.

Employing neutral impact collision ion scattering spectroscopy (NICISS), we have directly measured the concentration depth profiles (CDPs) of various monovalent ions at the vapor-formamide interface. NICISS provides CDPs of individual ions by measuring the energy loss of neutral helium atoms backscattered from the solution interface. CDPs at the vapor-formamide interface of Cl-, Br-, I-, Na+, K+, and Cs+ are measured and compared to elucidate the interfacial specific ion trends. We report a reverse Hofmeister series in the presence of inorganic ions (anion and cation) at the vapor-formamide interface relative to the water-vapor interface, and the CDPs are found to be independent of the counterion for most ions studied. Thus, ions at the surface of formamide follow a "Hofmeister paradigm" where the counterion does not impact the ion series. These specific ion trends are complemented with surface tension and X-ray absorption near-edge structure (XANES) measurements on formamide electrolyte solutions.

Reduced Recombination and Capacitor-like Charge Buildup in an Organic Heterojunction.

Organic photovoltaic (OPV) efficiencies continue to rise, raising their prospects for solar energy conversion. However, researchers have long considered how to suppress the loss of free carriers by recombination-poor diffusion and significant Coulombic attraction can cause electrons and holes to encounter each other at interfaces close to where they were photogenerated. Using femtosecond transient spectroscopies, we report the nanosecond grow-in of a large transient Stark effect, caused by nanoscale electric fields of ∼487 kV/cm between photogenerated free carriers in the device active layer. We find that particular morphologies of the active layer lead to an energetic cascade for charge carriers, suppressing pathways to recombination, which is ∼2000 times less than predicted by Langevin theory. This in turn leads to the buildup of electric charge in donor and acceptor domains-away from the interface-resistant to bimolecular recombination. Interestingly, this signal is only experimentally obvious in thick films due to the different scaling of electroabsorption and photoinduced absorption signals in transient absorption spectroscopy. Rather than inhibiting device performance, we show that devices up to 600 nm thick maintain efficiencies of >8% because domains can afford much higher carrier densities. These observations suggest that with particular nanoscale morphologies the bulk heterojunction can go beyond its established role in charge photogeneration and can act as a capacitor, where adjacent free charges are held away from the interface and can be protected from bimolecular recombination.

A Green Route to Conjugated Polyelectrolyte Interlayers for High-Performance Solar Cells.

Synthesis of fluorene-based conjugated polyelectrolytes was achieved via Suzuki polycondensation in water and completely open to air. The polyelectrolytes were conveniently purified by dialysis and analysis of the materials showed properties expected for fluorene-based conjugated polyelectrolytes. The materials were then employed in solar cell devices as an interlayer in conjunction with ZnO. The double interlayer led to enhanced power conversion efficiency of 10.75 % and 15.1 % for polymer and perovskite solar cells, respectively.

Dissecting a complex chemical stress: chemogenomic profiling of plant hydrolysates.

The efficient production of biofuels from cellulosic feedstocks will require the efficient fermentation of the sugars in hydrolyzed plant material. Unfortunately, plant hydrolysates also contain many compounds that inhibit microbial growth and fermentation. We used DNA-barcoded mutant libraries to identify genes that are important for hydrolysate tolerance in both Zymomonas mobilis (44 genes) and Saccharomyces cerevisiae (99 genes). Overexpression of a Z. mobilis tolerance gene of unknown function (ZMO1875) improved its specific ethanol productivity 2.4-fold in the presence of miscanthus hydrolysate. However, a mixture of 37 hydrolysate-derived inhibitors was not sufficient to explain the fitness profile of plant hydrolysate. To deconstruct the fitness profile of hydrolysate, we profiled the 37 inhibitors against a library of Z. mobilis mutants and we modeled fitness in hydrolysate as a mixture of fitness in its components. By examining outliers in this model, we identified methylglyoxal as a previously unknown component of hydrolysate. Our work provides a general strategy to dissect how microbes respond to a complex chemical stress and should enable further engineering of hydrolysate tolerance.

Effect of Side-Chain Modification on the Active Layer Morphology and Photovoltaic Performance of Liquid Crystalline Molecular Materials.

Controlling the nanoscale morphology of the photoactive layer by fine-tuning the molecular structure of semiconducting organic materials is one of the most effective ways to improve the power conversion efficiency of organic solar cells. In this contribution, we investigate the photovoltaic performance of benzodithiophene (BDT)-based p-type small molecules with three different side chains, namely alkyl-thio (BTR-TE), dialkylthienyl (BTR), and trialkylsilyl (BTR-TIPS) moieties substituted on the BDT core, when used alongside a nonfullerene acceptor. The side-chain changes on the BDT core are shown to have a profound effect on energy levels, charge generation, recombination, morphology, and photovoltaic performance of solid-state molecules. Compared with BTR and BTR-TIPS, BTR-TE-based single-junction binary blend solar cells show the best power conversion efficiency (PCE) of 13.2% due to improved morphology and charge transport with suppressed recombination. In addition, we also achieved relatively good performances for ternary blend solar cells with a PCE of 16.1% using BTR-TE as a third component. Our results show that side-chain modification has a significant effect on modulating active layer morphology, and in particular that thioether side-chain modification is an effective way to achieve optimum morphology and performance for organic photovoltaic (OPV) devices.

Morphological Requirements for Nanoscale Electric Field Buildup in a Bulk Heterojunction Solar Cell.

The morphology of organic semiconductors is critical to their function in optoelectronic devices and is particularly crucial in the donor-acceptor mixture that comprises the bulk heterojunction of organic solar cells. Here, energy landscapes can play integral roles in charge photogeneration, and recently have been shown to drive the accumulation of charge carriers away from the interface, resulting in the buildup of large nanoscale electric fields, much like a capacitor. In this work we combine morphological and spectroscopic data to outline the requirements for this interdomain charge accumulation, finding that this effect is driven by a three-phase morphology that creates an energetic cascade for charge carriers. By adjusting annealing conditions, we show that domain purity, but not size, is critical for an electro-absorption feature to grow-in. This demonstrates that the energy landscape around the interface shapes the movement of charges and that pure domains are required for charge carrier buildup that results in reduced recombination and large interdomain nanoscale electric fields.

Characterization of Miscanthus giganteus lignin isolated by ethanol organosolv process under reflux condition.

Miscanthus giganteus lignin was extracted by an organosolv process under reflux conditions (4 h) with varying concentrations of ethanol (65%, 75%, 85%, 95%) and 0.2 M hydrochloric acid as catalyst. The resulting lignin was extensively characterized by size exclusion chromatography (SEC), Fourier-transform infrared spectroscopy (FTIR), gas chromatography-mass spectrometry (GC/MS), two-dimensional nuclear magnetic resonance spectroscopy (2D-NMR), and chemical analysis (residual sugars, Klason lignin, ash). The predominant linkage units present were ß-O-4' (82-84%), resinol (6-7%), and phenylcoumaran (10-11%). The 65% ethanol solvent system gave the lowest lignin yield (14% of starting biomass) compared to 29-32% of the other systems. Increasing ethanol concentration resulted in decreasing carbohydrate content of the lignins (3.6-1.1%), a higher solubility in tetrahydrofuran (THF), a slight reduction of the molecular weight (M(w) 2.72-2.25 KDa), an increasing α-ethoxylation, and an increase in ethoxylated phenylpropenoic compounds (p-coumaric and ferulic acid), but the S/G ratio of the monolignols (0.63, GC/MS) and Klason lignin content (86-88%) were unaffected. An extraction method for these ethyl-esterified phenylpropenoids and smaller molecular weight lignin compounds was developed. The effect of reaction time (2, 4, and 8 h) was investigated for the 95% ethanol solvent system. Besides increased lignin yield (13-43%), a slight increase in M(w) (2.21-2.38 kDa) and S/G ratio (0.53-0.68, GC-MS) was observed. Consecutive extractions suggested that these changes were not from lignin modifications (e.g., condensations) but rather from extraction of lignin of different composition. The results were compared to similar solvent systems with 95% acetone and 95% dioxane.