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The development of technologies for continuous measurement of nitrogen forms in the soil is essential for optimizing the application of fertilizers in agriculture and preventing water-resource pollution. However, there is no effective commercial technology available for continuous monitoring of ammonium species in soil pore water. This work investigates an approach for real-time measurement of ammonium in soil water using near-infrared transmission spectroscopy and partial least squares regression (PLSR) for spectral analysis. The PLSR model was trained using soil pore water collected from various soils spiked with ammonium to achieve a wide concentration range. The monitoring approach was then validated through transport experiments in a soil column. The results demonstrated capabilities for real-time tracking of the temporal variation in soil ammonium concentration and potential utilization in agronomical or environmental sensing. [ABSTRACT FROM AUTHOR]

Lead halide perovskites attract much attention in recent years as a realistic solution for efficient and low‐cost solar cells. One of the interesting solar cell structures is the fully mesoporous‐carbon‐based perovskite solar cells. The mesoporous layers can be fabricated entirely by screen printing with the potential for upscaling. Herein, the two‐step deposition of perovskite in mesoporous‐carbon‐based perovskite solar cells is studied. The influence of the dipping time on the photovoltaic parameters is investigated using charge extraction and intensity‐modulated photovoltage spectroscopy (IMVS) measurements. A power conversion efficiency of 15% is observed for cells fabricated using two‐step deposition which is one of the highest reported for this solar cell structure. Stability characterizations at maximum power point (MPP) tracking show degradation with time, however a complete recovery of the devices in the dark is revealed. Analyzing the mechanism for this shows that the perovskite's unit cell shrinks during the recovery process due to internal stress relief. This interesting phenomenon opens the possibility to optimize the stability of these solar cells for commercial applications. [ABSTRACT FROM AUTHOR]

A tetra-n-butoxy zinc phthalocyanine (n-BuO)4ZnPc has been synthesized in a single step, starting from commercial precursors, and easily purified. The molecule can be solution processed to form an effective and inexpensive hole transport layer for organic and perovskite solar cells. These appealing features are suggested by the results of a series of chemical, optical, and voltammetric characterizations of the molecule, supported by the results of ab initio simulations. Preliminary measurements of (n-BuO)4ZnPc-methylammonium lead triiodide perovskite-based devices confirm such suggestion and indicate that the interface between the photoactive layer and the hole transporting layer is characterized by hole-extracting and electron-blocking properties, potentially competitive with those of other standards de facto in the field of organic hole transport materials, like the expensive Spiro-OMeTAD. [ABSTRACT FROM AUTHOR]

Abstract: The electronic properties of the heterojunction formed by chemical bath deposition of a thorium‐ and oxygen‐doped PbS nanostructured layer on GaAs substrate as a function of postgrowth thermal treatments are studied. A correlation is found between the heterojunction conductance and the duration of thermal treatment in air. In contrast to previous reports on the effect of air annealing on PbS films, where the conductance increased due to oxygen incorporation within the PbS, in this oxygen‐saturated system, the PbS properties are unaffected by exposure to oxygen. Control over the heterojunction conductance is achieved by tuning the interface oxide thickness, enabled by thermal treatment in air, resulting in the elimination of Fermi level pinning caused by interface induced gap states. The ability to control the interfacial insulator thickness post film‐growth is a unique feature of this system. [ABSTRACT FROM AUTHOR]

ABSTRACT: Donor–acceptor (D–A) conjugated polymers bearing non‐covalent configurationally locked backbones have a high potential to be good photovoltaic materials. Since 1,4‐dithienyl‐2,5‐dialkoxybenzene (TBT) is a typical moiety possessing intramolecular S…O interactions and thus a restricted planar configuration, it was used in this work as an electron‐donating unit to combine with the following electron‐accepting units: 3‐fluorothieno[3,4‐b]thiophene (TFT), thieno‐[3,4‐c]pyrrole‐4,6‐dione (TPD), and diketopyrrolopyrrole (DPP) for the construction of such D–A conjugated polymers. Therefore, the so‐designed three polymers, PTBTTFT, PTBTTPD, and PTBTDPP, were synthesized and investigated on their basic optoelectronic properties in detail. Moreover, using [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) as acceptor material, polymer solar cells (PSCs) were fabricated for studying photovoltaic performances of these polymers. It was found that the optimized PTBTTPD cell gave the best performance with a power conversion efficiency (PCE) of 4.49%, while that of PTBTTFT displayed the poorest one (PCE = 1.96%). The good photovoltaic behaviors of PTBTTPD come from its lowest‐lying energy level of the highest occupied molecular orbital (HOMO) among the three polymers, and good hole mobility and favorable morphology for its PC71BM‐blended film. Although PTBTDPP displayed the widest absorption spectrum, the largest hole mobility, and regular chain packing structure when blended with PC71BM, its unmatched HOMO energy level and disfavored blend film morphology finally limited its solar cell performance to a moderate level (PCE: 3.91%). © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 689–698 [ABSTRACT FROM AUTHOR]

The photochemical stability of encapsulated films of mixed halide perovskites with a range of MAPb(I1− xBr x)3 (MA=methylammonium) compositions (solid solutions) was investigated under accelerated stressing using concentrated sunlight. The relevance of accelerated testing to standard operational conditions of solar cells was confirmed by comparison to degradation experiments under outdoor sunlight exposure. We found that MAPbBr3 films exhibited no degradation, while MAPbI3 and mixed halide MAPb(I1− xBr x)3 films decomposed yielding crystallization of inorganic PbI2 accompanied by degradation of the perovskite solar light absorption, with faster absorption degradation in mixed halide films. The crystal coherence length was found to correlate with the stability of the films. We postulate that the introduction of Br into the mixed halide solid solution stressed its structure and induced more structural defects and/or grain boundaries compared to pure halide perovskites, which might be responsible for the accelerated degradation. Hence, the cause for accelerated degradation may be the increased defect density rather than the chemical composition of the perovskite materials. [ABSTRACT FROM AUTHOR]

Photosynthesis is used by plants, algae and bacteria to convert solar energy into stable chemical energy. The initial stages of this process-where light is absorbed and energy and electrons are transferred-are mediated by reaction centres composed of chlorophyll and carotenoid complexes. It has been previously shown that single small molecules can be used as functional components in electric and optoelectronic circuits, but it has proved difficult to control and probe individual molecules for photovoltaic and photoelectrochemical applications. Here, we show that the photocurrent generated by a single photosynthetic protein-photosystem I-can be measured using a scanning near-field optical microscope set-up. One side of the protein is anchored to a gold surface that acts as an electrode, and the other is contacted by a gold-covered glass tip. The tip functions as both counter electrode and light source. A photocurrent of ?10 pA is recorded from the covalently bound single-protein junctions, which is in agreement with the internal electron transfer times of photosystem I. [ABSTRACT FROM AUTHOR]

Carotenoids (Car) act as "wires" that discharge unwanted electrons in the reaction center of higher plants. One step in this "side-path" electron conduction is thought to be mediated by Car oxidation. We have carried out direct measurements of the conductance of single-Car molecules under potential control in a membrane-mimicking environment, and we found that when Car are oxidized conductance is enhanced and the electronic decay constant (β) is decreased. However, the neutral molecule may already be conductive enough to account for observed electron transfer rates. [ABSTRACT FROM AUTHOR]

Improved absorption is needed for thin-film organic solar cells to increase charge generation and/or reduce the thickness of the organic active film. Absorption enhancement by light trapping in a photonic crystal (PC) can be used to enhance the absorption in a patterned photo-active polymer blend. We used the finite difference time domain (FDTD) method to study the effect of combining the PC with different vertical layer configurations, including a hole transporting flash layer, used for charge separation and for increasing the photo-voltage, and a reflective metallic back electrode. The model was applied to P3HT:PCBM and pBBTDPP2:PCBM blends as the active materials, to examine the effect of different absorption spectra on the results. We found that the combination of PC and a reflector electrode is synergistic for enhancing the absorption in such devices, while the effect of the flash layer is minor. The combination of lateral and vertical reflections by the PC and the reflector, respectively, results in significant light scattering and enhancement of the absorption in a wide range of wavelengths. An increase of 30% to 60% (depending on the active material) in the number of absorbed photons of the solar spectrum was calculated compared to un-patterned blends. Broadband absorption enhancement in a realistic cell configuration is expressed as absorption enhancement of solar photons in a wide range of PC periods, i.e., the presence of periodic structuring is more important for absorption enhancement of the solar irradiation than the dimension of its period. [ABSTRACT FROM AUTHOR]

Electronic mapping of cross sections of a polycrystalline device, the n-CdS/p-CdTe solar cell, show that the photovoltaic and metallurgical junctions coincide to within experimental resolution (50 nm), which rules out both type conversion of CdS and buried homojunctions. Compositional analysis of the CdS supports this. Mapping was done using scanning capacitance, complemented by scanning Kelvin probe microscopy. Our results explain why a high-resistance transparent conducting oxide layer is needed as contact to the CdS for successful device operation. They define limits on inputs for modeling performance of these devices. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We use scanning probe microscopy-based methods for direct characterization of a single grain boundary and a single grain surface in solar cell-quality CdTe, deposited by closed-space vapor transport. We find that scanning capacitance microscopy can serve to study polycrystalline electronic materials, notwithstanding the strong topographical variations. In this way, we find a barrier for hole transport across grain boundaries, a conclusion supported by the much more topography-sensitive scanning kelvin probe microscopy, with some variation in barrier height between different boundaries. [ABSTRACT FROM AUTHOR]

Degradation rates in perovskite solar cells (PSCs) were previously shown to be bias dependent; however, little is known about the mechanisms and driving factors that account for such degradation. Herein, stability studies under concentrated sunlight are demonstrated as a powerful experimental methodology to investigate bias‐dependent PSC degradation mechanisms. Stress testing of encapsulated PSCs' stability shows that light intensity is more significant than the illumination dose for PSC degradation under short‐circuit (SC) conditions, whereas the dose is the determining factor under open‐circuit (OC) stressing. This indicates that different degradation mechanisms are dominant under different bias conditions. It is postulated that degradation at SC biasing is dominated by ion migration, facilitated by photogenerated defects. Degradation at OC biasing can be explained by photogenerated radicals acting as nonradiative recombination centers (charge traps), which are created via reactions with accumulated charge carriers. Trap formation upon OC biasing is in accordance with degradation of photoluminescence and OC voltage (VOC) observed under this stress. A combination of multiple mechanisms, all with reduced driving forces compared with OC /SC biasing, explains degradation at maximum power point biasing. Understanding the bias effect on PSC stability can elucidate the underlying degradation mechanisms and lead to routes to reduce them. [ABSTRACT FROM AUTHOR]

H2O2 is a sacrificial reductant that is often used as a hole scavenger to gain insight into photoanode properties. Here we show a distinct mechanism of H2O2 photo-oxidation on haematite (α-Fe2O3) photoanodes. We found that the photocurrent voltammograms display non-monotonous behaviour upon varying the H2O2 concentration, which is not in accord with a linear surface reaction mechanism that involves a single reaction site as in Eley-Rideal reactions. We postulate a nonlinear kinetic mechanism that involves concerted interaction between adions induced by H2O2 deprotonation in the alkaline solution with adjacent intermediate species of the water photo-oxidation reaction, thereby involving two reaction sites as in Langmuir-Hinshelwood reactions. The devised kinetic model reproduces our main observations and predicts coexistence of two surface reaction paths (bi-stability) in a certain range of potentials and H2O2 concentrations. This prediction is confirmed experimentally by observing a hysteresis loop in the photocurrent voltammogram measured in the predicted coexistence range. Understanding fundamental processes that occur using solar-to-fuel conversion materials is crucial for constructing effective renewable energy collection. Here, authors find the hydrogen peroxide light-driven hole-scavenging mechanism over haematite to proceed with two active sites rather than one [ABSTRACT FROM AUTHOR]

Post‐deposition processing of organolead halide films, by exposure to alkyl amine vapor and composition transformation, is an attractive approach for the formation of high‐quality and large‐scale perovskite films of desired compositions. However, the generalization of such composition transformation requires further understanding of the mechanism of the process. In this work MAPbI3, BA2PbI4, and OA2PbI4 (MA+: CH3NH3+, BA+: C4H9NH3+, and OA+: C8H17NH3+) are chosen as typical representatives of 3D and 2D organolead halide perovskites, and their transformations are systematically studied. It is found that the transformation can universally take place among these organolead iodides, irrespective of either from 3D to 2D or from 2D to 3D form. The important intermediates in these transformations have been identified to be alkyl amine‐bound lead iodides of well‐defined chemical composition and crystalline nature in solid state. Furthermore, such intermediates have unexpected good solubility in alcohol, enabling the use of ethanol as a processing solvent for fabrication of high‐quality perovskite films and solar cells. The so‐prepared perovskite solar cells display an average power conversion efficiency of 14.08% with the best one of 15.79%. These findings not only gain new insights on perovskite transformation mechanism, but also lead to developing an environmentally benign processing method for perovskite films and devices. Composition transformation is found mutually taking place among 2D and 3D organolead halide perovskites through alkyl amine‐bound intermediates with well‐defined compositions and unexpected good solubility in alcohol. This enables the use of ethanol as main processing solvent to prepare high quality perovskite films and solar cell devices. [ABSTRACT FROM AUTHOR]

Functionalized and fully characterized graphene-based lubricant additives are potential 2D materials for energy-efficient tribological applications in machine elements, especially at macroscopic contacts. Two different reduced graphene oxide (rGO) derivatives, terminated by hydroxyl and epoxy-hydroxyl groups, were prepared and blended with two different molecular weights of polyethylene glycol (PEG) for tribological investigation. Epoxy-hydroxyl-terminated rGO dispersed in PEG showed significantly smaller values of the friction coefficient. In this condition, PEG chains intercalate between the functionalized graphene sheets, and shear can take place between the PEG and rGO sheets. However, the friction coefficient was unaffected when hydroxyl-terminated rGO was coupled with PEG. This can be explained by the strong coupling between graphene sheets through hydroxyl units, causing the interaction of PEG with the rGO to be non- effective for lubrication. On the other hand, antiwear properties of hydroxyl-terminated rGO were significantly enhanced compared to epoxy-hydroxyl functionalized rGO due to the integrity of graphene sheet clusters. [ABSTRACT FROM AUTHOR]