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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]

The critical challenge for the commercialization of perovskite solar cells (PSCs) is their operational stability. PSCs’ outdoor operation exposes the cells to a combination of stress factors that are difficult to reproduce by indoor testing due to diurnal and seasonal variations. This highlights the need for outdoor testing under operational conditions. The effect of climate conditions on outdoor operational lifetime/ degradation of n‐i‐p PSCs is systematically studied herein. Their lifetime indicators are determined in different seasons, and correlated with the outdoor irradiance and temperatures measured simultaneously. Based on this outdoor measurement analysis and indoor light cycling stability tests, it is suggested that ambient temperatures induce a more significant effect than the irradiance on the PSC's lifetime/ degradation. The study also suggests different roles played by the temperatures during the diurnal light versus dark periods: the day/ light time maximum temperatures have a more significant effect on the long‐term degradation. In contrast, minimum temperatures during the night/ dark cycles significantly affected the diurnal reversible degradation and the initial fast degradation. The results show that the commonly used lifetime indicators T80 and T50 are climate‐dependent, and their use for comparative purposes is valid only if measured in similar climatic conditions. [ABSTRACT FROM AUTHOR]

We have studied the degradation of the photoluminescence (PL) of a phase-separated film of a polyfluorene blend, F8BT/PFO, on the submicron length scale using near-field scanning optical microscopy, visualizing the PL of blend compositions that do not exist macroscopically in equilibrium. In the initial scans, the topography and the PL were anticorrelated, as the emission was dominated by the PFO-rich phase. This behavior changed at longer illumination times, where the emission was dominated by the F8BT-rich phase; i.e., the topography and PL were correlated. Using macroscopic investigation of the mechanisms that govern the PL, we could explain the time dependence of the PL spatial distribution: while the degradation of F8BT was driven by photobleaching, both faster absorption degradation and photobleaching processes dominate the degradation of PFO. In addition, we found that energy transfer does not protect the PFO from degradation and does not improve its resistance to oxidation. [ABSTRACT FROM AUTHOR]

The efficiency of charge transferin electrochemical devices islargely determined by the ion concentration profile near the electrodesurface, i.e., the electrical double layer (EDL). Room temperatureionic liquids (RTILs) are attractive for electrochemical applicationsdue to their high charge density as well as for their tunable anion/cationdesign, low vapor pressure, and wide electrochemical window. The EDLstructure in RTILs is profoundly different from that in traditional(dilute) electrolytes in that opposite charges tend to layer in aspatially alternating, segregated structure that decays toward thebulk region. Such charge layering becomes crucial for applicationsthat require confinement of RTILs into narrow spaces, where RTILsare interfaced with nanostructured electrodes. Layering in the EDLis frequently explained by electrostatic interactions of the ionswith the electrode, assuming that RTILs are homogeneous liquids madeof ions only. However, a growing evidence points to the presence ofneutral and charged multi-ion species in RTIL bulk and that the EDLstructure is related to this bulk heterogeneity. These relations implyrich spatiotemporal competitions between bulk phases and structures,the electrode morphology, and the EDL layering. However, a mechanisticunderstanding of how the bulk properties of RTILs affect the mesoscaleorder in EDLs, as well as charge transport/transfer in the EDL, iscurrently lacking. To advance this gap, a mean-field approach thatextends the standard Poisson–Nernst–Planck model toaccount for ion association/dissociation and bulk phases is beingsuggested. An inclusive theoretical modeling can help with an understandingof the factors and mechanisms governing EDL structure formation andpredict the effect of the EDL structure on the interfacial electrochemicalproperties. [ABSTRACT FROM AUTHOR]

Highlights: [•] Pulsed electrodeposition enables super-filling of CuSCN onto ZnO nanowires. [•] Zero-potential intervals regenerate the electrolyte near-surface ion concentration. [•] The pulse sequence controlled the deposition rate and CuSCN stoichiometry. [•] Pulsed electrodeposited p-CuSCN/n-ZnO showed excellent diode characteristics. [ABSTRACT FROM AUTHOR]

• Two novel low bandgap thiazolothiazole-based polymers were synthesized. • Optimized small-area solar cells exhibited promising efficiency of 7.5% • Solar cells maintain of 60–70% of the initial efficiency in outdoor tests. • Slot die coated modules showed encouraging efficiency of 4.2%. One of the major challenges in the field of organic photovoltaics is associated with high-throughput manufacturing of efficient and stable organic solar cells. Practical realization of technologies for production of large-area organic solar cells requires the development of novel materials with a defined combination of properties ensuring sufficient reliability and scalability of the process in addition to good efficiency and operation stability of the devices. In this work, we designed two novel polymers comprising thiazolothiazole units and investigated their performance as absorber materials for organic solar cells and modules. Optimized small-area solar cells based on P1 /[70]PCBM ([6,6]-phenyl-C 71 -butyric acid methyl ester) blends exhibited promising power conversion efficiency (PCE) of 7.5%, while larger area modules fabricated using slot die coating showed encouraging PCE of 4.2%. Additionally, the fabricated devices showed promising outdoor stability maintaining 60–70% of the initial efficiency after 20 sun days being exposed to natural sunlight at the Negev desert. The obtained results feature the designed polymer P1 as a promising absorber material for a large-scale production of organic solar cells under ambient conditions. [ABSTRACT FROM AUTHOR]

Highlights: • PbSe absorber layers were grown by the Chemical-Bath-Deposition (CBD) technique in a nano-columnar morphology on n-type (1 0 0) oriented GaAs substrate, where the nano-columns are densely packed perpendicular to the substrate. • The spectral absorption edge and photoluminescence (PL) peak of these layers were blue shifted from the bulk bandgap of 4.7 μm to the extended SWIR range around 2.2 μm, due to quantum confinement effect. • Current voltage (I-V) measurements were carried out on different circular mesa sizes (250–2000 μm in diameter). • The area dependent current–voltage measurements indicate a densely packed layer with no apparent pinholes. • On the other hand, it was found out that surface leakage currents on the mesa perimeters are the dominant mechanism of the dark current. • A photo-response to SWIR illumination was evident, confirming the feasibility of using such structures as extended SWIR photodetectors. Abstract There is an increasing demand for detectors with extended Short Wavelength Infrared (SWIR) absorption at wavelengths between 1.6 μm and 2.8 μm. Towards that end, PbSe absorber layers were grown by the Chemical-Bath-Deposition (CBD) technique in a nano-columnar morphology on n-type (1 0 0) oriented GaAs substrate, where the nano-columns are densely packed perpendicular to the substrate. The spectral absorption edge and photoluminescence (PL) peak of these layers were blue shifted from the bulk bandgap of 4.7 μm to 2.2 μm, i.e., within the extended SWIR range, due to quantum confinement effect. Current voltage (I-V) measurements were carried out in a vertical geometry of different circular mesa sizes (250–2000 μm in diameter). The area dependent current–voltage measurements indicate a densely packed layer with no apparent pinholes. On the other hand, it was found out that surface leakage currents on the mesa perimeters are the dominant mechanism of the dark current. A photo-response to SWIR illumination was evident, confirming the feasibility of using such structures as extended SWIR photodetectors upon minimizing leakage currents using surface treatments. [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: 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]

We have studied columnar PbSe thin films obtained using chemical bath deposition. The columnar microstructure resulted from an oriented attachment growth mechanism, in which nuclei precipitating from solution attached along preferred crystallographic facets to form highly oriented, size-quantized columnar grains. This is shown to be an intermediate growth mechanism between the ion-by-ion and cluster growth mechanisms. A structural zone model depicting the active growth mechanisms is presented for the first time for semiconductor thin films deposited from solution. The columnar films showed well-defined twinning relations between neighboring columns, which exhibited 2D quantum confinement, as established by photoluminescence spectroscopy. In addition, anisotropic nanoscale electrical properties were investigated using current sensing AFM, which indicated vertical conductivity, while maintaining quantum confinement. [ABSTRACT FROM AUTHOR]

The application of luminescent down shifting (LDS) layers as alternative UV filters for CH 3 NH 3 PbI 3(1-x) Cl 3x perovskite solar cell (PSC) devices is reported. A combination of photo-absorption measurements and of device decay measurements during light soaking are used to verify the stability. The application of a UV filter or LDS layer was able to significantly retard photo-induced degradation with ∼18% drop in device power conversion efficiency (PCE) observed over 30 h for non-encapsulated devices, which is compared to ∼97% for an un-filtered device, also without encapsulation. Whilst the PCE of the PSC device decreases with the application of the LDS layer, the drop is not as significant as when a commercial UV filter is used. Considering that UV filters will be essential for the commercialization of PSCs, the work provides evidence that the LDS layer can act as an alternative UV filter in PSCs and can limit the drop in PCE that can be expected from the inclusion of a UV filter, thus providing an added benefit over commercial UV filters. [ABSTRACT FROM AUTHOR]

Perovskite photovoltaics offer a highly efficient and low-cost solar energy harvesting technology. However, the presence of lead (Pb) cations in photovoltaic halide perovskite (HaPs) materials is concerning, and quantifying the environmental hazard of accidental Pb2+ leaching into the soil is crucial for assessing the sustainability of this technology. Pb2+ from inorganic salts was previously found to remain in the upper soil layers due to adsorption. However, Pb-HaPs contain additional organic and inorganic cations, and competitive cation adsorption may affect Pb2+ retention in soils. Therefore, we measured, analyzed by simulations and report the depths to which Pb2+ from HaPs penetrates into 3 types of agricultural soil. Most of the HaP-leached Pb2+ is found to be retained already in the first cm of the soil columns, and subsequent rain events do not induce Pb2+ penetration below the first few cm of soil surface. Surprisingly, organic co-cations from the dissolved HaP are found to enhance the Pb2+ adsorption capacity in clay-rich soil, compared to non-HaP-based Pb2+ sources. Our results imply that installation over soil types with improved Pb2+ adsorption, and removal of only the contaminated topsoil, are sufficient means to prevent ground water contamination by HaP-leached Pb2+. [Display omitted] • We characterized soil depth profiles of lead leached from photovoltaic perovskites. • Lead from damaged perovskite solar cells is unlikely to contaminate groundwater. • Organic co-cations in perovskites enhance the lead adsorption capacity of soil. • Perovskite-lead retained at topsoil is x100 less than the soil adsorption capacity. • Solar cell installation over soils with increased organic/clay content is preferred. [ABSTRACT FROM AUTHOR]

Abstract: Photovoltaic devices usually exploit mid-range band-gap semiconductors which absorb in the visible range of the solar spectrum. However, much energy is lost in the IR and near-IR range. We combined the advantages of small band-gap, bulk-like PbS deposited by facile, cheap and direct chemical bath deposition (CBD), with the good electronic properties of ZnO and the large surface area of nanowires, towards low cost photovoltaic devices utilizing IR and near-IR light. Surprisingly, CBD of PbS on ZnO, and particularly on ZnO nanowires, was not studied hitherto. Therefore, the mechanism of PbS growth by chemical bath deposition on ZnO nanowires was studied in details. A visible proof is shown for a growth mechanism starting from amorphous Pb(OH)2 layer, that evolved into the ‘ion-by-ion’ growth mechanism. The growth mechanism and the resulting morphology at low temperatures were controlled by the thiourea concentration. The grain size affected the magnitude of the band-gap and was controlled by the deposition temperatures. Deposition above 40°C resulted in bulk-like PbS with an optical band-gap of 0.4eV. Methods were demonstrated for achieving complete PbS coverage of the complex ZnO NW architecture, a crucial requirement in optoelectronic devices to prevent shorts. Measurements of photocurrents under white and near-IR (784nm) illumination showed that despite a 200meV barrier for electron transfer at the PbS/ZnO interface, extraction of photo-electrons from PbS to the ZnO was feasible. The ability to harvest electrons from a narrow band-gap semiconductor deposited on a large surface-area electrode can advance the field towards high efficiency, low cost IR and near-IR sensors and third generation solar cells. [Copyright &y& Elsevier]

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]

Abstract: Local electrical transport measurements with scanning probe microscopy on polycrystalline (PX) p-CuInSe2 and p-Cu(In,Ga)Se2 films show that the photovoltaic and dark currents for bias voltages smaller than 1V flow mainly through grain boundaries (GBs), indicating inversion at the GBs. Photocurrent for higher bias flows mainly via the grains. Based on these results and our finding of ∼100meV GB band bending we deduce the potential landscape around the GBs. We suggest that high grain material quality, leading to large carrier mobilities, and electron–hole separation at the GBs, by chemical and electrical potential gradients, result in the high performance of these PX solar cells. [Copyright &y& Elsevier]

We report a cooperative study conducted between different laboratories to investigate organic solar cell degradation with respect to P3HT material properties and different solar cell architectures. Various batches of P3HT were collected from different suppliers reflecting commercial availability as well as properties variability. Among the materials properties explicitly considered were the molar mass, dispersity, regio-regularity, impurities by trace metals and intrinsic doping evaluated from radical concentrations. Each of the participating laboratories contributing test devices applied their own layer stack, i.e. their own device architecture and layout. This variation was appreciated as another parameter for evaluation. Even though a large amount of devices failed due to extrinsic degradation effects, indeed, some materials properties were found to be more important than others for obtaining long lifetimes and high stability of P3HT-based polymer solar cells. • P3HT:PCBM solar cells made from commercially available P3HTs were aged under three different ISOS protocols. • Solar cells were built by five different labs resulting in 5 different architectures. • The P3HT batches were studied for their properties like impurities, molar mass, dispersity, etc. • All P3HTs performed similar in regard to stability we concluded that commercially available P3HTs offer viable properties. • Layer stack and processor experience with P3HT used had a larger impact on stability than polymer properties. [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]