Recombination between Photogenerated and Electrode-Induced Charges Dominates the Fill Factor Losses in Optimized Organic Solar Cells.

Charge extraction in organic solar cells (OSCs) is commonly believed to be limited by bimolecular recombination of photogenerated charges. However, the fill factor of OSCs is usually almost entirely governed by recombination processes that scale with the first order of the light intensity. This linear loss was often interpreted to be a consequence of geminate or trap-assisted recombination.

Handwashing with soap after potential faecal contact: global, regional and country estimates.

Background: Limited data have been available on the global practice of handwashing with soap (HWWS). To better appreciate global HWWS frequency, which plays a role in disease transmission, our objectives were to: (i) quantify the presence of designated handwashing facilities; (ii) assess the association between handwashing facility presence and observed HWWS; and (iii) derive country, regional and global HWWS estimates after potential faecal contact.

Methods: First, using data from national surveys, we applied multilevel linear modelling to estimate national handwashing facility presence.

Efficiency Enhancement and Hysteresis Mitigation by Manipulation of Grain Growth Conditions in Hybrid Evaporated-Spin-coated Perovskite Solar Cells.

Perovskite solar cells have become a game changer in the field of photovoltaics by reaching power conversion efficiencies beyond 23%. To achieve even higher efficiencies, it is necessary to increase the understanding of crystallization, grain formation, and layer ripening. In this study, by a systematic variation of methylammonium iodide (MAI) concentrations, we changed the stoichiometry and thereupon the crystal growth conditions in MAPbI perovskite solar cells, prepared by a two-step hybrid evaporation-spin-coating deposition method.

Correct determination of charge transfer state energy from luminescence spectra in organic solar cells.

Generation and recombination of electrons and holes in organic solar cells occurs via charge transfer states located at the donor/acceptor interface. The energy of these charge transfer states is a crucial factor for the attainable open-circuit voltage and its correct determination is thus of utmost importance for a detailed understanding of such devices. This work reports on drastic changes of electroluminescence spectra of bulk heterojunction organic solar cells upon variation of the absorber layer thickness.

Detailed Investigation of Evaporated Perovskite Absorbers with High Crystal Quality on Different Substrates.

Dual-source vapor-phase deposition enables low-temperature fabrication of high-performance planar structure perovskite (CHNHPbI) solar cells (PSCs), applicable in tandem devices or for industrial production with high homogeneity. Herein, we report low-temperature fabrication of high-efficiency PSCs by dual-source vapor-phase deposition and significance of TiO surface modification with [6,6]-phenyl C butyric acid methyl ester (PCBM) on cell performance. Co-evaporation of PbI and CHNHI, as confirmed by X-ray diffraction and high-resolution transmission electron microscopy analyses, results in CHNHPbI layers with a well-crystallized tetragonal phase formed on both TiO and TiO/PCBM electron-transport layers (ETLs).

Towards a Sustainable Synthesis of Oxymethylene Dimethyl Ether by Homogeneous Catalysis and Uptake of Molecular Formaldehyde.

Oxymethylene dimethyl ethers (OME ; CH (-OCH -) O-CH , n=3-5) are a novel class of sustainable synthetic fuels, which are of increasing interest due to their soot-free combustion. Herein a novel anhydrous OME synthesis route is presented. Catalyzed by trimethyloxonium salts, dimethoxymethane takes up monomeric gaseous formaldehyde instantaneously and forms high purity OME at temperatures of 25-30 °C.

Development and application of an exchange model for anisotropic water diffusion in the microporous MOF aluminum fumarate.

Diffusion of water in aluminum fumarate was studied by means of pulsed field gradient (PFG) nuclear magnetic resonance (NMR). Due to water molecules exchanging between the intracrystalline anisotropic pore space and the isotropic intercrystalline void space the model of intracrystalline anisotropic diffusion fails to describe the experimental PFG NMR data at high observation times. Therefore, the two-site exchange model developed by Kärger is extended to the case of exchange between an anisotropic and an isotropic site.

Black silicon significantly enhances phosphorus diffusion gettering.

Black silicon (b-Si) is currently being adopted by several fields of technology, and its potential has already been demonstrated in various applications. We show here that the increased surface area of b-Si, which has generally been considered as a drawback e.g.

Green Synthesis of a New Al-MOF Based on the Aliphatic Linker Mesaconic Acid: Structure, Properties and In Situ Crystallisation Studies of Al-MIL-68-Mes.

A new aluminium metal-organic framework (MOF), based on the short aliphatic linker molecule mesaconic acid (H Mes; methylfumaric acid) is reported. Al-MIL-68-Mes with composition [Al(OH)(O C-C H -CO )]⋅n H O is obtained after short reaction times of 45 minutes under mild, aqueous synthesis conditions (95 °C). It exhibits a kagome-like framework structure with large hexagonal, and small trigonal channels (diameters of ≈6 and ≈2 Å, respectively) and a specific surface area of S ≈1040 m  g (V =0.

Distinguishing crystallization stages and their influence on quantum efficiency during perovskite solar cell formation in real-time.

Relating crystallization of the absorber layer in a perovskite solar cell (PSC) to the device performance is a key challenge for the process development and in-depth understanding of these types of high efficient solar cells. A novel approach that enables real-time photo-physical and electrical characterization using a graphite-based PSC is introduced in this work. In our graphite-based PSC, the device architecture of porous monolithic contact layers creates the possibility to perform photovoltaic measurements while the perovskite crystallizes within this scaffold.

Novel Low-Temperature Process for Perovskite Solar Cells with a Mesoporous TiO Scaffold.

The most efficient organic-inorganic perovskite solar cells (PSCs) contain the conventional n-i-p mesoscopic device architecture using a semiconducting TiO scaffold combined with a compact TiO blocking layer for selective electron transport. These devices achieve high power conversion efficiencies (15-22%) but mainly require high-temperature sintering (>450 °C), which is not possible for temperature-sensitive substrates. Thus far, comparably little effort has been spent on alternative low-temperature (<150 °C) routes to realize high-efficiency TiO-based PSCs; instead, other device architectures have been promoted for low-temperature processing.

Liquid-state carbon-13 hyperpolarization generated in an MRI system for fast imaging.

Hyperpolarized (HP) tracers dramatically increase the sensitivity of magnetic resonance imaging (MRI) to monitor metabolism non-invasively and in vivo. Their production, however, requires an extra polarizing device (polarizer) whose complexity, operation and cost can exceed that of an MRI system itself. Furthermore, the lifetime of HP tracers is short and some of the enhancement is lost during transfer to the application site.

Co-designing the next generation of home energy management systems with lead-users.

Home energy management systems are widely promoted as essential components of future low carbon economies. It is argued in this paper that assumptions surrounding their deployment, and the methods used to design them, emerge from discredited models of people and energy. This offers an explanation for why their field trial performance is so inconsistent.

UV Degradation and Recovery of Perovskite Solar Cells.

Although the power conversion efficiency of perovskite solar cells has increased from 3.81% to 22.1% in just 7 years, they still suffer from stability issues, as they degrade upon exposure to moisture, UV light, heat, and bias voltage.

Connecting charge transfer kinetics to device parameters of a narrow-bandgap polymer-based solar cell.

To achieve intrinsically light-weight flexible photovoltaic devices, a bulk-heterojunction-type active layer with a narrow-bandgap polymer is still considered as one of the most important candidates. Therefore, detailed information about the charge transfer efficiency from a photo-excited species on an electron-donating polymer to an electron acceptor is an important factor, given that it is among the most fundamental quantitative measures to understand the solar power conversion efficiency, in particular at the initial stage followed by primary exciton formation. To obtain accurate information in this regard, wide-range acceptor concentration-dependent transient absorption spectroscopy with femtosecond laser pulse excitation was performed using a representative narrow-bandgap polymer, commonly known as PTB7.

Electric-Field-Induced Degradation of Methylammonium Lead Iodide Perovskite Solar Cells.

Perovskite solar cells have great potential for high efficiency generation but are subject to the impact of external environmental conditions such as humidity, UV and sun light, temperature, and electric fields. The long-term stability of perovskite solar cells is an important issue for their commercialization. Various studies on the stability of perovskite solar cells are currently being performed; however, the stability related to electric fields is rarely discussed.

Ambient pressure synthesis of MIL-100(Fe) MOF from homogeneous solution using a redox pathway.

Micro- to mesoporous iron(iii) trimesate MIL-100(Fe) is a MOF of high interest for numerous applications. With regard to large-scale synthesis, e.g.

An Interesting Class of Porous Polymer--Revisiting the Structure of Mesoporous α-D-Polysaccharide Gels.

The processes involved in the transformation of non-porous, native polysaccharides to their highly porous equivalents introduce significant molecular complexity and are not yet fully understood. In this paper, we propose that distinct changes in polysaccharide local short-range ordering promotes and directs the formation of meso- and micro-pores, which are investigated here using N2 sorption, FTIR, and solid-state (13)C NMR. It is found that an increase in the overall double helical amylose content, and their local association structures, are responsible for formation of the porous polysaccharide gel phase.

Analysing the effect of crystal size and structure in highly efficient CH3NH3PbI3 perovskite solar cells by spatially resolved photo- and electroluminescence imaging.

CH3NH3PbI3 perovskite solar cells with a mesoporous TiO2 layer and spiro-MeOTAD as a hole transport layer (HTL) with three different CH3NH3I concentrations (0.032 M, 0.044 M and 0.

Efficient direct solar-to-hydrogen conversion by in situ interface transformation of a tandem structure.

Photosynthesis is nature's route to convert intermittent solar irradiation into storable energy, while its use for an industrial energy supply is impaired by low efficiency. Artificial photosynthesis provides a promising alternative for efficient robust carbon-neutral renewable energy generation. The approach of direct hydrogen generation by photoelectrochemical water splitting utilizes customized tandem absorber structures to mimic the Z-scheme of natural photosynthesis.

Impact of charge transport on current-voltage characteristics and power-conversion efficiency of organic solar cells.

This work elucidates the impact of charge transport on the photovoltaic properties of organic solar cells. Here we show that the analysis of current-voltage curves of organic solar cells under illumination with the Shockley equation results in values for ideality factor, photocurrent and parallel resistance, which lack physical meaning. Drift-diffusion simulations for a wide range of charge-carrier mobilities and illumination intensities reveal significant carrier accumulation caused by poor transport properties, which is not included in the Shockley equation.

Inkjet technology for crystalline silicon photovoltaics.

The world's ever increasing demand for energy necessitates technologies that generate electricity from inexhaustible and easily accessible energy sources. Silicon photovoltaics is a technology that can harvest the energy of sunlight. Its great characteristics have fueled research and development activities in this exciting field for many years now.

Multicycle water vapour stability of microporous breathing MOF aluminium isophthalate CAU-10-H.

The hydrothermal stability of aluminium hydroxide isophthalate MOF CAU-10-H was proven, under humid multi-cycling conditions. Detailed in situ thermogravimetric measurements and in situ powder X-ray diffraction analysis during water ad-/desorption were used. A reversible structural change during adsorption was detected and thereby exemplified the robustness of breathing-like MOFs over 700 water vapour ad/desorption cycles.