Closing Kok's cycle of nature's water oxidation catalysis.

The MnCaO cluster in photosystem II catalyzes water splitting through the S state cycle (i = 0-4). Molecular O is formed and the natural catalyst is reset during the final S → (S) → S transition. Only recently experimental breakthroughs have emerged for this transition but without explicit information on the S-state reconstitution, thus the progression after O release remains elusive.

Alternative Mechanism for O Formation in Natural Photosynthesis via Nucleophilic Oxo-Oxo Coupling.

O formation in photosystem II (PSII) is a vital event on Earth, but the exact mechanism remains unclear. The presently prevailing theoretical model is "radical coupling" (RC) involving a Mn(IV)-oxyl unit in an "open-cubane" MnCaO cluster, which is supported experimentally by the S state of cyanobacterial PSII featuring an additional Mn-bound oxygenic ligand. However, it was recently proposed that the major structural form of the S state of higher plants lacks this extra ligand, and that the resulting S state would feature instead a penta-coordinate dangler Mn(V)=oxo, covalently linked to a "closed-cubane" MnCaO cluster.

Water-in-salt electrolytes made saltier by Gemini ionic liquids for highly efficient Li-ion batteries.

The water-in-salt electrolytes have promoted aqueous Li-ion batteries to become one of the most promising candidates to overcome safety concerns/issues of traditional Li-ion batteries. A simple increase of Li-salt concentration in electrolytes can successfully expand the electrochemical stability window of aqueous electrolytes beyond 2 V. However, necessary stability improvements require an increase in complexity of the ternary electrolytes.

Electron-hopping across dye-sensitized mesoporous NiO surfaces.

To gain a deeper understanding of the underlying charge processes in dye sensitized photocathodes, lateral electron hopping across dye-sensitized NiO photocathodes was investigated. For dye-sensitized systems, hole hopping across photoanodes has been studied extensively in the literature but no expansive studies on electron hopping in sensitized photocathodes exist today. Therefore, an organic p-type dye (TIP) with donor-linker-acceptor design, showing high stability and electrochemical reversibility, was used to study the electron transfer dynamics (electron-hopping) between dyes with temperature dependent spectroelectrochemistry and computational simulations.

Electrostatic interactions and physisorption: mechanisms of passive cesium adsorption on Prussian blue.

The dangers posed by nuclear accidents necessitate developments in techniques for cesium removal. One such is the adsorption of cesium cations in Prussian blue (PB) materials, on which adsorption can be a substation process or pure physisorption. The underlying mechanism of the latter is not well understood, although a Langmuir isotherm is frequently used to model experimental results.

On closed-shell interactions between heavy main-group elements.

A series of di- and polymetal complexes involving closed-shell, heavy main-group atoms and ions shows a selection of special physical properties. These involve short metal-metal contacts, low entropies of formation and, most interestingly, strong Raman bands at low wavenumbers. These results together with the constitution of the coordination compounds, where the majority of electrons are assembled on the highly polarizable metal atoms and ions, experimental results have been interpreted in terms of direct, partial covalent metal-metal bonding.

On the non-existence of a square-planar pentaiodide coordination complex I(I).

The properties of two conformers of the pentaiodide ion, a V-shaped and regularly observed I ion, and a so far undetected square-planar coordination complex of II composition, have been investigated by computational methods. The latter compound is indicated by the analogy to the coordination chemistry of gold with halide ligands, as well as isoelectronic main-group compounds. Static and dynamic simulations at density-functional and semi-empirical level including effects of solvent and counter ions indicate that the square-planar II indeed represents a well-defined local minimum on the pentaiodide potential energy surface, albeit less stable than the typically observed V-shaped I.

Water-in-salt electrolytes - molecular insights to the high solubility of lithium-ion salts.

The recently established water-in-salt electrolyte (WISE) concept indicates the possible application of aqueous electrolytes in lithium-ion batteries (LiBs). The application of this type of highly concentrated electrolyte relies on a proper understanding of their thermodynamically stable solutions. Therefore, fundamental insights regarding the Li[TFSI] solubility in water are important for the rational design of reproducible and stable WISE.

Electrochemical impedance and X-ray absorption spectroscopy analyses of degradation in dye-sensitized solar cells containing cobalt tris(bipyridine) redox shuttles.

Electrochemical impedance spectroscopy (EIS) is a commonly used steady-state technique to examine the internal resistance of electron-transfer processes in solar cell devices, and the results are directly related to the photovoltaic performance. In this study, EIS was performed to study the effects of accelerated ageing, aiming for insights into the degradation mechanisms of dye-sensitized solar cells (DSSCs) containing cobalt tris(bipyridine) complexes as redox mediators. Control experiments based on aged electrolytes differing in concentrations of the redox couple components and cation co-additives were conducted to reveal the correlation of the cell degradation with external and internal properties.

Reversible Structural Isomerization of Nature's Water Oxidation Catalyst Prior to O-O Bond Formation.

Photosynthetic water oxidation is catalyzed by a manganese-calcium oxide cluster, which experiences five "S-states" during a light-driven reaction cycle. The unique "distorted chair"-like geometry of the MnCaO cluster shows structural flexibility that has been frequently proposed to involve "open" and "closed"-cubane forms from the S to S states. The isomers are interconvertible in the S and S states, while in the S state, the open-cubane structure is observed to dominate in (cyanobacteria) samples.

Sodium to cesium ions: a general ladder mechanism of ion diffusion in prussian blue analogs.

Prussian blue analogs (PBAs) form crystals with large lattice voids that are suitable for the capture, transport and storage of various interstitial ions. Recently, we introduced the concept of a ladder mechanism to describe how sodium ions inside a PBA crystal structure diffuse by climbing the frames formed by aligned cyanide groups in the host structure. The current work uses semi-empirical tight-binding density functional theory (DFTB) in a multiscale approach to investigate how differences in the size of the monovalent cation affect the qualitative and quantitative aspects of the diffusion process.

Effect of the Ancillary Ligand on the Performance of Heteroleptic Cu(I) Diimine Complexes as Dyes in Dye-Sensitized Solar Cells.

A series of heteroleptic Cu(I) diimine complexes with different ancillary ligands and 6,6'-dimethyl-2,2'-bipyridine-4,4'-dibenzoic acid (dbda) as the anchoring ligand were self-assembled on TiO surfaces and used as dyes for dye-sensitized solar cells (DSSCs). The binding to the TiO surface was studied by hard X-ray photoelectron spectroscopy for a bromine-containing complex, confirming the complex formation. The performance of all complexes was assessed and rationalized on the basis of their respective ancillary ligand.

Inkjet-Printed Electron Transport Layers for Perovskite Solar Cells.

Inkjet printing emerged as an alternative deposition method to spin coating in the field of perovskite solar cells (PSCs) with the potential of scalable, low-cost, and no-waste manufacturing. In this study, the materials TiO, SrTiO, and SnO were inkjet-printed as electron transport layers (ETLs), and the PSC performance based on these ETLs was optimized by adjusting the ink preparation methods and printing processes. For the mesoporous ETLs inkjet-printed from TiO and SrTiO nanoparticle inks, the selection of solvents for dispersing nanoparticles was found to be important and a cosolvent system is beneficial for the film formation.

Ladder Mechanisms of Ion Transport in Prussian Blue Analogues.

Prussian blue (PB) and its analogues (PBAs) are drawing attention as promising materials for sodium-ion batteries and other applications, such as desalination of water. Because of the possibilities to explore many analogous materials with engineered, defect-rich environments, computational optimization of ion-transport mechanisms that are key to the device performance could facilitate real-world applications. In this work, we have applied a multiscale approach involving quantum chemistry, self-consistent mean-field theory, and finite-element modeling to investigate ion transport in PBAs.

The dynamics of light-induced interfacial charge transfer of different dyes in dye-sensitized solar cells studied by molecular dynamics.

The charge-transport dynamics at the dye-TiO interface plays a vital role for the resulting power conversion efficiency (PCE) of dye sensitized solar cells (DSSCs). In this work, we have investigated the charge-exchange dynamics for a series of organic dyes, of different complexity, and a small model of the semiconductor substrate TiO. The dyes studied involve L1, D35 and LEG4, all well-known organic dyes commonly used in DSSCs.

Influence of TiO surface defects on the adsorption of N719 dye molecules.

Surface defects influence the dye adsorption on TiO used as a substrate in dye-sensitized solar cells (DSSCs). In this study, we have used different Ar sputtering doses to create a controlled density of defects on a TiO surface exposed to different pre-heating temperatures in order to analyse the influence of defects on the N719 dye adsorption. TiO was pre-treated using two different treatments.

Implicit Tandem Organic-Inorganic Hybrid Perovskite Solar Cells Based on Internal Dye Sensitization: Robotized Screening, Synthesis, Device Implementation, and Theoretical Insights.

Low-dimensional hybrid perovskite materials offer significantly improved stability as well as an extensive compositional space to explore. However, they suffer from poor photovoltaic performance as compared to the 3D perovskite materials because of poor charge-transport properties. Herein, we present the concept of internal dye-sensitized hybrid perovskite compounds involving five novel low-dimensional perovskite-type materials - incorporating triarylmethane, phenazinium and near-infrared (NIR) cyanine cationic dyes, respectively.

Conformational and Compositional Tuning of Phenanthrocarbazole-Based Dopant-Free Hole-Transport Polymers Boosting the Performance of Perovskite Solar Cells.

Conjugated polymers are regarded as promising candidates for dopant-free hole-transport materials (HTMs) in efficient and stable perovskite solar cells (PSCs). Thus far, the vast majority of polymeric HTMs feature structurally complicated benzo[1,2-:4,5-']dithiophene (BDT) analogs and electron-withdrawing heterocycles, forming a strong donor-acceptor (D-A) structure. Herein, a new class of phenanthrocarbazole ()-based polymeric HTMs (, , and ) has been synthesized by inserting a unit into a polymeric thiophene or selenophene chain with the aim of enhancing the π-π stacking of adjacent polymer chains and also to efficiently interact with the perovskite surface through the broad and planar conjugated backbone of the .

Efficient Naphthalene Imide-Based Interface Engineering Materials for Enhancing Perovskite Photovoltaic Performance and Stability.

The ways to overcome surface charge recombination and poor interface contact are still the central challenges for the development of inorganic-organic hybrid halide perovskite solar cells (PSCs). [6,6]-Phenyl C butyric acid methyl ester (PCBM) is commonly employed in PSCs, but it has some disadvantages including high charge recombination and poor surface coverage. Therefore, the addition of an interfacial engineering layer showing efficient surface passivation, electron extraction, and excellent interface contact can solve the above problems.

Comparison between Benzothiadizole-Thiophene- and Benzothiadizole-Furan-Based D-A-π-A Dyes Applied in Dye-Sensitized Solar Cells: Experimental and Theoretical Insights.

Three novel donor-acceptor-π-acceptor-type compounds (WS5, WS6, and WS7) were synthesized and investigated in dye-sensitized solar cells (DSSCs) exploring the effect of conjugated linkers on device performance. The new dyes showed strong light-harvesting ability in the visible region with relatively high molar absorption coefficients (>21 800 M cm). This can be attributed to their intrinsic charge transfer (CT) from the arylamine to the acceptor group.

Organic Salts as p-Type Dopants for Efficient LiTFSI-Free Perovskite Solar Cells.

Despite the ubiquity and importance of organic hole-transport materials in photovoltaic devices, their intrinsic low conductivity remains a drawback. Thus, chemical doping is an indispensable solution to this drawback and is essentially always required. The most widely used p-type dopant, FK209, is a cobalt coordination complex.

Single crystal structure and opto-electronic properties of oxidized Spiro-OMeTAD.

Single crystals of Spiro(TFSI)2 were grown, the optical and electronic properties were characterized and compared with neutral Spiro-OMeTAD. Density-functional theory was used to get insights into binding and band structure properties. The flat valence bands indicate a rather limited orbital overlap in Spiro(TFSI)2.