A Tour Within the Bis-Phenanthroline Copper Complex Family: from Electrochemical Features to Application as Redox Mediators in DSSCs

Sustainable energy production is one of the more serious challenges facing humanity to reduced and minimize the anthropogenic impact on the Planet. The conversion of the abundant solar light into energy is a promising solution. In this view photoelectrochemical devices such as dye-sensitized solar cells, DSSCs, and perovskite-based devices are among the most studied architectures for a direct production of electricity. The role of redox mediators in DSSCs was understated for at least a decade for the benefit of dye engineering resulting in a stagnation of cell conversion efficiency. The proposal of alternative redox couples to the classical I\u2013/I3\u2013 has opened the way towards new record performance (exceeding 14% at 1 sun, 1.5 AM). Electrochemistry could play a crucial role in the design of novel effective electron shuttles. Our work is aimed to reveal the potentiality of substituted bis-phenanthroline copper complexes as redox mediators in DSSCs, starting from a rationalization of their electrochemical features (i.e. E1/2 and kheter) as a function of ligand substituents. These structure vs activity relationships allowed to finely tune their electrochemical parameters to better fulfill features of ideal mediators. A tour around the electrochemical properties of these complexes will be presented together with results concerning formulation of efficient Cu-based electrolytes for DSSCs. Special attention will be paid to discuss correlations useful to draw a guideline for the synthesis of always best mediators. Acknowledgments SmartMatLab Centre for funding the research

Copper Complexes as Effective Competitors for Iodine-free Electrolytes in Dye-Sensitized Solar Cells

Dye-sensitized solar cells, DSSCs, are photoelectrochemical devices well contextualized within the global commitment for the progressive increase of the percentage of electric energy produced by renewable resources. In the last decade the development of novel redox mediators alternative to the ubiquitous iodine-based electrolyte (identified as one of the principal causes of the stagnant PCE values in which the research got bogged down) has been one of the hottest topic of research. Efforts of many scientists have been catalyzed by metal complexes as promising single electron mediators characterized by an easy modulation of many electrochemical and optical features requested to ideal electron shuttles. While tris(diimine) cobalt complexes largely monopolize recent literature, our group has focused on homoleptic 1,10-phenanthroline-based copper complexes relying on the fact that their intrinsic limitations, if suitable tailored, could represent the turning point toward a new generation of electron shuttles. Starting from \u201cstructure vs activity maps\u201d correlating ligand substitutions with the electrochemical features of this class of complexes, we have proposed convenient Cu-based redox couples based on bulky 2-substituted phenanthrolines that reached efficiency higher than 6%, more than doubling the PCE of cells filled with the unique benchmark copper-based redox shuttle (12/22, in figure below) and even exceeding performance of a control I\u2013/I3\u2013-based electrolyte

Bis(1,10-phenanthroline) copper complexes with tailored molecular architecture: from electrochemical features to application as redox mediators in dye-sensitized solar cells

In the last few years, copper coordination compounds turned out to be effective competitors of cobalt complexes as redox mediators in the formulation of iodine-free electrolytes for dye-sensitized solar cells (DSSCs). However, the lack of a clear correlation between electrochemical signatures of copper complexes (i.e. half-wave potential and heterogeneous electron transfer rate) and photoelectrochemical performance of solar devices makes difficult the optimization of their coordination sphere. Therefore, to partially fill this gap and to elucidate the intrinsic correlation between the molecular architecture of these complexes and their electrochemical features, we prepared four Cu+/2+redox couples in which the copper center is coordinated by two 1,10-phenanthrolines bearing various substituents in position 2. These complexes were well characterized, from both electrochemical and spectroscopic point of view, and tested as electron shuttles in lab-scale photoelectrochemical cells sensitized with two efficient \ucf\u80-extended benzothiadiazole dyes. It appeared that 2-aryl-1,10-phenanthrolines effectively combine suitable optical and electrochemical properties. While a fast electron transfer kinetics generally positively affects the dye regeneration process, an optimal balance between dye regeneration efficiency, mass transport and heterogeneous electron transfer at both the counter electrode and at the TiO2interface, must be achieved in order to optimize DSSC performance. Within our series, the top performer was [Cu(2-tolyl-1,10-phenanthroline)2]+/2+which achieved a relative 20% and 15% improvement in power conversion efficiency (under 100 mW s\ue2\u88\u921simulated AM 1.5G illumination) with respect to control cells filled with [Co(bpy)3]2+/3+(bpy = 2,2\ue2\u80\ub2-bipyridine) and I\ue2\u88\u92/I3\ue2\u88\u92electrolytes, respectively

Influence of alkoxy chains envelope on the interfacial photoinduced processes in tetraarylporphyrin-sensitized solar cells

The introduction of alkoxy chains in the molecular architecture of meso push-pull porphyrins is of paramount importance aiming at high performing dye-sensitized solar cells (DSSCs) based on these specific sensitizers. Recently, we have demonstrated that the same approach is fruitful even if it is applied to tetraarylporphyrins with an acceptor/anchoring substituent in the \u3b2-pyrrolic position. In particular, among the ortho-ortho, the ortho-para and the ortho-functionalization of the aryl rings with an octyloxy chain, we identified the latter as the most performing in the series, showing a good balance between the dye loading and the reduction of \u3c0-\u3c0 aggregation. Herein, focusing our attention on the mono-ortho-functionalized molecular structure, we have investigated the effect of the alkoxy chain length and nature on the reduction of dye-to-dye aggregation as well as on the enhancement of light harvesting capabilities, finding an almost linear relationship between the device photon conversion efficiency (PCE) and the alkoxy chain length both in the presence and in the absence of a co-disaggregating agent

On Image Contours of Projective Shapes

International audienceThis paper revisits classical properties of the outlines of solid shapes bounded by smooth surfaces, and shows that they can be established in a purely projective setting, without appealing to Euclidean measurements such as normals or curvatures. In particular, we give new synthetic proofs of Koenderink's famous theorem on convexities and concavities of the image contour, and of the fact that the rim turns in the same direction as the viewpoint in the tangent plane at a convex point, and in the opposite direction at a hyperbolic point. This suggests that projective geometry should not be viewed merely as an analytical device for linearizing calculations (its main role in structure from motion), but as the proper framework for studying the relation between solid shape and its perspective projections. Unlike previous work in this area, the proposed approach does not require an oriented setting, nor does it rely on any choice of coordinate system or analytical considerations

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Bis-Phenanthroline Copper Complexes as a Springboard for Alternative Electron Shuttles in Dye-Sensitized Solar Cells

Dye-sensitized solar cells, DSSCs, are photoelectrochemical devices well contextualized within the global commitment for the progressive increase of the percentage of electric energy produced by renewable resources. In the last decade the development of novel redox mediators alternative to the ubiquitous iodine-based electrolyte (identified as one of the principal causes of the stagnant PCE values in which the research got bogged down) has been one of the hottest topic of research. Efforts of many scientists have been catalyzed by metal complexes as promising single electron mediators characterized by an easy modulation of many electrochemical and optical features requested to ideal electron shuttles. While tris(diimine) cobalt complexes largely monopolize recent literature, our group has focused on homoleptic 1,10-phenanthroline-based copper complexes relying on the fact that their intrinsic limitations, if suitable tailored, could represent the turning point toward a new generation of electron shuttles. Starting from \u201cstructure vs activity maps\u201d correlating ligand substitutions with the electrochemical features of this class of complexes, we have synthesized convenient Cu-based redox couples based on bulky 2-substituted phenanthrolines that reached efficiency higher than 6%, more than doubling the PCE of cells filled with the unique benchmark copper-based redox shuttle (12/22, in figure below) and even exceeding performance of a control I\u2013/I3\u2013-based electrolyte

BIS-phenanthroline copper complexes in iodine-free electrolytes for DSSCs

Dye-sensitized solar cells, DSSCs, are photoelectrochemical devices well contextualized within the global commitment for the progressive increase of the percentage of electric energy produced by renewable resources. This technology should free us from all problems and risks related to fossil fuels exploitation, in favor of the ubiquitous and practically inexhaustible sunlight. Since the milestone paper of Graetzel and O\u2019Regan, dye engineering has been for many years the unique task of scientists to improve the photon-to-current conversion efficiency, PCE, of cells. Only in the last decade the crucial role played by redox mediators has emerged, attracting attention mainly on tris(diimine) cobalt complexes capable of raising PCEs up to 14%. In the frame of iodine-free electrolytes, our group has proposed novel homoleptic 1,10-phenanthroline copper complexes able to significantly exceed the unique effective literature benchmark proposed to date, based on neocuproine ligands. In this contribution we will present our results dealt with the study of how ligand substituents affect the electrochemical and optical features of this class of complexes so as to reduce light harvesting competition with dye and to overcome kinetic dichotomies active in DSSCs. These \u201cstructure vs activity maps\u201d have been then exploited to choose a selected ensemble of compounds to be tested in DSSCs as electron shuttles and to rationalize their photoelectrochemical performances. Particular attention was also dedicated to select a cathode material able to minimize the overpotential for the mediator regeneration reaction. As a result we have proposed a convenient Cu-based redox couple based on bulky 2-mesityl-4,7-dimethyl-1,10-phenanthrolines that, in combination with two completely different dyes (i.e. a Ru-based and an organic one), has more than doubled the PCE of cells filled with the benchmark neocuproine-based shuttles and has reached values even slightly higher than a equimolar I\u2013/I3\u2013 control electrolyte

Phenanthroline-based Copper complexes as redox mediators in DSSCs

The extraordinary energy dependence from fossil fuels has been forcing humanity to consider also other, and possibly renewable, sources. Among these the sunlight is probably the optimal task being ubiquitous, abundant, and practically inexhaustible. Since 90\u2019s of the last century dye-sensitized solar cells, DSSCs, have been studied as light-to-electricity-conversion devices alternative to the already mature silicon-based photovoltaic technology. Especially in the last years a lot of efforts have been made in the optimization of electrolytes for DSSCs, searching for efficient redox mediators that can overcome some intrinsic drawbacks of the most common I3-/I- redox couple. Among the possible classes of electron shuttles our research group has bet on first-row transition metal complexes, focusing on copper. In this contribution we will focus on substituted 1,10-phenanthroline-based copper complexes which revealed to be effective redox mediators characterized by i) a simple and high yielding synthesis, ii) a high chemical and electrochemical reversibility, iii) and an easy-tunable oxidation half-wave potential E1/2(Cu2+|Cu+) obtainable through modification of the diimine chelating scaffold. A quite complete characterization of the aforementioned N^N chelated copper complexes will be presented, resulting from a multi-technique approach which combined electrochemical and photoelectrochemical techniques (including electrochemical impedance spectroscopy) with time-resolved absorption spectroscopy. We will start with the electrochemical rationalization of their thermodynamic and kinetic features as a function not only of the ligand structure (and of the related complex geometry) but also of solvent and counteranion nature. After that we will show the results obtained employing copper complexes as redox mediators in DSSCs, screening different kinds of photoanodes and cathodes, different TiO2 sensitizers (both Ru-based and fully-organic dyes), and various electrolytes changing the absolute and relative content of oxidized and reduced form of the mediators. Up to now the best combination of cell components gave rise to a power conversion efficiency higher than 5% recorded under 100 mW cm-2 AM 1.5G illumination