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Electrochemical nitrogen reduction (E-NRR) is one of the most promising approaches to generate green NH3. However, scarce ammonia yields and Faradaic efficiencies (FE) still limit their use on a large scale. Thus, efforts are focusing on different E-NRR catalyst structures and formulations. Among present strategies, molecular electrocatalysts such as metal-porphyrins emerge as an encouraging option due to their planar structures which favor the interaction involving the metal center, responsible for adsorption and activation of nitrogen. Nevertheless, the high hydrophobicity of porphyrins limits the aqueous electrolyte–catalyst interaction lowering yields. This work introduces a new class of metal-porphyrin based catalysts, bearing hydrophilic tris(ethyleneglycol) monomethyl ether chains (metal = Cu(II) and CoII)). Experimental results show that the presence of hydrophilic chains significantly increases ammonia yields and FE, supporting the relevance of fruitful catalyst-electrolyte interactions. This study also investigates the use of hydrophobic branched alkyl chains for comparison, resulting in similar performances with respect to the unsubstituted metal-porphyrin, taken as a reference, further confirming that the appropriate design of electrocatalysts carrying peripheral hydrophilic substituents is able to improve device performances in the generation of green ammonia.

This work presents the next paradigm shift in solar energy technology in which a novel iodide-based DES-like mixture has been first investigated as an active electrolyte solvent in dye-sensitized solar cells (DSSCs) in the absence of any co-solvent and any external iodide source. The optimization of the cell design jointly with a bespoke dye functionalized with a hydrophobic chain, properly positioned along the molecular backbone, ensures (a) one of the highest power conversion efficiencies (PCEs) up to 4% for DSSCs based on non-VOC solvents, and (b) a remarkable temporal stability of nearly 95% over a period longer than 2 months. Higher power conversion efficiency values (up to 8.0%) than those reported in the literature with traditional sensitizers and environmentally friendly electrolytes (e.g., water-based electrolytes) have been achieved under low-light illumination. These results are very promising for the realization of next-generation nature-inspired low-cost and high-performing DSSC devices for indoor and outdoor applications.

Ammonia (NH3) stands as a cornerstone compound across industries, pivotal in agriculture, chemicals, and energy sectors. However, the conventional Haber-Bosch process demands high pressures, temperatures, and fossil fuels, calling for sustainable alternatives. Electrocatalytic Nitrogen Reduction Reactions (E-NRRs) and Photocatalytic Nitrogen Reduction Reactions (Photo-NRRs) present innovative routes, leveraging electricity and direct sunlight to convert nitrogen (N2) to NH3 under mild conditions, reducing emissions and softening energy requirements. Catalysts play a strategic role in these approaches, overcoming activation barriers and enhancing efficiency. However, some challenges still need to be addressed. Indeed, noble metals exhibit limits and their scarcity, geopolitical involvement, and often fluctuating costs inhibit large-scale use. Non-noble metals offer promise but require optimization and face durability concerns. Finally, carbon-based catalysts present challenges in optimization and doping. In this scenario, a molecular-based approach, comprising both specific single coordination-based molecules with transition metal centres and either metal centre coordination-based or fully organic multi-dimensional networks originating from direct molecular organic precursors, overcomes these issues while keeping the benefits of the previously mentioned classes of compounds. This mini-review explores the molecular approach to E-NRRs and Photo-NRRs from coordination compounds carrying porphyrins and phthalocyanines as organic ligands to polymeric networks based on coordination compounds between metallic centres and organic ligands (Metal-Organic Frameworks), and to networks of molecular organic units into multi-dimensional structures (Covalent Organic Frameworks). Mechanistic insights into E-NRRs and Photo-NRRs pathways elucidate N2 conversion to NH3. A critical comparative evaluation of reported catalysts has been carried out to highlight the limits and the possibili

Molecular doping can increase the conductivity of organic semiconductors and plays an increasingly important role in emerging and established plastic electronics applications. 4-(1,3-Dimethyl-2,3-dihydro-1H-benzimidazol-2-yl)-N,N-dimethylaniline (N-DMBI-H) and tris(pentafluorophenyl)borane (BCF) are established n- and p-dopants, respectively, but neither functions as a simple one-electron redox agent. Molecular hydrogen has been suggested to be a byproduct in several proposed mechanisms for doping using both N-DMBI-H and BCF. In this paper we show for the first time the direct detection of molecular hydrogen in the uncatalysed doping of a variety of polymeric and molecular semiconductors using these dopants. Our results provide insight into the doping mechanism, providing information complementary to that obtained from more commonly applied methods such as optical, electron spin resonance, and electrical measurements.

Climate change mitigation on a global scale will only be possible through the achievement of ambitious decarbonisation goals, requiring an energy transition that involves switching from fossil fuels to clean fuels such as hydrogen. The photocatalytic approach is one of the most studied methods for directly converting sunlight into hydrogen. In this work, we present the synthesis, characterization, and application of the PTZ1-HA dye, which was obtained by replacing the terminal conventional carboxylic anchoring moieties of a previously studied phenothiazine-based dye (PTZ1) with hydroxamic acid functionalities. The photoinduced performance of the two dyes as photosensitizers was compared in both dye-sensitized solar cells and dye-sensitized photocatalytic systems. PTZ1-HA-sensitized photocatalysts showed improved stability in hydrogen generation due to the introduction of the hydroxamic acid as an alternative anchor group, which was shown to slow down hydrolysis in aqueous media. Even though the light harvesting ability of PTZ1-HA was lower than that of PTZ1, the higher stability of PTZ1-HA-sensitized devices allowed for improved photocatalytic generation of H2 over prolonged periods. The superior long-term efficiency of the hydroxamic acid based dye is important in view of potential practical applications.

We experimentally investigate the two-photon absorption cross sections and spectra of eosin and hematoxylin for applications in nonlinear microscopy. The experiments are carried out on pure samples of the two dyes in DI-water solvent with different concentrations, in the typical range employed in standard staining procedures. Nonlinear fluorescence is excited by a line-shaped beam emitted by a Ti:Sapphire mode-locked laser in the wavelength range from 740 to 880 nm and is detected through a microscope setup. The two-photon absorption spectral response is systematically analyzed and discussed. Finally, the staining is applied on biological tissue samples, which are imaged by two-photon microscopy. Our results show that the employed dyes are fully suitable for applications in nonlinear imaging.

Deep Eutectic Solvents (DESs) have been widely used in many fields to exploit their ecofriendly characteristics, from green synthetic procedures to environmentally benign industrial methods. In contrast, their application in emerging solar technologies, where the abundant and clean solar energy is used to properly respond to most important societal needs, is still relatively scarce. This represents a strong limitation since many solar devices make use of polluting or toxic components, thus seriously hampering their eco-friendly nature. Herein, we review the literature, mainly published in the last few years, on the use of DESs in representative solar technologies, from solar plants to last generation photovoltaics, featuring not only their passive role as green solvents, but also their active behavior arising from their peculiar chemical nature. This collection highlights the increasing and valuable role played by DESs in solar technologies, in the fulfillment of green chemistry requirements and for performance enhancement, in particular in terms of long-term temporal stability.

The photogeneration of electricity and solar fuels by solar irradiation in photoelectrochemical cells is one of the sectors with the highest growth potential in the decarbonised society. However, the use of different components, in particular photosensitizers and catalysts, can present problems of charge transfer efficiency at the interface, leading to lower final efficiencies. In this work we present novel integrated photosensitizer-catalyst dyads based on robust and, at the same time, flexible host-guest non-covalent interactions through the use of calix[4]arene cavities. Current photogeneration in photoelectrochemical cells showed twice greater efficiency in the integrated calixarene-based host-guest dyads compared to the traditional architecture based on the separate photosensitizer-catalyst pair. Molecular dynamics studies have shown that the enhanced performance originates from an optimization of the distances between the centres of the photosensitizer, catalyst and semiconductor involved in the charge transfer processes, thus allowing a higher final efficiency of the charge photogeneration process.

A series of functionalized ferrocene derivatives carrying electron-donor and electron-withdrawing (hetero)aromatic substituents has been designed as potential alternative electrolyte redox couples for dye-sensitized solar cells (DSSC). The compounds have been synthesized and fully characterized in their optical and electrochemical properties. A general synthetic approach that implies the use of a microwave assisted Suzuki coupling has been developed to access a significative number of compounds. The presence of different electron-rich and electron-poor substituents provided fine tuning of optical properties and energy levels. HOMO and LUMO energy values showed that the substitution of one or two cyclopentadienyl rings of ferrocene can be successfully exploited to increase the maximum attainable voltage from a standard DSSC device using TiO2 as a semiconductor, opening the way to highly efficient, non-toxic, and cheap redox shuttles to be employed in solar energy technologies.

Dye-sensitized solar cells containing sugar-based natural deep eutectic solvents (NADESs) as active electrolyte solvents have been studied in terms of their photovoltaic (PV) properties, including main PV characteristics, incident photon-to-current efficiency, and impedance properties. Five monosaccharides were selected as NADES H-bond donors and investigated with a phenothiazine-based sensitizer carrying a glucose functionality and a glucose-based co-adsorbent (glucuronic acid) to explore directional intermolecular interactions and to improve the PV performance. The highest power conversion efficiencies were recorded for cells containing the glucose-based sensitizer in the presence of glucuronic acid in the sugar-based NADES. When one of these components was omitted, performances were lower, suggesting that the best response came from an interplay between the sugar-based units. Not only has the unprecedented use of a NADES as a fully natural and bio-renewable dye-sensitized solar cell medium been presented, but for the first time an active role of the electrolyte solvent has been reported and exploited to increase the performance of the solar device.

Hybrid lead halide perovskites have been revolutionary in the photovoltaic research field, reaching efficiencies comparable with the most established photovoltaic technologies, although they have not yet reached their competitors’ stability. The search for a stable configuration requires the engineering of the charge extraction layers; in this work, molecular doping is used as an efficient method for small molecules and polymers employed as hole transport materials in a planar heterojunction configuration on compact-TiO2. We proved the viability of this approach, obtaining significantly increased performances and reduced hysteresis on compact titania-based devices. We investigated the photovoltaic performance correlated to the hole transport material structure. We have demonstrated that the molecular doping mechanism is more reliable than oxidative doping and have verified that molecular doping in polymeric hole transport materials leads to highly efficient perovskite solar cells, with long-term stability.

The photoelectrochemical approach to photoinduced water splitting is gaining increasing interest for solar fuels generation. Dye-sensitized photoelectrochemical cells (DS-PEC) have been studied to improve the collection of the Vis range of solar radiation. Metal complexes have so far been the most investigated dyes but in recent years metal-free organic dyes have emerged as a new frontier for the evolution of the sector. This Minireview systematically describes the use of organic sensitizers and has been organized in terms of dye-sensitized photoactive electrode(s): photoanode; photocathode; tandem DS-PEC with photoanode and photocathode. The main classes of dyes are introduced and described in their key properties, device performance, and water splitting data. Thanks to the increasing number of articles, this review highlights the growing importance of organic sensitizers and their molecular design for a more efficient solar generation of clean fuels.

This review points out some of our recent advancements in dye-sensitized photocatalytic and photoelectrochemical hydrogen production. The dye sensitization of a semiconductor (SC) surface plays a central role. The dye has the task to improve the light harvesting of the system and guarantees a fast charge transfer to the SC, while avoiding charge recombination reactions that might reduce its efficiency. The introduction of different features and exploitation of molecular designs led to the development of twelve new dyes with a “push–pull” di-branched structure. The design of the molecular structure and geometry improves light harvesting, stability under long-term irradiation, and surface properties. The dyes have been investigated in a photocatalytic device, and then the most representative molecules have been studied also in photoelectrochemical cells (PEC), in the presence either of a sacrificial electron donor (SED), or of a water oxidation catalyst (WOC). The planar structure of the carbazole-based dye enhanced the photocatalytic hydrogen production activity almost tenfold compared to the phenothiazine derivative characterized by a butterfly-like structure; the latter was endowed with a better performance in the photoelectrochemical hydrogen production. Graphic abstract: [Figure not available: see fulltext.]

In the past decades, dye-sensitized solar conversion technologies have gained more and more interest in the scientific community. Dye-sensitized solar cells (DSCs) are a very promising technology that can combine the high-stability features common to the inorganic semiconductors and the wide flexibility of the organic compounds. Indeed, these novel solar cells are multi-component devices that can be prepared using different metal oxides as charge transport materials in combination with organometallic or organic sensitizers as absorber. Because of their great flexibility, they immediately became a source of great interest from different points of view, especially with regard to the studies of the phenomena of charge generation and transport. These phenomena are strictly related to the structure of the cell itself and the nature of the sensitizers.These cells can be made as n-type or p-type with a passive counter electrode, depending on the metal oxide semiconductor, as well as in combination in a tandem configuration with both active anode and cathode. However, the most important part of the cell is the sensitizer. Indeed, since their report, the rush to find novel more efficient sensitizers started. From the first ruthenium complex, the rush to more efficient and more stable dyes led to the production of a plethora of different molecular sensitizers, either organometallic and organic, capable of astonishing properties setting higher and higher the attainable efficiency and improving, the stability of the overall device. In this chapter, after a presentation of the main type of DSCs, attention will be paid to the photophysics of devices sensitized with metallo-porphyrins based dyes and the effect of the different functionalzation of their tetra-aryl porphyrinic core. Different techniques have been used to evaluate the main photophysics parameters to point out the critical effect of proper functionalization over the final efficiency of the devices.

The synthesis and characterization of two simple Ruthenium(II) complexes of the type [Ru(X^N)2(4,4′-dicarboxybipyridine)]+ (with X[dbnd]C, X^N[dbnd]benzoquinolinate, 1; with X[dbnd]N, X^N[dbnd]2-pyridyl tetrazolate, 2) and the exploitation of a new carbon doped anatase TiO2 paste in dye-sensitized solar cells (DSSCs) photoanode are described. In particular, glucose (C6H12O6) is used as a new chemical eco-friendly C-dopant during the doping process of anatase TiO2 nanoparticles. The proper combination of Ru(II) sensitizers and C-doped titania can afford efficient DSSC photoanodes. All the relevant photovoltaic parameters have been determined.

Introduction: Epilepsy has a growing frequency, particularly in the elderly. Several triggers may cause late-onset epilepsy; however, more than 20% of epilepsies, manifesting in the elderly, has an unknown etiology. Although cognition is frequently altered in patients affected by epilepsy, there is a paucity of studies specifically evaluating cognition in patients affected by late-onset epilepsy. The aim of the present study was to assess the cognitive profile of patients affected by late-onset epilepsy with an unknown etiology and followed for 12 months. Methods: Patients affected by diagnosed late-onset epilepsy with unknown etiology were included in this observation. All patients were evaluated at the time of diagnosis (baseline) and at follow-up (12 months later). We distributed patients in subgroups based on seizure type (focal seizures [FS], secondarily generalized seizures [SGS], primarily generalized seizures [GS]) and antiepileptic drug (AED) regimen (mono- vs. polytherapy). Cognition was evaluated through standardized neuropsychological testing. Results: Fifty-eight patients were included in this observation and distributed in three groups: 29 affected by FS, 14 affected by SGS, 15 affected by GS. Forty-five patients were in monotherapy, and 13 in polytherapy. The most frequent treatments were levetiracetam (n = 12), valproic acid (VPA) (n = 9), carbamazepine (n = 9), and oxcarbazepine (n = 7). We documented a significant decrease of Mini-Mental State Examination (MMSE) and memory scores at follow-up in the whole group. Verbal learning decreased exclusively in VPA users. Conclusion: Patients affected by late-onset epilepsy with unknown etiology showed a significant decline of cognition at follow-up, independently from number and efficacy of AEDs received. These results deserve verification in larger longitudinal cohorts.

The data presented in this article are related to the research article entitled “An unconventional helical push-pull system for solar cells” (Dova et al., 2019). This article provides: a) the cyclic voltammogram plots in solution of helical push-pull sensitizers and the corresponding precursors; b) the visualization of the leading natural transition orbital (NTO) pairs obtained by theoretical calculation of frontiers orbitals; c) J/V curves of dye-sensitized solar cells (DSSC) sensitized by the dyes, without 3a,7a-dihydroxy-5b-cholic acid (CDCA) as co-adsorbent agent; d) 1H and 13C NMR spectra of dyes.

The use of a hydrophobic eutectic solvent based on dl-menthol and a naturally occurring acid such as acetic acid has been tested as an eco-friendly electrolyte medium in dye-sensitized solar cells. In the presence of a de-aggregating agent and a representative hydrophobic organic photosensitizer, the corresponding devices displayed relatively good power conversion efficiencies in very thin active layers. In particular, the higher cell photovoltage detected in comparison to devices based on toxic and volatile organic compounds may stem from a more efficient interface interaction, as suggested by electrochemical impedance spectroscopy studies showing greater charge recombination resistance and electron lifetime.

Di-branched dyes based on a triphenylamino (TPA) donor core have been functionalized with different aromatic and heteroaromatic peripheral groups bonded to TPA as auxiliary donors and investigated as sensitizers in DSSC. The different aromatic and heteroaromatic substitution significantly perturbed the optical properties of the dyes compared to the unsubstituted TPA reference dye, in turn leading to enhanced photovoltaic performances in terms of photocurrent, photovoltage, and power conversion efficiency (PCE). The enhancement originated from improved strategic interface interactions between the dye-sensitized titania and the liquid electrolyte, as ascertained by current-voltage, quantum efficiency (IPCE), light harvesting properties (LHE), and impedance spectroscopy (EIS) studies.

Dye-sensitized photocatalytic H2 generation has been investigated using a metal-free phenothiazine-based donor-acceptor sensitizer (PTZ-GLU) in combination with coadsorbents. The coadsorption of the PTZ-GLU dye, functionalized with a glucose end-group, in combination with a glucose-based coadsorbent, afforded improved photocatalytic activity compared to the absence of coadsorbents, to the use of a conventional (chenodeoxycholic acid) coadsorbent, or by replacing the dye glucose functionality with an alkyl chain. The results suggest the strategic role of directional intermolecular dye-coadsorbent interactions on the semiconductor surface, as confirmed by first principles computational modeling, which likely suppressed detrimental recombination processes.

Metal-free di-branched organic sensitizers, containing different heteroaromatic (phenothiazine, phenoxazine and carbazole) donor moieties, have been investigated as photoactive anode sensitizers in the photoelectrochemical generation of oxygen and water splitting. Photoelectrochemical properties have been studied both in the presence of a sacrificial electron donor, to closely evaluate the charge-transfer phenomena and the external quantum efficiency, and with a common water oxidation catalyst, to preliminarily assess the photoelectrochemical water-splitting activity and oxygen production. The experimental performance trend, in terms of photogenerated charge and evolved gas, was phenothiazine>carbazole>phenoxazine, arising from superior light-harvesting capability and more efficient electron injection to the semiconductor.

Phenothiazine-, phenoxazine- and carbazole-based dyes have been synthesized and used as photosensitizers in Pt/TiO2 films for photocatalytic hydrogen generation. Compared to commonly used phenothiazine dyes, planar and sulphur-free carbazole derivatives showed different molecular and supramolecular features which in turn yielded greatly enhanced (one order of magnitude) H2 production performances.

Dye-sensitized solar cells (DSSCs) that use an aqueous (40 % w/w water content) choline chloride based deep eutectic solvent as an electrolyte medium have been investigated. The joint combination of the eutectic mixture and an appropriate hydrophilic sensitizer afforded a DSSC with a power conversion efficiency comparable to that using the same electrolyte composition but with conventional, toxic, and volatile solvents as the medium, which thereby paves the way to a new generation of eco-friendly, nature-inspired, low-cost solar devices.

In questo progetto di dottorato, abbiamo studiato nove molecole e materiali per applicazioni in celle solari di terza generazione e produzione fotocatalitica o fotoelettrochimica di H2. La prima parte di questo lavoro è stata focalizzata sullo studio di dispositivi DSSCs andando a studiare nuov fotosensibilizzatori a base organica, alcuni dei quali ottenuti da collaborazioni esterne, e diversi coloranti a base fenotiazinica recanti funzionalizzazioni differenti al fine di modularne proprietà ottiche e fotovoltaiche sia in presenza di elettroliti a base organica sia acquosa. celle solari a perovskiti (PSC) sono state studiate ed è stata sviluppata una procedura di fabbricazione affidabile. Uno studio di fattibilità circa l'integrazione in dispositivi multi-giunzione con mc-Si è stato fatto con successo. Diversi materiali di trasporto di lacune a base di idrazoni sono stati sintetizzati e le loro proprietà ottiche ed elettrochimiche sono state studiati. La mobilità dei portatori di questi nuovi materiali è stata studiata in transistor organici ad effetto di campo e sono stati impiegati in dispositivi PSC.Coloranti fenotiazinici ramificati, sono stati testati come fotosensibilizzatori nella produzione fotocatalitica di H2, in combinazione con un catalizzatore Pt / TiO2. Le proprietà ottiche ed elettrochimiche dei coloranti sono stati studiati, mostrando che un'attenta progettazione dei nuovi coloranti concessi migliorate proprietà ottiche. Nella produzione di H2 oltre 20 h, i nuovi sensibilizzatori rivelato stabilità migliorata dopo tempi di irraggiamento più lunghi e prestazioni migliorate, in termini di velocità di produzione H2 ed efficienze luce-combustibile, che sono stati per la prima volta associate ad una maggiore stabilità in produzione fotocatalitica H2 e all'assenza di degradazione del colorante. Colorante fenotiazinico analogo è stato funzionalizzato con una unità di glucosio periferico (PTZ-GLU) per aumentare la sua affinità con l'acqua e, In this PhD project, we studied molecules and new materials for application in third generation solar cells and photocatalytic or photoelectrochemical production of H2. The first part of this work was focused on the study of DSSCs devices going to investigate new organic-based photosensitizers, some of them obtained from external collaborations, and several phenothiazine based dyes bearing different functionalization to modulate optical and photovoltaic properties either in presence of organic and water based electrolyte. Perovskite solar cells (PSC) have also been studied and a reliable fabrication procedure have been developed. A study of feasibility about integration in multi-junction devices with mc-Si have been done successfully. Several hydrazone-based hole transport materials have been synthesized and their optical and electrochemical properties have been investigated. The mobility of carriers of these new materials have been studied in organic field effect transistor and they have been employed in PSC devices. Dibranched phenothiazine based dyes, were tested as photosensitizers in the photocatalytic production of H2, in combination with a Pt/TiO2 catalyst. The optical and electrochemical properties of the dyes were investigated, showing that careful design of the new dyes afforded enhanced optical properties. In the H2 production over 20 h, the new sensitizers revealed improved stability after longer irradiation times and enhanced performances, in terms of H2 production rates and light-to-fuel efficiencies, which were for the first time associated with enhanced stability under photocatalytic production of H2 and the absence of critical dye degradation. Analogous phenothiazine dye has been functionalized with a peripheral glucose unit (PTZ-GLU) to bust its affinity to water and enhance dye-sensitized photogeneration of H2. Compared to the corresponding alkyl derivative, as well as the common hydrophilic triethylene glycol substitution (PTZ-TEG); PTZ-GLU perfo

We adopted a procedure to achieve an optimised CH3NH3PbI3 layer in a planar TiO2 based Planar Heterojunction, which finally results in hysteresis-less and high-efficiency solar cells. We explored the optimisation of the perovskite film thickness, by using a super-saturated solution of CH3NH3I and PbI2 precursors, which also impact on the quality and size of perovskite domains, and the fine-tuning of the perovskite layer surface by a thermal-vacuum post-deposition treatment. Using this procedure, we have obtained a pinhole-free perovskite film with large grain size, reduced surface defects, and generate high photovoltaic performance almost independent on the voltage scan direction. Through photophysical characterization, we proved that the fine setting of the combined thermal-vacuum treatments results in extra-large grains, simultaneously offsetting film defect concentration. Our finding suggests how hysteresis can be efficiently stemmed by simply optimising perovskite processing conditions targeting different device layouts.[1] Moreover, we present a well know p-type doping material as an additive for the Hole Transport Material (HTM), 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane, i.e. F4TCNQ: we have tested various doping concentration in the two most used HTM material for perovskite-based solar cells, Spiro-OMeTAD and P3HT, defining the best doping condition and testing stability in months.

The production of hydrogen from sunlight and water is finding an increasingly important role in the production of clean fuels from sustainable and abundant energy sources. In this process, commonly referred to as artificial photosynthesis, the role of the dye sensitizer is critical for optimizing the harvesting of visible light and triggering the reduction reaction at the catalytic active site. In recent decades organometallic sensitizers have mainly been studied, often requiring the use of scarce and, in some cases, toxic elements. This microreview describes the state of the art in the use of metal-free organic sensitizers, highlighting advantages over their organometallic counterparts. The main design and synthetic strategies, specific properties, and device performances are presented. Thanks to recent advances and lower manufacturing costs, organic sensitizers seem set to be of increasing importance for next-generation clean fuels.

A thiophene-based donor-acceptor phenothiazine dye has been functionalized with a peripheral glucose unit (PTZ-GLU) to bust its affinity to water and enhance dye-sensitized photogeneration of hydrogen. Compared to the corresponding alkyl derivative (PTZ-ALK), as well as the common hydrophilic triethylene glycol substitution (PTZ-TEG), the sugar derivative shows a lower contact angle; PTZ-GLU performed twice more efficient than PTZ-TEG in the photogeneration of hydrogen in terms of evolved gas and turnover number.

Hybrid halide perovskite solar cells generally show differences in the power output depending on the voltage sweep direction, an undesired phenomenon termed hysteresis. Although the causes of this behavior have not yet been univocally determined, commonly, hysteresis heavily affects solar cells based on flat TiO2 as electron extracting layer. Herein, it is shown how perovskite material quality has a preeminent impact on hysteresis, and how combined deposition and post-deposition engineered manufacturing could lead to highly efficient and hysteresis-less solar cells, notwithstanding a planar TiO2-based layout. This methodology relies on solvent engineering during the casting process, leading to an ultra-flat, uniform, and thick film ensuring an optimal interface connection with the charge-extracting layer combined with post-deposition thermal and vacuum treatments, which merge the crystalline domains and cure the defects at the grain boundaries. This method allows obtaining perovskite active layer with superior optical properties, explaining the ideal device behavior and performances, therefore, a simple optimization of perovskite processing conditions can efficiently stem hysteresis targeting different device layouts. Power conversion efficiency of 15.4% and reduced hysteresis are achieved.

A series of push-pull triarylamine organic dyes containing the benzo[1,2-b:4,5-b′]dithiophene unit as a spacer and bearing alkyl chains in different positions of the molecule were synthesized. The new dyes 1-4 were characterized by optical and electrochemical measurements and density functional theory calculations and used as sensitizers in liquid dye-sensitized solar cells. The effect of alkyl chain position on dye properties and performances was investigated and dye 1, bearing two 3,7-dimethyloctyl groups on the benzodithiophene core, exhibited the best behaviour in term of light absorption and cell performance (PCE of 6.6%, to be compared with a PCE of 8.1% for N719-based device). The efficiency of the DSSC was highly dependent on the solvent used for the dye-sensitizing bath, which affects the position of the COOH/COO- equilibrium.

Multi-branched multi-anchoring metal-free dyes as photosensitizers for dye-sensitized solar cells (DSSCs) are reviewed. The article outlines design strategies, main synthetic routes and optical and photovoltaic properties of two families of multi-branched sensitizers: (a) D-(?-A)n (D = donor, ? = ?-spacer, A = acceptor/anchoring functionality) structures containing arylamine, carbazole, phenothiazine or phenoxazine derivatives as D groups, and (b) multi-donor multi-anchoring architectures from interconnected mono-branched D-?-A arms, together with X- and Y-shaped dyes. Although this class has been reported only in the last five years, a variety of molecular architectures, donors, and ?-spacers have been used and combined in multi-branched molecules. The multibranched geometry induces distinctive features including enhanced qualitative and quantitative optical properties, increased currents and quantum efficiencies, and control of molecular aggregation.

The amplification of Raman signals of the heteroaromatic cation 1-(N-methylpyrid-4-yl)-2-(N-methylpyrrol-2-yl)ethylene (PEP+)) bound to Au nanorods (NRs) was investigated at different excitation wavelengths to study the effect of the laser resonance with the absorption band of the PEP+ moiety and with the two plasmon oscillation modes of the NR. Two different PEP+ derivatives, differing in the length of the alkyl chain bearing the anchoring group, were used as target molecules. Raman spectra obtained exciting at 514 or at 785 nm (i.e., exciting the transverse or the longitudinal plasmon band) present a higher intensity than that at 488 nm suggesting a higher Raman amplification when the laser excitation wavelength is resonant with one of the two plasmon modes. Moreover, considering results of Discrete Dipole Approximation (DDA) calculations of the local field generated at the NR surface when either the transverse or the longitudinal plasmon modes are excited, we deduced that the resonance condition of the 514-nm laser excitation with the absorption band of the dye strongly contributes to the amplification of the Raman signal. © 2014 The Author(s).

The first use of PSn-b-PEOm-b-PSn block copolymers (PS = polystyrene, PEO = poly(ethylene oxide)) as solid hosts for iodine/iodide electrolytes in dye-sensitized solar cells (DSSCs) is described. Using the benchmark photosensitizer N719, DSSC based on the quasi solid-state electrolytes afforded efficiencies up to 6.7%, to be compared with an efficiency of 7.3% obtained in similar conditions with a conventional iodine/iodide liquid electrolyte. By varying the PS:PEO relative volume ratio in the block copolymers different properties and morphologies were obtained. Copyright © 2013 Wiley Periodicals, Inc.

Thiocyanate-free Ru(II) complexes as photosensitizers for dye-sensitized solar cells (DSSCs) are presented. These classes of complexes have gained in recent times increasing interest due to their more favorable long-term stability compared to conventional thiocyanate-based complexes such as benchmark dyes N719 and Z907. Here two classes of thiocyanate-free ruthenium(II) complexes have been reviewed: (a) bis-bipyridyl complexes bearing an ancillary cyclometallated bidentate ligand; (b) bipyridyl complexes bearing non-cyclometallated bidentate ancillary ligands. The article briefly outlines design strategies and optical and photovoltaic properties of these two families of ruthenium dyes. Although their photovoltaic performances is not as high as that of N719, recent increasing efforts by many research groups have allowed to achieve favorable light harvesting abilities, device photocurrents, and top-ranked power conversion efficiencies in combination with superior long-term stabilities, paving the way to efficient solar devices endowed with long-term chemical and thermal stability for viable large-scale commercialization of DSSCs.