A water-based and metal-free dye solar cell exceeding 7% efficiency using a cationic poly(3,4-ethylenedioxythiophene) derivative

Exploring zinc oxide morphologies for aqueous solar cells by a photoelectrochemical, computational, and multivariate approach

Dye-sensitized solar cells assembled with aqueous electrolytes are emerging as a sustainable photovoltaic technology suitable for safe indoor and portable electronics use. While the scientific community is exploring unconventional materials for preparing electrodes and electrolytes, this work presents the first study on zinc oxide as a semiconductor material to fabricate photoanodes for aqueous solar cells. Different morphologies (i.e., nanoparticles, multipods, and desert roses) are synthesized, characterized, and tested in laboratory-scale prototypes. This exploratory work, also integrated by a computational study and a multivariate investigation on the factors that influence electrode sensitization, confirms the possibility of using zinc oxide in the field of aqueous photovoltaics and opens the way to new morphologies and processes of functionalization or surface activation to boost the overall cell efficiency.

Redox Shuttle-Based Electrolytes for Dye-Sensitized Solar Cells: Comprehensive Guidance, Recent Progress, and Future Perspective

A redox electrolyte is a crucial part of dye-sensitized solar cells (DSSCs), which plays a significant role in the photovoltage and photocurrent of the DSSCs through efficient dye regeneration and minimization of charge recombination. An I^-/I₃ ^- redox shuttle has been mostly utilized, but it limits the open-circuit voltage (V _oc) to 0.7-0.8 V. To improve the V _oc value, an alternative redox shuttle with more positive redox potential is required. Thus, by utilizing cobalt complexes with polypyridyl ligands, a significant power conversion efficiency (PCE) of above 14% with a high V _oc of up to 1 V under 1-sun illumination was achieved. Recently, the V _oc of a DSSC has exceeded 1 V with a PCE of around 15% by using Cu-complex-based redox shuttles. The PCE of over 34% in DSSCs under ambient light by using these Cu-complex-based redox shuttles also proves the potential for the commercialization of DSSCs in indoor applications. However, most of the developed highly efficient porphyrin and organic dyes cannot be used for the Cu-complex-based redox shuttles due to their higher positive redox potentials. Therefore, the replacement of suitable ligands in Cu complexes or an alternative redox shuttle with a redox potential of 0.45-0.65 V has been required to utilize the highly efficient porphyrin and organic dyes. As a consequence, for the first time, the proposed strategy for a PCE enhancement of over 16% in DSSCs with a suitable redox shuttle is made by finding a superior counter electrode to enhance the fill factor and a suitable near-infrared (NIR)-absorbing dye for cosensitization with the existing dyes to further broaden the light absorption and enhance the short-circuit current density (J _sc) value. This review comprehensively analyzes the redox shuttles and redox-shuttle-based liquid electrolytes for DSSCs and gives recent progress and perspectives.

An Investigation on Gel-State Electrolytes for Solar Cells Sensitized with β-Substituted Porphyrinic Dyes

The presence of a liquid electrolyte in dye-sensitized solar cells (DSSCs) is known to limit the time stability of these devices due to leakage and evaporation phenomena. To overcome this issue, gel-state electrolytes may represent a good solution in order to maintain stability and good performances, albeit at lower costs. In the present work, two different kinds of gel-electrolytes, based on poly (methyl methacrylate) (PMMA) and nanoclay agents, were investigated in DSSC-devices sensitized using β-substituted Zn-porphyrins (namely ZnPC4 and ZnPC12) with enveloping alkoxy chains of different lengths, able to produce a coverage of the photoanode surface. The highest power conversion efficiency (PCE) values equal to 1.06 ± 0.04% and 1.55 ± 0.26% were obtained for ZnPC12 (with longer alkoxy chains) with PMMA- and nanoclay-based electrolytes respectively. The properties of the photoanode/electrolyte interface as well as the influence of the gelling agents on the final properties of the obtained devices were thoroughly characterized.

A Molecularly Tailored Photosensitizer with an Efficiency of 13.2% for Dye-Sensitized Solar Cells

Photosensitizers yielding superior photocurrents are crucial for copper-electrolyte-based highly efficient dye-sensitized solar cells (DSCs). Herein, two molecularly tailored organic sensitizers are presented, coded ZS4 and ZS5, through judiciously employing dithieno[3,2-b:2″,3″-d]pyrrole (DTP) as the π-linker and hexyloxy-substituted diphenylquinoxaline (HPQ) or naphthalene-fused-quinoxaline (NFQ) as the auxiliary electron-accepting unit, respectively. Endowed with the HPQ acceptor, ZS4 shows more efficient electron injection and charge collection based on substantially reduced interfacial charge recombination as compared to ZS5. As a result, ZS4-based DSCs achieve a power conversion efficiency (PCE) of 13.2% under standard AM1.5G sunlight, with a high short-circuit photocurrent density (J_sc ) of 16.3 mA cm^-2 , an open-circuit voltage (V_oc ) of 1.05 V and a fill factor (FF) of 77.1%. Remarkably, DSCs sensitized with ZS4 exhibit an outstanding stability, retaining 95% of their initial PCE under continuous light soaking for 1000 h. It is believed that this is a new record efficiency reported so far for copper-electrolyte-based DSCs using a single sensitizer. The work highlights the importance of developing molecularly tailored photosensitizers for highly efficient DSCs with copper electrolyte.

New and innovative microwave-assisted technology for synthesis of guar gum-grafted acrylamide hydrogel superabsorbent for the removal of acid red 8 dye from industrial wastewater

The goal of this study is to develop a new effective guar gum-grafted acrylamide hydrogel for wastewater treatment, abbreviated as (guar gum-g-acrylamide). For the non-biodegradable and hazardous synthetic acid red 8, the produced guar gum-g-acrylamide hydrogel is a promising thermally stable adsorbent. Microwave-aided technique, ammonium persulfate initiator, and N,N′-methylene-bis-acrylamide cross-linker are used to make a hydrogel comprising natural polysaccharides guar gum grafted by poly acrylamide. Fourier transformer infrared (FTIR) spectra and scanning electron microscopy (SEM) demonstrate that varied percentages of acrylamide successfully graft the backbone of guar gum. When the grafting percentage of acrylamide is raised, the hydrogel’s maximum adsorption capacity (qe) increases. At pH 1 of dye solution, maximum adsorption capacity (qe) is 18 mg.g−1, at pH 9; qe is decreased up to 8 mg.g−1. At 0.5 g.L−1 hydrogel, the dye has a low removal percentage (34%), but when the hydrogel dosage is increased to 8 g.L−1, the removal percentage increases to 90%. When the initial AR8 dye concentration was increased from 50 to 300 mg.L−1, the removal percentage reduced to 20% and the adsorbed quantity dye increased from 17 to 44 mg.g−1, but both parameters became limited above this dye concentration. Other ideal conditions for AR8 dye removal by the hydrogel include 60 min of contact time, 150 revolutions per minute (rpm), and a temperature of 20 degrees Celsius. The AR8 dye adsorption kinetic is pseudo-second order, assuming electrostatic interaction between the negatively charged AR8 dye molecules and the positively charged hydrogel-functional group. The adsorption values fit the Langmuir isotherm, with qmax. of 54.054 mg.g−1. The adsorbed quantity (qe) decreases as the temperature rises, indicating that dye molecules physisorbed on the hydrogel pores, and the maximum adsorption capacity is at 20 °C. The exothermic and spontaneity of adsorption were confirmed by the negative values of heat of adsorption (∆H°ads.) and standard Gibbs free energy of adsorption (∆G°ads.). The reusability of the hydrogel was validated after three cycles of desorption of AR8 dye from the hydrogel surface in alkaline solution.

Polymers in High-Efficiency Solar Cells: The Latest Reports

Third-generation solar cells, including dye-sensitized solar cells, bulk-heterojunction solar cells, and perovskite solar cells, are being intensively researched to obtain high efficiencies in converting solar energy into electricity. However, it is also important to note their stability over time and the devices' thermal or operating temperature range. Today's widely used polymeric materials are also used at various stages of the preparation of the complete device-it is worth mentioning that in dye-sensitized solar cells, suitable polymers can be used as flexible substrates counter-electrodes, gel electrolytes, and even dyes. In the case of bulk-heterojunction solar cells, they are used primarily as donor materials; however, there are reports in the literature of their use as acceptors. In perovskite devices, they are used as additives to improve the morphology of the perovskite, mainly as hole transport materials and also as additives to electron transport layers. Polymers, thanks to their numerous advantages, such as the possibility of practically any modification of their chemical structure and thus their physical and chemical properties, are increasingly used in devices that convert solar radiation into electrical energy, which is presented in this paper.

Photoelectrochemical Properties, Machine Learning, and Symbolic Regression for Molecularly Engineered Halide Perovskite Materials in Water

The machine learning techniques are capable of predicting virtual material design space and optimizing material fabrication parameters. In this article, we construct machine learning models to describe the photoelectrochemical properties of molecularly engineered halide perovskite materials based on CH₃NH₃PbI₃ in an aqueous solution and predict a complex multidimensional design space for the halide perovskite materials. The machine learning models are trained and tested based on an experimental photocurrent data set consisting of 360 data points with varying experimental conditions and dye structures. Machine learning algorithms including support vector machine (SVM), random forest, k-nearest neighbors, Rpart, Xgboost, and Kriging algorithms are compared, with the Kriging algorithm achieving the best accuracies (r = 0.99 and R² = 0.98) and SVM achieving the second best. A total of 50,905 data points representing the complex multidimensional design space are predicted via the machine-learned models to benefit the future perovskite studies. In addition, the symbolic regression based on the genetic algorithms effectively and automatically designs hybrid descriptors that outperform the individual descriptors. This article highlights the machine learning and symbolic regression methods for designing stable and high-performance halide perovskite materials and serves as a platform for further experimental optimization of halide perovskite materials.

Deep Eutectic Solvents in Solar Energy Technologies

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.

Effect of a locust bean gum based gel electrolyte with nanocomposite additives on the performance of a dye-sensitized solar cell

In this study, we proposed Mn3O4 and Mn3O4·CuS nanocomposites as novel inorganic additives in locust bean gum (LBG) gel electrolytes for application in an aqueous dye-sensitized solar cell (DSSC).

Managing the Nitrogen Cycle via Plasmonic (Photo)Electrocatalysis: Toward Circular Economy

As renewable energy sources are either intermittent in nature or remote in location, developing cost-effective, sustainable, modular systems and technologies to store and transport renewables at an industrial scale is imperative. Storing cheap renewable electricity into chemical bonds (i.e., chemical energy storage) could be a transformative opportunity for reliable and resilient grid energy storage. This approach enables renewables to be stored and shipped similarly to fossil fuels. Currently, the chemical industry primarily consumes fossil feedstock as an energy source, which has been the standard for over a century. A paradigm shift is required to move toward a more sustainable route for chemical synthesis by electrifying and decarbonizing the modern chemical industry. As renewable electricity costs decrease, (photo)electrosynthesis is gaining interest for synthesizing high-value and high-energy fuels and molecules in a clean, sustainable, and decentralized manner.The nitrogen cycle is one of the Earth's most critical biogeochemical cycles since nitrogen is a vital element for all living organisms. Artificial nitrogen fixation via a (photo)electrochemical system powered by renewables provides an alternative route to resource- and carbon-intensive thermochemical processes. (Photo)electrochemical nitrogen fixation at a large scale necessitates the discovery of active, selective, and stable heterogeneous (photo)electrocatalysts. In addition, the use of advanced in situ and operando spectroscopic techniques is needed to pinpoint the underlying reaction mechanisms. The selectivity of nitrogen (N₂) molecules on the catalyst surface and suppressing thermodynamically favorable side reactions (e.g., hydrogen evolution reaction) are the main bottlenecks in improving the rate of (photo)electrochemical nitrogen fixation in aqueous solutions. The rational design of electrode, electrolyte, and reactors is required to weaken the strong nitrogen-nitrogen triple bond (N≡N) at or near ambient conditions. This Account covers our group's recent advances in synthesizing shape-controlled hybrid plasmonic nanoparticles, including plasmonic-semiconductor and plasmonic-transition metal nanostructures with increased surface areas. The nanocatalysts' selectivity and activity toward nitrogen conversion are benchmarked in liquid- and gas-phase electrochemical systems. We leverage operando vibrational-type spectroscopy (i.e., surface-enhanced Raman spectroscopy (SERS)) to identify intermediate species relevant to nitrogen fixation at the electrode-electrolyte interface to gain mechanistic insights into reaction mechanisms, leading to the discovery of more efficient catalysts. Operando SERS revealed that the nitrogen reduction reaction (NRR) to ammonia on hybrid plasmonic-transition metal nanoparticle surfaces (e.g., Pd-Ag) occurs through an associative mechanism. In the NRR process, hydrazine (N₂H₄) is consumed as an intermediate species. A femtosecond pulsed laser is used to synthesize hybrid plasmonic photocatalysts with homogeneously distributed Pd atoms on a Au nanorod surface, resulting in enhanced optoelectronic and catalytic properties. The overarching goal is to develop modular photoelectrochemical systems for long-duration renewable energy storage. In the context of nitrogen fixation, we aim to propose strategies to manage the nitrogen cycle through the interconversion of N₂ and active nitrogen-containing compounds (e.g., NH₃, NO_x), enabling a circular nitrogen economy with sustainable and positive social and economic outcomes. The versatile approaches presented in this Account can inform future opportunities in (photo)electrochemical energy conversion systems and solar fuel-based applications.

Recent Advances on Pt-Free Electro-Catalysts for Dye-Sensitized Solar Cells

Since Prof. Grätzel and co-workers achieved breakthrough progress on dye-sensitized solar cells (DSSCs) in 1991, DSSCs have been extensively investigated and wildly developed as a potential renewable power source in the last two decades due to their low cost, low energy-intensive processing, and high roll-to-roll compatibility. During this period, the highest efficiency recorded for DSSC under ideal solar light (AM 1.5G, 100 mW cm-2) has increased from ~7% to ~14.3%. For the practical use of solar cells, the performance of photovoltaic devices in several conditions with weak light irradiation (e.g., indoor) or various light incident angles are also an important item. Accordingly, DSSCs exhibit high competitiveness in solar cell markets because their performances are less affected by the light intensity and are less sensitive to the light incident angle. However, the most used catalyst in the counter electrode (CE) of a typical DSSC is platinum (Pt), which is an expensive noble metal and is rare on earth. To further reduce the cost of the fabrication of DSSCs on the industrial scale, it is better to develop Pt-free electro-catalysts for the CEs of DSSCs, such as transition metallic compounds, conducting polymers, carbonaceous materials, and their composites. In this article, we will provide a short review on the Pt-free electro-catalyst CEs of DSSCs with superior cell compared to Pt CEs; additionally, those selected reports were published within the past 5 years.

Lignin-Based Polymer Electrolyte Membranes for Sustainable Aqueous Dye-Sensitized Solar Cells

In the quest for sustainable materials for quasi-solid-state (QS) electrolytes in aqueous dye-sensitized solar cells (DSSCs), novel bioderived polymeric membranes were prepared in this work by reaction of preoxidized kraft lignin with poly(ethylene glycol)diglycidylether (PEGDGE). The effect of the PEGDGE/lignin relative proportions on the characteristics of the obtained membranes was thoroughly investigated, and clear structure-property correlations were highlighted. In particular, the glass transition temperature of the materials was found to decrease by increasing the amount of PEGDGE in the formulation, indicating that polyethylene glycol chains act as flexible segments that increase the molecular mobility of the three-dimensional polymeric network. Concurrently, their swelling ability in liquid electrolyte was found to increase with the concentration of PEGDGE, which was also shown to influence the ionic transport efficiency within the membrane. The incorporation of these lignin-based cross-linked systems as QS electrolyte frameworks in aqueous DSSCs allowed the preparation of devices with excellent long-term stability under UV-vis light, which were found to be superior to benchmark QS-DSSCs incorporating state-of-the-art carboxymethylcellulose membranes. This study provides the first demonstration of lignin-based QS electrolytes for stable aqueous DSSCs, establishing a straightforward strategy to exploit the potential of lignin as a functional polymer precursor for the field of sustainable photovoltaic devices.

Electrocatalytic and structural properties and computational calculation of PAN-EC-PC-TPAI-I2 gel polymer electrolytes for dye sensitized solar cell application

In this study, gel polymer electrolytes (GPEs) were prepared using polyacrylonitrile (PAN) polymer, ethylene carbonate (EC), propylene carbonate (PC) plasticizers and different compositions of tetrapropylammonium iodide (TPAI) salt. Linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) measurements were done using non-blocking Pt-electrode symmetric cells. The limiting current (J_lim), apparent diffusion coefficient of triiodide ions and exchange current were found to be 12.76 mA cm⁻², 23.41 × 10⁻⁷ cm² s⁻¹ and 11.22–14.24 mA cm⁻², respectively, for the GPE containing 30% TPAI. These values are the highest among the GPEs with different TPAI contents. To determine the ionic conductivity, the EIS technique was employed with blocking electrodes. The GPE containing 30% TPAI exhibited the lowest bulk impedance, R_b (22 Ω), highest ionic conductivity (3.62 × 10⁻³ S cm⁻¹) and lowest activation energy. Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) techniques were utilized for structural characterization. Functional group interactions among PAN, EC, PC and TPAI were studied in the FTIR spectra of the GPEs. An up-shift of the XRD peak indicates the polymer–salt interaction and possible complexation of the cation (TPA⁺ ion) with the lone pair of electrons containing site –C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> N at the N atom in the host polymer matrix. On the other hand, computational study shows that TPAI-PAN based GPE possesses the lowest frontier orbital bandgap, which coincided with the enhanced electrochemical and electrocatalytic performance of GPE. The dye-sensitized solar cell (DSSC) fabricated with these GPEs showed that the J_SC (19.75 mA cm⁻²) and V_OC (553.8 mV) were the highest among the GPEs and hence the highest efficiency, η (4.76%), was obtained for the same electrolytes.

In this study, gel polymer electrolytes (GPEs) were prepared using polyacrylonitrile (PAN) polymer, ethylene carbonate (EC), propylene carbonate (PC) plasticizers and different compositions of tetrapropylammonium iodide (TPAI) salt.

Cobalt and Carbon Complex as Counter Electrodes in Dye-Sensitized Solar Cells

We developed cobalt and carbon complex materials as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs) to replace conventional platinum (Pt) CEs. Co12 and Co15, both of which are basic cobalt derivatives, showed good redox potential with a suitable open-circuit voltage (VOC); however, their poor electrical conductivity engendered a low short-circuit current (JSC) and fill factor (FF). Mixing them with carbon black (CB) improved the electrical conductivity of the CE; in particular, JSC and FF were considerably improved. Further improvement was achieved by combining cobalt derivatives and CB through thermal sintering to produce a novel CoCB material as a CE. CoCB had good electrical conductivity and electrocatalytic capability, and this further enhanced both JSC and VOC. The optimized device exhibited a power conversion efficiency (PCE) of 7.44%, which was higher than the value of 7.16% for a device with a conventional Pt CE. The conductivity of CoCB could be further increased by mixing it with PEDOT:PSS, a conducting polymer. The device’s JSC increased to 18.65 mA/cm2, which was considerably higher than the value of 14.24 mA/cm2 for the device with Pt CEs. The results demonstrate the potential of the cobalt and carbon complex as a CE for DSSCs.

An Overview on Anodes for Magnesium Batteries: Challenges towards a Promising Storage Solution for Renewables

Magnesium-based batteries represent one of the successfully emerging electrochemical energy storage chemistries, mainly due to the high theoretical volumetric capacity of metallic magnesium (i.e., 3833 mAh cm-3 vs. 2046 mAh cm-3 for lithium), its low reduction potential (-2.37 V vs. SHE), abundance in the Earth's crust (104 times higher than that of lithium) and dendrite-free behaviour when used as an anode during cycling. However, Mg deposition and dissolution processes in polar organic electrolytes lead to the formation of a passivation film bearing an insulating effect towards Mg2+ ions. Several strategies to overcome this drawback have been recently proposed, keeping as a main goal that of reducing the formation of such passivation layers and improving the magnesium-related kinetics. This manuscript offers a literature analysis on this topic, starting with a rapid overview on magnesium batteries as a feasible strategy for storing electricity coming from renewables, and then addressing the most relevant outcomes in the field of anodic materials (i.e., metallic magnesium, bismuth-, titanium- and tin-based electrodes, biphasic alloys, nanostructured metal oxides, boron clusters, graphene-based electrodes, etc.).

2D and 3D Immobilization of Carbon Nanomaterials into PEDOT via Electropolymerization of a Functional Bis-EDOT Monomer

Carbon nanomaterials (CNMs) and conjugated polymers (CPs) are actively investigated in applications such as optics, catalysis, solar cells, and tissue engineering. Generally, CNMs are implemented in devices where the relationship between the active elements and the micro and nanostructure has a crucial role. However, they present some limitations related to solubility, processibility and release or degradability that affect their manufacturing. CPs, such as poly(3,4-ethylenedioxythiophene) (PEDOT) or derivatives can hide this limitation by electrodeposition onto an electrode. In this work we have explored two different CNMs immobilization methods in 2D and 3D structures. First, CNM/CP hybrid 2D films with enhanced electrochemical properties have been developed using bis-malonyl PEDOT and fullerene C60. The resulting 2D films nanoparticulate present novel electrochromic properties. Secondly, 3D porous self-standing scaffolds were prepared, containing carbon nanotubes and PEDOT by using the same bis-EDOT co-monomer, which show porosity and topography dependence on the composition. This article shows the validity of electropolymerization to obtain 2D and 3D materials including different carbon nanomaterials and conductive polymers.

Synthesis and characterization of a conjugated porphyrin dyad entangled with carboxyl functionalized benzimidazolium: an efficient metal free sensitizer for DSSCs

Synthesis of a novel metal free porphyrin dyad with excellent electronic coupling and anti-aggregating stability via strong anchoring to semiconductor through six carboxyl groups exhibiting 6.9% PCE in a truly energy generating DSSC.

A single layer deposition of Li-doped mesoporous TiO2 beads for low-cost and efficient dye-sensitized solar cells

Cost-effective DSCs with superior electronic properties are gained by a reduction in electronic trap states and outstanding light scattering and harvesting.

Topology-Controlled Hydration of Polymer Network in Hydrogels for Solar-Driven Wastewater Treatment

Solar-driven interfacial evaporation provides a promising method for sustainable freshwater production. However, high energy consumption of vapor generation fundamentally restricts practicality of solar-driven wastewater treatment. Here a facile strategy is reported to control the hydration of polymer network in hydrogels, where densely cross-linked polymers serving as a framework are functionalized by a highly hydratable polymeric network. The hydration of polymer chains generates a large amount of weakly bounded water molecules, facilitating the water evaporation. As a result, the hydrogel-based solar evaporator can extract water from a variety of contaminants such as salts, detergents, and heavy metal components using solar energy with long-term durability and stability. This work demonstrates an effective way to tune the interaction between water and materials at a molecular level, as well as an energy-efficient water treatment technology toward wastewater containing complex contaminants.

A diketopyrrolopyrrole dye-based dyad on a porous TiO2 photoanode for solar-driven water oxidation

Dye-sensitised photoanodes modified with a water oxidation catalyst allow for solar-driven O2 evolution in photoelectrochemical cells. However, organic chromophores are generally considered unsuitable to drive the thermodynamically demanding water oxidation reaction, mainly due to their lack of stability upon photoexcitation. Here, the synthesis of a dyad photocatalyst (DPP-Ru) consisting of a diketopyrrolopyrrole chromophore (DPPdye) and ruthenium-based water oxidation catalyst (RuWOC) is described. The DPP-Ru dyad features a cyanoacrylic acid anchoring group for immobilisation on metal oxides, strong absorption in the visible region of the electromagnetic spectrum, and photoinduced hole transfer from the dye to the catalyst unit. Immobilisation of the dyad on a mesoporous TiO2 scaffold was optimised, including the use of a TiCl4 pretreatment method as well as employing chenodeoxycholic acid as a co-adsorbent, and the assembled dyad-sensitised photoanode achieved O2 evolution using visible light (100 mW cm-2, AM 1.5G, λ > 420 nm). An initial photocurrent of 140 μA cm-2 was generated in aqueous electrolyte solution (pH 5.6) under an applied potential of +0.2 V vs. NHE. The production of O2 has been confirmed by controlled potential electrolysis with a faradaic efficiency of 44%. This study demonstrates that metal-free dyes are suitable light absorbers in dyadic systems for the assembly of water oxidising photoanodes.

Hydrogel Electrolytes Based on Xanthan Gum: Green Route towards Stable Dye-Sensitized Solar Cells

The investigation of innovative electrolytes based on nontoxic and nonflammable solvents is an up-to-date, intriguing challenge to push forward the environmental sustainability of dye-sensitized solar cells (DSSCs). Water is one of the best choices, thus 100% aqueous electrolytes are proposed in this work, which are gelled with xanthan gum. This well-known biosourced polymer matrix is able to form stable and easily processable hydrogel electrolytes based on the iodide/triiodide redox couple. An experimental strategy, also supported by the multivariate chemometric approach, is used here to study the main factors influencing DSSCs efficiency and stability, leading to an optimized system able to improve its efficiency by 20% even after a 1200 h aging test, and reaching an overall performance superior to 2.7%. In-depth photoelectrochemical investigation demonstrates that DSSCs performance based on hydrogel electrolytes depends on many factors (e.g., dipping conditions, redox mediator concentrations, etc.), that must be carefully quantified and correlated in order to optimize these hydrogels. Photovoltaic performances are also extremely reproducible and stable in an open cell filled in air atmosphere, noticeably without any vacuum treatments.

Across the Board: Federico Bella on Electrochemical Nitrogen Reduction

In this series of articles, the board members of ChemSusChem discuss recent research articles that they consider of exceptional quality and importance for sustainability. This entry features Prof. F. Bella, who discusses the electrochemical reduction of nitrogen to produce ammonia through the addition of protons and electrons under mild conditions (25 °C, 1 atm). This reaction has the potential to replace the energy-intensive traditional Haber-Bosch process but faces several challenges and pitfalls.

Exploring Structure-Property Relationships in a Bio-Inspired Family of Bipodal and Electronically-Coupled Bistriphenylamine Dyes for Dye-Sensitized Solar Cell Applications

A bio-inspired family of organic dyes with bichromic-bipodal architectures were synthesized and tested in dye-sensitized solar cells (DSSC). These dyes are comprised of a D-π-D-A motif with two triphenylamine (TPA) units acting as donors (D) and two cyanoacetic acid acceptors (A) capable of binding to a titania semiconductor. The role of the thiophene π-spacer bridging the two TPA units was examined and the distal TPA (relative to TiO2) was modified with various substituents (-H, -OMe, -SMe, -OHex, -3-thienyl) and contrasted against benchmark L1. It was found that the two TPA donor units could be tuned independently, where π-spacers can tune the proximal TPA and R-substituents can tune the distal TPA. The highest performing DSSCs were those with -SMe, 3-thienyl, and -H substituents, and those with one spacer or no spacers. The donating abilities of R-substituents was important, but their interactions with the electrolyte was more significant in producing high performing DSSCs. The introduction of one π-spacer provided favourable electronic communication within the dye, but more than one was not advantageous.