Photoanodes for Aqueous Solar Cells: Exploring Additives and Formulations Starting from a Commercial TiO2 Paste

Whereas the commercialization of dye‐sensitized solar cells (DSSCs) is finally proceeding taking advantage of their low cost and tunable optical features, such as colour and transparency for both indoor and building‐integrated applications, the corresponding aqueous counterpart is still at its infancy. As the TiO2 electrode is a fundamental component for hybrid solar cells, this work investigates the effect of different molecular (α‐terpineol, propylene carbonate) and polymeric (polyethylene oxide, polyethylene glycol, carboxymethyl cellulose and xanthan gum) additives that can be introduced into a commercial TiO2 paste for for screen‐printing (or doctor blade). Among all, the addition of polyethylene glycol leads to the best cell performances, with markedly increased short‐circuit current density (+18 %) and power conversion efficiency (+48 %) with respect to the pristine (commercial) counterpart. When further explored at different concentration levels, electrodes fabricated from polyethylene glycol‐based pastes show different morphologies, thicknesses and performances, which are investigated through (photo)electrochemical, structural, physical‐chemical and microscopic techniques

Photoanodes for Aqueous Solar Cells: Exploring Additives and Formulations Starting from a Commercial TiO2 Paste

Whereas the commercialization of dye‐sensitized solar cells (DSSCs) is finally proceeding taking advantage of their low cost and tunable optical features, such as colour and transparency for both indoor and building‐integrated applications, the corresponding aqueous counterpart is still at its infancy. As the TiO2 electrode is a fundamental component for hybrid solar cells, this work investigates the effect of different molecular (α‐terpineol, propylene carbonate) and polymeric (polyethylene oxide, polyethylene glycol, carboxymethyl cellulose and xanthan gum) additives that can be introduced into a commercial TiO2 paste for for screen‐printing (or doctor blade). Among all, the addition of polyethylene glycol leads to the best cell performances, with markedly increased short‐circuit current density (+18 %) and power conversion efficiency (+48 %) with respect to the pristine (commercial) counterpart. When further explored at different concentration levels, electrodes fabricated from polyethylene glycol‐based pastes show different morphologies, thicknesses and performances, which are investigated through (photo)electrochemical, structural, physical‐chemical and microscopic techniques

Recent advances in eco-friendly and cost-effective materials towards sustainable dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs), as emerging photovoltaic technology, have been thoroughly and extensively investigated in the last three decades. Since their first appearance in 1991, DSSCs have gained increasing attention and have been classified as feasible alternatives to conventional photovoltaic devices due to their numerous advantages, such as cheap and simple preparation methods, the possibility of being integrated in buildings and astonishing performances under indoor and diffuse illumination conditions. Photoconversion efficiencies of up to 14% and 8% have been obtained for lab-scale devices and modules, respectively. Albeit the efforts made, these values seem arduous to be outdone, at least under simulated solar radiation. Nevertheless, recent lab-scale systems have demonstrated photoconversion efficiencies of up to 33% under indoor illumination (i.e. 1000 lux) leading to an actual Renaissance (or Revival) of these devices. It is worth mentioning that scientists in this field are developing innovative materials aiming at long-term and efficient devices, being the concept of sustainability often set apart. However, in light of effective commercialization of this technology, stability, efficiency and sustainability should be considered as the essential keywords. Nowadays, DSSCs are finding a “new way back” towards sustainability and rather a huge number of reports have focused on the preparation of green and cost-effective materials to replace the standard ones. In this scenario, the present review aims to give an overview of the most adopted strategies to enhance the sustainability of materials in classical DSSC components (e.g. sensitizer, redox couple, electrolyte and counter-electrode), including smart synthesis and deposition procedures, which currently represent utmost important topics in the scientific community

Platinum-free photoelectrochromic devices working with copper-based electrolytes for ultrastable smart windows

Photoelectrochromic systems are devices designed for large-scale manufacturing of smart windows, capable of changing their transmittance according to external environmental conditions. This communication proposes the replacement of the two most critical photoelectrochemical device components studied so far, namely the counter electrode and the redox mediator. Regarding the first, graphene nanoplatelets are used to replace platinum, maintaining both its optical and electrocatalytic properties, and at the same time reducing the device cost. Secondly, a copper-based redox pair was chosen to solve the corrosion problems typically encountered with the iodine-based mediator. The combination of the above components led to devices with high performance (coloration speeds in the order of seconds, with a maximum contrast ratio of 10.4 : 1), as well as the achievement of a long-term stability record (over 400 days) for these photoelectrochromic systems

Photoanodes for Aqueous Solar Cells: Exploring Additives and Formulations Starting from a Commercial TiO2 Paste

Whereas the commercialization of dye‐sensitized solar cells (DSSCs) is finally proceeding taking advantage of their low cost and tunable optical features, such as colour and transparency for both indoor and building‐integrated applications, the corresponding aqueous counterpart is still at its infancy. As the TiO2 electrode is a fundamental component for hybrid solar cells, this work investigates the effect of different molecular (α‐terpineol, propylene carbonate) and polymeric (polyethylene oxide, polyethylene glycol, carboxymethyl cellulose and xanthan gum) additives that can be introduced into a commercial TiO2 paste for for screen‐printing (or doctor blade). Among all, the addition of polyethylene glycol leads to the best cell performances, with markedly increased short‐circuit current density (+18 %) and power conversion efficiency (+48 %) with respect to the pristine (commercial) counterpart. When further explored at different concentration levels, electrodes fabricated from polyethylene glycol‐based pastes show different morphologies, thicknesses and performances, which are investigated through (photo)electrochemical, structural, physical‐chemical and microscopic techniques

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.)

An exploratory study of MoS2 as anode material for potassium batteries

Potassium-based batteries represent one of the emerging classes of post-lithium electrochemical energy storage systems in the international scene, due to both the abundance of raw materials and achievable cell potentials not far from those of lithium batteries. In this context, it is important to define electrodes and electrolytes that give reproducible performance and that can be used by different research groups as an internal standard when developing new materials. We propose molybdenum disulfide (MoS2) as a valid anode choice, being a commercial and easily processable material, the 2D layered structure of which is promising for large potassium ions reversible storage. It has been proven to work for hundreds of cycles, keeping a constant specific capacity around 100 mAh g−1 while also preserving its electrochemical interphase and morphology

Unreported resistance in the charge transport limits the photoconversion efficiency of aqueous dye-sensitised solar cells: An electrochemical impedance spectroscopy study

In this work, a thorough electrochemical impedance spectroscopy study is performed of both liquid and polymeric aqueous dye-sensitized solar cells (a-DSSCs), which are also compared with conventional organic solvent-based devices. The main purpose is unveiling phenomena limiting the efficiency of water-based photovoltaics. Indeed, electrochemical impedance spectroscopy spectra of a-DSSCs show two peculiar (and unreported) features that are not observed in organic-based DSSCs. The higher frequency one (R45°) is likely associated with a slowdown of the diffusion kinetics of the redox mediator: it is due to the breakdown of the hydrogen-bond network of the aqueous environment, which was also supported by density functional theory calculations. The lower-frequency feature is associated with the additional amount of energy required for the breakdown at the semiconductor/FTO interface of the adducts between protons (coming from the solvent) and electrons localized in the TiO2 surface trap-states. This ‘disruption energy’ results in a resistive element (RIC) that inversely correlates with the device efficiency. Very interestingly, RIC depends on the applied potential and becomes negligible only at much more positive values than VOC. Tailored equivalent circuits implementing simultaneously R45° and RIC are currently under investigation

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

Cardanol-Derived Epoxy Resins as Biobased Gel Polymer Electrolytes for Potassium-Ion Conduction

In this study, biobased gel polymer electrolyte (GPE) membranes were developed via the esterification reaction of a cardanol-based epoxy resin with glutaric anhydride, succinic anhydride, and hexahydro-4-methylphthalic anhydride. Nonisothermal differential scanning calorimetry was used to assess the optimal curing time and temperature of the formulations, evidencing a process activation energy of ∼65–70 kJ mol–1. A rubbery plateau modulus of 0.65–0.78 MPa and a crosslinking density of 2 × 10–4 mol cm–3 were found through dynamic mechanical analysis. Based on these characteristics, such biobased membranes were tested for applicability as GPEs for potassium-ion batteries (KIBs), showing an excellent electrochemical stability toward potassium metal in the −0.2–5 V voltage range and suitable ionic conductivity (10–3 S cm–1) at room temperature. This study demonstrates the practical viability of these biobased materials as efficient GPEs for the fabrication of KIBs, paving the path to increased sustainability in the field of next-generation battery technologies