Aqueous Dye-sensitized Solar Cells Research Articles

(Invited) Sustainable and Non-Toxic Hydrogel-Based Dye-Sensitized Solar Cell: Performance Evaluation Under Indoor Illumination

Indoor photovoltaics have gathered growing interest amongst researchers, as a mean to exploit the indoor lighting we use in our daily life to power small devices. Dye-sensitized solar cells (DSSCs) represent good candidates for such applications[1]. However, when it comes to indoor applications, there is an increased demand for non-toxic and non-flammable solvents for electrolytes. The implementation of water-based electrolytes is a promising way to address these issues, whilst also ensuring the eco-friendliness and sustainability of these devices[2]. In this work, aqueous gel electrolytes incorporating a iodide/triiodide redox couple were made with a bio-sourced polymer, xanthan gum[3]. DSSCs were assembled using screen-printed TiO2 semiconducting layers treated with TiCl4 and sensitized with an organic dye, D131. As counter electrode, Pt sputtered FTO was used. The performance of the cells was investigated under indoor light intensities between 500 and 1000 lux.[1]: Jilakian, M., & Ghaddar, T. H. (2022). Eco-Friendly Aqueous Dye-Sensitized Solar Cell with a Copper (I/II) Electrolyte System: Efficient Performance under Ambient Light Conditions. ACS Applied Energy Materials, 5(1), 257-265.[2]: Bella, F., Gerbaldi, C., Barolo, C., & Grätzel, M. (2015). Aqueous dye-sensitized solar cells. Chemical Society Reviews, 44(11), 3431-3473.[3]: Galliano, S., Bella, F., Bonomo, M., Viscardi, G., Gerbaldi, C., Boschloo, G., & Barolo, C. (2020). Hydrogel electrolytes based on xanthan gum: green route towards stable dye-sensitized solar cells. Nanomaterials, 10(8), 1585.

Impedance spectroscopy using microscopic reference electrodes to analyze different rate-determining steps in aqueous dye-sensitized solar cells using nitroxide radicals as redox mediators

For new components in dye-sensitized solar cells (DSSCs), identification and quantification of rate-limiting steps is needed to evaluate their applicability. This is particularly important if fundamental changes are studied. In this work, the use of a micro-reference electrode in DSSCs is proposed to increase the significance of electrochemical impedance spectroscopy. The recombination of charge carriers at the photoanode and the regeneration of redox mediators at the counter electrode, which typically occur on similar timescales, could be studied separately but simultaneously in cells under operating conditions. This is particularly useful in the study of water-based DSSCs. Here, cells with 2,2,6,6-Tetramethylpiperidinoxyl (TEMPO) or 4-Hydroxy-TEMPO (OH-TEMPO) as redox mediators using additives like 1-Methylbenzimidazole (MBI) are discussed. It was revealed that the charge transfer resistance (RCE) for the reduction of the oxidized redox mediator at the counter electrode (CE) limits the fill factor (FF) of such DSSCs. TEMPO/MBI electrolytes yielded low RCE and high FF, whereas OH-TEMPO in otherwise identical cells resulted in large RCE, low FF, and low conversion efficiencies. This indicates that the interface between the CE and the electrolyte significantly influences the DSSC performance of these cells and strongly depends on the electrolyte composition. Important optimization strategies could be discussed based on the present results.

Copper-Based Aqueous Dye-Sensitized Solar Cell: Seeking a Sustainable and Long-Term Stable Device

Copper-Based Aqueous Dye-Sensitized Solar Cell: Seeking a Sustainable and Long-Term Stable Device

Kinetics of Charge Transfer at Carbon-Based Counter Electrodes for Dye-Sensitized Solar Cells with Aqueous Electrolytes

Dye-sensitized solar cells (DSSCs) might provide a highly sustainable alternative for next generation photovoltaics. This is due to their low-energy production from abundant materials, short energy payback time, high efficiency under low illumination intensities (i.e., diffuse light or indoor conditions), and versatile concepts of applications. However, some commonly used electrolyte components are environmentally problematic. Acetonitrile or other volatile organic solvents, e.g., as well as carcinogenic cobalt complexes should not leak from DSSCs. Sealing foils, however, which are typically used to prevent such leakage, carry a risk of long-term failure.Replacing the organic solvent by water offers several advantages, as it is environmentally benign, less volatile and the cell function, further, cannot be damaged by the intrusion of water vapor. Instead of Co-complexes, e.g., the stable organic radical TEMPO (2,2,6,6-tretramethylpiperidine-1-oxyl) can serve as an alternative redox mediator with a highly positive redox potential (0.71 V vs. NHE). Using TEMPO, power conversion efficiencies (PCE) of up to 4.3% and high open-circuit voltages (V oc = 0.955 V) have been reported.[1] However, the use of TEMPO is limited by its solubility in water (C max < 0.15 M). Its derivative 4-hydroxy-TEMPO (OH-TEMPO) possesses a significantly higher solubility in water (C max > 2 M) and a more positive redox potential (0.81 V vs. NHE), making it a promising candidate as a redox mediator.In this work, we built DSSCs with TEMPO and OH-TEMPO based aqueous electrolytes, Y123-sensitized TiO2 photoanodes, and counter electrodes coated with poly(3,4-ethylenedioxythiphene) (PEDOT). For OH-TEMPO, the short-circuit current density (j sc) and open-circuit voltage were higher than with TEMPO, but the fill factor (FF) and the PCE were significantly lower. By impedance studies, large charge transfer resistances at the counter electrode (R CE) were obtained for OH-TEMPO in combination with additives such as 1-methylbenzimidazole (MBI), indicating a strong kinetic limitation of the OH-TEMPO+ reduction. However, we found that such additives as MBI or other organic compounds, are necessary to suppress recombination at the photoanode/electrolyte interface. Thus, we subsequently studied different counter electrode materials, such as platinum (reference), conducting polymers, and carbon materials, in contact to OH-TEMPO electrolytes with MBI to determine R CE and find suitable materials for the application in DSSCs.[1] Yang, W., Söderberg, M., Eriksson, A. I. K. & Boschloo, G. Efficient aqueous dye-sensitized solar cell electrolytes based on a TEMPO/TEMPO+ redox couple. RSC Advances 5, 26706–26709 (2015).

Unreported resistance in 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.

Eco-Friendly Aqueous Dye-Sensitized Solar Cell with a Copper(I/II) Electrolyte System: Efficient Performance under Ambient Light Conditions

Organic solvents used in electrolytes of dye-sensitized solar cells (DSCs) are generally toxic and not environmentally safe, which renders their use, especially in indoor solar modules, difficult. In this paper, an eco-friendly DSC is presented based on an aqueous electrolyte system where the redox couple is composed of a water-soluble polypyridyl copper complex, [Cu(I)(dc-dmbpy)2Cl/Cu(II)(dc-dmbpy)2Cl2, dc-dmbpy = 6,6′-dimethyl-2,2′-bipyridine-4,4′-dicarboxylate]. Good photo-conversion efficiencies (PCE % ∼ 7%) have been attained with this water-soluble redox couple under ambient light conditions when coupled with a ruthenium-based dye, C106. This is the first time such a copper complex is in an aqueous DSC and eventually lays a foundation for the further development of eco-friendly water-based DSCs.

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).

Continuous Solar Desalination of Brackish Water via a Monolithically Integrated Redox Flow Device

Several water/salt separation processes are currently being developed to employ sunlight for sustainable water desalination. Here, we report a redox flow process for solar desalination of brackish water, which integrated a redox flow desalination (RFD) system with an aqueous dye-sensitized solar cell (DSSC). The use of an iodide/triiodide redox electrolyte mediated light-to-electricity conversion at the photoanode and salt separation across ion-exchange membranes at relatively low voltages (< 0.5 V). The solar RFD process produced freshwater ([NaCl] < 1 g L–1) continuously from a 50-mM feed solution at 10.3 LMH productivity (L-freshwater m–2-area h–1) that increased to 28.8 LMH for a 20-mM feed solution. The process current efficiency was in the range of 73 ± 7%. The nonsolar RFD mode produced freshwater at a productivity of 41.1 LMH, energy consumption of 0.42 kWh m–3, and current efficiency of about 80%. Correlations derived for predicting the extent of salt removal for the different process parameters of the solar and nonsolar RFD processes indicated that the DSSC photocurrent is a critical factor for increasing freshwater productivity in the solar RFD mode. With further improvements in water-compatible photoanodes and redox electrolytes, the solar RFD could present a viable and sustainable approach for water desalination.

Xanthan‐Based Hydrogel for Stable and Efficient Quasi‐Solid Truly Aqueous Dye‐Sensitized Solar Cell with Cobalt Mediator

Aqueous Dye-Sensitized Solar Cells In article number 2000823, Federico Bella, Matteo Bonomo, and co-workers have successfully applied Design of Experiment to engineer the composition of the electrolyte in quasi-solid aqueous DSSCs that leads to photoconversion efficiency approaching 5% and remarkable stability. Aqueous dye-sensitized solar cells are an emerging alternative to enhance both lifetime and sustainability of traditional DSSCs.

Tin(IV) oxide nanoparticulate films for aqueous dye-sensitized solar cells

Reported solar conversion efficiencies of aqueous dye-sensitized solar cells (DSSCs) trail those of traditional organic electrolyte-based systems but offer the potential for lower environmental impact and overall cost. Methods for improving the photochemical activity of aqueous DSSCs could also impact progress in related fields such as solar fuels and solar batteries. This work presents the first study solely focused on the use of SnO2-based photoanodes for use in aqueous DSSCs. Material design and interfacial engineering are critical to the effective use of SnO2 in this context, and it is found that mesoporous films comprised of both large 1–2 μm flower-like SnO2 particles and small 10–20 nm spherical SnO2 particles provide better performance than films composed of only one particle type. Insulating TiO2 coatings further improve the performance, and this work presents a facile liquid phase deposition strategy under ambient conditions using an aqueous TiF62- solution that proves more effective than the widely used method with TiCl4 for fabricating high-performing SnO2@TiO2 photoanode surfaces. The best aqueous DSSCs reported here using cis-bis(isothiocyanato)-bis(2,2′-bipyridyl-4,4′-dicarboxylato)ruthenium(II) dye and simple I3-/I- electrolyte achieve a power conversion efficiency of 0.7% which eclipses the first reported TiO2-based DSSC using otherwise identical dye and electrolyte composition.

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.

Correction to: Natural rubber (Hevea Brasiliensis)-based quasi-solid electrolyte as a potential candidate for arresting recombination and improving performance in aqueous dye-sensitized solar cells

Correction to: Natural rubber (Hevea Brasiliensis)-based quasi-solid electrolyte as a potential candidate for arresting recombination and improving performance in aqueous dye-sensitized solar cells

Natural rubber (Hevea Brasiliensis)-based quasi-solid electrolyte as a potential candidate for arresting recombination and improving performance in aqueous dye-sensitized solar cells

We successfully fabricated dye sensitized solar cells (DSSCs) employing a quasi-solid state electrolyte based on pristine insulator natural rubber latex from Hevea brasiliensis and iodide electrolyte. Optimized devices exhibited a maximum power conversion efficiency (PCE) of 1.14% under simulated sunlight with 90 mW/cm2 illumination, 0.46% under 100 mW/cm2 and 7.85% under low intensity illumination of 1000 lx (Daylight LED). This gives a new perspective for the introduction of natural rubber latex abundant in nature as an additive to the water based redox mediator in order to improve the PCE in DSSC. A detailed study on the interfacial charge transfer in fabricated devices revealed that the introduction of rubber helped in arresting the back electron transfer, which was predominant in aqueous electrolyte based dye sensitized solar cell. This opens up opportunities for water-based electrolyte based on natural raw materials to be used in nature inspired DSSC technology.

Effect of the TiO2 Anchoring of a Hydrophobic Ionic Liquid in a Fully Aqueous DSSC

This article describes the effect on the efficiency of a fully aqueous dye-sensitized solar cell (DSSC) after the anchoring of the hydrophobic and halogen-free ionic liquid (IL) trioctylmethyl ammonium dodecanedioate (DTMA) on its titanium oxide (TiO2) photo-anode surface. In comparison with nontreated DTMA DSSCs, efficiency increments of 137% and 176% were observed when azo dye Red Reactive 2 and N3 dye were employed as sensitizers, respectively. Since V OC and I SC were increased, it was concluded that DTMA reinforced the dye-TiO2 anchoring, shifted negatively the levels of photo-anode conduction bands, improved electron injection, and reduced recombination losses.

Towards Improvement of Photovoltaic Performance of Aqueous Dye-sensitized Solar Cells by Tungsten-doped Mesoporous Nanobeads TiO2 Working Electrode

Tungsten doped (W-doped) TiO2 mesoporous nanobeads, possessing high surface area and superior scattering effect, were used for photoanode preparation. The W-doping would induce a positive shift of the TiO2 conduction band, and enhance the driving force for electron injection and collection efficiencies. The electrochemical impedance spectra indicated a retarded charge recombination and increased electron diffusion length after W-doping. By fine-tuning the W-doping concentration to 0.25%, aqueous DSCs produced a significant improved the open circuit voltage of 712 mV and a short circuit current of 7.05 mA·cm-2, leading to an overall increased power conversion efficiency of 3.40% at 1 000 W·m-2 simulated irradiation, which is roughly 25% enhancement compared to that without W-doping photoanode.

Photoanode for Aqueous Dye-Sensitized Solar Cells based on a Novel Multicomponent Thin Film.

Most of the dye-sensitized solar cells (DSSCs) developed so far use organic electrolytes and water-sensible sensitizers. The search for aqueous DSSCs, a promising technology for solar-energy conversion, implies finding materials that are stable in aqueous solution. In this study, Prussian blue (PB) was utilized as an innovative sensitizer in a photoanode for DSSCs and a novel synthetic approach to a carbon nanotubes/TiO2 /PB nanocomposite thin film was developed. The photoresponse was evaluated in a total aqueous electrolyte, and photocurrents of 600 μA cm-2 were achieved.

Finely tuning electrolytes and photoanodes in aqueous solar cells by experimental design

If opportunely developed and optimized, aqueous dye-sensitized solar cells can be considered a truly low impact photovoltaic device, with no toxic components. Here we report the use of design of experiments as a useful chemometric technique for the concurrent investigation of a series of experimental factors that directly influence the proper operation of these photoelectrochemical cells. Results obtained enlighten that a solid mathematical-statistical approach is fundamental to support the researchers and effectively drive the experiments towards the achievements of optimal operating conditions of any new energy device, thus bypassing the energy/time consuming steps of traditional monovariate one-factor-at-a-time method.

Mobilities of iodide anions in aqueous solutions for applications in natural dye-sensitized solar cells.

Dye-sensitized solar cells (DSSCs) composed of aqueous electrolytes represent an environmentally friendly, low-cost, and concrete alternative to standard DSSCs and typical solar cells. Although flammable and toxic organic-solvent-based electrolytes have so far been employed more than simpler (iodide) aqueous solutions, recently recorded efficiencies of water-based DSSCs suggest a trend inversion in the near future. Here, we present a study, based on both experiments and ab initio molecular dynamics simulations, in which assessments on the efficiencies of three water electrolytes commonly employed in DSSCs (i.e., LiI, NaI, and KI) are reported. In particular, by atomistically tracing the ability of the iodides as charge carriers and by experimentally measuring the generated currents, we demonstrate that NaI aqueous solutions are more efficient electrolytes than LiI and KI - in descending order - in transporting electrons in DSSCs under bias. Monitoring the role played by the hydration shells of the ionic species under an electric field, we interpret, by first-principles, the various iodide mobilities. This finding, when combined with general considerations on the cation-induced effects on the TiO2 electronic structure, is able to account for the distinct efficiencies of the investigated electrolytes.

Aqueous dye-sensitized solar cell based on new ruthenium diphenyl carbazide complexes

The major challenge of the operation of every solar cell based on dye including water splitting solar cell (WSSC) and dye sensitized solar cell (DSSC) is the using organic solvent medium which causes to decompose the solar cell structure, resulting environmental impact. Here, we synthesized and characterized two new ruthenium complexes with nitrogen and oxygen donor ligands for DSSC application which show good stability on TiO2 surface in water solvent. Interestingly, the DSSC based on [Ru(dcbpy)2(DPC)]Cl, where dcbpy = 4,4-dicarboxilic acid 2,2-bipyridin and DPC = diphenylcarbazide, was shown better efficiency in water than methanol dye loading as well as N3 as a benchmark sensitizer in the same condition. The DPC-based exhibited open circuit voltage (Voc) of 0.63 V, short-circuit current density (Jsc) of 2.5 mA/cm2 and fill factor (FF) of 70%, resulting an overall power efficiency of 1.12%. The incident-photon-to-current conversion efficiency (IPCE) value is also reached to 45% for [Ru(dcbpy)2(DPC)]Cl in the same condition It is proposed that the ruthenium complex containing nitrogen and oxygen donor ligands is more stability on TiO2 and prevent the decomposition of TiO2 porous under water solvent condition.

Probing the influence of lithium cation as electrolyte additive for the improved performance of p-type aqueous dye sensitized solar cells

NiO based p-type aqueous dye-sensitized solar cells (p-DSCs) with various lithium ion concentrations in electrolytes have been studied using a series of techniques. The existence of lithium ion can form an inside electric field near the NiO working electrode surface and restrain the charge recombination, as is demonstrated by the electrochemical impedance spectroscopy measurement. The narrowing of driving force after the addition of lithium ion does not affect the efficient charge injection, while the widened energetic difference between the valance band of NiO and the redox potential of the electrolyte contributes to the improvement of photovoltage. As a result, the optimal concentration of lithium ion is found to be 1.35 M and the corresponding average power conversion efficiency of P1-dye-sensitized aqueous p-DSCs is 0.40% (measured under standard AM 1.5 G test conditions), which almost doubles that without lithium ion addition. The results suggest a very facile method for the improvement of the photovoltaic performance of p-type aqueous DSCs.