Photo-Rechargeable Asymmetric Supercapacitors Exceeding Light-to-Charge Storage Efficiency over 21% under Indoor Light.

Photo-rechargeable energy storage devices are appealing for substantial research attention because of their possible applications in the Internet of Things (IoT) and low-powered miniaturized portable electronics. However, due to the incompatibility of the photovoltaics and energy storage systems (ESSs), the overall light-to-storage efficiency is limited under indoor light conditions. Herein, a porous carbon scaffold MnO-Mn3 O4 /C microsphere-based monolithic dye-sensitized photo-rechargeable asymmetric supercapacitor (DSPC) is fabricated. The integrated DSPC has a high areal specific capacitance of 281.9 mF cm-2 at the discharge rate of 0.01 mA cm-2 . The light-to-electrical conversion efficiency of the DSSC is 27.6% under the 1000 lux compact fluorescent lamp (CFL). The DSPC shows an outstanding light-to-charge storage efficiency of 21.6%, which is higher than that reported ever. Furthermore, the fabricated polymer gel electrolyte-based quasi-solid state (QSS) DSPC shows similar overall conversion efficiency with superior cycling capability. This work shows a convenient fabrication process for a wireless power pack of interest with outstanding performance.

Effects of Several Auxiliary Acceptors and Anchoring Groups on Charge Transfer and Photophysical Properties of D-A-π-A Type DSSCs: A DFT Study.

In this paper, we performed theoretical studies on the twelve D-A-π-A type organic dyes (G-1 ~ G-3, M-1 ~ M-3, J-1 ~ J-3, and S-1 ~ S-3) with 9-phenylcarbazole as the electron donor in anticipation of the application of these dyes in dye-sensitized solar cells (DSSCs). DFT and TD-DFT methods are applied to investigate in detail the molecular geometries, frontier molecular orbitals (FMOs), absorption spectra, charge density difference (CDD), and transition density matrix (TDM) of several dyes. The results show that the M-series (M-1 ~ M-3) dyes have the largest dihedral angles between the electron donor and the auxiliary acceptor and also has the largest energy gaps in HOMO-LUMO orbitals, which greatly reduces the charge transfer efficiency. Finally, the UV-Vis absorption spectra inferred that the anchoring groups modified with o-nitrobenzoic acid (G-3, M-3, J-3, S-3) can red-shift the absorption peaks of the dyes, which results in higher light-harvesting efficiency and improves the power conversion efficiency of DSSCs. Overall, all of these dyes contribute to the improvement of photovoltaic power conversion efficiency and have potential for application in DSSCs devices.

Water as Dual-Function Plasticizer and Cosolvent in Gel Electrolytes for Dye-Sensitized Solar Cells.

This study presents a novel approach to developing eco-friendly dye-sensitized solar cells (DSSCs) using natural and renewable materials for gel polymer electrolytes (GPEs), reducing reliance on unsustainable solvents. Water is added to polar aprotic solvents, specifically ethylene carbonate/propylene carbonate (EC/PC), across various mass fractions (0:100 to 100:0). An amphiphilic hydroxypropyl cellulose (HPC) natural polymer is employed to formulate GPEs within this water-EC/PC cosolvent system, achieving successful gelation up to 50:50 mass fractions. Incorporating water reduced the gel strength and viscosity of the GPEs. Water acted as a plasticizer, enhancing the polymer chains mobility, and creating a more flexible and permeable structure. This increased ion diffusion coefficients and ion mobility, resulting in a maximum ionic conductivity of 18.17 mS cm-1. The highest efficiency achieved in DSSCs using these GPEs is 5.81%, with elevated short-circuit current density and reduced recombination losses. However, some compositions experienced syneresis, affecting their stability. The GPE with a 40:60 mass fraction exhibited superior long-term stability because it is free from syneresis, though it achieved a lower efficiency (4.83%), making it the best-performing sample. This work demonstrates the feasibility and benefits of using gel polymer electrolytes in an aqueous system, improving DSSC efficiency and sustainability.

Effects of Ti3C2Tx MXene Addition to a Co Complex/Ionic Liquid-Based Electrolyte on the Photovoltaic Performance of Solar Cells.

Redox mediators comprising I-, Co3+, and Ti3C2Tx MXene were applied to dye-sensitized solar cells (DSCs). In the as-prepared DSCs (I-DSCs), wherein hole conduction occurred via the redox reaction of I-/I3- ions, the power conversion efficiency (PCE) was not altered by the addition of Ti3C2Tx MXene. The I-DSCs were exposed to light to produce Co2+/Co3+-based cells (Co-DSCs), wherein the holes were transferred via the redox reaction of Co2+/Co3+ ions. A PCE of 9.01% was achieved in a Co-DSC with Ti3C2Tx MXene (Ti3C2Tx-Co-DSC), which indicated an improvement from the PCE of a bare Co-DSC without Ti3C2Tx MXene (7.27%). It was also found that the presence of Ti3C2Tx MXene in the redox mediator increased the hole collection, dye regeneration, and electron injection efficiencies of the Ti3C2Tx-Co-DSC, leading to an improvement in both the short-circuit current and the PCE when compared with those of the bare Co-DSC without MXene.

Photofunctions in Hybrid Systems of Schiff Base Metal Complexes and Metal or Semiconductor (Nano)Materials.

Composite materials very often provide new catalytic, optical or other physicochemical properties not observed for each component separately. Photofunctions in hybrid systems are an interesting topic of great importance for industry. This review presents the recent advances, trends and possible applications of photofunctions of hybrid systems composed of Schiff base metal complexes and metal or semiconductor (nano)materials. We focus on photocatalysis, sensitization in solar cells (DSSC-dye sensitized solar cell), ligand-induced chirality and applications in environmental protection for Cr(VI) to Cr(III) reduction, in cosmetology as sunscreens, in real-time visualization of cellular processes, in bio-labeling, and in light activated prodrug applications.

Optically Transparent Gold Nanoparticles for DSSC Counter-Electrode: An Electrochemical Characterization.

A gold nanoparticles transparent electrode was realized by chemical reduction. This work aims to compare the transparent gold nanoparticles electrode with a more commonly utilized gold-film-coated electrode in order to investigate its potential use as counter-electrode (CE) in dye-sensitized solar cells (DSSCs). A series of DSSC devices, utilizing I-/I3- and Co(III)/(II) polypyridine redox mediators [Co(dtb)3]3+/2+; dtb = 4,4'ditert-butyl-2,2'-bipyridine)], were evaluated. The investigation focused firstly on the structural characterization of the deposited gold layers and then on the electrochemical study. The novelty of the work is the realization of a gold nanoparticles CE that reached 80% of average visible transmittance. We finally examined the performance of the transparent gold nanoparticles CE in DSSC devices. A maximum power conversion efficiency (PCE) of 4.56% was obtained with a commercial I-/I3--based electrolyte, while a maximum 3.1% of PCE was obtained with the homemade Co-based electrolyte.

Dye-sensitized photoelectrochemical water oxidation through a buried junction.

Water oxidation has long been a challenge in artificial photosynthetic devices that convert solar energy into fuels. Water-splitting dye-sensitized photoelectrochemical cells (WS-DSPECs) provide a modular approach for integrating light-harvesting molecules with water-oxidation catalysts on metal-oxide electrodes. Despite recent progress in improving the efficiency of these devices by introducing good molecular water-oxidation catalysts, WS-DSPECs have poor stability, owing to the oxidation of molecular components at very positive electrode potentials. Here we demonstrate that a solid-state dye-sensitized solar cell (ss-DSSC) can be used as a buried junction for stable photoelectrochemical water splitting. A thin protecting layer of TiO2 grown by atomic layer deposition (ALD) stabilizes the operation of the photoanode in aqueous solution, although as a solar cell there is a performance loss due to increased series resistance after the coating. With an electrodeposited iridium oxide layer, a photocurrent density of 1.43 mA cm-2 was observed in 0.1 M pH 6.7 phosphate solution at 1.23 V versus reversible hydrogen electrode, with good stability over 1 h. We measured an incident photon-to-current efficiency of 22% at 540 nm and a Faradaic efficiency of 43% for oxygen evolution. While the potential profile of the catalyst layer suggested otherwise, we confirmed the formation of a buried junction in the as-prepared photoelectrode. The buried junction design of ss-DSSs adds to our understanding of semiconductor-electrocatalyst junction behaviors in the presence of a poor semiconducting material.

A Review of Bacteriochlorophyllides: Chemical Structures and Applications.

Generally, bacteriochlorophyllides were responsible for the photosynthesis in bacteria. Seven types of bacteriochlorophyllides have been disclosed. Bacteriochlorophyllides a/b/g could be synthesized from divinyl chlorophyllide a. The other bacteriochlorophyllides c/d/e/f could be synthesized from chlorophyllide a. The chemical structure and synthetic route of bacteriochlorophyllides were summarized in this review. Furthermore, the potential applications of bacteriochlorophyllides in photosensitizers, immunosensors, influence on bacteriochlorophyll aggregation, dye-sensitized solar cell, heme synthesis and for light energy harvesting simulation were discussed.

Synthesis and Physico-Chemical Properties of Homoleptic Copper(I) Complexes with Asymmetric Ligands as a DSSC Dye.

To develop low-cost and efficient dye-sensitized solar cells (DSSCs), we designed and prepared three homoleptic Cu(I) complexes with asymmetric ligands, M1, M2, and Y3, which have the advantages of heteroleptic-type complexes and compensate for their synthetic challenges. The three copper(I) complexes were characterized by elemental analysis, UV-vis absorption spectroscopy, and electrochemical measurements. Their absorption spectra and orbital energies were evaluated and are discussed in the context of TD-DFT calculations. The complexes have high VOC values (0.48, 0.60, and 0.66 V for M1, M2, and Y3, respectively) which are similar to previously reported copper(I) dyes with symmetric ligands, although their energy conversion efficiencies are relatively low (0.17, 0.64, and 2.66%, respectively).

Recent Progress and Emerging Applications of Rare Earth Doped Phosphor Materials for Dye-Sensitized and Perovskite Solar Cells: A Review.

Although the efficiency of Dye-sensitized and Perovskite solar cell is still below the performance level of market dominance silicon solar cells, in last few years they have grabbed significant attention because of their fabrication ease using low-cost materials, and henceforth these cells are considered as a promising alternative to commercial photovoltaic devices. However, third generation solar cells have significant absorption in the visible region of solar spectrum, which confines their power conversion efficiency. Subsequently, the performance of current photovoltaics is significantly hampered by the transmission loss of sub-band-gap photons. To overcome these issues, rare earth doped luminescent materials is the favorable route followed to convert these transmitted sub-band-gap photons into above-band-gap light, where solar cells typically have significant light-scattering effects. Moreover, the rare earth based down/up conversion material facilitates the improvement in sensitization, light-scattering and device stability of these devices. This review provides insight into the application of various down/up conversion materials for Dye-sensitized and perovskite solar cell applications. Additionally, the paper discusses the techniques to improve the photovoltaic performance in terms of current density and photo voltage in detail.

Schiff Base Ancillary Ligands in Bis(diimine) Copper(I) Dye-Sensitized Solar Cells.

Five 6,6'-dimethyl-2,2'-bipyridine ligands bearing N-arylmethaniminyl substituents in the 4- and 4'-positions were prepared by Schiff base condensation in which the aryl group is Ph (1), 4-tolyl (2), 4-tBuC6H4 (3), 4-MeOC6H4 (4), and 4-Me2NC6H4 (5). The homoleptic copper(I) complexes [CuL2][PF6] (L = 1-5) were synthesized and characterized, and the single crystal structure of [Cu(1)2][PF6].Et2O was determined. By using the "surfaces-as-ligands, surfaces-as-complexes" (SALSAC) approach, the heteroleptic complexes [Cu(6)(Lancillary)]+ in which 6 is the anchoring ligand ((6,6'-dimethyl-[2,2'-bipyridine]-4,4'-diyl)bis(4,1-phenylene))bis(phosphonic acid)) and Lancillary = 1-5 were assembled on FTO-TiO2 electrodes and incorporated as dyes into n-type dye-sensitized solar cells (DSCs). Data from triplicate, fully-masked DSCs for each dye revealed that the best-performing sensitizer is [Cu(6)(1)]+, which exhibits photoconversion efficiencies (η) of up to 1.51% compared to 5.74% for the standard reference dye N719. The introduction of the electron-donating MeO and Me2N groups (Lancillary = 4 and 5) is detrimental, leading to a decrease in the short-circuit current densities and external quantum efficiencies of the solar cells. In addition, a significant loss in open-circuit voltage is observed for DSCs sensitized with [Cu(6)(5)]+, which contributes to low values of η for this dye. Comparisons between performances of DSCs containing [Cu(6)(1)]+ and [Cu(6)(4)]+ with those sensitized by analogous dyes lacking the imine bond indicate that the latter prevents efficient electron transfer across the dye.

Cause, Regulation and Utilization of Dye Aggregation in Dye-Sensitized Solar Cells.

As an important member of third generation solar cell, dye-sensitized solar cells (DSSCs) have the advantages of being low cost, having an easy fabrication process, utilizing rich raw materials and a high-power conversion efficiency (PCE), prompting nearly three decades as a research hotspot. Recently, increasing the photoelectric conversion efficiency of DSSCs has proven troublesome. Sensitizers, as the most important part, are no longer limited to molecular engineering, and the regulation of dye aggregation has become a widely held concern, especially in liquid DSSCs. This review first presents the operational mechanism of liquid and solid-state dye-sensitized solar cells, including the influencing factors of various parameters on device efficiency. Secondly, the mechanism of dye aggregation was explained by molecular exciton theory, and the influence of various factors on dye aggregation was summarized. We focused on a review of several methods for regulating dye aggregation in liquid and solid-state dye-sensitized solar cells, and the advantages and disadvantages of these methods were analyzed. In addition, the important application of quantum computational chemistry in the study of dye aggregation was introduced. Finally, an outlook was proposed that utilizing the advantages of dye aggregation by combining molecular engineering with dye aggregation regulation is a research direction to improve the performance of liquid DSSCs in the future. For solid-state dye-sensitized solar cells (ssDSSCs), the effects of solid electrolytes also need to be taken into account.

Enhanced Power Conversion Efficiency of Dye-Sensitized Solar Cells by Band Edge Shift of TiO2 Photoanode.

By simple soaking titanium dioxide (TiO2) films in an aqueous Na2S solution, we could prepare surface-modified photoanodes for application to dye-sensitized solar cells (DSSCs). An improvement in both the open-circuit voltage (Voc) and the fill factor (FF) was observed in the DSSC with the 5 min-soaked photoanode, compared with those of the control cell without any modification. The UV-visible absorbance spectra, UPS valence band spectra, and dark current measurements revealed that the Na2S modification led to the formation of anions on the TiO2 surface, and thereby shifted the conduction band edge of TiO2 in the negative (upward) direction, inducing an increase of 29 mV in the Voc. It was also found that the increased FF value in the surface-treated device was attributed to an elevation in the shunt resistance.

Are Alkynyl Spacers in Ancillary Ligands in Heteroleptic Bis(diimine)copper(I) Dyes Beneficial for Dye Performance in Dye-Sensitized Solar Cells?

The syntheses of 4,4'-bis(4-dimethylaminophenyl)-6,6'-dimethyl-2,2'-bipyridine (1), 4,4'-bis(4-dimethylaminophenylethynyl)-6,6'-dimethyl-2,2'-bipyridine (2), 4,4'-bis(4-diphenylaminophenyl)-6,6'-dimethyl-2,2'-bipyridine (3), and 4,4'-bis(4-diphenylaminophenylethynyl)-6,6'-dimethyl-2,2'-bipyridine (4) are reported along with the preparations and characterisations of their homoleptic copper(I) complexes [CuL2][PF6] (L = 1-4). The solution absorption spectra of the complexes exhibit ligand-centred absorptions in addition to absorptions in the visible region assigned to a combination of intra-ligand and metal-to-ligand charge-transfer. Heteroleptic [Cu(5)(Lancillary)]+ dyes in which 5 is the anchoring ligand ((6,6'-dimethyl-[2,2'-bipyridine]-4,4'-diyl)bis(4,1-phenylene))bis(phosphonic acid) and Lancillary = 1-4 have been assembled on fluorine-doped tin oxide (FTO)-TiO2 electrodes in dye-sensitized solar cells (DSCs). Performance parameters and external quantum efficiency (EQE) spectra of the DSCs (four fully-masked cells for each dye) reveal that the best performing dyes are [Cu(5)(1)]+ and [Cu(5)(3)]+. The alkynyl spacers are not beneficial, leading to a decrease in the short-circuit current density (JSC), confirmed by lower values of EQEmax. Addition of a co-absorbent (n-decylphosphonic acid) to [Cu(5)(1)]+ lead to no significant enhancement of performance for DSCs sensitized with [Cu(5)(1)]+. Electrochemical impedance spectroscopy (EIS) has been used to investigate the interfaces in DSCs; the analysis shows that more favourable electron injection into TiO2 is observed for sensitizers without the alkynyl spacer and confirms higher JSC values for [Cu(5)(1)]+.

Characteristics of Dye-Sensitized Solar Cell Assembled from Modified Chitosan-Based Gel Polymer Electrolytes Incorporated with Potassium Iodide.

In the present work, phthaloyl chitosan (PhCh)-based gel polymer electrolytes (GPEs) were prepared using dimethylformamide (DMF) as a solvent, ethyl carbonate (EC) as a co-solvent, and a set of five quaternaries of potassium iodide (KI) as a doping salt, which is a mixed composition of iodine (I2). The prepared GPEs were applied to dye-sensitized solar cells (DSSC) to observe the effectiveness of the electrolyte, using mesoporous TiO2, which was sensitized with N3 dye as the sensitizer. The incorporation of the potassium iodide-based redox couple in a polymer electrolyte is fabricated for dye-sensitized solar cells (DSSCs). The number of compositions was based on the chemical equation, which is 1:1 for KI:I2. The electrical performance of prepared GPE systems have been assessed using electrical impedance spectroscopy (EIS), and dielectric permittivity. The improvement in the ionic conductivity of PhCh-based GPE was observed with the rise of salt concentration, and the maximum ionic conductivity (4.94 × 10-2 S cm-1) was achieved for the 0.0012 mol of KI:I2. The study of dielectric permittivity displays that ions with a high dielectric constant are associated with a high concentration of added ions. Furthermore, the gel polymer electrolyte samples were applied to DSSCs to detect the conversion effectiveness of the electrolytes. For electrolytes containing various content of KI:I2 the highest conversion efficiency (η%) of DSSC obtained was 3.57% with a short circuit current density (Jsc) of 20.33 mA cm-2, open-circuit voltage (Voc) of 0.37 V, fill factor (FF) of 0.47, as well as a conductivity of 2.08 × 10-2 S cm-1.

Enhancing the Performance of Dye Sensitized Solar Cells Using Silver Nanoparticles Modified Photoanode.

In this study, silver nanoparticles were synthesized, characterized, and applied to a dye-sensitized solar cell (DSSC) to enhance the efficiency of solar cells. The synthesized silver nanoparticles were characterized with UV-Vis spectroscopy, dynamic light scattering, transmission electron microscopy, and field emission scanning electron microscopy. The silver nanoparticles infused titanium dioxide film was also characterized by Fourier transform infrared and Raman spectroscopy. The performance of DSSC fabricated with silver nanoparticle-modified photoanode was compared with that of a control group. The current and voltage characteristics of the devices as well as the electrochemical impedance measurements were also carried out to assess the performance of the fabricated solar cells. The solar-to-electric efficiency of silver nanoparticles based DSSC was 1.76%, which is quite remarkable compared to the 0.98% realized for DSSC fabricated without silver nanoparticles.

Synthesis, Spectral, Electrochemical and Photovoltaic Studies of A3 B Porphyrinic Dyes having Peripheral Donors.

Three new 'push-pull' A3 B Zn(II)porphyrin dyes having meso-pyrenyl, carbazolyl and phenothiazine as electron donors (A) and phenylcarboxylic acid as acceptor/anchor (B) were synthesized and utilized for DSSC application. The spectral and electrochemical redox properties of these new dyes were studied and compared with trans-A2 BC Zn(II) porphyrin dyes under similar experimental conditions. Red-shifted, broadened absorption peaks, lower fluorescence quantum yields, and shortened lifetimes were observed for the A3 B dyes as compared to zinc tetraphenylporphyrin control, ZnTPP. DFT optimized structures suggested effective charge separation related to enhanced charge injection efficiency. Driving force for electron injection (ΔGinj ) and dye regeneration (ΔGreg ) calculated from the spectral and electrochemical studies predicted facile electron injection from excited dye into semiconductor TiO2 in the constructed solar cells. Phenothiazine appended dye (KP-TriPTZ-Zn) showed the highest η value of 7.3 % for PCE with greater Jsc and Voc values due to its better light harvesting ability and reduced dye aggregation as compared to other dyes. Our studies demonstrate that the dyes having multiple electron-donating groups exhibit higher photon-to-current conversion efficiency.

Exploring the relevance of thiophene rings as bridge unit in acceptor-bridge-donor dyes on self-aggregation and performance in DSSCs.

The possibility of dye charge recombination in DSSCs remains a challenge for the field. This consists of: (a) back-transfer from the TiO2 to the oxidized dye and (b) intermolecular electron transfer between dyes. The latter is attributed to dye aggregation due to dimeric conformations. This leads to poor electron injection which decreases the photocurrent conversion efficiency. Most organic sensitizers are characterized by an Acceptor-Bridge-Donor (A-Bridge-D) arrangement that is commonly employed to provide charge separation and, therefore, lowering the unwanted back-transfer. Here, we address the intermolecular electron transfer by studying the dimerization and photovoltaic performance of a group of A-Bridge-D structured dyes. Specifically, eight famous sulfur containing π-bridges were analyzed (A and D remained fixed). Through quantum mechanical and molecular dynamics approaches, it was found that the formation of weakly stabilized dimers is allowed. The dyes with covalently bonded and fused thiophene rings as Bridges, 6d and 7d as well as 8d with a fluorene, would present high aggregation and, therefore, high probability of recombination processes. Conversely, using TiO2 cluster and surface models, delineated the shortest bridges to improve the adsorption energy and the stability of the system. Finally, the elongation of the bridge up to 2 and 3 units and their photovoltaic parameters were studied. These results showed that all the sensitizers are able to provide similar photocurrent outcomes, regardless of whether the bridge is elongated. © 2017 Wiley Periodicals, Inc.

Designing Eco-Sustainable Dye-Sensitized Solar Cells by the Use of a Menthol-Based Hydrophobic Eutectic Solvent as an Effective Electrolyte Medium.

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.

In-Situ Growth of CoS Nanoparticles Onto Electrospun Graphitized Carbon Nanofibers as an Efficient Counter Electrode for Dye-Sensitized Solar Cells.

One-dimensional graphitized carbon nanofibers (G-CNFs) were prepared by employing facile electrospinning technique using 10 wt% of polyacrylonitrile (PAN) solution in N,N-dimethyl formamide (DMF) as precursor followed by successive stabilization, carbonization and purification processes. Cobalt sulfide (CoS) nanoparticles were grown onto G-CNFs by hydrothermal method using cobalt chloride and L-cysteine as precursors. The results of X-ray diffraction (XRD) and Raman spectroscopy confirmed the phase formation and degree of graphitization, respectively. Field-emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM) images confirmed the morphology, growth and distribution of CoS nanoparticles over G-CNFs (CoS/G-CNFs). The electrochemical studies such as cyclic voltammetry (CV), electrochemical impedance and Tafel polarization revealed that CoS/G-CNFs have lower overpotential, low charge transfer resistance and higher exchange current density for triiodide (I− 3 reduction reaction. The superior electrocat- alytic activity of CoS/G-CNFs than std. Pt is due to combined contribution of interconnected pore structure with high surface area of G-CNFs and excellent electrocatalytic activity of CoS. In addition, the dye sensitized solar cell (DSSC) based on platinum-free CoS/G-CNFs has exhibited higher photo-conversion efficiency (PCE) under a simulated solar light irradiation of 100 mW cm−2 when compared to standard platinum (std. Pt) which is attributed to the synergistic effect of CoS with G-CNFs.