Far-red active unsymmetrical squaraine dyes containing N-arylated indoline donors for dye sensitized solar cells

Squaraine dyes possess sharp far-red active transition with high extinction coefficient and form aggregates on TiO2 surface. Aggregation of dyes on TiO2 has been considered as a detrimental factor for DSSC device performance, which can be controlled by appending alkyl groups to the dye structures. Hence by integrating alkylated (alkyl groups with both in-plane and out-of-plane) aryl group with indoline moiety to make it compatible with other electrolytes and for controlling the dye-aggregation, a series of squaraine acceptor-based dyes SQA4-6 have been designed and synthesized. SQA4-6 dyes showed absorption between 642 and 653 nm (λmax), photophysical and electrochemical studies indicated that the HOMO energy levels of this sets of dyes are well aligned with the potentials of I-/I 3 - and [Co(bpy)3]2+/3+ redox shuttles for better dye regeneration process. DSSC device efficiency of 3% has been achieved for SQA5 dye with iodolyte (I-/I 3 - ) electrolyte in the presence of 0.3 mM of chenodeoxycholic acid (CDCA). The IPCE profile of DSSC device fabricated with SQA4-6 dyes indicated the contribution of aggregated structures for the photocurrent generation.

Spinel cobalt-based binary metal oxides as emerging materials for energy harvesting devices: synthesis, characterization and synchrotron radiation-enabled investigation

The synthesis and characterization of spinel cobalt-based metal oxides (MCo2O4) with varying 3d-transition metal ions (Ni, Fe, Cu, and Zn) were explored using a hydrothermal process (140 °C for two hours) to be used as alternative counter electrodes for Pt-free dye-sensitized solar cells (DSSCs). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed distinct morphologies for each metal oxide, such as NiCo2O4 nanosheets, Cu Co2O4 nanoleaves, Fe Co2O4 diamond-like, and Zn Co2O4 hexagonal-like structures. The X-ray diffraction analysis confirmed the cubic spinel structure for the prepared MCo2O4 films. The functional groups of MCo2O4 materials were recognized in metal oxides throughout Fourier transform infrared (FTIR) analysis. The local structure analysis using X-ray absorption fine structure (XAFS) at Fe and Co K-edge identified octahedral (Oh) Co3+ and tetrahedral (Td) Co2+ coordination, with Zn2+ and Cu2+ favoring Td sites, while Ni3+ and Fe3+ preferred Oh active sites. Further investigations utilizing the Fourier transformation (FT) analysis showed comparable coordination numbers and interatomic distances ranked as Co-Cu > Co-Fe > Zn-Co > Co-Ni. Furthermore, the utilization of MCo2O4 thin films as counter electrodes in DSSC fabrication showed promising results. Notably, solar cells based on CuCo2O4 and ZnCo2O4 counter electrodes showed 1.9% and 1.13% power conversion efficiency, respectively. These findings indicate the potential of employing these binary metal oxides for efficient and cost-effective photovoltaic device production.

Impact of blocking layers based on TiO2 and ZnO prepared via direct current reactive magnetron sputtering on DSSC solar cells

The optimization of dye-sensitized solar cells (DSSCs) technology towards suppressing charge recombination between the contact and the electron transport layer is a key factor in achieving high conversion efficiency and the successful commercialization of this type of product. An important aspect of the DSSC structure is the front blocking layer (BL): optimizing this component may increase the efficiency of photoelectron transfer from the dye to the semiconductor by reduction charge recombination at the TiO2/electrolyte and FTO/electrolyte interfaces. In this paper, a series of blocking layer variants, based on TiO2 and ZnO:TiO2, were obtained using the reactive magnetron sputtering method. Material composition, structure and layer thickness were referred to each process parameters. Complete DSSCs with structure FTO/BL/m-TiO2@N719/ EL-HSE/Pt/FTO were obtained on such bases. In the final results, verification of opto-electrical parameters of these cells were tested and used for the conclusions on the optimal blocking layer composition. As the conclusion, application of blocking layer consists of neat TiO2 resulted in improvement of device efficiency. It should be noted that for TiO2:ZnO/CuxO and TiO2/CuxO cells, higher efficiencies were also achieved when pure TiO2 was used as window layer. Additionally it was proven that the admixture of ZnO phase inspires Voc and FF growth, but is overall unfavorable compared to pristine TiO2 blocking layer and the reference cell, according to the final cell efficiency.

Use of deep eutectic solvents in environmentally-friendly dye-sensitized solar cells and their physicochemical properties: a brief review

A novel way to mitigate the greenhouse effect is to use dye-sensitized solar cells (DSSCs) to convert carbon dioxide from the air into useful products, such as hydrocarbons, which can also store energy from the sun, a plentiful, clean, and safe resource. The conversion of CO2 can help reduce the impacts of greenhouse gas emissions that contribute to global warming. However, there is a major obstacle in using DSSCs, since many solar devices operate with organic electrolytes, producing pollutants including toxic substances. Therefore, a key research area is to find new eco-friendly electrolytes that can effectively dissolve carbon dioxide. One option is to use deep eutectic solvents (DESs), which are potential substitutes for ionic liquids (ILs) and have similar advantages, such as being customizable, economical, and environmentally friendly. DESs are composed of low-cost materials and have very low toxicity and high biodegradability, making them suitable for use as electrolytes in DSSCs, within the framework of green chemistry. The purpose of this brief review is to explore the existing knowledge about how CO2 dissolves in DESs and how these solvents can be used as electrolytes in solar devices, especially in DSSCs. The physical and chemical properties of the DESs are described, and areas are suggested where further research should be focused.

Fully Additively Manufactured Counter Electrodes for Dye-Sensitized Solar Cells

In dye-sensitized solar cells (DSSCs), the counter electrode (CE) plays a crucial role as an electron transfer agent and regenerator of the redox couple. Unlike conventional CEs that are generally made of glass-based substrates (e.g., FTO/glass), polymer substrates appear to be emerging candidates, owing to their intrinsic properties of lightweight, high durability, and low cost. Despite great promise, current manufacturing methods of CEs on polymeric substrates suffer from serious limitations, including low conductivity, scalability, process complexity, and the need for dedicated vacuum equipment. In the present study, we employ and evaluate a fully additive manufacturing route that can enable the fabrication of CEs for DSSCs in a high-throughput and eco-friendly manner with improved performance. The proposed approach sequentially comprises: (1) material extrusion 3-D printing of polymer substrate; (2) conductive surface metallization through cold spray particle deposition; and (3) over-coating of a thin-layer catalyzer with a graphite pencil. The fabricated electrodes are characterized in terms of microstructure, electrical conductivity, and photo-conversion efficiency. Owing to its promising electrical conductivity (8.5 × 104 S·m-1) and micro-rough surface structure (Ra ≈ 6.32 µm), the DSSCs with the additively manufactured CEs led to ≈2.5-times-higher photo-conversion efficiency than that of traditional CEs made of FTO/glass. The results of the study suggest that the proposed additive manufacturing approach can advance the field of DSSCs by addressing the limitations of conventional CE manufacturing platforms.

Size-Controlled Cu3VSe4 Nanocrystals as Cathode Material in Platinum-Free Dye-Sensitized Solar Cells

In this work, we report the first single-step, size-controlled synthesis of Cu3VSe4 cuboidal nanocrystals, with the longest dimension ranging from 9 to 36 nm, and their use in replacing the platinum counter electrode in dye-sensitized solar cells. Cu3VSe4, a ternary semiconductor from the class of sulvanites, is theoretically predicted to have good hole mobility, making it a promising candidate for charge transport in solar photovoltaic devices. The identity and crystalline purity of the Cu3VSe4 nanocrystals were validated by X-ray powder diffraction (XRD) and Raman spectroscopy. The particle size was determined from the XRD data using the Williamson-Hall equation and was found in agreement with the transmission electron microscopy imaging. Based on the electrochemical activity of the Cu3VSe4 nanocrystals, studied by cyclic voltammetry, the nanomaterials were further employed for fabricating counter electrodes (CEs) in Pt-free dye-sensitized solar cells. The counter electrodes were prepared from Cu3VSe4 nanocrystals as thin films, and the charge transfer kinetics were studied by electrochemical impedance spectroscopy. The work demonstrates that Cu3VSe4 counter electrodes successfully replace platinum in DSSCs. CEs fabricated with the Cu3VSe4 nanocrystals having an average particle size of 31.6 nm outperformed Pt, leading to DSSCs with the highest power conversion efficiency (5.93%) when compared with those fabricated with the Pt CE (5.85%).

Multifunctional Structure-Modified Quaternary Compounds Co9Se8-CuSe2-WSe2 Mixed with MWCNT as a Counter Electrode Material for Dye-Sensitized Solar Cells

In this study, a trimetallic selenide material with a hollow spherical structure (Co9Se8-CuSe2-WSe2) was synthesized through two consecutive solvothermal reactions. The synergistic effect between the quaternary elements, the benefits of the selenization of metals, and the unique morphology led to the prominent electrocatalytic ability of Co9Se8-CuSe2-WSe2 hollow spheres. Co9Se8-CuSe2-WSe2 hollow spheres were then mixed with oxygen plasma-treated multiwalled carbon nanotubes (MWCNT) as counter electrode (CE) material for dye-sensitized solar cells (DSSCs), achieving a photoelectric conversion efficiency (η) of 9.23% under one sun condition (AM 1.5G, 100 mW cm-2), surpassing the 8.08% of devices with platinum counter electrodes (PtCEs). For indoor conditions, a T5 light source was applied to the DSSCs with Co9Se8-CuSe2-WSe2 + MWCNT CE, and the efficiency increased to 14.14% under 3600 lx irradiance. Finally, Co9Se8-CuSe2-WSe2 + MWCNT CE demonstrated good stability with 92.23% retention after 1000 cycles of cyclic voltammetry, exceeding the 82.49% of PtCE. Therefore, Co9Se8-CuSe2-WSe2 + MWCNT shows potential as a substitute for platinum as CE material for DSSCs.

Screening novel candidates of ZL003-based organic dyes for dye-sensitized solar cells by modifying auxiliary electron acceptors: A theoretical study

In this work, a series of ZL003-based free-metal sensitizers with the donor-acceptor-π- conjugated spacer-acceptor (D-A-π-A) structure were designed by modifying auxiliary electron acceptors for the potential application in dye-sensitized solar cells. The energy levels of frontier molecular orbitals, absorption spectra, electronic transition, and photovoltaic parameters for all studied dyes were systematically evaluated using density functional theory (DFT)/time-dependent DFT calculations. Results illustrated that thienopyrazine (TPZ), selenadiazolopyridine (SDP), and thiadiazolopyridine (TDP) are excellent electron acceptors, and dye sensitizers functionalized by these acceptors have smaller HOMO-LUMO gaps, obviously red-shifted absorption bands and stronger light harvesting. The present study revealed that the photoelectric conversion efficiency (PCE) of ZL003 is around 13.42 % with a JSC of 20.21 mA·cm-2, VOC of 966 mV and FF of 0.688 under the AM 1.5G sun exposure, in good agreement with its experimental value (PCE = 13.6 ± 0.2 %, JSC = 20.73 ± 0.20 mA·cm-2, VOC = 956 ± 5 mV, and FF = 0.685 ± 0.005.). With the same procedure, the PCE values for M4, M6, and M7 were estimated to be as high as 19.93 %, 15.38 %, and 15.80 % respectively. Hence, these three dyes are expected to be highly efficient organic sensitizers applied in practical DSSCs.

Molecular Engineering of Photosensitizers for Solid-State Dye-Sensitized Solar Cells: Recent Developments and Perspectives

Dye-sensitized solar cells (DSSCs) are a feasible alternative to traditional silicon-based solar cells because of their low cost, eco-friendliness, flexibility, and acceptable device efficiency. In recent years, solid-state DSSCs (ss-DSSCs) have garnered much interest as they can overcome the leakage and evaporation issues of liquid electrolyte systems. However, the poor morphology of solid electrolytes and their interface with photoanodes can minimize the device performance. The photosensitizer/dye is a critical component of ss-DSSCs and plays a vital role in the device's overall performance. In this review, we summarize recent developments and performance of photosensitizers, including mono- and co-sensitization of ruthenium, porphyrin, and metal-free organic dyes under 1 sun and ambient/artificial light conditions. We also discuss the various requirements that efficient photosensitizers should satisfy and provide an overview of their historical development over the years.

MXene-modified electrodes and electrolytes in dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) have attracted much attention as promising tools in renewable energy conversion technology. This is mainly because of their beneficial qualities, such as their impressive efficiency levels and low-cost fabrication techniques. An overview of MXene-modified electrodes in DSSCs is given in this review article. MXenes are two-dimensional (2D) transition metal carbides or nitrides with remarkable properties such as high conductivity and large surface area. MXenes' properties make them an appealing material for various applications, including energy storage, catalysis, and electronic devices. MXene integration enhances ion transport, dye adsorption, and charge transport in DSSC electrodes. In-depth analysis of the use of 2D Mxene and integration with carbon nanotubes (CNTs), reduced graphene oxide (rGO), 2D MoS2, and hybrids like 2D-2D heterostructures for electrode modification in photovoltaics (PVs), including anodes, photoanodes, composite decorated electrodes, counter electrodes (CEs), and electrolytes, is provided in this review article. The effects on the performance metrics of various deposition techniques are discussed and assessed. The use of MXene-modified electrodes in DSSCs suggests potential for enhancing the performance and efficiency of these solar cells in general. The article examines this strategy's potential advantages and implications, illuminating the fascinating advancements in the area and emphasizing MXenes' potential as a valuable substance for renewable energy applications. We also discuss the difficulties and potential benefits of using MXene-modified electrodes in DSSCs and emphasize the need for additional study to enhance stability, optimize MXene integration techniques, and enhance long-term device performance. The scalability and potential of MXene-based electrode modifications for commercial applications are also covered, addressing issues and prospects for the future, focusing on the necessity of more study. Electrodes modified with MXenes can improve DSSC performance and advance sustainable energy conversion.

Magnetic field effects on the crystal structure, morphology, energy gap, and magnetic properties of manganese selenide nanoparticles synthesized by hydrothermal method

In this study, we synthesized manganese selenide under magnetic fields ranging from 0 to 800 gauss and investigated its optical, electrical, and magnetic properties. In the absence of a magnetic field, we observed the formation of MnSe nanorods. As the field strength increased, impurities arose. In the 250 G range, two rock salt structures emerged, altering the morphology from nanorods to cubes. Beyond 250 G, MnSe2 formed, returning to a nanorod morphology. Also, with the increase of the magnetic field, the energy gap of the synthesized compounds increased. To measure the electrical properties of the samples, the synthesized powders were compressed under the same pressure for a certain period of time, and it was observed that the synthesized samples showed insulating behavior in the presence of a magnetic field. For this reason, we performed current-voltage, resistance-temperature, and current-temperature analyses on the synthesized sample, at a constant voltage of 5 eV in the absence of a magnetic field.

A bacteriorhodopsin-based biohybrid solar cell using carbon-based electrolyte and cathode components

There is currently a high demand for energy production worldwide, mainly producing renewable and sustainable energy. Bio-sensitized solar cells (BSCs) are an excellent option in this field due to their optical and photoelectrical properties developed in recent years. One of the biosensitizers that shows promise in simplicity, stability and quantum efficiency is bacteriorhodopsin (bR), a photoactive, retinal-containing membrane protein. In the present work, we have utilized a mutant of bR, D96N, in a photoanode-sensitized TiO2 solar cell, integrating low-cost, carbon-based components, including a cathode composed of PEDOT (poly(3,4-ethylenedioxythiophene) functionalized with multi-walled carbon nanotubes (CNT) and a hydroquinone/benzoquinone (HQ/BQ) redox electrolyte. The photoanode and cathode were characterized morphologically and chemically (SEM, TEM, and Raman). The electrochemical performance of the bR-BSCs was investigated using linear sweep voltammetry (LSV), open circuit potential decay (VOC), and impedance spectroscopic analysis (EIS). The champion device yielded a current density (JSC) of 1.0 mA/cm2, VOC of -669 mV, a fill factor of ~24 %, and a power conversion efficiency (PCE) of 0.16 %. This bR device is one of the first bio-based solar cells utilizing carbon-based alternatives for the photoanode, cathode, and electrolyte. This may decrease the cost and significantly improve the device's sustainability.

Enhanced electrocatalytic properties in dye-sensitized solar cell via Pt/SBA-15 composite with optimized Pt constituent

The Low utilization and high cost of platinum counter electrode (CE) in the application of dye-sensitized solar cells has limited its large-scale manufacturing in the industry. Herein, a facile pyrolysis combination of Pt and SBA-15 molecular sieve (MS) formed 1.6-1.9 times higher amount and 2-3 times reduced dimension of Pt distributed within porous structure of SBA-15. The composite CE with 20 % of SBA-15 exhibited an enhanced power conversion efficiency of 9.31 %, exceeding that of absolute Pt CE (7.57 %). This superior performance owed to the promoted oxidation-reduction rate of I3-/I- pairs at the CE interface and the increased conductivity of CE materials attributed from well distributed Pt particles. This work has demonstrated the significance of utilizing porous molecular sieves for dispersing catalytic sites when designing a novel type of counter electrode and their application in DSSCs.

Recent progress in organic waste recycling materials for solar cell applications

Organic waste-derived solar cells (OWSC) are a classification of third-generation photovoltaic cells in which one or more constituents are fabricated from organic waste material. They are an inspirational complement to the conventional third-generation solar cell with the potential of revolutionizing our future approach to solar cell manufacture. This article provides a study and summary of solar cells that fall under the category of OWSC. OWSC own their merit to low cost of manufacturing and environmental friendliness. This review article reveals different organic waste raw materials, preparation-to-assembly methodologies, and novel approaches to solar cell manufacturing. Ideas for the optimization of the performance of OWSC are presented. The assembly configurations and photovoltaic parameters of reported OWSC are compared in detail. An overview of the trends in the research regarding OWSC in the past decade is given. Also, the advantages and disadvantages of the different solar cell technologies are discussed, and possible trends are proposed. Industrial organic waste raw materials such as paper, coal, and plastics are among the least explored and yet most attractive for solar cell fabrication. The power conversion efficiencies for the cited works are mentioned while emphasizing the products and functions of the organic waste raw materials used.

Indoor Photovoltaic Fiber with an Efficiency of 25.53% under 1500 Lux Illumination

Photovoltaic devices represent an efficient electricity generation mode. Integrating them into textiles offers exciting opportunities for smart electronic textiles-with the ultimate goal of supplying power for wearable technology-which is poised to change how electronic devices are designed. Many human activities occur indoors, so realizing indoor photovoltaic fibers (IPVFs) that can be woven into textiles to power wearables is critical, although currently unavailable. Here, a dye-sensitized IPVF is constructed by incorporating titanium dioxide nanoparticles into aligned nanotubes to produce close contact and stable interfaces among active layers on a curved fiber substrate, thus presenting efficient charge transport and low charge recombination in the photoanode. With the combination of highly conductive core-sheath Ti/carbon nanotube fiber as a counter electrode, the IPVF shows a certified power conversion efficiency of 25.53% under 1500 lux illuminance. Its performance variation is below 5% after bending, twisting, or pressing for 1000 cycles. These IPVFs are further integrated with fiber batteries as self-charging power textiles, which are demonstrated to effectively supply electricity for wearables, solving the power supply problem in this important direction.

Different Roles between PEDOT:PSS as Counter Electrode and PEDOT:Carrageenan as Electrolyte in Dye-Sensitized Solar Cell Applications: A Systematic Literature Review

Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) has been mostly used as a counter electrode to give a high performance of dye-sensitized solar cell (DSSC). Recently, PEDOT doped by carrageenan, namely PEDOT:Carrageenan, was introduced as a new material to be applied on DSSC as an electrolyte. PEDOT:Carrageenan has a similar synthesis process as PEDOT:PSS, owing to their similar ester sulphate (-SO₃H) groups in both PSS and carrageenan. This review provides an overview of the different roles between PEDOT:PSS as a counter electrode and PEDOT:Carrageenan as an electrolyte for DSSC applications. The synthesis process and characteristics of PEDOT:PSS and PEDOT:Carrageenan were also described in this review. In conclusion, we found that the primary role of PEDOT:PSS as a counter electrode is to transfer electrons back to cell and accelerate redox reaction with its superior electrical conductivity and high electrocatalytic activity. PEDOT:Carrageenan as an electrolyte has not shown the main role for regenerating the dye sensitized at the oxidized state, probably due to its low ionic conductivity. Therefore, PEDOT:Carrageenan still obtained a low performance of DSSC. Additionally, the future perspective and challenges of using PEDOT:Carrageenan as both electrolyte and counter electrode are described in detail.

New autonomous and self-signaling biosensing device for sarcosine detection

An early diagnosis is the gold standard for cancer survival. Biosensors have proven their effectiveness in monitoring cancer biomarkers but are still limited to a series of requirements. This work proposes an integrated power solution, with an autonomous and self-signaling biosensing device. The biorecognition element is produced in situ by molecular imprinting to detect sarcosine, a known biomarker for prostate cancer. The biosensor was assembled on the counter-electrode of a dye-sensitized solar cell (DSSC), simultaneously using EDOT and Pyrrole as monomers for the biomimetic process and the catalytic reduction of triiodide in the DSSC. After the rebinding assays, the hybrid DSSC/biosensor displayed a linear behavior when plotting the power conversion efficiency (PCE) and the charge transfer resistance (R_CT) against the logarithm of the concentration of sarcosine. The latter obtained a sensitivity of 0.468 Ω/decade of sarcosine concentration, with a linear range between 1 ng/mL and 10 μg/mL, and a limit of detection of 0.32 ng/mL. When interfacing an electrochromic cell, consisting of a PEDOT-based material, with the hybrid device, a color gradient between 1 ng/mL and 10 μg/mL of sarcosine was observed. Thus, the device can be used anywhere with access to a light source, completely equipment-free, suitable for point-of-care analysis and capable of detecting sarcosine within a range of clinical interest.

3D graphene: synthesis, properties, and solar cell applications

Three-dimensional (3D) graphene is one of the most important nanomaterials. This feature article highlights the advancements, with an emphasis on contributions from our group, in the synthesis of 3D graphene-based materials and their utilization in solar cells. Chemistries of graphene oxides, hydrocarbons, and alkali metals are discussed for the synthesis of 3D graphene materials. Their performances in dye-sensitized solar cells and perovskite solar cells (as counter electrodes, photoelectrodes, and electron extracting layers) were correlatively analyzed with their properties/structures (accessible surface area, electrical conductivity, defects, and functional groups). The challenges and prospects for their applications in photovoltaic solar cells are outlined.

Bifacial Dye-Sensitized Solar Cells Utilizing Visible and NIR Dyes: Implications of Dye Adsorption Behaviour

Bifacial dye-sensitized solar cells (DSSCs) were fabricated utilizing dye cocktails of two dyes, Z-907 and SQ-140, which have complementary light absorption and photon harvesting in the visible and near-infrared wavelength regions, for panchromatic photon harvesting. The investigation of the rate of dye adsorption and the binding strengths of the dyes on mesoporous TiO₂ corroborated the finding that the Z-907 dye showed a rate of dye adsorption that was about >15 times slower and a binding that was about 3 times stronger on mesoporous TiO₂ as compared to SQ-140. Utilizing the dye cocktails Z-907 and SQ-140 from ethanol, the formation of the dye bilayer, which was significantly influenced by the ratio of dyes and adsorption time, was demonstrated. It was demonstrated that the dyes of Z-907 and SQ-140 prepared in 1:9 or 9:1 molar ratios favoured the dye bilayer formation by subtly controlling the adsorption time. In contrast, the 1:1 ratio counterpart was prone to form mixed dye adsorption; the best performance of the BF-DSSCs was shown when a dye cocktail of Z-907 and SQ-140 in a molar 9:1 ratio was used to prepare a photoanode for 1 h of dye adsorption. The BF-DSSCs thus exhibited PCEs of 4.23% and 3.48% upon the front and rear side light illuminations, a cumulated PCE of 7.71%, and a very good BBF of 83%.

Combustion-Assisted Polyol Reduction Method to Prepare Highly Transparent and Efficient Pt Counter Electrodes for Bifacial Dye-Sensitized Solar Cells

A combustion-assisted polyol reduction (CPR) method has been developed to deposit electrocatalytically efficient and transparent Pt counter electrodes (CEs) for bifacial dye-sensitized solar cells (DSSCs). Compared with conventional thermal decomposition of Pt precursors, CPR allows for a decrease in reduction temperature to 150 °C. The low-temperature processing is attributed to adding an organic fuel, acetylacetone (Hacac), which provides extra heat to lower reduction energy. In addition, the stable Pt complexes can simultaneously be formed in ethylene glycol (EG) and Hacac system, which leads to Pt nanoparticle size regulation. A ratio of Hacac to EG is optimized to achieve excellent electrocatalytic activity and high visible light transmittance for CEs. The bifacial DSSCs fabricated with CPR-Pt CEs (EG : Hacac=1 : 16) reach efficiencies of 6.71±0.16% and 6.41±0.15% in front and back irradiations, respectively.

Design of blueberry anthocyanin/TiO2 composite layer-based photoanode and N-doped porous blueberry-derived carbon-loaded Ni nanoparticle-based counter electrode for dye-sensitized solar cells

P25/PBP (TiO₂, anthocyanins) prepared by combining PBP (blueberry peels) with P25, and N-doped porous carbon-supported Ni nanoparticles (Ni@NPC-X) prepared using blueberry-derived carbon were used for the application as photoanode and the counter electrode, respectively, in dye-sensitized solar cells (DSSCs) to create a new perspective for blueberry-based photo-powered energy systems. PBP was introduced into the P25 photoanode and carbonized to form a C-like structure after annealing that improved its adsorption capacity for N719 dye, contributing a 17.3% higher power conversion efficiency (PCE) of P25/PBP-Pt (5.82%) than that of P25-Pt (4.96%). The structure of the porous carbon changes from a flat surface to a petal-like structure due to the N doping by melamine, and the specific surface area increases. N-doped three-dimensional porous carbon supported the loading and reduced the agglomeration of Ni nanoparticles, reducing the charge transfer resistance, and providing a fast electron transfer path. The doping of Ni and N on the porous carbon worked synergistically to enhance the electrocatalytic activity of the Ni@NPC-X electrode. The PCE of the DSSCs assembled by Ni@NPC-1.5 and P25/PBP was 4.86%. Also, the Ni@NPC-1.5 electrode exhibited 116.12 F g^-1 and a capacitance retention rate of 98.2% (10 000 cycles), further confirming good electrocatalysis and cycle stability.

Functional Fiber Materials to Smart Fiber Devices

The development of fiber materials has accompanied the evolution of human civilization for centuries. Recent advances in materials science and chemistry offered fibers new applications with various functions, including energy harvesting, energy storing, displaying, health monitoring and treating, and computing. The unique one-dimensional shape of fiber devices endows them advantages to work as human-interfaced electronics due to the small size, lightweight, flexibility, and feasibility for integration into large-scale textile systems. In this review, we first present a discussion of the basics of fiber materials and the design principles of fiber devices, followed by a comprehensive analysis on recently developed fiber devices. Finally, we provide the current challenges facing this field and give an outlook on future research directions. With novel fiber devices and new applications continuing to be discovered after two decades of research, we envision that new fiber devices could have an important impact on our life in the near future.

D-A-D-based Unsymmetrical Thiosquaraine Dye for the Dye-Sensitized Solar Cells†

In dye-sensitized solar cell, modulating the electronic properties of the sensitizer by varying the donor, π-spacer, acceptor and anchoring groups help optimizing the structure of the dye for better device performance. Here, a donor-acceptor-donor-based unsymmetrical thiosquaraine sensitizer (SQ5S) has been designed and synthesized. Photophysical, electrochemical, theoretical and photovoltaic characterizations of SQ5S dye have been compared with its oxygen analog, SQ5. The incorporation of the sulfur atom in the acceptor unit of SQ5S dye showed an intense peak at 688 nm, which was 38 nm of red-shifted and showed the panchromatic light harvesting response with the onset of 850 nm compared with SQ5 dye. The LUMO and HOMO energy levels are well aligned with the conduction band of TiO₂ and the redox potential of electrolyte for the charge injection and the dye-regeneration processes, respectively. Photovoltaic efficiency of 1.51% (V_OC 610 mV, J_SC 3.07 mA cm^-2 , ff 81%) has been achieved for SQ5S dye, whereas SQ5 showed the device performance of 5.43% (V_OC 723 mV, J_SC 9.3 mA cm^-2 , ff 80%). The decreased device performance for the dye SQ5S has been attributed to the favorable intersystem crossing process associated with the photoexcited SQ5S that reduces the driving force for the charge injection process.

Solvent-Dependent Functional Aggregates of Unsymmetrical Squaraine Dyes on TiO2 Surface for Dye-Sensitized Solar Cells

Alkyl group wrapped donor-acceptor-donor (D-A-D) based unsymmetrical squaraine dyes SQ1, SQ5, and SQS4 were used to evaluate the effect of sensitizing solvents on dye-sensitized solar cell (DSSC) efficiency. A drastic change in DSSC efficiency was observed when the photo-anodes were sensitized in acetonitrile (bad solvent when considering dye solubility) and chloroform (good solvent) with an Iodolyte (I^-/I₃^-) electrolyte. The DSSC device sensitized with squaraine dyes in acetonitrile showed better photovoltaic performance with enhanced photocurrent generation and photovoltage compared to the device sensitized in chloroform. In a good sensitizing solvent, dyes with long hydrophobic alkyl chains are deleterious forming aggregates on the TiO₂ surface, which results in an incident photon-to-current conversion efficiency (IPCE) response mostly from monomeric and dimeric structures. Meanwhile, a bad sensitizing solvent facilitates the formation of well-packed self-assembled structures on the TiO₂ surface, which are responsible for a broad IPCE response and high device efficiencies. The photoanode sensitized in the bad sensitizing solvent showed enhanced V_OC values of 642, 675, and 699 mV; J_SC values of 6.38, 11.1, and 11.69 mA/cm²; and DSSC device efficiencies of 3.0, 5.63, and 6.13% for the SQ1, SQ5, and SQS4 dyes in the absence of a coadsorbent (chenodeoxycholic acid (CDCA)), respectively, which were further enhanced by CDCA addition. Meanwhile, the photoanode sensitized in the good sensitizing solvent showed relatively low photovoltaic V_OC values of 640, 652, and 650 mV; J_SC values of 5.78, 6.79, and 6.24 mA/cm²; and device efficiencies of 2.73, 3.35, and 3.20% for SQ1, SQ5, and SQS4 in the absence of CDCA, respectively, which were further varied with equivalents of CDCA. The best DSSC device efficiencies of 6.13 and 3.20% were obtained for SQS4 without CDCA, where the dye was sensitized in acetonitrile (bad) and chloroform (good) sensitizing solvents, respectively.

Electrodeposited PPy@TiO2 and PEDOT@TiO2 Counter Electrodes for [Co(bpy)3]2+/3+ Redox Mediator-Based Dye-Sensitized Solar Cells

The main goal of this work is to enhance the catalytic performance of PPy and PEDOT films toward the Co2+/Co3+ redox couple. PPy and PEDOT films were electrodeposited separately on a porous TiO2 template to assess their suitability as alternative catalysts in dye-sensitized solar cells (DSSC) based on the [Co(bpy)3]2+/3+ redox shuttle. The obtained PPy@TiO2 and PEDOT@TiO2 counter electrodes displayed much rougher surfaces. Electrochemical studies indicate the superior catalytic activity of both the electrodeposited electrodes toward Co3+ reduction, as indicated by lower charge transfer resistance than that of pristine films and even that of Pt electrodes. Therefore, the fabricated DSSC devices with these counter electrodes achieved higher power conversion efficiencies compared to cells with pristine PPy and PEDOT counter electrodes, or even with a Pt counter electrode. Interestingly, the assembled DSSC device with a PEDOT@TiO2 counter electrode displayed the highest performance among all with a power conversion efficiency of 6.62%, which is better than that obtained by the device with a Pt electrode (6.07%).

In-Situ Grafting of Single-Atomic Titanium-Nitrogen Moiety onto Carbon Nanostructures for Efficient Photovoltaic Devices

Early transition metals offer promising orthogonal reactivity to catalytic processes promoted by late transition metals. Nevertheless, exploiting variable single-atomic configurations as reactive centers is hitherto not well documented owing to their oxophilic nature. Herein we report an in-situ grafting strategy that employs nitrogenated holey carbon nitrides as a scaffold and invokes the reasonably good match of temperature-dependent pyrolysis to stabilize an atomic titanium-nitrogen (Ti₁N₂OH) moiety onto the hierarchical porous carbon support (Ti₁/NC-SAC). The Ti₁/NC-SAC as the cathode in dye-sensitized solar cells assembly exhibited superior electrocatalytic activity toward the triiodine reduction reaction, comparable to the conventional Pt cathode. DFT studies theoretically identified that the intrinsic robust triiodine reduction activity is essentially governed by the unique edge-hosted Ti sites, from both aspects, near-optimal adsorption of I intermediate and electron-donating ability. This work sheds light on the rational design of Ti-based SACs and their applications in photovoltaic fields.

Unusual enhancement in efficiency of DSSCs upon modifying photoanodes with reduced graphene oxide

Reduced graphene oxide (rGO) has emerged as an excellent interfacial material for improvising the performance of dye-sensitized solar cells (DSSC). Herein, we have applied rGO as interfacial layers between a fluorine doped tin oxide (FTO) coated glass substrate and semiconducting material TiO₂ in a photoanode of a DSSC which showed an unusual enhancement in generating a photocurrent in comparison to the control (without rGO layers). An electrochemical impedance spectroscopy (EIS) study was performed to gain the mechanistic insights into such a remarkable enhancement of photoelectric conversion efficiency (PCE) which revealed improved charge transfer and suppressed charge recombination due to high-electrical conductivity and probably more negative work function of our rGO material compared to the bare TiO₂ photoanode.

A facile method for synthesis rGO/Ag nanocomposite and its uses for enhancing photocatalytic degradation of Congo red dye

The enhancing breakdown of dyes using facile, novel and eco-friendly photocatalyst without remaining any hazards secondary intermediates from the dye species regarded one of the most challenges to the healthy world. A novel facile method was used to synthesize reduced graphene oxide (rGO) with various doping ratios of silver nanoparticles (Ag NPs) and applied as photocatalyst to enhancing removal of Congo red (CR) dye using UV light irradiation from aqueous solution. Some characterization features such as UV-diffuse reflectance spectra, TEM, SEM, FTIR, X-ray diffraction, and EDX were measured to demonstrate the energy gap, morphology, size distribution, crystalline nature, phase structure, and elemental compositions of as-synthesized nanoparticles. The effect of some important factors such as pH of solution, initial CR concertation (Co), amount of rGO@Ag (g) and contact time (t) were studied to detect the optimum adsorption condition. The results indicated that, the maximum CR dye photodegradation is obtained at pH 7, 120 min, 50 mg/L initial CR concentration and 0.4 g/L photocatalyst dosage. The photodegradation data declared that, the higher the Ag doping ratio, the higher the degrading efficiency. Isotherm and kinetic studies showed that Langmuir and Freundlich models and the pseudo-second-order model are well fitting the adsorption process with maximum CR adsorption values ranging between 86.95 and 98.04 mg/L with corresponding R2 > 0.99.

Dual-electron-enhanced effect in K-doped MoS2 few layers for high electrocatalytic activity as the counter electrode in dye-sensitized solar cells

Designing counter electrodes (CEs) with high efficiency and understanding the mechanism of dye-sensitized solar cells (DSSCs) are still challenges. In this paper, we synthesized K-doped molybdenum disulfide (K-MoS₂) with few layers and it has a great enhancement effect on the electrocatalytic activity compared to pure MoS₂ CE and reference Pt CE. A dual electron-path model is proposed to explain the mechanism, which is supported by first-principles calculations. When an electron in MoS₂ is transferred to the triiodide, the K atoms can act as an electron reservoir to provide another electron in a short time to improve the catalytic activity. So the proposed dual-electron effect in this paper is helpful to understand the charge transfer mechanism on the interfaces of these CEs and may be crucial for obtaining high photoelectric efficiencies in DSSCs.

Electrodeposited PEDOT/Nafion as Catalytic Counter Electrodes for Cobalt and Copper Bipyridyl Redox Mediators in Dye-Sensitized Solar Cells

PEDOT-based counter electrodes for dye-sensitized solar cells (DSSCs) are generally prepared by electrodeposition, which produces polymer films endowed with the best electrocatalytic properties. This translates in fast regeneration of the redox mediator, which allows the solar cell to sustain efficient photoconversion. The sustainable fabrication of DSSCs must consider the scaling up of the entire process, and when possible, it should avoid the use of large amounts of hazardous and/or inflammable chemicals, such as organic solvents for instance. This is why electrodeposition of PEDOT-based counter electrodes should preferably be carried out in aqueous media. In this study, PEDOT/Nafion was electrodeposited on FTO and comparatively evaluated as a catalytic material in DSSCs based on either cobalt or copper electrolytes. Our results show that the electrochemical response of PEDOT/Nafion toward Co(II/III-) or Cu(I/II)-based redox shuttles was comparable to that of PEDOT/ClO4 and significantly superior to that of PEDOT/PSS. In addition, when tested for adhesion, PEDOT/Nafion films were more stable for delamination if compared to PEDOT/ClO4, a feature that may prove beneficial in view of the long-term stability of solar devices.

Composition, Morphology, and Interface Engineering of 3D Cauliflower-Like Porous Carbon-Wrapped Metal Chalcogenides as Advanced Electrocatalysts for Quantum Dot-Sensitized Solar Cells

Designing a low-cost, highly efficient, and stable electrocatalyst that can synergistically speed up the reduction of polysulfide electrolytes while operative for long periods in the open air is critical for the practical application of quantum dot-sensitized solar cells (QDSSCs), but it remains a challenging task. Herein, a simple, straightforward, and two-step nanocomposite engineering approach that simultaneously combines metallic copper chalcogenides (MC) either Cu_{2- x} S or Cu_{2- x} Se with S, N dual-doped carbon (SNC) sources for devising high-quality counter electrode (CE) film are reported. First, the hierarchically assembled MC nanostructures are obtained using microwave-assisted synthesis. Second, these MCs are embedded within an ordered macro-meso-microporous carbon matrix to obtain Cu_{2- x} S@C or Cu_{2- x} SeS@C CE. These CEs are demonstrated to have composition dependents crystal structure, surface morphologies, photovoltaic performance, and electrochemical properties. In terms of power conversion efficiency (PCE), the Cu_{2- x} SeS@C (9.89%) and Cu_{2- x} S@C-CE (8.96%) constructed QDSSCs outperform both Cu_{2- x} Se (8.96%) and Cu_{2- x} S-constructed (7.79%) QDSSCs, respectively. The enhanced PCE could be attributed to the synergistic interaction of S and N dopants with MC interfaces that can not only enrich electric conductivity, and a higher surface-to-volume ratio but also offers a 3D network for superior charge transport at the interface.

MOF-derived CuxS double-faced-decorated carbon nanosheets as high-performance and stable counter electrodes for quantum dots solar cells

The development of highly-catalytic counter electrode (CE) materials is vital to the construction of quantum dot-sensitized solar cells (QDSCs) but is still challenging. Here, a novel self-assembly double-faced decorated carbon nanosheets with MOF-derived Cu_xS nanospheres (DF-Cu_xS/C NSs) were prepared as high-performance hybrid CEs for improving the catalytic activity towards polysulfide electrolytes and enhancing the performance of QDSCs. It is shown that the MOF-derived Cu_xS nanospheres disperse well on the surface of the carbon NSs in the obtained DF-Cu_xS/C NSs hybrids. Electrochemical characterization demonstrated that the DF-Cu_xS/C NSs with moderate mass ratio exhibited enhanced electrocatalytic activity towards the reduction of the polysulfide redox couple (S_n^2-/S^2-) and decreased charge transfer resistance at the interface of the CE/electrolyte. Benefitting from the merits of this novel hybrid CE, the power conversion efficiency (PCE) of the CdSeTe QDs-based QDSCs is increased to 9.39%, which is higher than the pristine carrageenan (CA)-derived CEs (5.84%) and Cu-BTC-derived CEs (7.74%). With the further optimization of the substrate, the highest PCE of 11.36% was achieved based on the Ti mesh substrate supported hybrid CE.

Efficient and Stable Fiber Dye-Sensitized Solar Cells Based on Solid-State Li-TFSI Electrolytes with 4-Oxo-TEMPO Derivatives

Fiber-shaped dye-sensitized solar cells (FDSSCs) with flexibility, weavablity, and wearability have attracted intense scientific interest and development in recent years due to their low cost, simple fabrication, and environmentally friendly operation. Since the Grätzel group used the organic radical 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as the redox system in dye-sensitized solar cells (DSSCs) in 2008, TEMPO has been utilized as an electrolyte to further improve power conversion efficiency (PCE) of solar cells. Hence, the TEMPO with high catalyst oxidant characteristics was developed as a hybrid solid-state electrolyte having high conductivity and stability structure by being integrated with a lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) film for FDSSCs. The optimized 4-Oxo TEMPO (OX) based solid-state FDSSC (SS-FDSSC) showed the PCE of up to 6%, which was improved by 34.2% compared to that of the reference device with 4.47%. The OX-enhanced SS-FDSSCs reduced a series resistance (R_s) resulting in effective electron extraction with improved short-circuit current density (J_SC), while increasing a shunt resistance (R_sh) to prevent the recombination of photo-excited electrons. The result is an improvement in a fill factor (FF) and consequently a higher value for the PCE.

PEDOT-Carbon Nanotube Counter Electrodes and Bipyridine Cobalt (II/III) Mediators as Universally Compatible Components in Bio-Sensitized Solar Cells Using Photosystem I and Bacteriorhodopsin

In nature, solar energy is captured by different types of light harvesting protein-pigment complexes. Two of these photoactivatable proteins are bacteriorhodopsin (bR), which utilizes a retinal moiety to function as a proton pump, and photosystem I (PSI), which uses a chlorophyll antenna to catalyze unidirectional electron transfer. Both PSI and bR are well characterized biochemically and have been integrated into solar photovoltaic (PV) devices built from sustainable materials. Both PSI and bR are some of the best performing photosensitizers in the bio-sensitized PV field, yet relatively little attention has been devoted to the development of more sustainable, biocompatible alternative counter electrodes and electrolytes for bio-sensitized solar cells. Careful selection of the electrolyte and counter electrode components is critical to designing bio-sensitized solar cells with more sustainable materials and improved device performance. This work explores the use of poly (3,4-ethylenedioxythiophene) (PEDOT) modified with multi-walled carbon nanotubes (PEDOT/CNT) as counter electrodes and aqueous-soluble bipyridine cobaltII/III complexes as direct redox mediators for both PSI and bR devices. We report a unique counter electrode and redox mediator system that can perform remarkably well for both bio-photosensitizers that have independently evolved over millions of years. The compatibility of disparate proteins with common mediators and counter electrodes may further the improvement of bio-sensitized PV design in a way that is more universally biocompatible for device outputs and longevity.

Enhanced Performance of Carbon-Selenide Composite with La0.9Ce0.1NiO3 Perovskite Oxide for Outstanding Counter Electrodes in Platinum-Free Dye-Sensitized Solar Cells

For large-scale applications, dye-sensitized solar cells (DSSCs) require the replacement of the scarce platinum (Pt)-based counter electrode (CE) with efficient and cheap alternatives. In this respect, low-cost perovskite oxides (ABO₃) have been introduced as promising additives to composite-based CEs in Pt-free DSSCs. Herein, we synthesized composites from La_0.9Ce_0.1NiO₃ (L) perovskite oxide and functionalized-multiwall-carbon-nanotubes wrapped in selenides derived from metal-organic-frameworks (f-MWCNT-ZnSe-CoSe₂, “F”). L and F were then mixed with carbon black (CB) in different mass ratios to prepare L@CB, F@CB, and L@F@CB composites. The electrochemical analysis revealed that the L@F@CB composite with a mass ratio of 1.5:3:1.5 exhibits better electrocatalytic activity than Pt. In addition, the related DSSC reached a better PCE of 7.49% compared to its Pt-based counterpart (7.09%). This improved performance is the result of the increase in the oxygen vacancy by L due to the replacement of La with Ce in its structure, leading to more active sites in the L@F@CB composites. Moreover, the F@CB composite favors the contribution to the high electrical conductivity of the hybrid carbon nanotube–carbon black, which also offers good stability to the L@F@CB CE by not showing any obvious change in morphology and peak-to-peak separation even after 100 cyclic voltammetry cycles. Consequently, the corresponding L@F@CB-based device achieved enhanced stability. Our work demonstrates that L@F@CB composites with a low cost are excellent alternatives to Pt CE in DSSCs.

Influence of Nitrogen and Sulfur Doping of Carbon Xerogels on the Performance and Stability of Counter Electrodes in Dye Sensitized Solar Cells

In this work, carbon xerogels (CXGs) doped with nitrogen or sulfur have been investigated as DSSC counter electrodes. CXGs have been prepared by a sol–gel method from resorcinol and formaldehyde and subsequent carbonization. Nitrogen doping has been carried out by introducing melamine into the synthesis process along with resorcinol and formaldehyde, while sulfur has been incorporated by direct reaction of the carbon material with elemental sulfur. The counter electrodes for DSSCs have been prepared by airbrushing on conductive glass (fluorine-doped tin oxide, FTO), and their electrochemical behavior has been evaluated, observing that the introduction of heteroatoms such as nitrogen or sulfur leads to an improvement in efficiency compared to the undoped material thanks to a decrease in charge transfer resistance.

Solar energy conversion using first row d-block metal coordination compound sensitizers and redox mediators

The use of renewable energy is essential for the future of the Earth, and solar photons are the ultimate source of energy to satisfy the ever-increasing global energy demands. Photoconversion using dye-sensitized solar cells (DSCs) is becoming an established technology to contribute to the sustainable energy market, and among state-of-the art DSCs are those which rely on ruthenium(ii) sensitizers and the triiodide/iodide (I3 -/I-) redox mediator. Ruthenium is a critical raw material, and in this review, we focus on the use of coordination complexes of the more abundant first row d-block metals, in particular copper, iron and zinc, as dyes in DSCs. A major challenge in these DSCs is an enhancement of their photoconversion efficiencies (PCEs) which currently lag significantly behind those containing ruthenium-based dyes. The redox mediator in a DSC is responsible for regenerating the ground state of the dye. Although the I3 -/I- couple has become an established redox shuttle, it has disadvantages: its redox potential limits the values of the open-circuit voltage (V OC) in the DSC and its use creates a corrosive chemical environment within the DSC which impacts upon the long-term stability of the cells. First row d-block metal coordination compounds, especially those containing cobalt, and copper, have come to the fore in the development of alternative redox mediators and we detail the progress in this field over the last decade, with particular attention to Cu2+/Cu+ redox mediators which, when coupled with appropriate dyes, have achieved V OC values in excess of 1000 mV. We also draw attention to aspects of the recyclability of DSCs.

Solid-state dye-sensitized solar cells using polymeric hole conductors

The present review presents the application of electronically conducting polymers (conducting polymers) as hole conductors in solid-state dye solar cells (S-DSSCs). At first, the basic principles of dye solar cell operation are presented. The next section deals with the principles of electrochemical polymerisation and its photoelectrochemical variety, the latter being an important, frequently-used technique for generating conducting polymers and hole conductors in DSSCs. Finally, two varieties of S-DSSC configurations, those of dry S-DSSC and of S-DSSCs incorporating a liquid electrolyte, are discussed.