Graphene nanoplatelets doped with N at its edges as metal-free cathodes for organic dye-sensitized solar cells

Phase transitions and morphology control of Langmuir Blodget (LB) films of graphene oxide

HYPOTHESIS

Understanding the Langmuir film formation process of flexible and soft materials like graphene oxide (GO) is essential, as it shows different trends compared to the conventional surface pressure-area (π-A) and compressional modulus (ε) isotherms of hard materials. Additionally, the size distribution and mechanical properties of the GO are assumed to affect the distinctive Langmuir-Blodgett (LB) film morphologies, such as overlaps and wrinkles.

EXPERIMENT

To gain a deeper insights of phase transitions in GO LB films, we propose a novel analysis of elastic tensile modulus versus surface pressure (|ε|-π) isotherms. This approach involves applying adequate compression to the GO sheets to generate an elastic force, followed by measuring the |ε|-π isotherms during the film's expansion. Additionally, we compared the surface morphology of GO LB films deposited under identical conditions using various GO colloidal solutions, each containing sheets with different size distributions.

FINDING

Upon expanding the GO Langmuir film after sufficient compression, a rapid stress release is observed leading to a clear inflection in the |ε|-π isotherms, indicating a phase transition from solid to liquid. Therefore, this study provides comprehensive insights into the behavior of GO Langmuir films. Furthermore, we demonstrated that morphological features, such as wrinkles and overlaps in GO LB films, can be effectively controlled by adjusting the size distribution and mechanical properties of GO sheets in the colloidal solution.

Robust luminogens as cutting-edge tools for efficient light emission in recent decades

Blue luminogens play a vital role in white lighting and potential metal-free fluorescent materials and their high-lying excited states contribute to harvesting triplet excitons in devices. However, in TADF-OLEDs (ΔEST < 0.1 eV), although T1 excitons transfer to S1via RISC with 100% IQE, the longer lifetime of blue TADF suffers from efficiency roll-off (RO). In this case, hybridized local and charge transfer (HLCT) materials have attracted significant interest in lighting owing to their 100% hot exciton harvesting and enhanced efficiency. Both academics and industrialists widely use the HLCT strategy to improve the efficiency of fluorescent organic light-emitting diodes (FOLEDs) by harvesting dark triplet excitons through the RISC process. Aggregation-induced emissive materials (AIEgens) possess tight packing in the aggregation state, and twisted AIEgens with HLCT behaviour have a shortened conjugation length, inducing blue emission and making them suitable candidates for OLED applications. TTA-OLEDs are used in commercial BOLEDs because of their moderate efficiency and reasonable operation lifetime. In this review, we discuss the devices based on TTA fluorophores, TADF fluorophores, HLCT fluorophores, AIEgens and HLCT-sensitized fluorophores (HLCT-SF), which break through the statistical limitations.

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

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

Nitrogen doped carbonaceous materials as platinum free cathode electrocatalysts for oxygen reduction reaction (ORR)

Comparison of physicochemical properties and electrocatalytic behavior of different N-doped carbonaceous materials as potential catalysts for oxygen reduction reaction (ORR) was attended. Ball-milling of graphite with melamine and solvothermal treatment of graphite oxide, graphene nanoplatelets (GNP) with ammonia were used as preparation methods. Elemental analysis and N2 physisorption measurements revealed the synthesis of N-doped materials with strongly different morphological parameters. Contact angle measurements proved that all three samples had good wettability properties. According to analysis of XRD data and Raman spectra a higher nitrogen concentration corresponded to a smaller size of crystallites of the N-doped carbonaceous material. Surface total N content determined by XPS and bulk N content assessed by elemental analysis were close, indicating homogenous inclusion of N in all samples. Rotating disc electrode tests showed that these N-doped materials weremuch less active in acidic medium than in an alkaline environment. Although the presence of in-plane N species is regarded to be advantageous for the ORR activity, no particular correlation was found in these systems with any type of N species. According to Koutecky–Levich analysis, both the N-containing carbonaceous materials and the reference Pt/C catalyst displayed a typical one-step, four-electron ORR route. Both ball-milled sample with high N-content but with low SSA and solvothermally synthesized N-GNP with high SSA but low N content showed significant ORR activity. It could be concluded that beside the total N content other parameters such as SSA, pore structure, structural defects, wettability were also essential for achieving high ORR activity.

Obtaining N-Enriched Mesoporous Carbon-Based by Means of Gamma Radiation

In this paper, we present the results of the gamma irradiation method to obtain N-doped mesoporous activated carbons. Nitrogen-enriched mesoporous carbons were prepared from three chosen commercial activated carbons such as Carbon Black OMCARB C-140, KETJENBLACK EC-600JD and PK 1-3 Norit. HRTEM, SEM, Raman spectra, elemental analysis, XPS studies and widely approved N₂ adsorption-desorption measurements allowed us to evaluate the effectiveness of N atom insertion and its influence on the BET surface area and the pore structure of modified carbons. The obtained materials have an exceptionally high N content of up to 3.2 wt.%. Additionally, selected N-doped activated carbons were fully characterized to evaluate their applicability as carbon electrode materials with particular emphasis on Oxygen Reduction Reaction (ORR). The proposed method is a relatively facile, efficient and universal option that can be added to the already known methods of introducing heteroatoms to different carbons.

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.

Enhanced Oxygen Reduction Catalysis of Carbon Nanohybrids from Nitrogen-Rich Edges

The edge doping effect would help improve the carbon-based electrocatalysis. Herein, we present an all-mechanical technique for the fabrication of cut, exfoliated N-doped carbon nanotubes (C, E-N-CNTs). Such nanohybrids with an edge-N-rich structure are obtained through sequential doping and mechanical treatments of the pristine bulk-CNTs. The C, E-N-CNT/carbon black (C, E-N-CNT/C) demonstrates exciting oxygen reduction reaction (ORR) electrocatalysis with exceptionally low-onset potential (E₀, 913 mV versus RHE) and satisfactory half-wave potential (E_1/2, merely -7.3 mV shift compared with that of commercial 20% platinum/C (Pt/C)). Besides, the C, E-N-CNT/C presents significantly enhanced durability and tolerance in chronoamperometry test with methanol injection compared with the Pt/C. Our work would facilitate the mass production and full exploration of nonmetallic electrocatalysts.

Highly Effective Methods of Obtaining N-Doped Graphene by Gamma Irradiation

The design and fabrication of a new effective manufacturing method of heteroatom-doped carbon materials is still ongoing. In this paper, we present alternative and facile methods to obtain N-rich graphene with the use of low energy gamma radiation. This method was used as a pure and facile method for altering the physical and chemical properties of graphene. The obtained materials have an exceptionally high N content-up to 4 wt %. (dry method) and up to 2 wt %. (wet method). High-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectra and X-ray photoelectron spectroscopy (XPS) studies allowed us to evaluate the quality of the obtained materials. The presented results will provide new insights in designing and optimizing N-doped carbon materials potentially for the development of anode or cathode materials for electrochemical device applications, especially supercapacitors, metal-air batteries and fuel cells. Nitrogen atoms are exclusively bonded as quaternary groups. The method is expandable to the chemical insertion of other heteroatoms to graphene, especially such as sulfur, boron or phosphorus.

Recent progress on nanostructured carbon-based counter/back electrodes for high-performance dye-sensitized and perovskite solar cells

Dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs) favor minimal environmental impact and low processing costs, factors that have prompted intensive research and development. In both cases, rare, expensive, and less stable metals (Pt and Au) are used as counter/back electrodes; this design increases the overall fabrication cost of commercial DSSC and PSC devices. Therefore, significant attempts have been made to identify possible substitutes. Carbon-based materials seem to be a favorable candidate for DSSCs and PSCs due to their excellent catalytic ability, easy scalability, low cost, and long-term stability. However, different carbon materials, including carbon black, graphene, and carbon nanotubes, among others, have distinct properties, which have a significant role in device efficiency. Herein, we summarize the recent advancement of carbon-based materials and review their synthetic approaches, structure-function relationship, surface modification, heteroatoms/metal/metal oxide incorporation, fabrication process of counter/back electrodes, and their effects on photovoltaic efficiency, based on previous studies. Finally, we highlight the advantages, disadvantages, and design criteria of carbon materials and fabrication challenges that inspire researchers to find low cost, efficient and stable counter/back electrodes for DSSCs and PSCs.

Highly Active Carbon-Based Electrocatalysts for Dye-Sensitized Solar Cells: A Brief Review

Dye-sensitized solar cells (DSSCs) have emerged as promising alternatives to traditional silicon-based solar cells due to their relatively high conversion efficiency, low cost, flexibility, and environmentally benign fabrication processes. In DSSCs, platinum (Pt)-based materials used as the counter electrode (CE) exhibit the superior catalytic ability toward the reduction reaction of triiodide ions, which are attributed to their excellent catalytic activity and high electrical conductivity. However, Pt-based materials with high cost and limited supply hinder them from mass production. Developing highly active and stable CE materials without noble metals has been a persistent challenge for the practical application in DSSCs. Recently, a number of earth-abundant catalysts, especially carbon-based materials, display high activity, low cost, and good stability that render them attractive candidates to replace Pt in DSSCs. Herein, we will briefly review recent progress on carbon-based electrocatalysts as CEs in DSSC applications. The strategies of improving the catalytic activity of carbon-based materials such as structural engineering and/or heteroatom doping will be introduced. The active sites toward the reduction reaction of triiodide ions summarized from experimental results or theoretical calculation will also be discussed. Finally, the futuristic prospects and challenges of carbon-based electrocatalysts as CEs in DSSCs will be briefly mentioned.

Low-Cost Counter-Electrode Materials for Dye-Sensitized and Perovskite Solar Cells

It is undoubtable that the use of solar energy will continue to increase. Solar cells that convert solar energy directly to electricity are one of the most convenient and important photoelectric conversion devices. Though silicon-based solar cells and thin-film solar cells have been commercialized, developing low-cost and highly efficient solar cells to meet future needs is still a long-term challenge. Some emerging solar-cell types, such as dye-sensitized and perovskite, are approaching acceptable performance levels, but their costs remain too high. To obtain a higher performance-price ratio, it is necessary to find new low-cost counter materials to replace conventional precious metal electrodes (Pt, Au, and Ag) in these emerging solar cells. In recent years, the number of counter-electrode materials available, and their scope for further improvement, has expanded for dye-sensitized and perovskite solar cells. Generally regular patterns in the intrinsic features and structural design of counter materials for emerging solar cells, in particular from an electrochemical perspective and their effects on cost and efficiency, are explored. It is hoped that this recapitulative analysis will help to make clear what has been achieved and what still remains for the development of cost-effective counter-electrode materials in emerging solar cells.

Oxidative Dehydrogenation of Ethylbenzene into Styrene by Fe-Graphitic Catalysts

Carbon-based catalysts have attracted much attention for the dehydrogenation (DH) of organic molecules, due to their rich active sites, high conversion efficiency, and selectivity. However, because of their poor stability at high operation temperature and relatively high cost, their practical applications have been limited. Here, we report a simple ball-milling-induced mechanochemical reaction which can introduce iron (Fe) and different functional groups (mostly stable aromatic C═O after heat-treatment) along the edges of graphitic nanoplatelets. The resulting Fe-graphitic nanoplatelets (Fe-XGnPs, X = H, C, N, or V) provide active sites for the oxidative dehydrogenation (ODH) of ethylbenzene into styrene. Among them, Fe-NGnPs (X = N) displayed the highest performance for styrene production at low temperature (∼11.13 mmol g^-1 h^-1, 450 °C) with high selectivity and durability.

Edge-Functionalized Graphene Nanoplatelets as Metal-Free Electrocatalysts for Dye-Sensitized Solar Cells

A scalable and low-cost production of graphene nanoplatelets (GnPs) is one of the most important challenges for their commercialization. A simple mechanochemical reaction has been developed and applied to prepare various edge-functionalized GnPs (EFGnPs). EFGnPs can be produced in a simple and ecofriendly manner by ball milling of graphite with target substances (X = nonmetals, halogens, semimetals, or metalloids). The unique feature of this method is its use of kinetic energy, which can generate active carbon species by unzipping of graphitic CC bonds in dry conditions (no solvent). The active carbon species efficiently pick up X substance(s), leading to the formation of graphitic CX bonds along the broken edges and the delamination of graphitic layers into EFGnPs. Unlike graphene oxide (GO) and reduced GO (rGO), the preparation of EFGnPs does not involve toxic chemicals, such as corrosive acids and toxic reducing agents. Furthermore, the prepared EFGnPs preserve high crystallinity in the basal area due to their edge-selective functionalization. Considering the available edge X groups that can be selectively employed, the potential applications of EFGnPs are unlimited. In this context, the synthesis, characterizations, and applications of EFGnPs, specifically, as metal-free carbon-based electrocatalysts for dye-sensitized solar cells (DSSCs) in both cobalt and iodine electrolytes are reviewed.

Highly conductive and stable graphene/PEDOT:PSS composite as a metal free cathode for organic dye-sensitized solar cells

Platinum (Pt) as the counter electrode (CE) in dye-sensitized solar cells (DSSCs) is expensive and non-optimal for cobalt(ii/iii) redox couples, which can tune and improve the performance of DSSCs, thus motivating the search for replacements of the Pt CE. Graphene nanoplatelets (GnPs) are possible alternatives to Pt CEs but they are mechanically unstable as CEs due to their poor substrate adhesion. Here we report a new type of PEDOT:PSS (PP)/GnP (PPG) composite that maintains the catalytic performance of GnPs with enhanced adhesion to the substrate via a conductive PEDOT matrix. The resultant PPG exhibited extremely low charge-transfer resistance (R_ct) compared to Pt in its role as an electrocatalyst toward a Co(bpy)₃^2+/3+ (bpy = 2,2′-bipyridine) redox couple, and displayed extremely high electrochemical stability for Co(bpy)₃³⁺ reduction even after 1000 cycles. The inter-stacking of GnP layers between PEDOT and PSS was confirmed by XPS and Raman spectra. It helps to delocalize charges in the PEDOT backbone and rapidly transfers electrons from the external circuit to Co(bpy)₃³⁺. This reduces the R_ct and ultimately improves the photovoltaic performance. The DSSC based on Y123 sensitizer and PPG-CE showed a higher photovoltaic performance of 8.33% than its Pt counterpart does (7.99%) under the optimized conditions.

We report the development of a highly stable PEDOT:PSS/graphene (PP/GnP) composite-based counter electrode (CE) for high-performance dye-sensitized solar cells (DSSCs) in conjunction with Y123 sensitizer and Co(bpy)₃^2+/3+ (bpy = 2,2'-bypyridine) redox couple.

Construction of structurally diverse luminescent lead(ii) fluorinated coordination polymers based on auxiliary ligands

Four novel Pb(ii) fluorinated coordination polymers were obtained by hydrothermal reaction of lead nitrate with 2,4,5,6-tetrafluoroisophthalic acid (H₂TFIPA) in the presence of corresponding N-donor auxiliary ligands and photoluminescent properties of the all complexes have also been investigated.

Coffee Waste-Derived Hierarchical Porous Carbon as a Highly Active and Durable Electrocatalyst for Electrochemical Energy Applications

Nitrogen-doped porous carbon materials have been highlighted as promising alternatives to high-cost platinum in various electrochemical energy applications. However, protocols to generate effective pore structure are still challenging, which hampers mass production and utilization of carbon materials. Here, we suggest a facile and effective method for hierarchical porous carbon by a single-step carbonization of coffee waste (CW) with ZnCl₂. The CW, which is one of the most earth-abundant organic waste, can be successfully converted to nitrogen-doped porous carbon. It shows outstanding oxygen reduction activity and durability comparable to the state-of-the-art platinum, and the half-wave potential is also comparable to the best metal-free electrocatalysts in alkaline media. Finally, we apply it to counter electrode of dye-sensitized solar cell, whose photovoltaic efficiency surpasses the one made with conventional platinum electrode. We demonstrate the feasibility of our strategies for highly efficient, cheap, and environment-friendly electrocatalyst to replace platinum in various electrochemical energy applications.

Synergistically Enhanced Electrochemical Performance of Ni3S4-PtX (X = Fe, Ni) Heteronanorods as Heterogeneous Catalysts in Dye-Sensitized Solar Cells

Platinum (Pt)-based alloys are considerably promising electrocatalysts for the reduction of I^-/I₃^- and Co²⁺/Co³⁺ redox couples in dye-sensitized solar cells (DSSCs). However, it is still challenging to minimize the dosage of Pt to achieve comparable or even higher catalytic efficiency. Here, by taking full advantages of the Mott-Schottky (M-S) effect at the metal-semiconductor interface, we successfully strategize a low-Pt-based M-S catalyst with enhanced electrocatalytic performance and stability for the large-scale application of DSSCs. The optimized M-S electrocatalyst of Ni₃S₄-Pt₂X₁ (X = Fe, Ni) heteronanorods is constructed by rationally controlling the ratio of Pt to transition metal in the hybrids. It was found that the electrons transferred from Ni₃S₄ to Pt₂X₁ at their interface under the Mott-Schottky effect result in the concentration of electrons onto Pt₂X₁ domains, which subsequently accelerates the regeneration of both I^-/I₃^- and Co²⁺/Co³⁺ redox shuttles in DSSCs. As a result, the DSSC with Ni₃S₄-Pt₂Fe₁ manifests an impressive power conversion efficiency (PCE) of 8.79% and 5.56% for iodine and cobalt-based electrolyte under AM1.5G illumination, respectively. These PCEs are obviously superior over those with Ni₃S₄-Pt, PtFe, Ni₃S₄, and pristine Pt electrodes. The strategy reported here is able to be further expanded to fabricate other low-Pt-alloyed M-S catalysts for wider applications in the fields of photocatalysis, water splitting, and heterojunction solar cells.

Nitrogen and phosphorus dual-doped graphene as a metal-free high-efficiency electrocatalyst for triiodide reduction

Alternative high-performance electrocatalysts for triiodide (I₃^-) reduction of low-cost dye-sensitized solar cells (DSSCs) are urgently sought after. To address the concerned issues, we report a facile strategy for engineering the nitrogen and phosphorus dual-doped graphene (NPG) via an efficient ball-milling process, followed by a simple thermal annealing approach utilizing melamine (C₃H₆N₆) and triphenylphosphine ((C₆H₅)₃P) as the N and P source, respectively. When employed as the counter electrode (CE) in DSSCs, such a metal-free material exhibits excellent electrocatalytic activity towards the I₃^-/I^- redox reaction. Dual-doping of N and P heteroatoms can markedly enhance the photovoltaic performance of DSSCs by a synergistic effect and a high conversion efficiency of 8.57% is achieved, which is superior to Pt CE, and much higher than that of the single-component N- or P-doped graphene electrodes. In addition, the NPG CE also shows an outstanding electrochemical stability. The present results demonstrate that the NPG as a low-cost and high-efficiency electrocatalyst for reduction of I₃^- will be one of the promising CE materials in DSSCs.

Edge Functionalization of Graphene and Two-Dimensional Covalent Organic Polymers for Energy Conversion and Storage

Edge functionalization by selectively attaching chemical moieties at the edge of graphene sheets with minimal damage of the carbon basal plane can impart solubility, film-forming capability, and electrocatalytic activity, while largely retaining the physicochemical properties of the pristine graphene. The resultant edge-functionalized graphene materials (EFGs) are attractive for various potential applications. Here, a focused, concise review on the synthesis of EFGs is presented, along with their 2D covalent organic polymer (2D COP) analogues, as energy materials. The versatility of edge-functionalization is revealed for producing tailor-made graphene and COP materials for efficient energy conversion and storage.

High-surface-area nanomesh graphene with enriched edge sites as efficient metal-free cathodes for dye-sensitized solar cells

Exploiting cost-effective and highly efficient counter electrodes (CEs) has been a persistent objective for practical application of dye-sensitized solar cells (DSSCs). Here, we present an efficient CE by using pure three-dimensional (3D) nanomesh graphene frameworks (NGFs) which are synthesized via a template-directed chemical vapor deposition (CVD) approach. The high-surface-area 3D NGFs associated with the enriched surface edge defects make it very efficient towards I3(-) reduction even without any Pt catalyst. More interestingly, by virtue of the interpenetrating graphene frameworks, the NGFs exhibit excellent electron conductivity, thus leading to facile charge transfer. Consequently, the DSSCs with pure NGFs as CEs display a power conversion efficiency of 7.32%, which is comparable to that of Pt as CEs (7.28%), thereby exhibiting great potential as low-cost and highly efficient CE materials for large-scale deployment of DSSCs.

Multiple-color aggregation-induced emission (AIE) molecules as chemodosimeters for pH sensing

A series of 4-N,N-dimethylaminoaniline salicylaldehyde Schiff-base derivatives (DAS) were facilely prepared. They exhibit typical AIE properties with various fluorescence emissions and high fluorescence quantum yields in an aggregated state. DAS exhibit unique pH-dependent optical properties, which indicated their potential applications in pH sensing.

Edge-selenated graphene nanoplatelets as durable metal-free catalysts for iodine reduction reaction in dye-sensitized solar cells

Metal-free carbon-based electrocatalysts for dye-sensitized solar cells (DSSCs) are sufficiently active in Co(II)/Co(III) electrolytes but are not satisfactory in the most commonly used iodide/triiodide (I(-)/I3 (-)) electrolytes. Thus, developing active and stable metal-free electrocatalysts in both electrolytes is one of the most important issues in DSSC research. We report the synthesis of edge-selenated graphene nanoplatelets (SeGnPs) prepared by a simple mechanochemical reaction between graphite and selenium (Se) powders, and their application to the counter electrode (CE) for DSSCs in both I(-)/I3 (-) and Co(II)/Co(III) electrolytes. The edge-selective doping and the preservation of the pristine graphene basal plane in the SeGnPs were confirmed by various analytical techniques, including atomic-resolution transmission electron microscopy. Tested as the DSSC CE in both Co(bpy)3 (2+/3+) (bpy = 2,2'-bipyridine) and I(-)/I3 (-) electrolytes, the SeGnP-CEs exhibited outstanding electrocatalytic performance with ultimately high stability. The SeGnP-CE-based DSSCs displayed a higher photovoltaic performance than did the Pt-CE-based DSSCs in both SM315 sensitizer with Co(bpy)3 (2+/3+) and N719 sensitizer with I(-)/I3 (-) electrolytes. Furthermore, the I3 (-) reduction mechanism, which has not been fully understood in carbon-based CE materials to date, was clarified by an electrochemical kinetics study combined with density functional theory and nonequilibrium Green's function calculations.

Electrocatalytic activity of NiO on silicon nanowires with a carbon shell and its application in dye-sensitized solar cell counter electrodes

To improve the catalytic activity of a material, it is critical to maximize the effective surface area by directly contacting the electrolyte. Nanowires are a promising building block for catalysts in electrochemical applications because of their large surface area. Nickel oxide (NiO) decoration was achieved by drop-casting a nickel-dissolved solution onto vertically aligned silicon nanowire arrays with a carbon shell (SiNW/C). Based on the hybridization of the NiO and silicon nanowire arrays with a carbon shell this study aimed to achieve a synergic effect for the catalytic activity performance. This study demonstrated that the resulting nanomaterial exhibits excellent electrocatalytic activity and performs well as a counter electrode for dye-sensitized solar cells (DSSCs). The compositions of the materials were examined using X-ray diffraction, X-ray photoelectron spectroscopy, and energy dispersive spectroscopy. Their micro- and nano-structures were investigated using scanning electron microscopy and transmission electron microscopy. The electrochemical activity toward I(-)/I3(-) was examined using cyclic voltammetry and electrochemical impedance spectroscopy. The obtained peak power conversion efficiency of the DSSC based on the NiO@SiNW/C counter electrode was 9.49%, which was greater than that of the DSSC based on the Pt counter electrode.

Earth Abundant Silicon Composites as the Electrocatalytic Counter Electrodes for Dye-Sensitized Solar Cells

Earth abundant silicon compounds, including Si3N4, SiO2, SiS2, and SiSe2, were introduced as the electrocatalytic materials for the counter electrodes (CE) in dye-sensitized solar cells (DSSCs). Among these silicon-based materials, Si3N4, SiS2, and SiSe2 were applied in DSSCs for the first time. In the presence of a conducting binder, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (

PEDOT

PSS), various silicon-based composites (Si3N4/PEDOT:PSS, SiO2/PEDOT:PSS, SiS2/PEDOT:PSS, and SiSe2/PEDOT:PSS) were successfully coated on the ITO substrates via a simple drop-coating process. In a composite film, silicon-based nanoparticles provided attractive electrocatalytic ability and plenty of electrocatalytic active sites for the triiodine ion (I3(-)) reduction.

PEDOT

PSS not only acted as a good conducting binder for silicon-based nanoparticles, but also provided a continuous polymer matrix to increase the electron transfer pathways. By adjusting the weight percent (1-5 wt %) of the silicon-based nanoparticles (Si3N4, SiO2, SiS2, and SiSe2) with respect to the weight of

PEDOT

PSS, the composite films containing 5 wt % Si3N4 (denoted as Si3N4-5) and 5 wt % SiSe2 (denoted as SiSe2-5) both reached excellent electrocatalytic abilities and rendered the good cell efficiencies (η) of 8.2% to their DSSCs. It can be said that both Si3N4-5 and SiSe2-5 are promising electrocatalytic materials to replace the rare and expensive Pt (η = 8.5%).

Facile formation of a hierarchical TiO2–SnO2 nanocomposite architecture for efficient dye-sensitized solar cells

Hierarchical TiO₂–SnO₂ nano-architecture for efficient DSSC.

Ultralong In2S3 Nanotubes on Graphene Substrate with Enhanced Electrocatalytic Activity

Ultralong one-dimensional (1D) nanostructures including nanowires or nanotubes have been extensively studied because of their widespread applications in many fields. Although a lot of methods have been reported to prepare In2S3 nanotubes, approaching these nanotubes through one-pot solution synthesis is still extremely difficult, probably because of the intrinsic isotropic crystal growth characteristic of In2S3. In this article, we demonstrated a self-assembly approach for hydrothermal synthesis of In2S3 nanotubes/graphene composites, which contain ultralong (up to 10 μm) In2S3 nanotubes on graphene substrate. The influence of several important synthetic parameters on the final products has been systematically investigated. Importantly, the as-prepared In2S3 nanotubes/graphene composites can be easily cast on FTO to form a film, which can be used as a counter electrode. Our research indicates that the as-fabricated counter electrode exhibits excellent electrocatalytic activity toward the iodide species (I-/I3-) reduction reaction and very high energy conversion efficiency (8.01%) in dye-sensitized solar cells.