A simple one-step hydrothermal synthesis of cobalt nickel selenide/graphene nanohybrid as an advanced platinum free counter electrode for dye sensitized solar cell

Advances in Hierarchical Inorganic Nanostructures for Efficient Solar Energy Harvesting Systems

The urgent need to address the global energy and environmental crisis necessitates the development of efficient solar-power harvesting systems. Among the promising candidates, hierarchical inorganic nanostructures stand out due to their exceptional attributes, including a high specific surface area, abundant active sites, and tunable optoelectronic properties. In this comprehensive review, we delve into the fundamental principles underlying various solar energy harvesting technologies, including dye-sensitized solar cells (DSSCs), photocatalytic, photoelectrocatalytic (water splitting), and photothermal (water purification) systems, providing a foundational understanding of their operation. Thereafter, the discussion is focused on recent advancements in the synthesis, design, and development of hierarchical nanostructures composed of diverse inorganic material combinations, tailored for each of these solar energy harvesting systems. We meticulously elaborate on the distinct synthesis methods and conditions employed to fine-tune the morphological features of these hierarchical nanostructures. Furthermore, this review offers profound insights into critical aspects such as electron transfer mechanisms, band gap engineering, the creation of hetero-hybrid structures to optimize interface chemistry through diverse synthesis approaches, and precise adjustments of structural features. Beyond elucidating the scientific fundamentals, this review explores the large-scale applications of the aforementioned solar harvesting systems. Additionally, it addresses the existing challenges and outlines the prospects for achieving heightened solar-energy conversion efficiency.

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.

High-performance EMI shielding effectiveness of Fe3O4-3D rPC nanocomposites: a systematic optimization in the X-band region

In this work, the microwave absorption (MWA) performance of a Fe3O4-3D reduced porous carbon nanocomposite (3D rPC NC) in the X-band region is reported. Three different shields are fabricated by altering the ratio of Fe3O4 nanoparticles (NPs) and 3D rPC and evaluating their microwave (MW) shielding performance with appropriate in-wearing instruments due to their minimum thickness. The chemical interaction between Fe3O4 NPs and 3D rPC is examined from chemical composition analysis of Fe3O4-3D rPC (1 : 2 ratio), which is confirmed by the presence of the Fe-O-C bond in the O 1s spectrum obtained from XPS analysis and subsequent analysis using FESEM images. Furthermore, it is found from N2 adsorption/desorption analysis that 3D rPC possesses a huge surface area of 787.312 m2 g-1 and showcases a type-V isotherm (mesoporous and/or microporous) behavior. The dielectric and magnetic losses of Fe3O4-3D rPC with a 1 : 2 ratio (tan δεr = 1.27 and tan δμr = 5.03) are higher than those of Fe3O4 NPs, 3D rPC and their NCs due to its magnetic and electrical conducting pathways modifying the material's polarization and dipole moment. The lightweight, polymer-free Fe3O4-3D rPC (1 : 2) NCs with minimum thickness on the order of 0.5 mm exhibited a higher total shielding effectiveness (SET = 41.285 dB), and it effectively blocked 99.9963% of the transmittance due to electric and magnetic polarization resulting from the presence of a heterogeneous interface surface.

Near-infrared photoactive Ag-Zn-Ga-S-Se quantum dots for high-performance quantum dot-sensitized solar cells

The high light-harvesting ability of quantum dots (QDs) plays an eminent role in the performance of solar cells. In this study, we synthesized Ag-Zn-Ga-S-Se-based alloyed QDs by colloidal hot injection and characterized them. The X-ray photoelectron spectrum analysis confirms the +1, +2, +3, -2, and -2 oxidation states of, respectively, Ag, Zn, Ga, S, and Se in the QDs, and the energy-dispersive X-ray spectrum analysis confirms the 1:1:1:1.5:1.5 stoichiometric ratio of, respectively, Ag, Zn, Ga, S, and Se. These two results indicate the formation of I-II-III-VI₃-type alloyed crystals (AgZnGaS_1.5Se_1.5 nanocrystals). TEM image analysis reveals the QD nature of the synthesized Ag-Zn-Ga-S-Se nanocrystals. The X-ray diffraction pattern confirms the hexagonal structure. Due to the near-infrared light absorption capability, the synthesized QDs were used as the sensitizer to fabricate QDSCs. The fabricated QDSCs were characterized by using electrochemical impedance spectroscopy and photovoltaic performance studies. The fabricated QDSC have superior electrochemical activity with a photoconversion efficiency of 4.91%.

NiCoSe4nanoparticles derived from nickel-cobalt Prussian blue analogues on N-doped reduced graphene oxide for high-performance asymmetric supercapacitors

Synthesis of NiHCCo precursors via simple co-precipitation and nickel-cobalt tetraselenide composites grown on nitrogen-doped reduced graphene oxide (NiCoSe₄/N-rGO) were fabricated using solvothermal method. The introduction of N-rGO used as a template effectively prevented agglomeration of NiCoSe₄nanoparticles and provided more active sites, which greatly increased the electrochemical and electrical conductivity for NiCoSe₄/N-rGO. NiCoSe₄/N-rGO-20 presents a remarkably elevated specific capacity of 120 mA h g^-1under current density of 1 A g^-1. NiCoSe₄/N-rGO-20 demonstrates an excellent cycle life and achieves a remarkable 83% retention rate over 3000 cycles with 10 A g^-1. NiCoSe₄/N-rGO-20//N-rGO asymmetric supercapacitor was constructed based on the NiCoSe₄/N-rGO-20 as an anode, N-rGO as cathode by using 2 mol l^-1KOH as an electrolyte. NiCoSe₄/N-rGO-20//N-rGO ASC demonstrates an ultra-big energy density of 14 Wh kg^-1and good circulation stability in the power density of 902 W kg^-1. It is doubled in comparison to the NiCoSe₄/N-rGO-20//rGO asymmetric supercapacitor (7 Wh kg^-1). The NiCoSe₄/N-rGO-20//N-rGO ASC capacity retention is still up to 93% over 5000 cycles (5 A g^-1). The results reveal that this device would be a prospective cathode material of supercapacitors in actual applications.

Emergence of Ni-Based Chalcogenides (S and Se) for Clean Energy Conversion and Storage

Nickel chalcogenide (S and Se) based nanostructures intrigued scientists for some time as materials for energy conversion and storage systems. Interest in these materials is due to their good electrochemical stability, eco-friendly nature, and low cost. The present review compiles recent progress in the area of nickel-(S and Se)-based materials by providing a comprehensive summary of their structural and chemical features and performance. Improving properties of the materials, such as electrical conductivity and surface characteristics (surface area and morphology), through strategies like nano-structuring and hybridization, are systematically discussed. The interaction of the materials with electrolytes, other electro-active materials, and inactive components are analyzed to understand their effects on the performance of energy conversion and storage devices. Finally, outstanding challenges and possible solutions are briefly presented with some perspectives toward the future development of these materials for energy-oriented devices with high performance.

Cobalt and Carbon Complex as Counter Electrodes in Dye-Sensitized Solar Cells

We developed cobalt and carbon complex materials as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs) to replace conventional platinum (Pt) CEs. Co12 and Co15, both of which are basic cobalt derivatives, showed good redox potential with a suitable open-circuit voltage (VOC); however, their poor electrical conductivity engendered a low short-circuit current (JSC) and fill factor (FF). Mixing them with carbon black (CB) improved the electrical conductivity of the CE; in particular, JSC and FF were considerably improved. Further improvement was achieved by combining cobalt derivatives and CB through thermal sintering to produce a novel CoCB material as a CE. CoCB had good electrical conductivity and electrocatalytic capability, and this further enhanced both JSC and VOC. The optimized device exhibited a power conversion efficiency (PCE) of 7.44%, which was higher than the value of 7.16% for a device with a conventional Pt CE. The conductivity of CoCB could be further increased by mixing it with PEDOT:PSS, a conducting polymer. The device’s JSC increased to 18.65 mA/cm2, which was considerably higher than the value of 14.24 mA/cm2 for the device with Pt CEs. The results demonstrate the potential of the cobalt and carbon complex as a CE for DSSCs.

The hole transporting behaviour of Cu2AgInS4 and Cu2AgInSe4 for a carbon electrode-based perovskite solar cell

In this work, quaternary Cu₂AgInS₄ (CAIS) and Cu₂AgInSe₄ (CAISe) nanoparticles (NPs) were synthesised by a simple hot injection method and their photovoltaic behaviour were studied in detail for PSC.

Research on the Preparation and Spectral Characteristics of Graphene/TMDs Hetero-structures

The Van der Waals (vdWs) hetero-structures consist of two-dimensional materials have received extensive attention, which is due to its attractive electrical and optoelectronic properties. In this paper, the high-quality large-size graphene film was first prepared by the chemical vapor deposition (CVD) method; then, graphene film was transferred to SiO₂/Si substrate; next, the graphene/WS₂ and graphene/MoS₂ hetero-structures were prepared by the atmospheric pressure chemical vapor deposition method, which can be achieved by directly growing WS₂ and MoS₂ material on graphene/SiO₂/Si substrate. Finally, the test characterization of graphene/TMDs hetero-structures was performed by AFM, SEM, EDX, Raman and PL spectroscopy to obtain and grasp the morphology and luminescence laws. The test results show that graphene/TMDs vdWs hetero-structures have the very excellent film quality and spectral characteristics. There is the built-in electric field at the interface of graphene/TMDs heterojunction, which can lead to the effective separation of photo-generated electron-hole pairs. Monolayer WS₂ and MoS₂ material have the strong broadband absorption capabilities, the photo-generated electrons from WS₂ can transfer to the underlying p-type graphene when graphene/WS₂ hetero-structures material is exposed to the light, and the remaining holes can induced the light gate effect, which is contrast to the ordinary semiconductor photoconductors. The research on spectral characteristics of graphene/TMDs hetero-structures can pave the way for the application of novel optoelectronic devices.

Biomass-derived carbon boosted catalytic properties of tungsten-based nanohybrids for accelerating the triiodide reduction in dye-sensitized solar cells

Manganese tungstate (MnWO₄), zinc tungstate (ZnWO₄), and copper tungstate (CuWO₄) embedded biomass-derived carbon (MWO-C, ZWO-C, CWO-C) was synthesized by hydrothermal treatment and investigated as counter electrode (CE) catalysts to test electrochemical activity. Biomass-derived carbon was used as the shape controlling agent, which changed the morphology of MWO from spherical to spindle-like. Owing to the synergistic effect between tungsten-based bimetal oxides and biomass-derived carbon, the MWO-C, ZWO-C, and CWO-C catalysts exhibited enhanced electrochemical performance in dye-sensitized solar cells (DSSCs) system. The MWO-C, ZWO-C and CWO-C catalysts in DSSCs showed outstanding power conversion efficiency (PCE) of 7.33%, 7.61%, and 6.52%, respectively, as compared with 7.04% for Pt based devices. Biomass-derived carbon improves the catalytic properties of tungsten-based nanohybrids. The results showed that biomass-derived carbon-enhanced inorganic compound as CE catalysts are promising alternatives to Pt-based CE catalysts for energy conversion devices.

High-Efficiency Dye-Sensitized Solar Cells Based on Kesterite Cu2ZnSnSe4 Inlaid on a Flexible Carbon Fabric Composite Counter Electrode

Composite counter electrodes have been shown to be a practical and effective strategy in dye-sensitized solar cell (DSSC) application. In this work, we designed and prepared a single-crystal Cu₂ZnSnSe₄ (CZTSe) plate structure on flexible carbon fabric as a DSSC cathode, which combines the best of the two worlds, namely, the superior catalytic activity and hierarchical microstructure of kesterite CZTSe and the high conductivity and expanded framework of carbon fabric. The composite counter electrode presented a power conversion efficiency of 8.45% and a long-term bending reservation. The remarkable device property is due to the high catalytic activity, good adherence to conductive matrix grains, effective electron migration, and quick iodide species diffusion of the novel cathode. Our results suggest that the CZTSe@carbon fabric composite could be a high-efficiency Pt-free cathode in DSSCs.

Stoichiometry-Controlled MoxW1-xTe2 Nanowhiskers: A Novel Electrocatalyst for Pt-Free Dye-Sensitized Solar Cells

Novel polymorphic Mo_xW_1-xTe₂-based counter electrodes possess high carrier mobility, phase-dependent lattice distortion, and surface charge density wave to boost the charge-transfer kinetics and electrocatalytic activity in dye-sensitized solar cells (DSSCs). Here, we report the syntheses of stoichiometry-controlled binary and ternary Mo_xW_1-xTe₂ nanowhiskers directly on carbon cloth (CC), denoted by Mo_xW_1-xTe₂/CC, with an atmospheric chemical vapor deposition technique. The synthesized Mo_xW_1-xTe₂/CC samples, including 1T'-MoTe₂/CC, T_d-WTe₂/CC, T_d-Mo_0.26W_0.73Te_2.01/CC, and 1T'- & T_d-Mo_0.66W_0.32Te_2.02/CC, were then employed as different counter electrodes to study their electrochemical activities and efficiencies in DSSCs. The photovoltaic parameter analysis manifests that Mo_xW_1-xTe₂/CCs are more stable than a standard Pt/CC in the I^-/I₃^- electrolyte examined by cyclic voltammetry over 100 cycles. A 1T'- & T_d-Mo_0.66W_0.32Te_2.02/CC-based DSSC can achieve a photocurrent density of 16.29 mA cm^-2, a maximum incident photon-to-electron conversion efficiency of 90% at 550 nm excitation, and an efficiency of 9.40%, as compared with 8.93% of the Pt/CC counterpart. Moreover, the 1T'- & T_d-Mo_0.66W_0.32Te_2.02/CC shows lower charge-transfer resistance (0.62 Ω cm²) than a standard Pt/CC (1.19 Ω cm²) in electrocatalytic reactions. Notably, Mo_xW_1-xTe₂ nanowhiskers act as an electron expressway by shortening the path of carrier transportation in the axial direction from a counter electrode to electrolytic ions to enhance the reaction kinetics in DSSCs. This work demonstrates that the nanowhisker-structured 1T'- & T_d-Mo_0.66W_0.32Te_2.02/CC with high carrier mobility and robust surface states can serve as a highly efficient counter electrode in DSSCs to replace the conventional Pt counter electrode for electrocatalytic applications.

Review of fabrication methods of large-area transparent graphene electrodes for industry

Graphene is a two-dimensional material showing excellent properties for utilization in transparent electrodes; it has low sheet resistance, high optical transmission and is flexible. Whereas the most common transparent electrode material, tin-doped indium-oxide (ITO) is brittle, less transparent and expensive, which limit its compatibility in flexible electronics as well as in low-cost devices. Here we review two large-area fabrication methods for graphene based transparent electrodes for industry: liquid exfoliation and low-pressure chemical vapor deposition (CVD). We discuss the basic methodologies behind the technologies with an emphasis on optical and electrical properties of recent results. State-of-the-art methods for liquid exfoliation have as a figure of merit an electrical and optical conductivity ratio of 43.5, slightly over the minimum required for industry of 35, while CVD reaches as high as 419.

Influence of a bifunctional linker on the loading of Cu2AgInS4 QDs onto porous TiO2 NFs to use as an efficient photoanode to boost the photoconversion efficiency of QDSCs

Quaternary Cu₂AgInS₄ quantum dots anchored more onto porous TiO₂ NFs through a linker, 3-mercaptopropionic acid exhibits higher photoconversion efficiency of QDSC than that of the same anchored without a linker.

A Bi2Te3 Topological Insulator as a New and Outstanding Counter Electrode Material for High-Efficiency and Endurable Flexible Perovskite Solar Cells

Inverted flexible perovskite solar cells (PSCs) typically employ expensive metals as the counter electrodes, which are brittle and corrodible by perovskite, leading to a sharp performance drop under continuous bending, air exposure, thermal stress, or light illumination and eventually retard the commercialization. Herein, a low-cost Bi₂Te₃ counter electrode was employed by using a simple thermal evaporation process. The resultant device achieved an excellent power conversion efficiency of 18.16%, which was among the highest reported efficiencies, much higher than the reference Ag PSC (15.90%). The improvement should be attributed to the intrinsic suppressed electron backscattering in a Bi₂Te₃ topological insulator. Simultaneously, the Bi₂Te₃ device obtained a significantly improved mechanical flexibility and long-term operational stability. The present strategy will help to open up a new avenue for future commercialization of flexible photovoltaic applications.

Tungsten oxide nanostructures and nanocomposites for photoelectrochemical water splitting

Hydrogen production from photoelectrochemical (PEC) water splitting using semiconductor photocatalysts has attracted great attention to realize clean and renewable energy from solar energy. The visible light response of WO3 with a long hole diffusion length (∼150 nm) and good electron mobility (∼12 cm2 V-1 s-1) makes it suitable as the photoanode. However, WO3 suffers from issues including rapid recombination of photoexcited electron-hole pairs, photo-corrosion during the photocatalytic process due to the formation of peroxo-species, sluggish kinetics of photogenerated holes, and slow charge transfer at the semiconductor/electrolyte interface. This work highlights the approaches to overcome these drawbacks of WO3 photoanodes, including: (i) the manipulation of nanostructured WO3 photoanodes to decrease the nanoparticle size to promote hole migration to the WO3/electrolyte interface which benefits the charge separation; (ii) doping or introducing oxygen vacancies to improve electrical conductivity; exposing high energy crystal surfaces to promote the consumption of photogenerated holes on the high-active crystal face, thereby suppressing the recombination of photogenerated electrons and holes; (iii) decorating with co-catalysts to reduce the overpotential which inhibits the formation of peroxo-species; (iv) other methods such as coupling with narrow band semiconductors to accelerate the charge separation and controlling the crystal phase via annealing to reduce defects. These approaches are reviewed with detailed examples.