Recent advances in alloy counter electrodes for dye-sensitized solar cells. A critical review

Natural resources for dye-sensitized solar cells

While the development of dye-sensitized solar cells (DSSCs) has been ongoing for more than 30 years, the currently obtained efficiency is unsatisfactory. However, the study of DSSC development has produced a fundamental understanding of cell performance and inspired other devices, such as perovskite cell solar cells. DSSCs consist of a dye-sensitized photoanode, a counter electrode, and a redox couple in the electrolyte system. Each of the components has an important role and cofunctions with each other to obtain a high power conversion efficiency. Various modifications to each DSSC component have been applied to improve their performance. Additionally, to generate improvements, the effort to reduce production costs has been crucial. The utilization of natural sources for DSSC components is a possible solution to this issue. The utilization of natural resources also aims to increase the value of the natural resource itself. In this review, the applications of various natural sources for DSSC components are described, as well as the modification efforts that have been made to enhance their performance. The discussion covers the utilization of natural dye for sensitizer dyes in liquid DSSC applications: (1) utilization of biopolymers for quasi-solid DSSC electrolytes, (2) green synthesis methods for photoanode semiconductors, and (3) development of natural carbon counter electrodes. The detailed factors that influence improvements in cell performance are also addressed.

Self-Assembly Synthesis of the MoS2/PtCo Alloy Counter Electrodes for High-Efficiency and Stable Low-Cost Dye-Sensitized Solar Cells

In this work, MoS₂ microspheres/PtCo-alloy nanoparticles (MoS₂/PtCo-alloy NPs) were composited via a novel and facile process which MoS₂ is functionalized by poly (N-vinyl-2-pyrrolidone) (PVP) and self-assembled with PtCo-alloy NPs. This new composite shows excellent electrocatalytic activity and great potential for dye-sensitized solar cells (DSSCs) as a counter electrode (CE) material. Benefiting from heterostructure and synergistic effects, the MoS₂/PtCo-alloy NPs exhibit high electrocatalytic activity, low charge-transfer resistance and stability in the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) test. Meanwhile, a high power-conversion efficiency (PCE) of 8.46% is achieved in DSSCs with MoS₂/PtCo-alloy NP CEs, which are comparable to traditional Pt CEs (8.45%). This novel composite provides a new high-performance, stable and cheap choice for CEs in DSSCs.

Synergetic Effects of Hybrid Carbon Nanostructured Counter Electrodes for Dye-Sensitized Solar Cells: A Review

This article provides an overview of the structural and physicochemical properties of stable carbon-based nanomaterials and their applications as counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). The research community has long sought to harvest highly efficient third-generation DSSCs by developing carbon-based CEs, which are among the most important components of DSSCs. Since the initial introduction of DSSCs, Pt-based electrodes have been commonly used as CEs owing to their high-electrocatalytic activities, thus, accelerating the redox couple at the electrode/electrolyte interface to complete the circuit. However, Pt-based electrodes have several limitations due to their cost, abundance, complicated facility, and low corrosion resistance in a liquid electrolyte, which further restricts the large-area applications of DSSCs. Although carbon-based nanostructures showed the best potential to replace Pt-CE of DSSC, several new properties and characteristics of carbon-CE have been reported for future enhancements in this field. In this review, we discuss the detailed synthesis, properties, and performances of various carbonaceous materials proposed for DSSC-CE. These nano-carbon materials include carbon nanoparticles, activated carbon, carbon nanofibers, carbon nanotube, two-dimensional graphene, and hybrid carbon material composites. Among the CE materials currently available, carbon-carbon hybridized electrodes show the best performance efficiency (up to 10.05%) with a high fill factor (83%). Indeed, up to 8.23% improvements in cell efficiency may be achieved by a carbon-metal hybrid material under sun condition. This review then provides guidance on how to choose appropriate carbon nanomaterials to improve the performance of CEs used in DSSCs.

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.

Novel urchin-like FeCo oxide nanostructures supported carbon spheres as a highly sensitive sensor for hydrazine sensing application

Herein, we successfully fabricated a novel nanostructure based on hierarchical urchin-like FeCo oxide supported carbon spheres (FeCo Oxide/CSs) via a two-step hydrothermal method followed by a simple annealing step at 300 °C under air. It was found that such urchin-like FeCo Oxide/CSs structure exhibited superior catalytic activity towards hydrazine oxidation to CSs, Fe Oxide/CSs, Co Oxide/CSs, and FeCo Hydroxide/CSs material. In this regard, the FeCo Oxide/CSs displayed a wide linear detection range of 0.1-516.6 μM, low detection limit of 0.1 μM, and long-term stability. The material also showed good selectivity towards hydrazine detection in the presence of various interferences, such as uric acid, ascorbic acid, urea, dopamine, Na⁺, SO₄^2-, K⁺, and Cl-. The excellent sensing performance of the FeCo Oxide/CSs was assumed to the unique hierarchical urchin structure with the high density and uniformity of nano-sized FeCo Oxide nanoneedles, which produced massive electroactive sites and enhanced charge transfer ability. The achieved results implied that the FeCo Oxide/CSs may be a great candidate for sensitive hydrazine detection.

Synthesis of Surfactant-Free and Morphology-Controllable Vanadium Diselenide for Efficient Counter Electrodes in Dye-Sensitized Solar Cells

In this study, a transition-metal selenide, vanadium diselenide (VSe₂), with various morphologies was synthesized by employing a surfactant-free hydrothermal method under varied temperature conditions (190-220 °C). Although the physical properties of VSe₂ have been studied before, only limited morphological change or application were explored. This study, for the first time, applied VSe₂ as the electrocatalytic counter electrode (CE) in dye-sensitized solar cells (DSSCs) and showed an attractive cell efficiency. The mechanism of forming the tunable VSe₂ morphologies is proposed. The evaluation of solar cell efficiency shows the correlation between morphology and electrocatalytic properties. It was further shown that VSe₂-200 with the cauliflower-like morphology shows the highest cell performance of DSSC with an efficiency of 9.23 ± 0.07% under 1 sun irradiance, superior to that of the Pt-based DSSC (8.48 ± 0.08%). An electrochemical technique equipped with a rotating disk electrode system was introduced to confirm the high electrocatalytic performance with this particular morphology. The optimized VSe₂ demonstrated good long-term stability with 78% retention after 500 cycles of the consecutive cyclic voltammetry, compared to 60% for the Pt CE. The control in morphology in vanadium diselenide synthesis and its usage in Pt-free CE DSSC have advanced the progress in electrochemistry.

A revolution of photovoltaics: persistent electricity generation beyond solar irradiation

The integration utilization of solar energy and waste energies by photovoltaics is regarded as a promising solution to resolve energy crisis and environmental pollution problems.

Time Evolution Characterization of Atmospheric-Pressure Plasma Jet (APPJ)-Synthesized Pt-SnOx Catalysts

We characterize the time evolution (≤120 s) of atmospheric-pressure plasma jet (APPJ)-synthesized Pt-SnOx catalysts. A mixture precursor solution consisting of chloroplatinic acid and tin(II) chloride is spin-coated on fluorine-doped tin oxide (FTO) glass substrates, following which APPJ is used for converting the spin-coated precursors. X-ray photoelectron spectroscopy (XPS) indicates the conversion of a large portion of metallic Pt and a small portion of metallic Sn (most Sn is in oxidation states) from the precursors with 120 s APPJ processing. The dye-sensitized solar cell (DSSC) efficiency with APPJ-synthesized Pt-SnOx CEs is improved greatly with only 5 s of APPJ processing. Electrochemical impedance spectroscopy (EIS) and Tafel experiments confirm the catalytic activities of Pt-SnOx catalysts. The DSSC performance can be improved with a short APPJ processing time, suggesting that a DC-pulse nitrogen APPJ can be an efficient tool for rapidly synthesizing catalytic Pt-SnOx counter electrodes (CEs) for DSSCs.

NiS submicron cubes with efficient electrocatalytic activity as the counter electrode of dye-sensitized solar cells

In this work, nickel sulfide (NiS) submicron cubes, synthesized by an easy hydrothermal method, were investigated as an efficient electrocatalytic material of dye-sensitized solar cells (DSSCs), to our knowledge, for the first time. Part of the NiS submicron cubes were grown together in a hydrothermal procedure and formed the connected submicron cube cluster. The NiS submicron cubes (with a diameter of 300-800 nm) showed excellent electrocatalytic activity and presented superior photovoltaic performance when it was used as an electrocatalytic material for the counter electrode (CE) of DSSCs. The CE composed of the NiS submicron cubes could achieve a photovoltaic efficiency of 6.4%, showing their superior performance compared with the typical Pt electrode (which with the corresponding conversion efficiency was 5.3% at the same condition). The low-cost NiS submicron cube electrode could be a competitive candidate to replace the traditional Pt electrode in DSSCs. The simple composition procedure of NiS submicron cubes could enable the low-cost mass production of an efficient NiS submicron cube electrode to be easily accomplished.

Utility of Pt in PtNi alloy counter electrodes as a new avenue for cost effective and highly efficient liquid junction photovoltaic devices

This study presents the synthesis of PtNi alloys with different volume ratios of Pt and Ni precursors in mixture solutions using dry plasma reduction under atmospheric pressure and low temperature. The developed materials are applied as efficient counter electrodes (CEs) in dye-sensitized solar cells (DSCs). The investigation of the Pt utility in PtNi alloys for electrocatalytic activity, and cost effective and highly efficient DSCs are also investigated. Compared with the reference electrodes (Pt and Ni CEs), the developed PtNi alloy CEs exhibit better reversibility as indicated by the peak-to-peak separation and better catalytic activity for the regeneration of iodide ions from triiodide ions. Thus, the DSC with the developed PtNi CEs provides higher efficiency than that of the device fabricated with the reference electrodes.

Effect of annealing atmosphere on quaternary chalcogenide-based counter electrodes in dye-sensitized solar cell performance: synthesis of Cu2FeSnS4 and Cu2CdSnS4 nanoparticles by thermal decomposition process

Straightforward synthesis of stoichiometrically controlled quaternary chalcogenide nanoparticles is a challenge. Annealing atmosphere has effect on morphology, elemental composition, electrical properties, electrochemical catalytic activity of the CFTS and CCdTS films.

Counter electrodes in dye-sensitized solar cells

This article panoramically reviews the counter electrodes in dye-sensitized solar cells, which is of great significance for the development of photovoltaic and photoelectric devices.

Efficient synthesis of triarylamine-based dyes for p-type dye-sensitized solar cells

The class of triarylamine-based dyes has proven great potential as efficient light absorbers in inverse (p-type) dye sensitized solar cells (DSSCs). However, detailed investigation and further improvement of p-type DSSCs is strongly hindered by the fact that available synthesis routes of triarylamine-based dyes are inefficient and particularly demanding with regard to time and costs. Here, we report on an efficient synthesis strategy for triarylamine-based dyes for p-type DSSCs. A protocol for the synthesis of the dye-precursor (4-(bis(4-bromophenyl)amino)benzoic acid) is presented along with its X-ray crystal structure. The dye precursor is obtained from the commercially available 4(diphenylamino)benzaldehyde in a yield of 87% and serves as a starting point for the synthesis of various triarylamine-based dyes. Starting from the precursor we further describe a synthesis protocol for the dye 4-{bis[4′-(2,2-dicyanovinyl)-[1,1′-biphenyl]-4-yl]amino}benzoic acid (also known as dye P4) in a yield of 74%. All synthesis steps are characterized by high yields and high purities without the need for laborious purification steps and thus fulfill essential requirements for scale-up.

23327Enhanced photoelectric conversion efficiency of dye-sensitized solar cells by the incorporation of flower-like Bi2S3:Eu3+ sub-microspheres

In this paper, TiO₂-Bi₂S₃ and TiO₂-Bi₂S₃:Eu³⁺ composite photoanodes were successfully designed, which can not only fully absorb visible light but also transfer the electron from Bi₂S₃ to TiO₂ conduction band due to the narrow band gap and high conduction band of Bi₂S₃. Compared to pure TiO₂ cell, the photoelectric conversion efficiencies of TiO₂-Bi₂S₃ and TiO₂-Bi₂S₃:Eu³⁺ composite cells were increased significantly. In addition, the efficiency of TiO₂-Bi₂S₃:Eu³⁺ composite cells were higher than that of TiO₂-Bi₂S₃ cell which could be attributed to the larger BET surface area of Bi₂S₃:Eu³⁺. The electron transport and interfacial recombination kinetics were investigated by the electrochemical impedance spectroscopy and intensity-modulated photocurrent/photovoltage spectroscopy. The results indicated that the interfacial resistance of the TiO₂-dye|I₃⁻/I⁻ electrolyte interface of TiO₂-Bi₂S₃:Eu³⁺ composite cell was much bigger than that of pure TiO₂ cell. In addition, the TiO₂-Bi₂S₃:Eu³⁺ cell has longer electron recombination time and longer electron transport time than pure TiO₂ cell. The charge collection efficiency of TiO₂-Bi₂S₃:Eu³⁺ composite cell was higher than that of pure TiO₂ cell.

Shape-controlled synthesis of PtPd alloys as a low-cost and efficient counter electrode for dye-sensitized solar cells

Dry plasma reduction is an excellent approach for easy synthesis of PtPd alloys with different sizes, shapes and distributions through simply controlling the volume ratio of the Pt and Pd precursor solution under atmospheric pressure.