MoS2 nanosheets based counter electrodes: An alternative for Pt-free dye-sensitized solar cells

Long-Term Stable Complementary Electrochromic Device Based on WO3 Working Electrode and NiO-Pt Counter Electrode

Complementary electrochromic devices (ECDs) composed of WO₃ and NiO electrodes have wide applications in smart windows. However, they have poor cycling stability due to ion-trapping and charge mismatch between electrodes, which limits their practical application. In this work, we introduce a partially covered counter electrode (CE) composed of NiO and Pt to achieve good stability and overcome the charge mismatch based on our structure of electrochromic electrode/Redox/catalytic counter electrode (ECM/Redox/CCE). The device is assembled using a NiO-Pt counter electrode with WO₃ as the working electrode, and PC/LiClO₄ containing a tetramethylthiourea/tetramethylformaminium disulfide (TMTU/TMFDS²⁺) redox couple as the electrolyte. The partially covered NiO-Pt CE-based ECD exhibits excellent EC performance, including a large optical modulation of 68.2% at 603 nm, rapid switching times of 5.3 s (coloring) and 12.8 s (bleaching), and a high coloration efficiency of 89.6 cm²·C^-1. In addition, the ECD achieves a good stability of 10,000 cycles, which is promising for practical application. These findings suggest that the structure of ECC/Redox/CCE could overcome the charge mismatch problem. Moreover, Pt could enhance the Redox couple's electrochemical activity for achieving high stability. This research provides a promising approach for the design of long-term stable complementary electrochromic devices.

Novel 2D-AuSe nanostructures as effective platinum replacement counter electrodes in dye-sensitized solar cells

Studies to improve the efficiency of dye-sensitized solar cells (DSSCs) include, but are not limited to, finding alternatives such as 2D layered materials as replacement counter electrodes (CEs) to the commonly used Pt. Herein, we report for the first time, the use of AuSe as a counter electrode for the reduction of triiodide ions (I₃⁻) to iodide ions (I⁻). The colloidal synthesis of gold selenide nanostructures produced α-AuSe and β-AuSe dominated products as determined by XRD. Electron microscopy showed α-AuSe having belt-like structures while β-AuSe had a plate-like morphology. EDS mapping confirmed the elemental composition and homogeneity of the AuSe CEs. Cyclic voltammetry curves of the AuSe CEs displayed the double set of reduction–oxidation peaks associated with the reactions in the I₃⁻/I⁻ electrolyte and therefore were comparable to the Pt CV curve. The α-AuSe CE showed better electrocatalytic activity with a reduction current of 6.1 mA than that of β-AuSe and Pt CEs, which were 4.2 mA and 4.8 mA, respectively. The peak-to-peak separation (ΔE_pp) for the α-AuSe CE was also more favourable with a value of 532 mV over that of the β-AuSe CE of 739 mV however, both values were larger than that of the Pt CE, which was found to be 468 mV. The EIS and Tafel plot data showed that α-AuSe had the best catalytic activity compared to β-AuSe and was comparable to Pt. The DSSC using α-AuSe as a CE had the highest PCE (6.94%) as compared to Pt (4.89%) and β-AuSe (3.47%). The lower efficiency for Pt was attributed to the poorer fill factor. With these novel results, α-AuSe is an excellent candidate to be used as an alternative CE to Pt in DSSCs.

Studies to improve the efficiency of dye-sensitized solar cells (DSSCs) include, but are not limited to, finding alternatives such as 2D layered materials as replacement counter electrodes (CEs) to the commonly used Pt.

Solution-processed two-dimensional materials for next-generation photovoltaics

In the ever-increasing energy demand scenario, the development of novel photovoltaic (PV) technologies is considered to be one of the key solutions to fulfil the energy request. In this context, graphene and related two-dimensional (2D) materials (GRMs), including nonlayered 2D materials and 2D perovskites, as well as their hybrid systems, are emerging as promising candidates to drive innovation in PV technologies. The mechanical, thermal, and optoelectronic properties of GRMs can be exploited in different active components of solar cells to design next-generation devices. These components include front (transparent) and back conductive electrodes, charge transporting layers, and interconnecting/recombination layers, as well as photoactive layers. The production and processing of GRMs in the liquid phase, coupled with the ability to "on-demand" tune their optoelectronic properties exploiting wet-chemical functionalization, enable their effective integration in advanced PV devices through scalable, reliable, and inexpensive printing/coating processes. Herein, we review the progresses in the use of solution-processed 2D materials in organic solar cells, dye-sensitized solar cells, perovskite solar cells, quantum dot solar cells, and organic-inorganic hybrid solar cells, as well as in tandem systems. We first provide a brief introduction on the properties of 2D materials and their production methods by solution-processing routes. Then, we discuss the functionality of 2D materials for electrodes, photoactive layer components/additives, charge transporting layers, and interconnecting layers through figures of merit, which allow the performance of solar cells to be determined and compared with the state-of-the-art values. We finally outline the roadmap for the further exploitation of solution-processed 2D materials to boost the performance of PV devices.

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.

Platinum-free dye-sensitized solar cells by flower-like mixed-phase CoxSy/NixSy/MoxSy composites

Fabricated DSSCs using Co_xS_y/Ni_xS_y/Mo_xS_y composites as counter electrodes showed an enhanced photoconversion efficiency.

Polyoxometalate modified transparent metal selenide counter electrodes for high-efficiency bifacial dye-sensitized solar cells

We present a facile one-step hydrothermal approach for the growth of PW₁₁Co/Co_0.85Se on a conductive glass substrate, which could be used as transparent CE in bifacial DSSCs with enhanced front and back efficiencies of 7.56% and 5.82%, respectively.

Investigating Various Permutations of Copper Iodide/FeCu Tandem Materials as Electrodes for Dye-Sensitized Solar Cells with a Natural Dye

This work presents the synthesis and deposition of CuI and FeCu materials on copper substrates for dye-sensitized solar cell applications. FeCu is a metastable alloy of iron and copper powders and possesses good optical and intrinsic magnetic properties. Coupled with copper iodide as tandem layers, the deposition of these two materials was permutated over a pure copper substrate, characterized and then tested within a solar cell. The cell was sensitized with a natural dye extracted from a local desert plant (Calotropis gigantea) and operated with an iodine/triiodide electrolyte. The results show that the best layer arrangement was Cu/FeCu/CuI, which gave an efficiency of around 0.763% (compared to 0.196% from reported cells in the literature using a natural sensitizer).

MoS2 coated CoS2 nanocomposites as counter electrodes in Pt-free dye-sensitized solar cells

Expensive Pt counter electrodes remain an obstacle for the commercialization of dye-sensitized solar cells (DSSCs). Therefore, research focusing on low-cost alternative counter electrode materials has been considered important for their commercialization. Here, the fabrication of dye-sensitized solar cells has been performed utilizing CoS₂ and MoS₂ coated CoS₂ nanocomposite materials as the counter electrode, which are synthesized via a hydrothermal route involving low-cost precursor materials. The experimental results obtained from XRD, XPS, EDX, SEM, TEM, and Raman etc. have confirmed the successful formation of CoS₂ and MoS₂ coated CoS₂ nanocomposites. The electrochemical characterization of these materials is performed, which suggests that the electrocatalytic activity towards the liquid iodine electrolyte of these materials is as good as that of the conventional Pt counter electrodes. So, dye-sensitized solar cell devices are fabricated by interpolating a (cis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylato)ruthenium(ii)) dye-loaded TiO₂ photoanode and CoS₂, MoS₂ coated CoS₂ and Pt counter electrodes using iodine/iodide as a liquid electrolyte. The devices fabricated with CoS₂ counter electrodes have shown an open circuit voltage of 790 mV, a short circuit current of 11.9 mA cm^-2, a fill factor of 0.54, and a power conversion efficiency of 6%. On the other hand, the device based on a Pt counter electrode has shown an open circuit voltage of 773 mV, a short circuit current of 13.4 mA cm^-2, a fill factor of 0.54, and a power conversion efficiency of 6.6%. In addition, MoS₂ coated with a CoS₂ counter electrode has shown the best performance with an open circuit voltage of 763 mV, a short circuit current of 20.1 mA cm^-2, a fill factor of 0.42, and a power conversion efficiency of 7.6%.

Metal Sulphides and Their Carbon Supported Composites as Platinum-Free Counter Electrodes in Dye-Sensitized Solar Cells: A Review

Energy sufficiency is a critical requirement for the economic prosperity of modern countries. Efficient harnessing of solar energy using technologies such as the dye-sensitized solar cell could solve the energy problem which persistently plagues developing countries. Despite having a simple operational procedure and modest power conversion efficiency of 13.8%, the dye-sensitized solar cell consists of an expensive platinum counter electrode which makes commercial success futile. Thus, this review intends to establish the progress researchers have attained in the development of sulphide based counter electrodes as alternatives to platinum, thereby lowering cost of production. Metallic sulphides are good electrocatalysts and cheap, hence, they possess the necessary requirements for effective functional counter electrodes. Furthermore, ternary metallic sulphides are known to exhibit higher efficiencies stemming from the synergistic effect produced by the co-existence of two metal ions in a crystal structure, which is believed to induce greater catalytic capability. Incorporation of metallic sulphides with carbon materials, which are exceptional electrical conductors, could potentially produce more efficient counter electrodes. In that regard, this review seeks to establish the effect recently developed composite counter electrodes comprising metallic sulphides and carbon-based materials have induced on the functionality of the counter electrode (CE).