Effect of crystallization of Cu₂ZnSnSxSe₄-x counter electrode on the performance for efficient dye-sensitized solar cells

Defected MoS2 Modified by Vanadium-Substituted Keggin-Type Polyoxometalates as Electrocatalysts for Triiodide Reduction in Dye-Sensitized Solar Cells

The rational design of efficient triiodide reduction reaction catalysts that are dependent on cheap and ample elements on Earth has become a challenge. As an extremely encouraging non-noble metallic catalyst, MoS₂ requires effective strategies to improve the site accessibility, inherent conductivity, and structural stability. Here, vanadium-substituted Keggin-type polyoxometalates (POMs) can be used as electron aggregates to modify manganese (Mn)-doped MoS₂ through the electrochemical deposition strategy, thereby improving the charge transfer ability of MoS₂ to I^-/I₃^- redox pairs and accelerating the reduction of I₃^-. Additionally, with the increase in the number of vanadium atoms substituted in POMs, the conduction band of POMs and MoS₂ can also match better, which effectively reduces the energy loss and is more conducive to charge transfer. Meanwhile, the deposition of POMs can improve the stability of metastable MoS₂. When POMs/MoS₂ materials are used as the counter electrodes of dye-sensitized solar cells, the power conversion efficiency (PCE) obtained is 7.27%, which is higher than that of platinum (Pt) (6.07%). The PCE can still maintain the initial 96% after 9 days. This work provides a valuable way for the improvement of platinum-free catalysts with minimal expense, basic process, high efficiency, and good stability.

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.

Highly dispersed redox-active polyoxometalates’ periodic deposition on multi-walled carbon nanotubes for boosting electrocatalytic triiodide reduction in dye-sensitized solar cells

Highly dispersed POM nanoparticles as functional components have been deposited on CNTs to produce periodic functionalized CNTs. The obtained Co₄PW₉/CNTs CE exhibits the best photovoltaic performance with a PCE of 7.60%, higher than both pure CNTs and Pt CE.

Synthesis of Wurtzite Cu2ZnSnS4 Nanosheets with Exposed High-Energy (002) Facets for Fabrication of Efficient Pt-Free Solar Cell Counter Electrodes

Two-dimensional (2D) semiconducting nanomaterials have generated much interest both because of fundamental scientific interest and technological applications arising from the unique properties in two dimensions. However, the colloidal synthesis of 2D quaternary chalcogenide nanomaterials remains a great challenge owing to the lack of intrinsic driving force for its anisotropic growth. 2D wurtzite Cu₂ZnSnS₄ nanosheets (CZTS-NS) with high-energy (002) facets have been obtained for the first time via a simple one-pot thermal decomposition method. The CZTS-NS exhibits superior photoelectrochemical activity as compared to zero-dimensional CZTS nanospheres and comparable performance to Pt counter electrode for dye sensitized solar cells. The improved catalytic activity can be attributed to additional reactive catalytic sites and higher catalytic reactivity in high-energy (002) facets of 2D CZTS-NS. This is in accordance with the density functional theory (DFT) calculations, which indicates that the (002) facets of wurtzite CZTS-NS possess higher surface energy and exhibits remarkable reducibility for I₃^- ions. The developed synthetic method and findings will be helpful for the design and synthesis of 2D semiconducting nanomaterials, especially eco-friendly copper chalcogenide nanocrystals for energy harvesting and photoelectric applications.

A 3D architecture composite of porous vanadium nitride nanoribbons and reduced graphene oxide as a high-efficiency counter electrode for dye-sensitized solar cells

A three-dimensional (3D) porous architecture combining porous vanadium nitride nanoribbons with reduced graphene oxide was prepared through a hydrothermal process and subsequent thermal annealing in an ammonia/argon mixed atmosphere. Then, the obtained 3D porous vanadium nitride nanoribbon/reduced graphene oxide (PVNN/RGO) composite was explored as the counter electrode of dye-sensitized solar cells (DSCs). As evidenced by the electrochemical measurements, the 3D PVNN/RGO composite demonstrates excellent electrocatalytic performance, which is comparable to that of Pt. This can be attributed to the fact that the 3D architecture composite of porous vanadium nitride and reduced graphene oxide can simultaneously provide a favorable electrolyte diffusion channel, a fast electron-transport network, and an abundance of efficient electrocatalytic active sites. By employing such PVNN/RGO composite as the counter electrode, the fabricated DSC can achieve a conversion efficiency of 7.43%, which is comparable to that of the conventional Pt counter electrode (7.74%). Therefore, the 3D PVNN/RGO composite is a promising low-cost alternative to the expensive Pt as a counter electrode in DSCs.

3D PVNN/RGO composite electrode with hierarchical porosity exhibits superior photovoltaic performance competing with that of the conventional Pt electrode.

Selenization of Cu2ZnSnS4 Enhanced the Performance of Dye-Sensitized Solar Cells: Improved Zinc-Site Catalytic Activity for I3. ACS APPLIED MATERIALS & INTERFACES 2017;9:37662-37670. [PMID: 29019395 DOI: 10.1021/acsami.7b09642]

Cu₂ZnSnS₄ (CZTS) and Cu₂ZnSn(S,Se)₄ (CZTSSe) as promising photovoltaic materials have drawn much attention because they are environmentally benign and earth-abundant elements. In this work, the monodispersed, low-cost Cu₂ZnSnS₄ nanocrystals with small size have been controllably synthesized via a wet chemical routine. And CZTSSe could be easily prepared after selenization of CZTS. When they are employed as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs), the power conversion efficiency (PCE) has been improved from 3.54% to 7.13% as CZTS is converted to CZTSSe, which is also compared to that of Pt (7.62%). The exact reason for the enhanced catalytic activity of I₃^- is discussed with the work function and density functional theory (DFT) when CZTSSe converted from CZTS. The results of a Kelvin probe suggest that the work function of CZTSSe (5.61 eV) is closer to that of Pt (5.65 eV) and higher than that of CZTS, which matched the redox shuttle potential better. According to the theory calculation, all the atomic and bond populations changed significantly when Se replaced partly the S on the CZTS system, especially in the Zn site. During the catalytic process as CEs, the adsorption energy obviously increased compared to those at other sites when I₃^- adsorbed on the Zn site in CZTSSe. So, Zn plays an important role for the reduction of I₃^- after CZTS is converted to CZTSSe. Based on above analysis, the reason for enhanced performance of DSSCs when CZTS converted to CZTSSe is mainly due to the enhancement of Zn-site activity. This work is beneficial for understanding the catalytic reaction mechanism of CZTS(Se) as CEs of DSSCs.

Microwave assisted synthesis of MoS2/nitrogen-doped carbon shell–core microspheres for Pt-free dye-sensitized solar cells

Novel MoS₂/nitrogen-doped carbon shell–core microsphere counter electrodes of dye-sensitized solar cells with a high efficiency of 6.2%.

Significant Broadband Photocurrent Enhancement by Au-CZTS Core-Shell Nanostructured Photocathodes

Copper zinc tin sulfide (CZTS) is a promising material for harvesting solar energy due to its abundance and non-toxicity. However, its poor performance hinders their wide application. In this paper gold (Au) nanoparticles are successfully incorporated into CZTS to form Au@CZTS core-shell nanostructures. The photocathode of Au@CZTS nanostructures exhibits enhanced optical absorption characteristics and improved incident photon-to-current efficiency (IPCE) performance. It is demonstrated that using this photocathode there is a significant increase of the power conversion efficiency (PCE) of a photoelectrochemical solar cell of 100% compared to using a CZTS without Au core. More importantly, the PCE of Au@CZTS photocathode improved by 15.8% compared to standard platinum (Pt) counter electrode. The increased efficiency is attributed to plasmon resonance energy transfer (PRET) between the Au nanoparticle core and the CZTS shell at wavelengths shorter than the localized surface plasmon resonance (LSPR) peak of the Au and the semiconductor bandgap.

Nitrogen-doped carbon microspheres counter electrodes for dye-sensitized solar cells by microwave assisted method

Nitrogen-doped carbon microspheres were synthesized for counter electrodes of dye-sensitized solar cells with a high efficiency of 6.28%.

Solution-Processed Cu2ZnSn(S,Se) 4 Thin-Film Solar Cells Using Elemental Cu, Zn, Sn, S, and Se Powders as Source

Solution-processed approach for the deposition of Cu2ZnSn (S,Se)4 (CZTSSe) absorbing layer offers a route for fabricating thin film solar cell that is appealing because of simplified and low-cost manufacturing, large-area coverage, and better compatibility with flexible substrates. In this work, we present a simple solution-based approach for simultaneously dissolving the low-cost elemental Cu, Zn, Sn, S, and Se powder, forming a homogeneous CZTSSe precursor solution in a short time. Dense and compact kesterite CZTSSe thin film with high crystallinity and uniform composition was obtained by selenizing the low-temperature annealed spin-coated precursor film. Standard CZTSSe thin film solar cell based on the selenized CZTSSe thin film was fabricated and an efficiency of 6.4 % was achieved.

Fine Tuning of Nanocrystal and Pore Sizes of TiO2 Submicrospheres toward High Performance Dye-Sensitized Solar Cells

In general, the properties and performance of mesoporous TiO2 are greatly dependent on its crystal size, crystallinity, porosity, surface area, and morphology; in this regard, design and fine-tuning the crystal and pore sizes of the TiO2 submicrospheres and investigating the effect of these factors on the properties and photoelectric performance of dye-sensitized solar cells (DSSCs) is essential. In this work, uniform TiO2 submicrospheres were synthesized by a two-step procedure containing hydrolysis and solvothermal process. The crystal and pore sizes of the TiO2 submicrospheres were fine-tuned and controlled in a narrow range by adjusting the quantity of NH4OH during the solvothermal process. The effect of crystal and pore size of TiO2 submicrosphere on the performance of the DSSCs and their properties including dye-loading capacity, light scattering effect, power conversion efficiency (PCE), incident photon-to-electron conversion efficiencies (IPCEs), and electron recombination were compared and analyzed. The results show that increasing pore size plays a more significant role in improving the dye-loading capacity and PCE than increasing surface area, and an overall PCE value of 8.62% was obtained for the device with a 7.0 μm film thickness based on the TiO2 submicrospheres treated with 0.6 mL of NH4OH. Finally, the best TiO2 submicrosphere based photoanode film was optimized by TiCl4 treatment, and increasing film thickness and a remarkable PCE up to 11.11% were achieved.

One-Pot Synthesis of Mesoporous TiO₂ Micropheres and Its Application for High-Efficiency Dye-Sensitized Solar Cells

TiO2 microspheres are of great interest for a great deal of applications, especially in the solar cell field. Because of their unique microstructure and light-scattering effect, TiO2 microsphere-based solar cells often exhibit superior photovoltaic performance. Hence, exploring new suitable TiO2 microspheres for high-efficiency solar cells is essential. In this work, we demonstrate a facile one-pot solvothermal approach for synthesis of TiO2 microspheres using acetone as solvent. The as-prepared TiO2 microspheres are composed of densely interconnected nanocrystals and possess a high specific surface area up to 138.47 m(2) g(-1). As the photoanode, the TiO2 microsphere-based DSSC gives higher dye loading and light adsorption ability as well as longer electron lifetime, resulting in higher short-circuit current value and superior power conversion efficiency (PCE) compared with Dyesol 18 nm TiO2 nanoparticle paste. Finally, the TiO2 microsphere-based DSSC were optimized by adding a TiO2 nanocrystal underlayer and TiCl4 post-treatment, giving a high PCE of 10.32%.

Controlling available active sites of Pt-loaded TiO2 nanotube-imprinted Ti plates for efficient dye-sensitized solar cells

The counter electrode (CE) of dye-sensitized solar cells (DSSCs) plays an important role for transferring electrons and catalyzing the I-/I3- reduction. Active surface area of the substrate determines the reduction sites of the deposited catalyst as well as the catalytic ability of the CE. An effective method for enhancing and controlling the active surface area of metal plates is provided in this study. The Ti plates are imprinted by TiO2 nanotubes (TNT) via the technique of anodization along with the ultrasonic vibration process. The available active area of imprinted Ti plates is controlled by varying the anodization voltage to produce TNT imprints with different diameters and depths. A solar-to-electricity conversion efficiency (η) of 9.35% was obtained for the DSSC with a TNT-imprinted Ti plate as the CE substrate, while the cell with an imprint-free Ti plate shows an η of 7.81%. The enhanced η is due to the improved electrocatalytic ability of the CE by using the TNT-imprinted Ti plate as the substrate with higher active surface area.