Counter Electrode For Dye-sensitized Solar Cells Research Articles

Photovoltaic Characteristics of Multiwalled Carbon Nanotube Counter-Electrode Materials for Dye-Sensitized Solar Cells Produced by Chemical Treatment and Addition of Dispersant

Multiwalled carbon nanotubes (MWCNTs) have excellent electrical conductivity and good chemical stability, and are used as counter electrodes in dye-sensitized solar cells (DSSCs). The counter electrodes collect electrons from the external circuit and catalyze the redox reaction in the electrolyte. Electrocatalysis is an important step for generating energy from triiodide reduction in DSSCs. In this study, chemically treated MWCNTs were investigated for improving the photovoltaic performance of DSSCs. The MWCNTs were modified through chemical oxidation with sulfuric acid/nitric acid (H2SO4/HNO3) or potassium persulfate/sodium hydroxide (K2S2O8/NaOH). Nanocellulose (CNC) was used as a dispersant to improve the photovoltaic performance and dispersibility as an alternative material for counter electrodes in DSSCs. The counter electrodes were prepared on fluorine-doped tin oxide (FTO) glass substrates by spin coating nanofluids. Morphological and structural investigations were performed using scanning transmission electron microscopy (TEM), Fourier-transform infrared (FTIR) spectroscopy, and Raman spectroscopy. The electrical conductivity and UV light absorption of the DSSCs were analyzed to evaluate their photovoltaic performance. The results of these analyses showed that chemical functionalization and addition of CNC were effective for increasing the electrical conductivity and UV light absorption. Finally, all result trends were the same. Increasing the dispersibility of the counter electrode was found to improve the reduction of I3− at the interface between the MWCNTs and the electrolyte, thereby, improving the energy conversion efficiency.

CVD-graphene/graphene flakes dual-films as advanced DSSC counter electrodes

The use of graphene‐based electrodes is burgeoning in a wide range of applications, including solar cells, light emitting diodes, touch screens, field‐effect transistors, photodetectors, sensors and energy storage systems. The success of such electrodes strongly depends on the implementation of effective production and processing methods for graphene. In this work, we take advantage of two different graphene production methods to design an advanced, conductive oxide- and platinum-free, graphene-based counter electrode for dye-sensitized solar cells (DSSCs). In particular, we exploit the combination of a graphene film, produced by chemical vapor deposition (CVD) (CVD-graphene), with few-layer graphene (FLG) flakes, produced by liquid phase exfoliation. The CVD-graphene is used as charge collector, while the FLG flakes, deposited atop by spray coating, act as catalyst for the reduction of the electrolyte redox couple (i.e. - and Co+2/+3). The as-produced counter electrodes are tested in both - and Co+2/+3-based semitransparent DSSCs, showing power conversion efficiencies of 2.1% and 5.09%, respectively, under 1 SUN illumination. At 0.1 SUN, Co+2/+3-based DSSCs achieve a power conversion efficiency as high as 6.87%. Our results demonstrate that the electrical, optical, chemical and catalytic properties of graphene-based dual films, designed by combining CVD-graphene and FLG flakes, are effective alternatives to FTO/Pt counter electrodes for DSSCs for both outdoor and indoor applications.

Surface-Supported Metal-Organic Framework Thin-Film-Derived Transparent CoS1.097@N-Doped Carbon Film as an Efficient Counter Electrode for Bifacial Dye-Sensitized Solar Cells.

An effective design for counter electrode (CE) catalytic materials with superior catalytic activity, excellent stability, low cost, and a facile fabrication process is urgently needed for industrialization of dye-sensitized solar cells (DSSCs). Herein, we report a facile in situ method to fabricate transparent CoS1.097 anchored on an N-doped carbon film electrode through sulfurization of a cobalt-metalloporphyrin metal-organic framework thin film on fluorine-doped tin oxide glass. The transparent film as counter electrode in bifacial DSSCs exhibited higher power conversion efficiency (9.11% and 6.64%), respectively, from front and rear irradiation than that of Pt (8.04% and 5.87%). The uniformly dispersed CoS1.097 nanoparticles on an N-doped carbon film provide a large catalytic active area and facilitate the electron transfer, which leads to the excellent catalytic ability of the CoS1.097@N-doped carbon film. In addition, the in situ preparation of the uniform film with a nanosheet structure offers high electrical conductivity and unobstructed access for the diffusion of triiodide to available electroactive sites, resulting in excellent device performance with superior long-term stability over 1000 h under natural conditions.

Shape Control Iron Pyrite Synthesized by Hot Injection Method: Counter Electrode for Efficient Dye-Sensitized Solar Cells

The cubic and spherical shaped iron pyrite (FeS2) nanocrystals were synthesized in a pure phase form by an efficient hot injection method. These FeS2 nanocrystals were used as a counter electrode (CE) alternative to the conventional Pt CE in dye-sensitized solar cells (DSSCs) owing to its tremendous optical properties and low-cost. The obtained FeS2 nanocrystalline materials with excellent shape and phase purity were confirmed through XRD and Raman spectroscopy data. From Tafel, and impedance spectroscopy studies, the catalytic activity FeS2 CEs are found to be comparable with that of Pt CE. Along with the I3−/I− electrolyte, photo-conversion efficiency is found to be 6.9% (spherical), 6.2% (cubic) for the FeS2 CE, and 7% for Pt CE. The excellent performance of the FeS2 CE in DSSCs makes it a distinctive choice among the various CE materials studied including low-cost photovoltaics.

Facile fabrication of PVA nanofiber coated with PEDOT as a counter electrode for dye-sensitized solar cell

Polyvinyl alcohol (PVA) nanofibers coated with poly(3,4-ethylenedioxythiophene) (PEDOT) as a counter electrode (CE) is a promising material to substitute platinum CE for dye-sensitized solar cell due to the high conductivity of PEDOT and high surface area to volume ratio of PVA. PVA nanofibers and PEDOT were prepared through facile techniques of electrospinning and electropolymerization, respectively. Field emission scanning electron microscopy revealed that PEDOT was distributed evenly on PVA nanofibers with porous cauliflower-like structure. PVA/PEDOT nanofibers CE had low charge transfer resistance (Rct) and possessed a good electrocatalytic activity with a low value of peak-to-peak separation (Epp = 0.34 V), thus an improved efficiency of 2.11% was obtained in comparison to platinum (1.14%), PEDOT (1.39%) and PVA nanofibers (0.017%).

Pt-free, low-cost and efficient counter electrode with carbon wrapped VO2(M) nanofiber for dye-sensitized solar cells

The present study reports the use of one-dimensional carbon wrapped VO2(M) nanofiber (VO2(M)/C) as a cost-effective counter electrode for dye-sensitized solar cells (DSSCs); where M denotes monoclinic crystal system. Uniform short length nanofiber was synthesised by a sol-gel based simple and versatile electrospinning and post carbonization technique. The investigation of nanostructure and morphological analysis were performed by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), and transmission electron microscope (TEM) with EDAX. The electrochemical response was comprehensively characterized by cyclic voltammetry, electrochemical impedance spectroscopy and Tafel polarization. The electrochemical analysis of the VO2(M)/C nanofiber counter electrode exhibits significant electrocatalytic activity towards the reduction of triiodide and low charge transfer resistance at the electrode-electrolyte interface. The DSSCs fabricated with carbon-wrapped VO2(M) nanofiber CE showed high power conversion efficiency of 6.53% under standard test condition of simulated 1SUN illumination at AM1.5 G, which was comparable to the 7.39% observed for conventional thermally decomposed Pt CE based DSSC under same test conditions. This result encourages the next step of modification and use of low-cost VO2(M) as an alternate counter electrode for DSSCs to achieve a substantial efficiency for future energy demand.

Performance and stability of counter electrodes based on reduced few-layer graphene oxide sheets and reduced graphene oxide quantum dots for dye-sensitized solar cells

Graphene-based materials represent an attractive alternative to platinum in dye-sensitized solar cells (DSSC) counter electrodes to contribute to an efficient conversion of solar energy into electricity. Despite the slower kinetics of carbon for the reduction of triiodide compared to platinum, they are characterized by low cost and promising stability. In this work, two different materials are investigated: reduced few-layer graphene oxide (rFLGO) and reduced graphene oxide quantum dots (rGOQD). The electrochemical performance of DSSC assembled with either rFLGO or rGOQD at the counter electrode is correlated to their most important physico-chemical features. The domain size of graphene sheets had an important effect on the performance at the counter electrode, with quantum dots performing 13% higher efficiency than rFLGO, correlated with a higher density of active sites. Both graphene nanostructures exhibited a better stability behavior upon electrochemical cycling and seasoning of the cells as compared to Pt counter electrode.

Facile Synthesis and Characterization of Two Dimensional SnO2-Decorated Graphene Oxide as an Effective Counter Electrode in the DSSC

SnO2-decorated graphene oxide (SnO2/GO) was synthesized by the modified Hummers’s method, followed by a chemical incorporation of SnO2 nanoparticles. Then, the nanocomposite was used as anon-precious counter electrode in a dye-sensitized solar cell (DSSC). Although GO has a relatively poor electrical conductivity depending essentially on the extent of the graphite oxidation, presence of SnO2 enhanced its structural and electrochemical properties. The Pt-free counter electrode exhibited a distinct catalytic activity toward iodine reduction and a low resistance to electron transfer. Moreover, the decorated GO provided extra active sites for reducing I3− at the interface of the CE/electrolyte. In addition, the similarity of the dopant in the GO film and the fluorine-doped tin oxide (FTO) substrate promoted a strong assimilation between them. Therefore, SnO2-decorated GO, as a counter electrode, revealed an enhanced photon to electron conversion efficiency of 4.57%. Consequently, the prepared SnO2/GO can be sorted as an auspicious counter electrode for DSSCs.

Formation of CoTe2 embedded in nitrogen-doped carbon nanotubes-grafted polyhedrons with boosted electrocatalytic properties in dye-sensitized solar cells

Developing high active and earth-abundant electrocatalysts is a challenge for commercialization of dye-sensitized solar cells (DSSCs). Herein, a designed synthesis of CoTe2 nanoparticles embedded in nitrogen-doped carbon nanotubes-grafted polyhedron (CoTe2@NCNTs) using zeolitic imidazolate framework-67 (ZIF-67) as template is reported. Benefiting from the high surface area induced by the in situ growth of CNTs and the synergistic effect between CoTe2 and the N-doped nanostructured carbon, CoTe2@NCNTs hybrids exhibit remarkable catalytic activity toward the reduction of I3− ions. When employed as counter electrode (CE) of DSSCs, CoTe2@NCNTs hybrids deliver overwhelming power conversion efficiency (PCE) of 9.02%, possessing ~12% improvement compared with the Pt CE (8.03%). This study provides an emerging substitute for traditional Pt CE and a strategy to synthesize efficient electrocatalysts via rational surface engineering.

2D Schottky Junction between Graphene Oxide and Transition‐Metal Dichalcogenides: Photoresponsive Properties and Electrocatalytic Performance

Abstract2D graphene is conductor and not a semiconductor. 2D transition—metal dichalcogenides (TMD) is a semiconductor and not a conductor. Preparing 2D composite material that simultaneously possesses both advantages of graphene and TMD has proven to be challenging. In this work, both 2D‐WS2/2D‐GO and 2D‐MoS2/2D‐GO composites with few layer thickness are synthesized. The electronic structure indicates a high content of Mo4+ 3d5/2 and W4+4f7/2 with lower binding energy in the 2D composite, which is ascribed to partial loss of surface sulfur atoms in 2D composites and the newly formed heteroatomic bond of CWS and CMoS. The Schottky junction between 2D‐GO and 2D‐TMD (2D G‐T junction) is established and exhibits obvious photoelectric responses. Superior electrocatalytic properties of the two 2D‐composites are attributable to the 2D Schottky Junction between 2D‐TMDs and 2D‐GO. Interlayer electronic coupling in 2D Schottky Junction (2D G‐T junction) activates inert sites on the 2D surface of 2D‐TMDs or GO. The power conversion efficiency of dye‐sensitized solar cells (DSCs) based on 2D‐WS2/2D‐GO is 9.54% under standard solar illumination intensity (AM1.5, 100 mW cm−2). The value is one of the highest reported efficiencies for DSCs based on Pt‐free counter electrodes. Finally, 2D‐WS2/2D‐GO composites exhibit excellent stability as counter electrode of DSCs.

Phase‐Engineered Weyl Semi‐Metallic MoxW1‐xTe2 Nanosheets as a Highly Efficient Electrocatalyst for Dye‐Sensitized Solar Cells

The emerging Weyl semi‐metals with robust topological surface states are very promising candidates to rationally develop new‐generation electrocatalysts for dye‐sensitized solar cells (DSSCs). In this study, a chemical vapor deposition (CVD) method to synthesize highly crystalline Weyl semi‐metallic MoxW1‐xTe2 nanocrystals, which are applied for the counter electrode (CE) of DSSCs for the first time, are employed. By controlling the temperature‐dependent phase‐engineered synthesis, the nanocrystal grown at 760 °C exhibits the mixed phases of semiconducting Td‐ & 2H‐Mo0.32W0.67Te2.01 with charge carrier density of (1.20 ± 0.02) × 1019 cm−3; whereas, the nanocrystal synthesized at 820 °C shows a single phase of semi‐metallic Td‐Mo0.29W0.72Te1.99 with much higher carrier density of (1.59 ± 0.04) × 1020 cm−3. In the cyclic voltammetry (CV) analysis over 200 cycles, the MoxW1‐xTe2‐based electrodes show better stability in the I−/I3− electrolyte than a Pt electrode. In DSSC tests, a Td‐Mo0.29W0.72Te1.99‐decorated CE achieves the efficiency (η) of 8.85%, better than those CEs fabricated with Td‐ & 2H‐Mo0.32W0.67Te2.01 (7.81%) and sputtered Pt (8.01%). The electrochemical impedance spectra reveal that the Td‐Mo0.29W0.72Te1.99 electrode possesses low charge‐transfer resistance in electrocatalytic reactions. These exceptional properties make Weyl semi‐metallic Td‐MoxW1‐xTe2 a potential electrode material for a wide variety of electrocatalytic applications.

Economical and highly efficient Pt-free counter electrode for dye-sensitized solar cells

Fe-Co nanoparticle-incorporated carbon nanofibers ((Fe-Co)-CNFs) were obtained by a simple and flexible electrospinning method and were further pre-oxidized and carbonized under a high-temperature nitrogen atmosphere for application as counter electrodes for highly efficient platinum-free dye-sensitized solar cells (DSSCs). Electrochemical characterizations revealed that the (Fe-Co)-CNFs showed excellent electrocatalytic activity for the I3−/I− redox couple. Photoelectric performance tests have shown that dye-sensitized solar cells equipped with (Fe-Co)-CNF counter electrodes have comparable photovoltaic efficiency to platinum counter electrode cells. This is because the graphite properties of these fibers rendered them electronically conducting. One-dimensional nanofibers provide oriented electron transport pathways, while lapped fibers form a three-dimensional mesoporous network, enhancing the contact with the electrolyte, and hence leading to faster ionic reaction kinetics. This study demonstrates that (Fe-Co)-CNFs can be used as low-cost high-efficiency counter electrodes for DSSCs.

Polypyrrole/Ionic Liquid/Au Nanoparticle Counter-Electrodes for Dye-Sensitized Solar Cells: Improving Charge-Transfer Resistance at the CE/Electrolyte Interface

To provide a viable alternative for counter electrodes used in dye sensitized solar cells, polypyrrole (PPy) based films have been synthesized via electrochemical deposition in the presence of the ionic liquid 1-butyl-3-methylimidazolium bis-(trifluoromethanesulfonyl) imidate (NTf2) and incorporated with gold nanoparticles (Aunanop). The films were analyzed by SEM, UV-Vis-NIR, Raman, Electrochemical impedance spectroscopy, Cyclic voltammetry and Conductivity measurements. The presence of the ionic liquid is found to result in a more conductive film, to improve catalytic reduction of I3− and the electrochemical reversibility of the electrode. In addition to increase conductivity, impedance spectroscopy has shown that incorporating Aunanop in the PPy/NTf2 film helps improving the interfacial charge transportation, the electrocatalytic properties and solar energy conversion efficiency. DSSCs assembled with PPy based CE presented nearly the same J-V characteristic parameters as observed from conventional Pt based device.

Fabrication of a counter electrode for dye-sensitized solar cells (DSSCs) using a carbon material produced with the organic ligand 2-methyl-8-hydroxyquinolinol (Mq).

Dye sensitized solar cells (DSSCs) are low cost solar cells and their fabrication process is easy relative to silicon based solar cells. Platinum can be replaced with carbon materials as counter electrodes in DSSCs because of their good catalytic properties and low cost. A carbon material was produced by carbonization of an organic ligand (2 methyl 8-hydroxy quinolinol (Mq)) at high temperature in flowing argon gas. Polyvinylpyrrolidone (PVP) was used as a surfactant for making carbon slurry from carbon produced using Mq. For the fabrication of the counter electrode, a carbon coating was prepared by using the doctor blading technique and the carbon slurry was coated on the FTO substrate. DSSCs based on the carbon counter electrode exhibit a higher Voc of 0.75 V than that of the Pt counter electrode (0.69 V). DSSCs based on the carbon material showed a power conversion efficiency (PCE) of 4.25% and fill factor (FF) of 0.51 which are slightly lower than those of the platinum (Pt) based counter electrode which showed a PCE of 5.86% and FF of 0.68.

Increased power conversion efficiency of dye-sensitized solar cells with counter electrodes based on carbon materials.

The good catalytic activity, resistance to iodine corrosion, and stability of carbon materials make them ideally suited for the fabrication of counter electrodes used in dye-sensitized solar cells (DSSCs). Different carbon materials have been used to make counter electrodes, and each has its own advantages, such as good film formation or high electric conductivity. Herein, various carbon materials were mixed and employed for preparing counter electrodes in DSSCs. Both fine film morphology and improved charge-carrier transport were obtained, and the power conversion efficiency of the DSSCs was thus increased. Accordingly, a cell efficiency of 6.29% was obtained by the DSSC with a counter electrode composed of the optimum mixture of carbon nanotubes, graphite, conductive carbon black, and graphene. Furthermore, DSSCs with a flexible counter electrode were fabricated using the optimum carbon material mixture, and the corresponding DSSCs achieved a power conversion efficiency of 4.32%.

Three-dimensional graphene networks and RGO-based counter electrode for DSSCs.

Graphene is considered to be a potential replacement for the traditional Pt counter electrode (CE) in dye-sensitized solar cells (DSSCs). Besides a high electron transport ability, a close contact between the CE and electrolyte is crucial to its outstanding catalytic activity for the I3−/I redox reaction. In this study, reduced graphene oxide (RGO) and three-dimensional graphene networks (3DGNs) were used to fabricate the CE, and the graphene-based CE endowed the resulting DSSC with excellent photovoltaic performance features. The high quality and continuous structure of the 3DGNs provided a channel amenable to fast transport of electrons, while the RGO afforded a close contact at the interface between the graphene basal plane and electrolyte. The obtained energy conversion efficiency (η) was closely related to the mass fraction and reduction degree of the RGO that was used. Corresponding optimization yielded, for the DSSCs based on the 3DGN–RGO CE, a value of η as high as 9.79%, comparable to that of the device using a Pt CE and hence implying promising prospects for the as-prepared CE.

Soft-Templated Tellurium-Doped Mesoporous Carbon as a Pt-Free Electrocatalyst for High-Performance Dye-Sensitized Solar Cells.

Among various photovoltaic devices, dye-sensitized solar cells (DSSCs) are one of the most potentially clean and renewable energy conversion devices because of their low fabrication cost, environmentally friendly nature, and high power conversion efficiency. However, the use of rare metals such as Pt counter electrodes (CEs) is one of the major drawbacks of DSSC devices for broad real-life applications. In this regard, alternative materials to Pt CEs have been long sought for DSSCs employing both cobalt and iodine redox couples. Therefore, in this study, soft-templated tellurium-doped mesoporous carbons (Te-SMCs) were synthesized for the first time by the simple pyrolysis of PAN- b-PBA block copolymer in the presence of a tellurium precursor for replacing the Pt CE. To confirm the chemical composition and porosity, the as-prepared Te-SMC materials were evaluated by elemental analysis (XPS and EDS) and nitrogen sorption isotherms measurement. The as-prepared Te-SMC materials contained mainly mesopores and retained the three-dimensional hierarchical graphite-like structure with many defect sites. They displayed doping levels with nitrogen of 9.15 atom % and tellurium of 0.15 atom % and had a specific surface area of 540 m2 g-1. Therefore, these characteristics enabled the development of a high-performance CE in DSSCs with cobalt and iodine redox couples. As a result of its catalytic performance, Te-SMC exhibited outstanding electrocatalytic activity as well as a significantly improved electrochemical stability than those of Pt CE for both redox couples even after 1000 potential cycles. The results show that a maximum conversion efficiency of 11.64 and 9.67% could be achieved under one sun illumination (AM 1.5G) for SGT-021/Co(bpy)32+/3+- and N719/I-/I3--based devices with Te-SMC CEs, and their power conversion efficiency is superior to the corresponding device with Pt CEs.

Nitrogen-Enriched Hollow Carbon Spheres Coupled with Efficient Co–Nx–C Species as Cathode Catalysts for Triiodide Reduction in Dye-Sensitized Solar Cells

Hollow carbon spheres (hCSs) have recently been emerging as low-cost and promising cathode catalysts toward triiodide reduction for dye-sensitized solar cells (DSSCs). However, it is still challenging and questionable for hCSs-based counter electrodes (CEs) to compete with traditional Pt CEs in DSSCs. Herein, nitrogen-enriched hCSs with atomically dispersed Co–Nx–C moieties (Co–N–hCSs) are synthesized via a calcination of cobalt-ions-absorbed N-enriched hollow copolymer sphere precursor. As inferred from cyclic voltammetry, electrochemical impedance spectroscopy, and Tafel polarization curves, the Co–N–hCSs display superior electrocatalytic activity and electrochemical stability. This excellent catalytic behavior can essentially be attributed to the high intrinsic electrocatalytic activity derived from the Co–Nx–C moieties, along with the robust N-enriched hollow sphere structure. As a result, the DSSCs with Co–N–hCSs as counter electrodes present an encouraging power conversion efficiency of 7.71%, which...

Electrospinning synthesis and electrocatalytic performance of iron oxide/carbon nanofibers composites as a low-cost efficient Pt-free counter electrode for dye-sensitized solar cells

The exploration of low-cost and efficient counter electrodes (CEs) in dye-sensitized solar cells (DSSCs) is of great significance in view of potential application of DSSCs. Herein, the Fe2O3/CNFs composites are synthesized by electrospin method and a facile hydrothermal method, and the composites of Fe2O3/CNFs is used as a low-cost counter electrode for DSSCs. Scanning electron microscopy measurement shows that Fe2O3 nanoparticles have been evenly located on the exterior of CNFs, providing abundant catalytic active sites for triiodide reduction. The one dimensional CNFs has a high conductivity, which could effectively reduce the agglomeration of Fe2O3 nanoparticles, thus increasing the specific surface area of the material and facilitating the rapid transmission of ions and electrons in the electrolyte. The synergistic effect of Fe2O3/CNFs composite leads to high electrocatalytic activity. Consequently, DSSCs devices constructed with an Fe2O3/CNFs composite based on CE afford a decent power conversion efficiency of 7.48%, higher than the expensive Pt CE based DSSCs (6.97%).

CePd‐Nanoparticles‐Incorporated Carbon Nanofibers as Efficient Counter Electrode for DSSCs

AbstractIn this study, the cerium‐palladium (CePd) incorporated carbon nanofibers (CNFs) were manufactured by low‐cost and versatile electrospinning technique and successfully applied as a counter electrode to fabricate the dye‐sensitized solar cells (DSSCs). The utilized physiochemical techniques, X‐ray diffractometer (XRD), X‐ray photoelectron spectroscopy (XPS), field‐emission scanning electron microscope (FESEM), and transmission electron microscope (TEM) confirmed the formation of carbon nanofibers (CNFs) incorporated by Ce and Pd nanoparticles. CePd incorporated CNFs were preliminary presented good electrocatalytic activity towards the iodide redox couple, as investigated by cyclic voltammetry. The DSSC fabricated using CePd incorporated CNFs based counter electrode (CE) attained an applicable power conversion efficiency (PCE) of 4.52% along with open circuit voltage (VOC) of 0.739 V, a short‐circuit current density (JSC) of 11.42 mA/cm2 and fill factor (FF) of 0.54. According to primary results, the CePd incorporated CNFs based CE is a promising, and cost‐effective alternative CE for photoelectrochemical devices.