Application of mesoporous carbon to counter electrode for dye-sensitized solar cells

The mesoporous carbons were prepared by the carbonation of the triblock copolymer F127/phloroglucinol-formaldehyde composite self-assembled in an acid medium and employed as the catalyst for triiodide reduction in dye-sensitized solar cells (DSCs). The characteristics of mesoporous carbon were analyzed by scanning electron microscopy, transmission electron microscopy, N₂ sorption measurement and X-ray diffraction. The mesoporous carbon with low crystallinity exhibited Brunauer-Emmett-Teller surface area of 400 m² g⁻¹, pore diameter of 6.8 nm and pore volume of 0.63 cm³ g⁻¹. The photovoltaic performances of DSCs with mesoporous carbon counter electrode were improved by increasing the carbon loading on counter electrode due to the charge-transfer resistance of mesoporous carbon counter electrode decreasing with the increase of the carbon loading. However, further carbon loading increase has no obvious effect on the photovoltaic performance of DSCs with carbon electrode when carbon loading exceeds 300 μg cm⁻². The overall conversion efficiency of 6.18% was obtained by DSCs composed of mesoporous carbon counter electrode with the carbon loading of 339 μg cm⁻². This value is comparable to that of DSCs with conventional platinum counter electrode.     

High-performance carbon counter electrode for dye-sensitized solar cells

Here, we reported that a new carbon electrode prepared with an activated carbon was superior to a Pt sputtered electrode as the counter electrode of dye-sensitized solar cells. The photovoltaic performance was largely influenced by the roughness factor of carbon electrode. The open-circuit voltage increased by about 60 mV using the carbon counter electrode compared to the Pt counter electrode because of positive shift of the formal potential for I₃⁻/I⁻ couple.     

High-performance polypyrrole nanoparticles counter electrode for dye-sensitized solar cells

Polypyrrole (PPy) nanoparticle was synthesized and coated on a conducting FTO glass to construct PPy counter electrode used in dye-sensitized solar cell (DSSC). Scanning electron microscope images show that PPy with porous and particle diameter in 40–60 nm is covered on the FTO glass uniformly and tightly. Cyclic voltammograms of I₂/I⁻ system measurement reveals that the PPy electrode has smaller charge-transfer resistance and higher electrocatalytic activity for the I₂/I⁻ redox reaction than that Pt electrode does. Overall energy conversion efficiency of the DSSC with the PPy counter electrode reaches 7.66%, which is higher (11%) than that of the DSSC with Pt counter electrode. The excellent photoelectric properties, simple preparation procedure and inexpensive cost allow the PPy electrode to be a credible alternative used in DSSCs.     

Investigation of catalytic activity of glassy carbon with controlled crystallinity for counter electrode in dye-sensitized solar cells

Glassy carbon (GC) with controlled crystallinity has been used as catalytic material for counter electrode in dye-sensitized solar cells (DSC), with emphasis on understanding their catalytic activity for the triiodide reduction. The GC with low crystallinity showed high catalytic activity for the triiodide reduction. The enhanced catalytic activity was attributed to increased graphene stacks and active sites in the GC. The active sites in the GC for catalysis were located at the edges of graphene stacks. The conversion efficiency of DSC was more related to the catalytic activity of the GC than the sheet resistance of GC layer. Therefore, GC with low crystallinity as catalytic materials for counter electrode resulted in DSC with high conversion efficiency.     

VC@C composites derived from polyoxovanadate assisted by dicyandiamide as low-cost platinum-free counter electrode electrocatalyst for dye-sensitized solar cells

Vanadium-based carbides have been applied as Pt-free counter electrodes (CEs) electro-catalysts for dye-sensitized solar cells (DSSCs) due to the advantages of earth-abundant reserves, diverse composition, ease modification, and low cost. Herein, the polyoxovanadate (NH₄)₂V₆O₁₆ as V source assisted by dicyandiamide (C₂H₄N₄) as C source via simply physical mixing by ball-milling to assemble VC@C precursors. And then, five different VC@C composites derived from precursors with mass ratios of dicyandiamide to polyoxovanadate of 5:1, 10:1, 15:1, 20:1 and 25:1 at 900 °C, and further achieved power conversion efficiencies (PCEs) of 5.4%, 5.6%, 6.6%, 6.2% and 5.1% as CEs for regenerate traditional I₃⁻/I⁻ couple in the encapsulated DSSCs, respectively. The effects of different mass ratio of dicyandiamide on the catalytic performances of VC@C composite CEs were also assessed using cyclic voltammetry, electrochemical impedance spectroscopy and Tafel polarization experiments. The photocurrent-photovoltage (J-V) results indicated that VC@C composites CEs had high conductivity and rich number of active sites, which indicated that VC@C composites could be a cost-effective and high-performance alternative Pt-based CEs catalyst for DSSCs.     

High-performance and low platinum loading Pt/Carbon black counter electrode for dye-sensitized solar cells

Pt/Carbon black counter electrode for dye-sensitized solar cells (DSSCs) was prepared by reducing H₂PtCl₆ with NaBH₄ in carbon black. The Pt/Carbon black electrode had a high electrocatalytic activity for iodide/triiodide redox reaction. Using the Pt/Carbon black counter electrode, DSSC achieved 6.72% energy conversion efficiency under one sun illumination. Pt/Carbon black electrode shows the same energy conversion efficiency and lower cost compared with Pt electrode, which makes it available in DSSCs practical applications.     

A high-performance counter electrode based on poly(3,4-alkylenedioxythiophene) for dye-sensitized solar cells

A poly(3,3-diethyl-3,4-dihydro-2H-thieno-[3,4-b][1,4]dioxepine) (PProDOT-Et₂) counter electrode prepared by electrochemical polymerization on a fluorine-doped tin oxide (FTO) glass substrate was incorporated in a platinum-free dye-sensitized solar cell (DSSC). The surface roughness and I⁻/I₃⁻ redox reaction behaviors based on PProDOT-Et₂, poly(3,4-propylenedioxythiophene) (PProDOT), poly(3,4-ethylenedioxythiophene) (PEDOT), and sputtered-Pt electrodes were characterized, and their performances as counter electrodes in DSSCs were compared. Cells fabricated with a PProDOT-Et₂ counter electrode showed a higher conversion efficiency of 7.88% compared to cells fabricated with PEDOT (3.93%), PProDOT (7.08%), and sputtered-Pt (7.77%) electrodes. This enhancement was attributed to increases in the effective surface area and good catalytic properties for I₃⁻ reduction. In terms of the film thickness effect, the fill factor was strongly dependent on the deposition charge capacity of the PProDOT-Et₂ layer, but the aggregation of PProDOT-Et₂ in thicker layers (>80 mC cm⁻²) resulted in decreases in J_SC and the cell conversion efficiency. The charge transfer resistances (R_ct1) of the PProDOT-Et₂ counter electrodes had the lowest value of ∼18 Ω at a deposition charge capacity of 40 mC cm⁻². These results indicate that films with high conductivity, high active surface area, and good catalytic properties for I₃⁻ reduction can potentially be used as the counter electrode in a high-performance DSSC.     

Performance variation of carbon counter electrode based dye-sensitized solar cell

The effect of dark and room temperature aging on the performance of carbon counter electrode based dye-sensitized solar cell (DSSC) has been investigated. Using nano size carbon as a counter electrode material, DSSC with power conversion efficiency of 7.56% was fabricated. Storing the devices in the dark at room temperature enhanced both the open-circuit voltage (V_OC) and fill-factor (FF) but reduced the short-circuit current density (J_SC). After 60 days of aging, carbon counter electrode DSSC retains 84% of its initial day efficiency (η). The variation in the current–voltage parameters was explained on the basis of electrochemical impedance spectroscopic (EIS) analysis.     

Dye-sensitized titania aerogels as photovoltaic electrodes for electrochemical solar cells

We describe the fabrication and performance of dye-sensitized photoanodes derived from TiO₂ aerogel. Nanocrystalline titania aerogel is a bicontinuous, nanostructured pore–solid architecture featuring specific surface areas of 85–150 m²/g and a continuous mesoporous network, allowing chemisorption of high concentrations of sensitizing dye and rapid mass-transport of electron-transfer mediators. Considerable design and processing flexibility arises with aerogels because the continuous pore–solid networks are fixed by the supercritical drying process, allowing the creation of multifunctional, nanostructured films of single or multiple layers. Titania aerogels can be processed as powders and deposited as nearly opaque films from 2 μm to >35-μm thick while retaining their bicontinuous nanoscale networks. Two-layer, 30-μm-thick TiO₂ aerogel films yield incident photon-to-electron conversion efficiency (IPCE) values of 85% in the 500–600 nm range and 52% at 700 nm with N719 as a sensitizing dye and after correcting for transmittance of the 3.2-mm-thick FTO-coated glass substrates at these wavelengths.     

High-performance counter electrode based on nitrogen-doped porous carbon nanoribbons for quantum dot-sensitized solar cells

Nitrogen-doped porous carbon nanoribbons (NPCNs) are facilely prepared by carbonization of polypyrrole (PPy) nanotubes followed by a chemical activation process. NPCN counter electrodes are subsequently fabricated by depositing NPCNs onto Ti mesh for quantum dot-sensitized solar cells (QDSCs). Electrochemical tests are carried out to evaluate the electrocatalytic performance of obtained NPCN electrode. The data of electrochemical tests suggest that the NPCN electrode has a superior electrocatalytic ability towards polysulfide (S₂²⁻/S²⁻) electrolyte regeneration reaction and displays a high stability in polysulfide electrolyte. The excellent electrocatalytic performance of NPCN electrode can be ascribed to their large surface area, 2D porous nanoribbon morphology, and nitrogen atom doping, which provides abundant electrocatalytic active sites and facilitates the electrolyte diffusion. Consequently, a power conversion efficiency of 3.27% is obtained by using NPCN electrode as the counter electrode for QDSC. This efficiency is close to the QDSC assembled with commonly used PbS electrode (4.0%).     

Facile fabrication of efficient,low-cost Cu2ZnSnSe4 cathode for highly-performance dye-sensitized solar cells

Kesterite-structure Cu₂ZnSnSe₄ (CZTSe) has been recommended to be a promising Pt-free counter electrode (CE) candidate for dye-sensitized solar cells (DSSCs), owing to its excellent catalytic activity, hierarchical microstructure, and natural abundance. Herein, based on a facile electrodeposition method and mild solvothermal treatment, we prepared great-crystallinity CZTSe nanostructure on FTO substrate as DSSCs cathode directly, demonstrating a satisfied power conversion efficiency of 7.56% and a relatively long-operation life performance. The impressive performance was ascribed from the CZTSe thin film good adhering to conductive substrate, high catalytic activity, effective photo-generated electron migration, and low charge transfer resistance at the interface of the catalytic material and substrate. Our present results prove that the CZTSe nanostructure is a promising and effective Pt-free counter cathode in dye-sensitized solar cells.     

Dye-sensitized solar cells based on electrospun polymer blends as electrolytes

We prepared electrospun polymer nanofibers by the electrospinning method and investigated about their applications to dye-sensitized solar cells (DSSCs). Electrospun poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) and PVDF-HFP/polystyrene (PS) blend nanofibers were prepared and examined the uptake, the ionic conductivity, and the porosity by impedance measurement and Scanning Electron Microscope (SEM). The best results of V_oc, J_sc, FF, and efficiency of the DSSC devices using the electrospun PVDF-HFP/PS(3:1) blend nanofibers were 0.76 V, 11.8 mA/cm², 0.66, and 5.75% under AM 1.5.     

Dye-sensitized solar cells based on semiconductor morphologies with ZnO nanowires

ZnO nanowires and structures that combine nanowires and nanoparticles were used as the wide band gap semiconducting photoelectrode in dye-sensitized solar cells (DSSCs). The nanowires provide a direct path from the point of photogeneration to the conducting substrate and offer alternative semiconductor network morphologies to those possible with sintered nanoparticles. Growing nanowires with dendrite-like branched structure greatly enhances their surface area, leading to improved light harvesting and overall efficiencies. Hybrid cells based on a combination of nanowires and nanoparticles can be tailored to take advantage of both the high surface area provided by the nanoparticles and the improved electron transport along a nanowire network. Solar cells made from branched nanowires showed photocurrents of 1.6 mA/cm², internal quantum efficiencies of 70%, and overall efficiencies of 0.5%. Solar cells made from appropriate hybrid morphologies show photocurrents of 3 mA/cm² and overall efficiencies of 1.1%, while both the nanowire and hybrid cells show larger open circuit voltages than nanoparticle cells.     

Electrospun Co-TiC nanoparticles embedded on carbon nanofibers: Active and chemically stable counter electrode for methanol fuel cells and dye-sensitized solar cells

Cobalt-titanium carbide nanoparticles (Co-TiC NPs) embedded on carbon nanofibers (composite) were prepared by electrospinning of a solution containing cobalt acetate tetrahydrate (CoAc), titanium (IV) isopropoxide (TIIP) and polyvinylpyrrolidone (PVP) in acetic acid and ethanol. It was then subjected to a carbonation process at a low temperature (850 °C) since the composite contains metal carbide. The obtained composite, as an efficient electrode, was used as an alternative to Pt-free counter electrode (CE) for fuel cells (FCs) and dye-sensitized solar cells (DSSCs). Cyclic voltammetry (CV) and chronoamperatory (CA) tests were used to measure the composite electrode's performance in methanol oxidation. The results showed that the introduced composite could enhance both methanol electro-oxidation and electrochemical stability as the low onset potential and high current density of the composite electrode were obtained at 189 mV and ～90 mA cm^?2 vs. Ag/AgCl, respectively. The composite also was examined in dye-sensitized solar cells as counter electrode (CE). The results showed that the composite electrode was effective, providing stable electrocatalytic activity (ECA) and conductivity, indicating the composite can improve catalytic activity in triiodide reduction. The short-circuit current density (J_sc), open circuit voltage (V_OC), fill factor (FF), and energy conversion efficiency (η) were found to be ～9.98 mA cm^?2, 0.758 V, 0.507 and 3.87%, respectively. The high ECA could be attributed to the synergic effects from all the pristine components.     

Carbon-nanofiber counter electrodes for quasi-solid state dye-sensitized solar cells

Carbon-nanofibers (CNFs) with antler and herringbone structures are studied as a tri-iodide (I₃⁻) reduction electrocatalyst in combination with the liquid electrolyte or an alternative stable quasi-solid state electrolyte. The catalytic properties of the counter electrode (CE) are characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The doctor bladed low temperature CNFs-CE has faster I₃⁻ reduction rate and low charge transfer resistance (R_CT) of ∼0.5 Ω cm² than platinum (Pt) (∼2.3 Ω cm²) due to the nanofiber stacking morphology. Its herringbone and antler structures with graphitic layers lead to defect rich edge planes and larger diameter of CNFs facilitate the electron transfer kinetics. The cells with CNF counter electrodes are showing promising energy conversion efficiency greater than 7.0% for the glass based devices and 5.0% for the flexible cells filled with the quasi-solid state electrolyte, which is similar to Pt performance. Application of CNFs-CE in flexible and quasi-solid state electrolyte increases the possibility of roll to roll process, low cost and stable dye-sensitized solar cells (DSCs).     

Dye-sensitized solar cells based on anatase TiO2 hollow spheres/carbon nanotube composite films

Dye-sensitized solar cells (DSSCs) based on anatase TiO₂ hollow spheres (TiO2HS)/multi-walled carbon nanotubes (CNT) nanocomposite films are prepared by a directly mechanical mixing and doctor blade method. The prepared samples are characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, UV-vis absorption spectroscopy and N₂ adsorption-desorption isotherms. The photoelectric conversion performances of the DSSCs based on TiO2HS/CNT composite film electrodes are also compared with commercial-grade Degussa P25 TiO₂ nanoparticles (P25)/CNT composite solar cells at the same film thickness. The results indicate that the photoelectric conversion efficiencies (η) of the TiO2HS/CNT composite DSSCs are dependent on CNT loading in the electrodes. A small amount of CNT clearly enhances DSSC efficiency, while excessive CNT loading significantly lowers their performance. The former is because CNT enhance the transport of electrons from the films to FTO substrates. The latter is due to high CNT loading shielding the visible light from being adsorbed by dyes.     

Charge transfer resistance of spray deposited and compressed counter electrodes for dye-sensitized nanoparticle solar cells on plastic substrates

Electrochemical impedance spectroscopy was used to determine the effective charge transfer resistances of porous dye-sensitized solar cell counter electrodes prepared by low-temperature spray deposition and compression of conductive carbon and platinized Sb-doped SnO₂ powders on indium tin oxide-coated plastic substrates. The charge transfer resistances were 0.5–2 and 8–13 Ω cm², respectively, when using 3-methoxypropionitrile as the electrolyte solvent. The manufacturing method used lends itself to produce mechanically stable and even-quality electrodes in an easy and fast manner.     

Pt–NiO nanophase electrodes for dye-sensitized solar cells

A new type of counter electrode comprising of Pt and NiO biphase was prepared an RF magnetron cosputtering system for a dye-sensitized solar cell (DSSC). Transmission electron microscope images, transmission electron diffraction patterns, and X-ray diffraction patterns of the Pt–NiO electrodes confirmed the formation of a nanosized Pt polycrystalline phase of 7 nm mixed with porous amorphous NiO phase. The short-circuit current density and cell efficiency were increased from 0.22 to 0.30 mA/cm² and from 2.1% to 2.8%, respectively, and almost constant open-circuit voltage and fill factor, 0.53 V and 63%, respectively, were observed.     

Facile fabrication of low-cost low-temperature carbon-based counter electrode with an outstanding fill factor of 73% for dye-sensitized solar cells

Developing chemically inert, electrically conductive, and catalytically active counter electrodes (CEs) to replace conventional Pt-based ones is highly desirable for dye-sensitized solar cells. Herein, we reported a facile, cost-effective, and low-temperature synthesis pathway to develop carbon-based CEs. The performance of homemade carbon paste (H-CP)–based CE (H-CE) was compared with that of commercial carbon paste (C-CP)–based CE (C-CE) and Pt-based CE (Pt-CE). The scanning electron microscope (SEM) results showed that H-CE demonstrated a penetrable surface structure which facilitates the diffusion of electrolyte through the carbon electrode. This phenomenon enhanced the triiodide reduction with respect to C-CE having a compact structure that limits the electrolyte diffusion. The charge transfer properties and catalytic activities of the investigated devices were explored using electrochemical impedance spectroscopy and Tafel polarization measurements; the obtained results indicated that the device based on H-CE revealed relatively lower charge transfer resistance and higher exchange current density compared with C-CE-based device. The current-voltage measurements showed that the device based on H-CE has a power conversion efficiency of 2.70%, which was about 1.6 times higher than that of the device based on C-CE (1.68%). Furthermore, a fill factor of 73% was achieved for the device based on H-CE, which outperformed the Pt-based device (69%) and was among one of the highest values obtained in the literature. Also, a tape adhesion test performed on H-CP-coated glass substrate displayed its excellent robustness.