3D graphene from CO2 and K as an excellent counter electrode for dye‐sensitized solar cells

3D graphene, which was synthesized directly from CO₂ via its exothermic reaction with liquid K, exhibited excellent performance as a counter electrode for a dye‐sensitized solar cell (DSSC). The DSSC has achieved a high power conversion efficiency of 8.25%, which is 10 times larger than that (0.74%) of a DSSC with a counter electrode of the regular graphene synthesized via chemical exfoliation of graphite. The efficiency is even higher than that (7.73%) of a dye‐sensitized solar cell with an expensive standard Pt counter electrode. This work provides a novel approach to utilize a greenhouse gas for DSSCs.     

Effects of graphene counter electrode and CdSe quantum dots in TiO2 and ZnO on dye‐sensitized solar cell performance

Fabrication and performance study of dye‐sensitized solar cells using different counter electrodes and photoanodes is reported. Spin coated, E‐beam coated platinum, and graphene electrodes were used as counter electrodes. Different combinations of TiO₂ nanoparticle and ZnO nanorods (NRs) with CdSe quantum dots were prepared and used as photoanodes. The photoanodes comprising of both ZnO NRs and TiO₂ nanoparticles have shown improved performances in short‐circuit current density and open‐circuit voltage comparing the devices fabricated using only ZnO NR or TiO₂ nanoparticles. The inclusion of CdSe quantum dots has been found to increase the performance of dye‐sensitized solar cell for all the photoanodes. In case of counter electrodes, the cells fabricated with graphene showed improved performance. Copyright © 2014 John Wiley & Sons, Ltd.     

Electrospun porous Fe2O3 nanotubes as counter electrodes for dye‐sensitized solar cells

Porous Fe₂O₃ nanostructures were synthesized through electrospinning of Fe (NO₃)₃/polyvinylpyrrolidone followed by calcination in air. The morphology of the resultant Fe₂O₃ was tuned by changing the ratio between Fe (NO₃)₃ and the polymer matrix. The performance of these nanostructures as counter electrodes in dye‐sensitized solar cells (DSSCs) was investigated. It was found that nanotubes exhibit significantly higher catalytic efficiency toward reducing I^?/I₃^? electrolytes than nanorods and nanobelts, showing a photoelectric conversion efficiency of 4.0%, also superior to a range of transition metal oxides. Furthermore, the nanotube‐based counter electrode showed lower resistance than other Fe₂O₃ nanostructures. These results were attributed to the high specific surface area (90.2 m² g^?1) of the nanotubes, which provides a large reaction site and can promote the charge transfer at the electrode/electrolyte interfaces. The low cost and ease of mass production make Fe₂O₃ nanotube a promising candidate to replace Pt as the counter electrode in DSSCs.     

A review on PEDOT‐based counter electrodes for dye‐sensitized solar cells

The dye‐sensitized solar cell (DSSC) is a promising alternative for the Si solar cell due to its low‐cost and easy fabrication. As a novel conductive polymer, poly(3,4‐ethylenedioxythiophene) (PEDOT) has attracted much attention for DSSCs. In this review article, the progress of PEDOT‐based counter electrodes for DSSCs is presented. First, the properties and structure of PEDOT are briefly described, and its feasibility as a DSSC counter electrode is demonstrated. Then, the effect of various treatments on the electrical conductivity and catalytic activity of PEDOT as well as its stability is examined. Furthermore, efficient and low‐cost composite counter electrodes consisting of PEDOT and other materials are deeply discussed. Finally, an outlook for PEDOT counter electrodes is provided. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis of carbon nanomaterials for dye‐sensitized solar cells

In this paper, it was demonstrated that Na₂O can react with CO to produce carbon nanofibers at 500 °C and carbon nanosheets at 550 °C. Furthermore, the nanosheets exhibited excellent performance as a counter electrode for a dye‐sensitized solar cell (DSSC), leading to a high power conversion efficiency of 7.57%. The efficiency is larger than that (4.72%) of a DSSC with the carbon nanofiber counter electrode and even comparable with that of an expensive Pt‐based DSSC. Copyright © 2015 John Wiley & Sons, Ltd.     

Bridging TiO2 nanoparticles using graphene for use in dye‐sensitized solar cells

The use of graphene to bridge TiO₂ particles in the photoanode of dye‐sensitized solar cell for reduced electrical resistance has been investigated. The difficulty in dispersing graphene in TiO₂ paste was overcome by first dispersing graphene oxide (GO) into the TiO₂ paste. The GO was then reduced to graphene after the sintering of TiO₂. This is shown through transmission electron microscopy and X‐ray photoelectron spectroscopy analysis. Cell performance was evaluated using a solar simulator, incident photon to electron conversion efficiency, intensity modulated photocurrent/photovoltage spectroscopy under blue light, and electrochemical impedance spectroscopy. Depending on the amount of graphene in the photoanode, the cell performance was enhanced to different degrees. A maximum increase of 11.4% in the cell efficiency has been obtained. In particular, the inclusion of graphene has reduced the electron diffusion time by as much as 23.4%, i.e. from 4.74 to 3.63 ms and increased the electron lifetime by as much as 42.3%, i.e. from 19.58 to 27.85 ms. Copyright © 2014 John Wiley & Sons, Ltd.     

N‐doped titania powders prepared by different nitrogen sources and their application in quasi‐solid state dye‐sensitized solar cells

Nitrogen‐doped TiO₂ nanocrystalline particles are synthesized by a microwave‐assisted hydrothermal growth method using different amines (Dipropylamine, Diethanolamine and Ammonium hydroxide) as nitrogen sources. Characterization of the nanoparticles was performed with X‐ray diffraction, UV–vis diffuse reflectance spectroscopy, Field Emission Scanning Electron Microscopy and X‐ray Photoelectron Spectroscopy. The prepared N‐doped TiO₂ nanoparticles exhibit pure anatase phase with average diameter of 9 nm and reduced optical energy gap compared to undoped TiO₂. Immobilization of N‐doped and pure TiO₂ nanoparticles on SnO₂:F conductive glass substrates was successfully performed by using doctor‐blade technique and paste of the aforementioned nanoparticles. A series of N‐doped TiO₂ photoelectrodes with varying N dopant source and concentrations were fabricated for quasi‐solid state dye‐sensitized solar cells. The N‐doped solar cells achieve an overall conversion efficiency ranging from 4.0 to 5.7% while undoped TiO₂ showed 3.6%. The basic difference to the electrical performance of the cells is focused to the enhancement in the current density of N‐doped TiO₂‐based cells which was from 11% to 58% compared with undoped TiO₂ cells. Current densities were directly proportional with nitrogen doping level in TiO₂ lattice which differs depending on the amine source nature such as basicity differences, hydrogen bonding abilities and steric inherences. Copyright © 2013 John Wiley & Sons, Ltd.     

Low‐cost dye‐sensitized solar cells with ball‐milled tellurium‐doped graphene as counter electrodes and a natural sensitizer dye

This paper presents a facile and economic development of dye‐sensitized solar cells using a nonprecious counter electrode made from ball‐milled tellurium‐doped graphene (Te‐Gr) and a natural sensitizer extracted from Calotropis gigantea leaves. The prepared materials were characterized using various techniques, such as Raman spectroscopy, X‐ray diffraction (XRD), atomic force microscopy (AFM), impedance spectroscopy, and scanning electron microscopy with built‐in energy‐dispersive X‐ray spectroscopy (SEM with EDS). The electrochemical activity of the produced counter electrodes and the impedance of the fabricated cells were examined and discussed to devise plans for future enhancement of cell performance. A clear pattern of improvement was found when using cost‐effective Te‐Gr relative to the costly platinum counter electrodes, especially when compared with cells employing another natural sensitizer. The results show approximately 51% enhancement over chlorophyll‐based cells made from spinach, where the added advantage in our approach is the utilization of an abundant plant extract with little nutritional appeal.     

Use of single‐wall carbon nanohorns as counter electrodes in dye‐sensitized solar cells

The catalytic activity of single‐wall carbon nanohorns (SWNH) as counter electrodes (CE) of dye‐sensitized solar cells (DSC) was studied for the iodide/triiodide redox reaction. The catalytic activities of SWNH and high surface SWNH (HS‐SWNH) obtained by partial oxidation of SWNH were assessed based on charge‐transfer resistances (R_ct) and current–voltage curves. A half‐cell configuration was used, and CE performances were compared to CEs made of carbon black (CB) and Pt. A CE assembled with HS‐SWNH and mixed with 10 wt.% of hydroxyethyl cellulose (HEC) ‐ HS‐SWNH/HEC was found to have the highest electrocatalytic activity (lowest R_ct) among all the carbon‐based CEs tested when annealed at 180 °C (R_ct = 141 Ω cm²); however, a very thick film (several tens of µm) would be required in order to perform comparably to a Pt CE. The annealing of such CE at higher temperatures (above 400 °C) did not improve its catalytic activity, contrary to the other studied carbonaceous CEs. The redox catalytic activity of SWNH and HS‐SWNH decorated with Pt was also studied on a half‐cell configuration and compared to that of Pt/CB and pristine Pt. The Pt/SWNH/HEC CE showed the highest electrocatalytic activity per mass of Pt, needing just 50% of Pt load to yield the same electrocatalytic activity of a DSC equipped with a Pt CE, but having half of its transparency. Additionally, applications in temperature‐sensitive substrates are envisioned for the Pt/SWNH/HEC CE due to the use of lower annealing temperatures. Copyright © 2012 John Wiley & Sons, Ltd.     

Novel Cu–carbon nanofiber composites for the counter electrodes of dye‐sensitized solar cells

Copper (Cu)‐catalyzed carbon nanofibers (CNFs) were used as an alternative of the conventional platinum‐noble‐metal‐based catalyst at the counter electrode (CE) of a dye‐sensitized solar cell (DSSC). The CNFs were grown on activated carbon microfiber powder (PACF) using chemical vapor deposition (CVD) and the Cu nanoparticles (NPs). The Cu NPs served simultaneous roles: (i) as the CVD catalyst for the growth of the CNFs; (ii) as an enhancer of the electrode conductivity; and (iii) as a catalyst for the reduction reaction. The Cu‐CNF composite was applied as a thin layer on the fluorine‐doped tin oxide glass using the simple doctor blade method. The prepared Cu‐NP‐dispersed PACF/CNF composite was characterized using various spectroscopic techniques, including scanning electron microscopy, Fourier transform infrared ray, X‐ray diffraction, Raman spectroscopy, and transmission electron microscopy. The electrochemical tests showed that the Cu‐PACF/CNFs had a high electrocatalytic activity and low charge transfer resistance (1.26 Ω cm²), using the cyclic voltammetry and electrochemical impedance spectroscopy measurements. The DSSC fabricated with Cu‐PACFs/CNFs exhibited a power conversion efficiency value of 4.36%, open circuit voltage of 0.75 V, short circuit current density of 11.12 mA cm^?2, and fill factor of 54%. The prepared transition metal–CNF composite was simple to develop and can potentially be used as an efficient catalyst at the CE of DSSCs. Copyright © 2014 John Wiley & Sons, Ltd.     

Reduced graphene oxide–titania nanocomposite‐modified photoanode for efficient dye‐sensitized solar cells

We report the successful application of reduced graphene oxide–titania (rGO–TiO₂) nanocomposite as an efficient photoanode for dye‐sensitized solar cell (DSSC). The DSSC assembled with the rGO–TiO₂‐modified photoanode demonstrated an enhanced solar to electrical energy conversion efficiency of 4.74% compared with the photoanode of DSSC composed with unmodified TiO₂ (2.19%) under full sunlight illumination (100 mW/cm², AM 1.5G) as a result of the better charge collection efficiency of rGO, which reduced the back electron transfer process. Influence of the rGO content on the overall efficiency was also investigated, and the optimal rGO content for TiO₂ was 0.5 mg. Further, the modification of rGO–TiO₂ on the compact layer TiO₂ surface led to an increase in efficiency to 5.83%. The superior charge collection and enhanced solar energy conversion efficiency of the rGO–TiO₂ nanocomposite makes it to be used as a promising alternative to conventional photoanode‐based DSSCs. Copyright © 2015 John Wiley & Sons, Ltd.     

A novel dual mechanism in dye‐sensitized solar cells

An innovative dye‐sensitized solar cell based on achiote seeds with a new dual electrical generation mechanism is presented. This dye‐sensitized solar cell, in addition to the well‐known mechanism, where the conduction electrons are released from the dye molecules due to their interaction with photons, shows a distinct chemical mechanism that produces an effective electric current under dark conditions. Both mechanisms operate simultaneously; however, the electrical signal obtained from the photoelectrical mechanism is stronger. Additionally, during a rapid transition from darkness to illuminate conditions, non‐linear oscillations in the current signal are produced when the system is shifted rapidly far from equilibrium conditions. Copyright © 2017 John Wiley & Sons, Ltd.     

Synthesis and application of Fe3O4@nanocellulose/TiCl as a nanofiller for high performance of quasisolid‐based dye‐sensitized solar cells

In this research, to optimize the surface of the photoanode, two different types of surface coatings were used and their effects on the photovoltaic parameters were investigated. Also, to compare the two different electrolytic systems based on liquid and gel‐state electrolyte, the novel magnetic core‐shell nanocellulose/titanium chloride (Fe₃O₄@)NCs/TiCl) nanocomposite was introduced into a polymeric system as a nanofiller to decrease the crystallinity of the polymer and enhance the diffusion of triiodide ions in quasisolid‐state dye‐sensitized solar cells (QS‐DSSCs). For this purpose, Fe₃O₄@)NCs/TiCl was synthesized by coprecipitation of Fe³⁺ and Fe²⁺ ions in the presence of nanocellulose and then used as magnetic support for bonding TiCl₄ to prepare QS‐DSSCs. Containing a 10.0 wt% magnetic nanocomposite, it displayed a higher apparent diffusion coefficient (D_app) for I₃^? ions (4.10 × 10^?6 cm²/s) than the gel polymeric electrolyte (GPE) did (1.35 × 10^?6 cm²/s). GPEs were characterized using various techniques including current density‐voltage curves, AC impedance measurements, and linear sweep voltammetry (LSV). The photovoltaic values for the short‐circuit current density (J_sc), open‐circuit voltage (V_OC), and fill factor (FF) and the energy conversion efficiency (η) of the novel Fe₃O₄@NCs/TiCl nanocomposite–based QS‐DSSCs were 14.90 mA cm^?2, 0.757 V, 64%, and 7.22%, respectively.     

Recent advances in photo‐anode for dye‐sensitized solar cells: a review

Dye‐sensitized solar cell (DSSC) attracts immense interest in the last few decades due to its various attractive features such as low production cost, ease of fabrication and relatively high conversion efficiency, which make it a strong competitor to the conventional silicon‐based solar cell. In DSSC, photo‐anode performs two important functions, viz. governs the collection and transportation of photo‐excited electrons from dye to external circuit as well as acts as a scaffold layer for dye adsorption. The photo‐anode usually consists of wide band gap semiconducting metal oxides such as titanium dioxide (TiO₂) and zinc oxide (ZnO) deposited on the transparent conducting oxide substrates. The morphology and composition of the semiconductor oxides have significant impact on the DSSC photovoltaic performance. Therefore, enormous research efforts have been undertaken to investigate the influences of photo‐anode modifications on DSSC performance. The modifications can be classified into three categories, namely interfacial modification through the introduction of blocking and scattering layer, doping with non‐metallic anions and metallic cations and replacing the conventional mesoporous semiconducting metal oxide films with one‐dimensional or two‐dimensional nanostructures. In the present review, the previously mentioned modifications on photo‐anode are summarized based on the recent findings, with particular emphasis given to published works for the past 5 years. Copyright © 2017 John Wiley & Sons, Ltd.     

Preparation of N‐doped graphene‐based electrode via electrochemical method and its application in vanadium redox flow battery

An N‐doped graphene electrode has been prepared by cyclic voltammetric method in 5.0 M of HNO₃ solution on a graphite‐based electrode at room temperature. The modification of the electrode surface with different types of N‐containing groups, such as nitro groups, pyrrolic N, and pyridinic N, has been controlled by changing the scanned potential ranges. The formation of an N‐doped graphene electrode has been confirmed by scanning electron microscopic, atomic force microscopic, X‐ray photoelectron, and Raman spectroscopic methods. The prepared N‐doped graphene‐modified electrodes have been used in positive electrolyte of a vanadium‐based redox flow battery. As positive electrodes, the electrochemically modified electrodes prepared in 5.0 M of HNO₃ solution ?1.0 to (+1.9) and ?0.7 to (+1.9) V had more than 140 and 120 mA/cm² anodic and cathodic peak currents, respectively, in vanadium redox battery. This fast, low‐cost, and environmentally friendly method can be used in many application areas, such as optical devices, (bio)sensors, energy storage materials, and electronic devices.     

Evaluation of decay photocurrent measurements in dye‐sensitized solar cells: Application to laser beam‐induced current technique

The use of the laser beam‐induced current (LBIC) technique in photovoltaic devices is widespread, but its use in photoelectrochemical cells, such as dye‐sensitized solar cells (DSSCs), is limited due to the configuration of these devices. The main reason is the very slow response time of DSSCs in the decay process, and therefore LBIC scans take too long to perform. We have designed a procedure published in the literature to correct the photocurrent values obtained by the LBIC technique, based on an algorithm that uses a decreasing mono‐exponential model. This work presents a study of the decay measurements in DSSCs using several functions, in order to improve the algorithm designed. It concludes that functions such as a decreasing bi‐exponential or Becquerel function generate better fits to experimental data. Copyright © 2010 John Wiley & Sons, Ltd.     

Novel improvements in the sensitizers of dye‐sensitized solar cells for enhancement in efficiency—a review

In the present review article, we have focused our study on the novel improvements that have been brought about in the molecular design of various sensitizers for application in dye‐sensitized solar cells (DSSCs). The sensitizers based on noble metals such as ruthenium, osmium, and rhenium showed high efficiency, but their cost and complicated synthesis restrict their wide applications. Further, to reduce the cost of fabrication of DSSCs, researchers are focusing their interest in organic sensitizers. In this context, organic dyes have offered several possibilities, as by improving their molecular structure brings about improvement in the light harvesting ability of dyes, and with the help of such dyes, optimal DSSCs have been fabricated. Further, to reduce the cost of DSSCs, researchers are also focusing on natural sensitizers such as betacyanin and anthocyanin or chlorophyll, as natural sensitizers are easy to prepare, cost effective, and environmentally friendly. With the help of these natural sensitizers, eco‐friendly and more cost‐effective DSSCs can be fabricated. Thus, we found from our study that beside metal‐based sensitizers, organic and natural sensitizers also offer a vast potential for the optimization of efficiency in DSSCs. Copyright © 2015 John Wiley & Sons, Ltd.     

Dye-sensitized solar cells using graphene-based carbon nano composite as counter electrode

We demonstrated a counter electrode in dye-sensitized solar cells (DSSCs) using the graphene-based multi-walled carbon nanotubes (GMWNTs) structure. Graphene layers were prepared by drop casting on a SiO₂/Si substrate and multi-walled carbon nanotubes (MWNTs) were synthesized on graphene layers using iron catalyst by chemical vapor deposition. The structural properties of GMWNTs were investigated by transmission electron microscope and field-emission scanning electron microscopy. The GMWNTs sheets were lifted off from the Si substrate by buffered oxide etching and were transplanted on fluorine-doped tin oxide glass by Van der Waals force as a counter electrode. From the electrochemical impedance spectroscopy and energy conversion efficiencies, electrochemical properties of GMWNTs were comparable with those of MWNTs counter electrode. The results suggested that GMWNTs were one of the candidates for a counter electrode for dye-sensitized solar cells.     

Deprotonated curcumin as a simple and quick available natural dye for dye sensitized solar cells

In the present study, deprotonation of curcumin dye using potassium carbonate was performed successfully, which produced fairly stable deprotonated dye with a large bathochromic shift in the visible light absorption spectrum. The light-harvesting efficiency of this deprotonated dye was investigated in TiO₂-based dye sensitized solar cells, which exhibited an energy conversion efficiency of 0.91%, and this value is 8.3 times higher than that of the dye sensitized solar cells with curcumin photosensitizer without deprotonation.     

Nitrogen‐doped self‐shrinking porous 3D graphene capacitor deionization electrode

Traditional three‐dimensional (3D) graphene has a large pore structure, which makes the graphene structure not well interact with the anion and cation during the desalination process, thereby restricting the capacitive deionization (CDI) ability of the 3D graphene. In this work, we prepared a nitrogen‐doped self‐shrinking porous 3D graphene electrode by adding a pyrrole monomer to a graphene oxide solution, which was then applied to a CDI electrode. The results show that the electrochemical performance of the as‐prepared nitrogen‐doped self‐shrinking porous 3D graphene (NSPG) is significantly improved. Compared with traditional 3D graphene, NSPG has a denser pore structure with a larger specific surface area, thus exhibiting a good CDI performance: The NSPG electrode has an electroadsorption capacity of 13.16 mg/g.