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.     

Synthesis of TiO2 nanoparticles at low hydrothermal temperature and its performance for DSSC sensitized using natural dye extracted from Melastoma malabathricum L. seeds

Efficiency of a dye‐sensitized solar cell (DSSC) device depends on its semiconductor layer and the sensitizing dye to absorb the light. This work seeks to obtain the best solvent for the natural dye extraction from Melastoma malabathricum L. seeds. The extracted dye is used as sensitizer on TiO₂ nanoparticles produced via hydrothermal but optimized at relatively low temperature. Infrared characterization of the extracted dyes showed differences in functional groups using different solvents, whereas ultraviolet visible examination of the dyes showed differences in intensity along the spectrum ranges of 600 to 400 nm with maximum absorption around 550 to 500 nm. Thermal analysis revealed that the natural dye should be stable around room temperature. Analysis on the synthesized TiO₂ nanoparticles showed that the average crystallite size reported in the previous work is consistent with crystallite sizes observed in the transmission electron microscope images. Photoactivity examination showed that the DSSC sensitized using natural dye extracted with ethanol containing 20% distilled water on TiO₂ synthesized at 150°C has an efficiency of 5.7%, whereas the one on commercial TiO₂ P25 Degussa has an efficiency of 3.0%. The DSSC device sensitized using commercial dye on TiO₂ synthesized at 150°C has an efficiency of 4.4%, whereas the one on TiO₂ P25 Degussa has an efficiency of 4.0%. This result is promising for further development of the DSSC device using TiO₂ nanoparticles synthesized at low hydrothermal temperature and sensitized with the natural dye.     

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 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.     

Soft‐template synthesis of high surface area mesoporous titanium dioxide for dye‐sensitized solar cells

In the present work, 10 to 14 nm titania nanoparticles with high‐packing density are synthesized by the soft‐template method using a range of cationic surfactants including cetyl trimethylammonium bromide (CTAB), Sodium dodecyl sulfate (SDS), and dodecyl trimethylammonium bromide (DTAB). The synthesized nanoparticles are used as a photoanode material in dye solar cells. Density functional theory (DFT) simulations reproduce our experimental results of charge transfer and strong interaction between the TiO₂ and N719. N719‐TiO₂ complex establishes strong electrostatic bonding through H of the dye with the O of TiO₂ surface. Solar cell efficiency of 6.08% with 12.63 mA/cm², 793 mV, and 48.5% for short circuit current density, open circuit voltage, and fill factor, respectively, are obtained under 1 sun illumination for the dye‐sensitized solar cell (DSSC) using a film of mesoporous TiO₂ synthesized from the SDS surfactant. On the other hand, the 21 nm commercial TiO₂ powder (P25) device results in 4.60% efficiency under similar conditions. Electrochemical impedance spectroscopic studies show that the SDS device has lesser charge transport resistance than the other devices because of its higher surface area, packing density, and dye loading capacity. Our results show that employing high packing density‐based TiO₂ nanoparticles represents a commercially viable approach for highly beneficial photoanode development for future DSSC applications.     

Aqueous dye-sensitized solar cell based on new ruthenium diphenyl carbazide complexes

The major challenge of the operation of every solar cell based on dye including water splitting solar cell (WSSC) and dye sensitized solar cell (DSSC) is the using organic solvent medium which causes to decompose the solar cell structure, resulting environmental impact. Here, we synthesized and characterized two new ruthenium complexes with nitrogen and oxygen donor ligands for DSSC application which show good stability on TiO₂ surface in water solvent. Interestingly, the DSSC based on [Ru(dcbpy)₂(DPC)]Cl, where dcbpy = 4,4-dicarboxilic acid 2,2-bipyridin and DPC = diphenylcarbazide, was shown better efficiency in water than methanol dye loading as well as N3 as a benchmark sensitizer in the same condition. The DPC-based exhibited open circuit voltage (V_oc) of 0.63 V, short-circuit current density (J_sc) of 2.5 mA/cm² and fill factor (FF) of 70%, resulting an overall power efficiency of 1.12%. The incident-photon-to-current conversion efficiency (IPCE) value is also reached to 45% for [Ru(dcbpy)₂(DPC)]Cl in the same condition It is proposed that the ruthenium complex containing nitrogen and oxygen donor ligands is more stability on TiO₂ and prevent the decomposition of TiO₂ porous under water solvent condition.     

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.     

Enhancement in the photostability of natural dyes for dye‐sensitized solar cell (DSSC) applications: a review

The advancements in the generation of solar cells have created a landmark to design a cost‐effective, less weight, biocompatible, and environmental‐friendly solar cell. Dye‐sensitized solar cells (DSSCs) have become a topic of significant research in the recent years because of their imperative role in the zone of harvesting energy from the renewable source, and it appears to be a promising candidate for the triumph because of its low cost and ease of preparation. The use of synthetic dyes as a sensitizer for DSSC provides better efficiency and high durability. Unfortunately, they suffer from several margins such as higher cost and usage of toxic materials. These downsides have opened up for alternative sensitizer such as biocompatible natural dyes. Natural dyes contain plant pigments such as carotenoid, flavonoid, betalains, and chlorophyll that act as sensitizers (dye) for DSSC. But, the efficiency of natural dyes is not up to the mark mainly due to photoinstability of natural dye in the presence of sunlight that leads to photodegradation. The stability issues are mainly due to interaction of natural dyes with photoelectrode. The photoelectrodes in DSSC are semiconductor materials with superior characteristic of photocatalytic activity (PCA). The PCA of titanium dioxide (TiO₂) generates high energetic free electrons on the surface of film that produce free radical ions in contact with moisture. These free radical ions readily degrade the organic matter present nearby (natural dye in DSSC). Thus, the PCA of photoelectrode is responsible for the photodegradation of dyes causing photoinstability. The main objective of this review is to study the photoinstability of natural dyes in DSSC. In this regard, the DSSC is concentrated into sections, and the stability issues due to PCA of photoelectrode are studied individually in the view of considering the DSSC operating with iodide‐based electrolytes and platinum as counter electrode only. Various algae groups are featured as a study tool to overview the dye interaction with photoelectrode. It highlights the application of Z‐scheme of photosynthesis to DSSC to have a broader perception on the working of DSSC and also shows some of the ways for improving the stability of dyes by suppressing or reducing the PCA of photoelectrode. Copyright © 2017 John Wiley & Sons, Ltd.     

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.     

Dye sensitized solar cells incorporating obliquely deposited titanium oxide layers

Porous films of titanium oxide were deposited by oblique reactive electron beam evaporation. Both as-deposited and annealed samples of these films were structurally characterized by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The as-deposited films were found to consist of amorphous columns with a very fine structure while the annealed films consisted of polycrystalline anatase columns whose fine structure showed evidence of conglomeration. These films were sensitized with a photoactive dye and implemented into a dye sensitized solar cell (DSSC) configuration as the electron collecting electrode. Solar cells incorporating annealed titanium oxide films fabricated at deposition angles between 60° and 75° produced higher short current densities than conventional DSSC based on colloidal TiO₂ film measured under the same conditions. The best performing solar cell incorporating annealed titanium oxide films was found to have a photoelectric conversion efficiency of 4.1%.     

A quasi solid-state dye-sensitized solar cell containing binary ionic liquid and polyaniline-loaded carbon black

A quasi solid-state dye-sensitized solar cell (DSSC) is fabricated using 1-propyl-3-methylimidazolium iodide (PMII) and polyaniline-loaded carbon black (PACB) as the composite electrolyte. The electrolyte without added iodine is sandwiched between TiO₂ working electrode and platinum counter electrode (CE). A power conversion efficiency (η) of 5.81% is achieved with this type of cell. With the addition of 1-ethyl-3-methylimidazolium thiocyanate (EMISCN), a low-viscosity ionic liquid (IL), the cell with the binary ionic liquid (bi-IL) renders an efficiency of 6.15%, the best for any quasi solid-state DSSC without the addition of iodine. To fabricate a low cost DSSC using the bi-IL, the platinum layer of the counter electrode is replaced with a polymer layer, 3,3-diethyl-3,4-dihydro-2H-thieno-[3,4-b][1,4] dioxepine (PProdot-Et₂) through electrodeposition, and the corresponding DSSC shows an efficiency of 5.27%. At-rest stability of the quasi solid-state DSSC with bi-IL is compared with that of a liquid electrolyte DSSC at room temperature; the power conversion efficiency of the former shows a decrease of hardly 3% after 1000 h, while that of the latter shows a decrease of about 30%. The quasi solid-state cell shows unfailing durability at 70 °C.     

Novel dye based photoelectrode for improvement of solar cell conversion efficiency

We have explored the application of natural dyes extracted from beetroot in Dye sensitized solar cell (DSSC). The main pigment is betacyanin which was obtained by separation and purification from the extract. The photo electrochemical performance of the DSSC based on these dyes showed that the photo voltage and photocurrent 435 mV, 9.86 mA, respectively. The overall conversion efficiency of nano WO₃ coated TiO₂ dye-sensitized solar cells exhibits a higher conversion efficiency of 2.2%. The photo electrochemical performance of beetroot extract demonstrate that betacyanin dye was the most effectual component of the sensitizer for DSSC because of the simple preparation technique, widely available and low cheap cost.     

Algal buffer layers for enhancing the efficiency of anthocyanins extracted from rose petals for natural dye‐sensitized solar cell (DSSC)

Natural dye‐sensitized solar cells (DSSCs) are becoming promising candidates for replacing synthetic dyes. Anthocyanins, a flavonoid pigment which is responsible for the coloration in fruits and flowers, have shown productive results in employing them as natural dye for DSSC. But unfortunately, they exhibit low efficiency compared with synthetic dyes. Probing the reasons for the low efficiency of anthocyanin paves way for finding solution to increase the efficiency. This paper lists the important factors that are responsible for anthocyanin instability in DSSC. As a remedial measure, this paper introduces two buffer layer made of algal byproducts—sodium alginate and Spirulina. Rutile phase TiO₂ nanorods prepared by hydrothermal method were used as photoelectrode and are subsequently characterized by X ray diffraction, transmission electron microscopy, and optical studies. The use of sodium alginate above the photoelectrode has proved to improve the dye concentration in the film by introducing more hydroxyl groups on the surface of TiO₂. Anthocyanins extracted from rose petals using citric acid as solvent were used as dye for DSSC. Prior to the sensitization process with anthocyanin dye, the TiO₂ film (with sodium alginate) was sensitized with Spirulina. The chlorophylls, xanthophylls, phycocyanins, and amino acids present in Spirulina assist the anthocyanins to bond with TiO₂ efficiently. This helps in enhancing the efficiency of anthocyanins of rose dye from 0.99% to 1.47%.     

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.     

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.     

A new method to evaluate the feasibility of a dye in DSSC application

Search for better photo sensitizers has always been a challenge in the field of dye sensitized solar cell (DSSC). This paper suggests a new method to identify a good dye for DSSC through the evaluation of energy levels of dye–TiO₂ complex. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the complex are evaluated using cyclic voltammetry (CV) and spectroscopic technique. These energy levels have been used to predict the performance of the solar cell even without fabricating a cell. The authenticity of this method is also revalidated through the correlation of efficiency of practical cell. Copyright © 2017 John Wiley & Sons, Ltd.     

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.     

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.     

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.     

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.