Materials For Dye-sensitized Solar Cells Research Articles

Exfoliated Molybdenum Disulfide for TiO2 Based Dye Sensitized Solar Cells

Photochemical properties of transition metal dichalcogenides have been studied for more than 30 years, providing promising results as photocatalysts for energy applications. Recent works on these layered materials, particularly on molybdenum disulfide (MoS2), demonstrate that structural changes provoke different electron transitions in the system. MoS2 is a nonprecious metal, relatively earth abundant, and stable, which possess three main crystalline structure types: 2H, 3R and 1T; with hexagonal, rhombohedral, and trigonal unit cells, respectively. The thermodynamically stable 2H phase can be affected by chemical reactions such as the intercalation of small molecules. A common reactive used to complete this intercalation is n-butyllithium (n-BuLi), since lithium ions strongly interact with MoS2 layers. The quantity of lithium ions inside the layers may fluctuate depending on the duration of the reaction and the concentration of n-BuLi. This interaction produce a LixMoS2 specie that can react with water to exfoliate the MoS2 layers. MoS2 chemical treatments can affect the oxidation state of MoS2 and its photoabsorption behavior, hence altering its physicochemical properties. These changes provide the opportunity to produce new materials and interfaces, improving properties such as radiation absorption and electron mobility range. These two characteristics make exfoliated MoS2 an excellent material to be tested in dye sensitized solar cells (DSC), especially for the anode of this device. Solar cells normally use expensive organometallic ruthenium based dyes, which decompose under high temperature. In contrast, exfoliated MoS2 (E-MoS2) is a stable inorganic compound, which can also absorb in the visible region where a relatively high concentration of sunlight photons are available. Two approaches are studied in this work; 1) the use of exfoliated MoS2 as enhancer for electron transfer reactions and 2) as a substitute of ruthenium based dyes. Exhaustive physicochemical characterization of the MoS2 during the intercalation and exfoliation process was accomplished using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), Raman Spectroscopy and Ultraviolet and Visible Absorption (UV/Vis). The E-MoS2 was further tested in a dye sensitized solar cell. Finally, Electrochemical Impedance Spectroscopy (EIS) was done to obtain an insight of the electron process occurring in these two approaches. Previous results provide evidence of the potential use of exfoliated MoS2 in this photovoltaic devices E-MoS2 layers were produced after a lithium intercalation, exfoliation and purification synthesis, and an exhaustive physicochemical characterization was completed. The characterization demonstrated structural and chemical modifications, which affect electron transitions in the E-MoS2 product. DSCs devices were employed to test this E-MoS2 in two different setups: 1) as a layered formation with TiO2 thin film and 2) as a dye-substitute in a hybrid form with TiO2, both at the anode. In the first approach, an increase in photovoltage was detected on the DSC device during testing. Between a 10 fold increase at low wavelength (e.g. 330 nm) and two-fold at higher wavelength (e.g. 370nm). EIS results show lower resistances and higher effective lifetime. In this layered structured thin film between E-MoS2 and TiO2 a MoS2 optical-reflection effect may have caused an increases in the number of electron-hole pairs produced in the cell. Improvements in the electron transfer processes between the iodide/E-MoS2/TiO2 interphase are also a possible explanation of these results. Surprisingly, EIS shows higher resistances compared with the device having an E-MoS2-TiO2 layered structured thin film DSC. A possible explanation is a low E-MoS2 chemisorb process on TiO2, where the nanocomposite may be degraded while the photochemistry develops. We can conclude that E-MoS2 could offer an alternative material in DSC by enhancing the photochemical behavior, yet further studies are needed to attend stability concerns of the material.

A high performance cobalt sulfide counter electrode for dye-sensitized solar cells

A cobalt sulfide (CoS) thin film is deposited on fluorine doped SnO2 (FTO) glass by repetitive electrophoretic deposition (EPD) and ion exchange deposition (IED), then the thin film is treated with sodium borohydride or/and sulfuric acid solution. The film is used as the counter electrode of dye-sensitized solar cells (DSSCs), and is characterized by field emission scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy and Tafel measurements. The results show that the CoS counter electrode has a honeycomb-like morphology with large specific surface area, good catalytic activity for reduction of I3−, lower charge-transfer and series resistances, which result in the better electrochemical property of CoS counter electrodes. Under a simulated solar light irradiation of 100mWcm−2, the DSSC based on the CoS counter electrode achieves a power conversion efficiency of 7.72%, thus, synthesized CoS can serve as an efficient Pt-free counter electrode material for DSSCs.

Facile conversion of rutile titanium dioxide nanowires to nanotubes for enhancing the performance of dye-sensitized solar cells

It has been proven that growing longer nanowires (NWs) with larger surface areas is not always a feasible way to increase the conversion efficiency of dye-sensitized solar cells (DSSCs) because the photogenerated electrons and holes may have higher recombination rates as the electron travel distance increases. In this work, we employed a convenient hydrothermal selective etching method to convert single-crystalline rutile TiO2 NW arrays to nanotube (NT) arrays. The resulting NTs retain many characteristics of the initial unetched NWs, such as the orientation, crystal structure, and geometry size (in terms of length and outer diameter). When used as photoanode materials in DSSCs, the as-prepared TiO2 NTs have achieved 112.5% enhancement in the overall power conversion efficiency compared to the initial unetched NWs. The significantly improved performance is credited to 1) the newly created inner surfaces, 2) the increased surface roughness, and 3) the unchanged electron travel distance. Our findings shed light on a new, general way to enhance the performance of the current NW-based DSSCs by simply converting initial NWs to NTs.

Carbon black-derived graphene quantum dots composited with carbon aerogel as a highly efficient and stable reduction catalyst for the iodide/tri-iodide couple.

A microwave-assisted oxidative cleavage process is developed to prepare graphene quantum dots (GQDs) from carbon black. The size evolution of the resulting carbonaceous products is studied. In one hour, GQDs of a size less than 10 nm and thickness less than 2 nm are obtained. These GQDs are further composited with mesoporous carbon aerogels (CA) by a filtration process to form GQD-decorated CA composites (GQD/CA). The GQD/CA composite is applied as a catalyst electrode for the reduction of I3(-) to I(-), a critical electrolyte regeneration reaction in dye-sensitized solar cells (DSSCs). Also investigated are Pt electrodes, the expensive traditional counter electrode material for DSSCs, and plain CA electrodes for comparison. Based on data derived from cyclic voltammograms and Tafel plots, the GQD/CA composite exhibits catalytic efficiencies comparable to that of Pt electrodes and better than that of plain CA electrodes. The GQD/CA electrodes, however, surpass the Pt electrodes in terms of long-term stability. The cathodic current drops significantly after 500 cycles for the Pt and plain CA electrodes, whereas the cathodic current is slightly increased for the GQD/CA electrodes. The GQD/CA composite thus proves to be an inexpensive, efficient, and stable alternative to Pt as the counter electrode material for DSSCs.

Engineered Interfacial and Configuration Design of Double Layered SnO2@TiO2-ZnO Nanoplates Ternary Heterostructures for Efficient Dye-Sensitized Solar Cells

The engineered interfacial and configuration design of anode materials plays pivotal role in photovoltaic performance of solar cells. Here we demonstrated a double layered SnO2@TiO2-ZnO nanoplates composite films on fluorine-doped tin oxide (FTO) substrate as photoanodes for high-performance dye-sensitized solar-cells (DSSCs). The results indicate that DSSCs based on double layered SnO2@TiO2-ZnO nanoplates composite film (∼5.55%) show an obvious 29.1% increase of power conversion efficiency as compared to the single layered SnO2@TiO2 nanoparticles photoelectrode with the same thickness of ∼18.5μm. Intensity-modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS) as well as electrochemical impedance spectra (EIS) measurements show that the double layered SnO2@TiO2-ZnO nanoplates film has faster electron transport rate and slower electron recombination rate than the SnO2@TiO2 one. Furthermore, final power conversion efficiency has been optimized to reach up ∼6.37% (Jsc of 17.18mAcm−2,Voc of 742mV and FF of 0.50) for the double layered SnO2@TiO2-ZnO nanoplates film photoanodes with the introduction of additional SnO2 blocking layer which would suppress the electron recombination between FTO glass and electrolyte. One of the specific advantages of the unique structure is the engineered integration of different promising materials, which made it possible to take full advantages of the superior dye adsorption, charge collection, charge transfer dynamics as well as optical scattering simultaneously. This study provides a scheme to selective combination of specific semiconductors metal oxides, namely, SnO2, TiO2 and ZnO, into an ideal photoanode configuration according to the feasible electron injection and transport dynamics, which has been regarded as promising photoanode materials for DSSCs. Fundamentally, this unique structure not only enables the high-efficiency solar cells application, but also provides a scheme for the inspiration of materials integration and guidance of effective materials surface and interfacial modification.

Platinum-free binary Fe–Co nanofiber alloy counter electrodes for dye-sensitized solar cells

Exploration of cost-effective counter electrodes (CEs) has been a long-term objective for dye-sensitized solar cells (DSSCs). In the current work, binary Fe–Co nanofiber alloys are pioneerly synthesized by a low-temperature hydrothermal reduction approach and employed as CE materials for DSSCs. Owing to the rapid charge-transfer, electrical conduction, and electrocatalysis, the binary Fe–Co nanofiber alloy CE based DSSCs have reasonable power conversion efficiencies. An optimal efficiency of 5.06% is recorded from DSSC using FeCo2 nanofiber alloy CE. The relatively high conversion efficiency, low cost in combination with simple preparation, and scalable components demonstrates the potential use of Fe–Co alloy CEs in robust DSSCs.

Layer-by-layer self-assembly of TiO2 hierarchical nanosheets with exposed {001} facets as an effective bifunctional layer for dye-sensitized solar cells.

Layer-by-layer self-assembled TiO2 hierarchical nanosheets with exposed {001} facets have been successfully fabricated via a simple one-step solvothermal reaction. The anatase TiO2 layer-by-layer hierarchical nanosheets (TiO2 LHNs) exhibit favorable light scattering effect and large surface area, owing to their layer-by-layer hierarchical structure. When applied to the dye-sensitized solar cells (DSSCs), the layer-by-layer hierarchical structure with exposed {001} facet could effectively enhance light harvesting and dye adsorption, followed by increasing the photocurrent of DSSCs. As a result, the photoelectric conversion efficiency (η) of 7.70% has been achieved for the DSSCs using TiO2 LHNs as the bifunctional layer, indicating 21% improvement compared to the pure Degussa P25 (6.37%) as photoanode. Such enhancement can be mainly ascribed to the better light scattering capability of TiO2 LHNs, higher dye adsorption on TiO2 LHN {001} facets, and longer lifetime of the injected electrons in TiO2 LHNs compared to P25, which are examined by UV-vis spectrophotometry and electrochemical impedance spectroscopy under the same conditions. These remarkable properties of TiO2 LHNs make it a promising candidate as a bifunctional scattering material for DSSCs.

Metal sulfide counter electrodes for dye-sensitized solar cells: A balanced strategy for optical transparency and electrochemical activity

Dye-sensitized solar cells (DSSCs) have obtained exciting progress in improving energy conversion efficiency and cutting material cost in recent years. It is found that many kinds of inorganic compounds have promising potential to replace platinum as counter electrode materials for DSSCs. Actually, to a thin film electrode, preparation of the thin film is the same important as choice of active materials, because quality of the films has a direct effect on electrochemical and optical performance of the final counter electrodes. In this paper, a general strategy is developed to prepare transparent and high-efficient metal sulfide counter electrodes. In the route, the Group VIIIB metal sulfides are formed as compact, homogenous and stable films on fluorine-doped tin oxide conductive glass from a precursor organic solution by spin coating, and the film thickness can be readily converted to reach the balance between optical transparency and electrochemical activity. Among the Group VIIIB metal sulfides, the nickel sulfide film with the thickness of 100 nm shows the high transparency and energy conversion efficiency of 7.37%, higher than that of the DSSC using platinum electrode. The results provide a new and facile alternative to prepare high-efficient and transparent sulfide counter electrodes for DSSCs.

Podlike N-doped carbon nanotubes encapsulating FeNi alloy nanoparticles: high-performance counter electrode materials for dye-sensitized solar cells.

Podlike nitrogen-doped carbon nanotubes encapsulating FeNi alloy nanoparticles (Pod(N)-FeNi) were prepared by the direct pyrolysis of organometallic precursors. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel polarization measurements revealed their excellent electrocatalytic activities in the I(-)/I3(-) redox reaction of dye-sensitized solar cells (DSSCs). This is suggested to arise from the modification of the surface electronic properties of the carbon by the encapsulated metal alloy nanoparticles (NPs). Sequential scanning with EIS and CV further showed the high electrochemical stability of the Pod(N)-FeNi composite. DSSCs with Pod(N)-FeNi as the counter electrode (CE) presented a power conversion efficiency of 8.82%, which is superior to that of the control device with sputtered Pt as the CE. The Pod(N)-FeNi composite thus shows promise as an environmentally friendly, low-cost, and highly efficient CE material for DSSCs.

Podlike N‐Doped Carbon Nanotubes Encapsulating FeNi Alloy Nanoparticles: High‐Performance Counter Electrode Materials for Dye‐Sensitized Solar Cells

AbstractPodlike nitrogen‐doped carbon nanotubes encapsulating FeNi alloy nanoparticles (Pod(N)‐FeNi) were prepared by the direct pyrolysis of organometallic precursors. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel polarization measurements revealed their excellent electrocatalytic activities in the I−/I3− redox reaction of dye‐sensitized solar cells (DSSCs). This is suggested to arise from the modification of the surface electronic properties of the carbon by the encapsulated metal alloy nanoparticles (NPs). Sequential scanning with EIS and CV further showed the high electrochemical stability of the Pod(N)‐FeNi composite. DSSCs with Pod(N)‐FeNi as the counter electrode (CE) presented a power conversion efficiency of 8.82 %, which is superior to that of the control device with sputtered Pt as the CE. The Pod(N)‐FeNi composite thus shows promise as an environmentally friendly, low‐cost, and highly efficient CE material for DSSCs.

The Role of Physical Techniques on the Preparation of Photoanodes for Dye Sensitized Solar Cells

Dye sensitized solar cells (DSSCs) have attracted numerous research, especially in the context of enhancing their efficiency and durability, due to the low-cost and environmentally friendly nature of photovoltaic (PV) technology. The materials in DSSCs are vital towards the realization of these goals, since many of the important components are influenced by their respective preparation and deposition methods. This review aims to detail the research and development aspects of the different physical methods with the purpose of evaluating their prospects and corresponding limitations. The diversity of consideration and criteria includes thin film applications, material characteristics, and process technology that need to be taken into account when selecting a specific deposition method. Choosing a deposition method is not as simple as it seems and is rendered quite complicated due to various factors. Usually, a researcher will evaluate techniques based on factors such as the different preparations and deposition technology with materials’ and substrates’ type, specified applications, costs, and efficiencies.

Research and Development Aspects on Chemical Preparation Techniques of Photoanodes for Dye Sensitized Solar Cells

The importance of dye sensitized solar cells (DSSCs) as a low-cost and environmentally friendly photovoltaic (PV) technology has prompted many researchers to improve its efficiency and durability. The realization of these goals is impossible without taking into account the importance of the materials in DSSCs, so the focus on the preparation/deposition methods is essential. These methods can be either chemical or physical. In this study, the chemical applied methods that utilize chemical reaction to synthesize and deposit the materials are covered and categorized according to their gas phase and liquid phase precursors. Film processing techniques that can be used to enhance the materials' properties postpreparation are also included for further evaluation in this study. However, there is a variety of consideration, and certain criteria must be taken into account when selecting a specific deposition method, due to the fact that the fabrication conditions vary and are unoptimized.

Low-temperature self-assembled vertically aligned carbon nanofibers as counter-electrode material for dye-sensitized solar cells

Low-temperature AC–DC PECVD is employed for direct growth of vertically aligned carbon nanofibers (VACNFs) on ordinary transparent conductive glass as counter-electrode material for dye-sensitized solar cells (DSSCs). To the best of our knowledge, this is the first report on utilization of VACNFs grown directly on ordinary FTO-coated glass as a cost-effective catalyst material in DSSCs. According to the FESEM images, the as-grown arrays are well aligned and dense, and offer uniform coverage on the surface of the substrate. In-plane and out-of-plane conductivity measurements reveal their good electrical conductivity, and Raman spectroscopy suggests a high number of electrocatalytic active sites, favoring charge transport at the electrolyte/electrode interface. Hybrid VACNF/Pt electrodes are also fabricated for performance comparison with Pt and VACNF electrodes. X-ray diffraction results verify the crystallization of Pt in hybrid electrodes and further confirm the vertical alignment of carbon nanofibers. Electrochemical characterization indicates that VACNFs provide both high catalytic and good charge transfer capability, which can be attributed to their high surface area, defect-rich and one-dimensional structure, vertical alignment and low contact resistance. As a result, VACNF cells can achieve a comparable performance (∼5.6%) to that of the reference Pt cells (∼6.5%). Moreover, by combination of the excellent charge transport and catalytic ability of VACNFs and the high conductivity of Pt nanoparticles, hybrid VACNF/Pt cells can deliver a performance superior to that of the Pt cells (∼7.2%), despite having a much smaller amount of Pt loading, which raises hopes for low-cost large-scale production of DSSCs in the future.

Electrospun Hierarchical TiO2 Nanorods with High Porosity for Efficient Dye-Sensitized Solar Cells

Ultraporous anatase TiO2 nanorods with a composite structure of mesopores and macropores fabricated via a simple microemulsion electrospinning approach were first used as photoanode materials for high-efficiency dye-sensitized solar cells (DSSCs). The special multiscale porous structure was formed by using low-cost paraffin oil microemulsion droplets as the soft template, which can not only provide enhanced adsorption sites for dye molecules but also facilitate the electrolyte diffusion. The morphology, porosity, and photovoltaic and electron dynamic characteristics of the porous TiO2 nanorod based DSSCs were investigated in detail by scanning electron microscopy (SEM), N2 sorption measurements, current density-voltage (J-V) curves, UV-vis diffuse reflectance spectra, electrochemical impedance spectroscopy (EIS), intensity modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS), and open-circuit voltage decay (OCVD) measurements. The results revealed that, although fewer amounts of dyes were anchored on the porous TiO2 nanorod films, they exhibited stronger light scattering ability, fast electrolyte diffusion, and extended electron lifetime compared to the commercial P25 nanoparticles. A power conversion efficiency of 6.07% was obtained for the porous TiO2 nanorod based DSSCs. Moreover, this value can be further improved to 8.53% when bilayer structured photoanode with porous TiO2 nanorods acting as the light scattering layer was constructed. This study demonstrated that the porous TiO2 nanorods can work as promising photoanode materials for DSSCs.

High-efficient dye-sensitized solar cells with all-inorganic Cu2ZnSnSe4 counter-electrode by ligand exchange

For the first time, we synthesized all-inorganic Cu2ZnSnSe4 nanocrystals (CZTSe NCs) by ligand exchange strategy using a simple metal-free chalcogenide compound [(NH4)2S] as the inorganic ligand. The results of I–V and Hall-effect measurement illuminated that all-inorganic CZTSe films reveal the excellent electron-transfer performance. When the all-inorganic CZTSe NCs films used as counter electrode (CE) in dye-sensitized solar cells (DSSCs), the photocurrent density increases significantly from 4.48 (OLA-capped CZTSe NCs) to 14.17mA/cm2 (all-inorganic CZTSe NCs). A higher efficiency of η=7.06% was achieved for all-inorganic CZTSe films as CE in DSSCs. The photovoltaic results showed that high temperature annealing can be avoided for all-inorganic CZTSe films as CE. Cyclic voltammetry (CV) results and electrochemical impedance spectroscopy (EIS) showed the all-inorganic CZTSe films as CE exhibited good electrocatalytic activity and high conductivity, which demonstrated that all-inorganic CZTSe NCs would serve as an effective CE material in DSSCs.

Highly efficient dye-sensitized solar cell developed by using sheet like TiO2 prepared by a novel route

A novel and facile route has been developed for preparing TiO2 nanopowder with crystalline anatase phase. This titanium dioxide powder prepared by using diethylamine (DEA) as capping agent, (TiO2)DEA, has been characterized for its crystalline structure, surface morphology, and optical property by XRD, SEM, and absorption spectrum respectively. SEM micrograph of (TiO2)DEA nano-powder revealed sheet like structure, XRD showed the anatase crystalline form and absorption spectrum provided the optical band gap of the prepared material as Eg ≈ 3.27 eV. This (TiO2)DEA nanopowder was used to prepare its thin film photoelectrode using doctor's blade method. The solar cell constructed with this semiconductor electrode sensitized by N719 provided short circuit photocurrent (Jsc) 7.28 mA cm−2, open circuit potential (Voc) 750 mV, fill factor (FF) 0.74 and overall conversion efficiency (η) 4.0% under illumination with light of 100 mW cm−2 intensity. The maximum IPCE obtained with such cell was 50%. These significantly high values of cell parameters have proven that the method developed during present work provided a very good quality (TiO2)DEA powder for its application in dye-sensitized solar cell (DSSC). For comparison sake, the TiO2 powder was also prepared using ammonia, instead of DEA, as capping agent keeping all other experimental conditions identical. When this (TiO2)am powder was used as photoanode and sensitized by N719, the cell outputs achieved were Jsc = 6.20 mA cm−2, Voc = 640 mV, FF = 0.72 and η = 2.86% under illumination with light of 100 mW cm−2 intensity. The maximum IPCE obtained with such cell was 42%. This has clearly established that the quality of (TiO2)DEA was superior than (TiO2)am for its use as photoanode material in DSSC.

Computational design of concomitant type-I and type-II porphyrin sensitized solar cells

Structures and electronic properties of porphyrins with various Donor (D)-Acceptor (A) functionalization adsorbed on TiO2 (anatase) nanoparticles are studied using DFT calculations. Adsorption of porphyrin leads to a substantial loss of planarity (puckering) for the porphyrin rings due to the stabilization of the system by the interaction of the lone-pair of electrons of the N-atoms of porphyrin with the Ti-atoms of anatase. For free porphyrin, the mode of binding to anatase is from the top-site, while for the binding of D-A functionalized porphyrin, side-wise interactions are stabilized via anchoring groups on the A (-SO3H, -PO3H2 and -CO2H). Adsorption of porphyrin on TiO2 changes the relative ordering of HOMO and LUMO levels compared to that of the free molecule and bare TiO2 nanoparticles which critically effects their performance for dye sensitized solar cells (DSSCs). The relative energy differences between the LUMO of the free molecule and LUMO of molecule···TiO2 complex (ε2) and LUMO of molecule···TiO2 complex and CB (conduction band) of bare TiO2 (ε3) are proposed as two key parameters for determining the suitability of the material for functioning as a DSSC material. Coupling of the porphyrin ring with nanoparticles leads to the appearance of additional optically-active states due to dye → TiO2 charge-transfer (CT) transitions. This leads to a possibility for these dyes to act as type-II DSSC materials as well. We suggest that there exists no such general rule that only different sets of molecules are suitable for type-I and type-II DSSCs. Concentration dependent UV-Vis absorption spectra measurements can be a simple experimental test to detect a mechanistic switch-over between type-I and type-II DSSC processes in dyes.

Efficiency enhancement of dye-sensitized solar cells (DSSCs) using ligand exchanged CuInS2 NCs as counter electrode materials

Exploring inorganic ligand capped nanocrystals (NCs) as counter electrode (CE) materials for dye-sensitized solar cells (DSSCs) with high conversion efficiency. Here, we reported the preparation of inorganic ligand capped CuInS2 NCs through a ligand exchange strategy. After ligand exchange, the organic ligand capped on the surface of CuInS2 NCs were exchanged to inorganic ligand S2− without changing the shape, size distribution and crystal structure of CuInS2 NCs. When used as CE materials for dye-sensitized solar cells, the inorganic ligand capped CuInS2 NCs films showed higher electrocatalytic activity and electrical conductivity, thus can significantly improve the efficiency of DSSCs. It should be noted that the conversion efficiency of the DSSC increased by 17 times after the organic ligand capped CuInS2 NCs were exchanged with the inorganic ligand. The study in this work may pave a new pathway to explore highly electrical conductivity materials for DSSCs.

Synthesis and application of core-shell Au–TiO2nanowire photoanode materials for dye sensitized solar cells

Dye sensitized solar cells (DSSCs) have been widely studied as alternatives for generation of electricity from sunlight due to their efficiency and cost effectiveness. Increasing the electron transport out of the metal oxide is important in achieving higher efficiency. Enhancing light absorption can also improve cell efficiency. The motive of this work was to synthesize and use Au–TiO2 core-shell nanowires as anode materials in DSSCs in order to increase cell efficiency by enhancing electron transport out of the oxide and/or increasing light collection efficiency. TiO2 nanotubes were first grown in alumina templates using a sol–gel method. Gold nanowires were subsequently grown in the pores of these tubes by electrodeposition. Resulting nano-structured arrays were characterized using electron microscopy and diffraction techniques; the results show that the wires were highly aligned and well separated. The current–voltage (J–V) behavior for the Au–TiO2 core-shell nanowire based DSSCs was compared to the J–V data for TiO2 nanotube based DSSCs, indicating substantial improvements upon incorporation of the Au core nanowires. TiCl4 treatment of the Au–TiO2 core-shell nanowire structures resulted in further efficiency improvements.

Trends in patent applications for dye-sensitized solar cells

Dye-sensitized solar cell (DSC) technology has grown into a massive field of research and development with a fast increasing number of scientific publications and patent applications. We have created a database for patents and patent applications that deal with dye-sensitized solar cell technology. In this paper the database has been used to analyze the number of patent applications over time, as well as technical, organizational, and geographical trends in patent applications for dye-sensitized solar cells. Activity in relation to DSC patents seriously took off after the millennium, with the majority of DSC patent applications coming from Asia. Almost 90% of the documents in the database derive from Japan, China, and Korea. From a technical perspective, approximately 75% of the DSC patent applications deal with DSC materials, mainly semiconductor materials, dyes, electrolytes, and device substrates. The DSC patent situation is complex and we recommend any potential manufacturer of DSC devices and/or DSC components to carefully analyze their freedom-to-operate.