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Materials with different nanostructures can have diverse physical properties, and they exhibit unusual properties as compared to their bulk counterparts. Therefore, the structural control of desired nanomaterials is intensely attractive to many scientific applications. In this brief review, we mainly focus on reviewing our recent reports based on the materials of graphene and the transition metal chalcogenide, which have various low-dimensional nanostructures, in relation to the use of electrocatalysts in electrochemical energy applications; moreover, related literatures were also partially selected for discussion. In addition, future aspects of the nanostructure design related to the further enhancement of the performance of pertinent electrochemical energy devices will also be mentioned.

Boron nitride (BN) is newly introduced as a non-metal electro-catalyst for the counter electrode of a dye-sensitized solar cell (DSSC). By applying a conductive binder of sulfonated poly(thiophene-...

Since Prof. Grätzel and co-workers achieved breakthrough progress on dye-sensitized solar cells (DSSCs) in 1991, DSSCs have been extensively investigated and wildly developed as a potential renewable power source in the last two decades due to their low cost, low energy-intensive processing, and high roll-to-roll compatibility. During this period, the highest efficiency recorded for DSSC under ideal solar light (AM 1.5G, 100 mW cm−2) has increased from ~7% to ~14.3%. For the practical use of solar cells, the performance of photovoltaic devices in several conditions with weak light irradiation (e.g., indoor) or various light incident angles are also an important item. Accordingly, DSSCs exhibit high competitiveness in solar cell markets because their performances are less affected by the light intensity and are less sensitive to the light incident angle. However, the most used catalyst in the counter electrode (CE) of a typical DSSC is platinum (Pt), which is an expensive noble metal and is rare on earth. To further reduce the cost of the fabrication of DSSCs on the industrial scale, it is better to develop Pt-free electro-catalysts for the CEs of DSSCs, such as transition metallic compounds, conducting polymers, carbonaceous materials, and their composites. In this article, we will provide a short review on the Pt-free electro-catalyst CEs of DSSCs with superior cell compared to Pt CEs; additionally, those selected reports were published within the past 5 years.

The production of hydrogen via the water splitting process is one of the most promising technologies for future clean energy requirements, and one of the best related challenges is the choice of the most highly efficient and cost effective electrocatalyst. Conventional electrocatalysts based on precious metals are rare and very-expensive for large-scale production of hydrogen, demanding the exploration for low-cost earth abundant alternatives. In this context, extensive works from both theoretical and experimental investigations have shown that two-dimensional (2D) layered materials have gained considerable attention as highly effective electrocatalytic materials for electrical-driven hydrogen production because of their unique layered structure and exciting electrical properties. This review highlights recent advancements on 2D layered materials, including graphene, transitional metal dichalcogenides (TMDs), layered double hydroxides (LDHs), MXene, and graphitic carbon nitride (g-C3N4) as cost-effective and highly efficient electrocatalysts for hydrogen production. In addition, some fundamental aspects of the hydrogen evolution reaction (HER) process and a wide ranging overview on several strategies to design and synthesize 2D layered material as HER electrocatalysts for commercial applications are introduced. Finally, the conclusion and futuristic prospects and challenges of the advancement of 2D layered materials as non-precious HER electrocatalysts are briefly discussed.

The formation of thin and uniform capacitive layers for fully interacting with an electrolyte in a supercapacitor is a key challenge to achieve optimal capacitance. Here, we demonstrate a binder-free and flexible supercapacitor with the electrode made of cobalt oxide nanoparticle (CoO NP)-wrapped graphene hollow nanoballs (GHBs). The growth process of Co(OH)2 NPs, which could subsequently be thermally annealed to CoO NPs, was monitored by in situ electrochemical liquid transmission electron microscopy (TEM). In the dynamic growth of Co(OH)2 NPs on a film of GHBs, the lateral formation of fan-shaped clusters of Co(OH)2 NPs spread over the surface of GHBs was observed by in situ TEM. This CoO-GHBs/CC electrode exhibits high specific capacitance (2238 F g-1 at 1 A g-1) and good rate capability (1170 F g-1 at 15 A g-1). The outstanding capacitive performance and good rate capability of the CoO-GHBs/CC electrode were achieved by the synergistic combination of highly pseudocapacitive CoO and electrically conductive GHBs with large surface areas. A solid-state symmetric supercapacitor (SSC), with CoO-GHBs/CCs used for both positive and negative electrodes, exhibits high power density (6000 W kg-1 at 8.2 Wh kg-1), high energy density (16 Wh kg-1 at 800 W kg-1), cycling stability (∼100% capacitance retention after 5000 cycles), and excellent mechanical flexibility at various bending positions. Finally, a serial connection of four SSC devices can efficiently power a red light-emitting diode after being charged for 20 s, demonstrating the practical application of this CoO-GHBs/CC-based SSC device for efficient energy storage.

Dye-sensitized solar cell (DSSC) is one of the third generation solar cells converting solar light into electricity that attracted a remarkable research interest globally due to their simple device fabrication processes in ambient conditions and reasonable cell efficiency for commercialization; moreover, the advantages on colorfulness, possible plasticity, and high conversion efficiencies under indoor illumination also render DSSC to play a crucial role in energy-harvesting systems for green buildings. To eliminate the electrolyte leakage issues in traditional DSSCs (i.e., cells with organic solvent-based electrolytes), new class of ionic liquids, namely poly(ionic liquid)s, are recently investigated and used as the quasi/all–solid state electrolyte to improve the cell durability. Herein, we give a short review on the poly(ionic liquid)s to be used as the quasi/all–solid state electrolytes in DSSCs. Finally, the future perspectives for the development of poly(ionic liquid)s for DSSCs are also briefly discussed.

Nitrogen-doped graphene hollow nanoballs (N-GHBs) were synthesized in chemical vapor deposition (CVD) reaction using melamine as a chemical precursor via an in situ nitrogen-doping approach. In the CVD reaction, N-GHBs were deposited directly on carbon cloth (CC) to be used as an efficient metal-free electrocatalyst for dye-sensitized solar cell (DSSC) applications. The highly curved N-GHBs could avoid the self-assembly restacking of planar graphene sheets, which usually occurred during the film preparation. Keeping oxygen contaminations from N-GHBs, the characteristic electrical conductivity of graphene was preserved in the as-synthesized N-GHBs. By controlling the evaporation temperature of melamine, the nitrogen-doping content of 8.7–14.0% and different nitrogen-doped configurations in N-GHBs could be adjusted. The catalytic activities of different nitrogen-doped states in N-GHBs toward the triiodide (I 3− ) reduction in DSSCs were investigated, revealing that the pyridinic and quaternary nitrogens, rather than the total nitrogen doping level, in N-GHBs are mainly responsible for their catalytic activities in DSSCs. For solar cell applications, the high surface area and heteroatomic nitrogens of GHBs can remarkably improve the catalytic activity toward the triiodide reduction, lower the charge-transfer resistance, and enhance the corresponding photovoltaic performance (7.53%), which is comparable to that (7.70%) of a standard sputtered Pt counter electrode-based cell. These exceptional properties allow N-GHBs/CC to act as a promising electrocatalytic electrode for DSSC and other electrochemical energy applications.

We have synthesized a metal-free composite ink that contains graphene dots (GDs) and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) that can be used on paper to serve as the counter electrode in a flexible dye-sensitized solar cell (DSSC). This paper-based GD/PEDOT:PSS electrode is low-cost, light-weight, flexible, environmentally friendly, and easy to cut and process for device fabrication. We determined the GD/PEDOT:PSS composite effectively fills the dense micro-pores in the paper substrate, which leads to improved carrier transport in the electrode and a 3-fold enhanced cell efficiency as compared to the paper electrode made with sputtered Pt. Moreover, the DSSC with the paper electrode featuring the GD/PEDOT:PSS composite did not fail in photovoltaic tests even after bending the electrode 150 times, whereas the device made with the Pt-based paper electrode decreased in efficiency by 45% after such manipulation. These exceptional properties make the metal-free GD/PEDOT:PSS composite ink a promising electrode material for a wide variety of flexible electronic applications.

A titanium oxide-selenide (TiO1.1Se0.9) composite material was successfully obtained on a flexible substrate of carbon cloth (CC); this TiO1.1Se0.9/CC electrode was used as the counter electrode (CE) in a dye-sensitized solar cell (DSSC). Each carbon fiber in the CC was wrapped with a composite layer of TiO1.1Se0.9, and the composite layer contained TiO1.1Se0.9 nanospheres and one-dimensional (1D) nanorods. Thus, each carbon fiber with its TiO1.1Se0.9 layer has a hierarchical core–shell structure, in which the carbon fiber acts as a one-dimensional conductive core for electron transfer and the TiO1.1Se0.9 layer around the fiber functions as an electro-catalytic shell. In iodide-based electrolyte, the DSSC with the TiO1.1Se0.9/CC exhibits a power conversion efficiency (η) of 9.47%, which is higher than cells with CEs of Pt/CC (7.75%) and pristine TiO2/CC (4.90%). Under dim light conditions, the best TiO1.1Se0.9/CC electrode rendered its cell an η of 10.00% at 0.5 sun and the best η of 10.39% at 0.1 sun. In cobalt-based electrolytes, a DSSC with the TiO1.1Se0.9/CC shows an attractive η of 10.32% at 1.0 sun, the best η of 10.47% at 0.5 sun, and an impressive η of 10.20% at 0.1 sun. The earth abundant and low-cost TiO1.1Se0.9 is a promising alternative to Pt for the CE of a DSSC in both iodide and cobalt electrolytes.

A novel organic sensitizer, coded CR147, is applied to sensitize a ZnO–based dye–sensitized solar cell (DSSC). The common problem of ZnO dissolution and Zn 2+ /dye agglomeration, caused by the use of ruthenium–based dyes, is solved by the application of this CR147 dye. The highest power conversion efficiency ( η ) of 4.77% is achieved for the DSSC using a photoanode with a film of commercial ZnO nanoparticles (C ZnO) and the CR147 dye, while the η is only 3.41% for the DSSC with the commercial N719 dye. The cell performance with the CR147 dye is further improved by using a photoanode with the double layer ZnO film (D–ZnO), composed of an underlayer with coral–like ZnO nanocrystals and an overlayer with hexagonal club–like ZnO submicrocrystals. The DSSC with the D–ZnO film exhibits an η of 6.89%, which is ca. 45% higher than that of the DSSC with the C ZnO film (4.77%). This higher efficiency is attributed to the superior charge transfer and light–scattering abilities provided by coral–like ZnO nanocrystals and hexagonal clubs–like ZnO submicrocrystals, respectively, with reference to these parameters of C ZnO.

We synthesize heteroatoms-doped graphene hollow nanoballs (GHBs) on flexible carbon cloth (CC) substrates via chemical vapor deposition (CVD) reaction to be used as an efficient non-noble electrocatalyst in dye-sensitized solar cells (DSSCs). The as-synthesized heteroatoms-doped GHBs/CC, including nitrogen-doped GHBs, sulfur-doped GHBs, and nitrogen and sulfur-codoped GHBs (denoted by N-GHBs/CC, S-GHBs/CC and N,S-GHBs/CC, respectively), are used as an efficient counter electrode (CE) in DSSCs. Unlike planar graphene sheets, the highly curved GHBs can avoid self-assembly restacking to provide high surface areas for electrocatalytic reactions. In addition, the heteroatomic incorporation in GHBs can reduce the charge-transfer resistance to enhance the electrocatalytic activity. Among these doped GHB samples, N,S-GHBs show the best catalytic performance due to the synergistic effect from both electronic and geometric changes, caused by the N- and S-dopings, respectively. The DSSC with a N,S-GHB CE exhibits the power conversion efficiency of 9.02%, comparable to that (8.90%) of a Pt-based counterpart.

A hierarchical cobalt oxide (Co3O4)-functionalized silicon carbide nanowire (SiC NW) array electrode is synthesized on 4H-SiC(0001) substrates and investigated for use in the oxygen evolution reaction (OER) of water splitting. Ni-catalyzed chemical vapor deposition is employed to obtain vertically-aligned SiC NWs, and electrodeposition is used to functionalize the nanowires with hierarchical Co3O4 nano-clusters and a thin Co3O4 layer on the top side and the side-walls of the NWs, respectively. By using the Co3O4-functionalized SiC NW electrode for OER, the overpotential required to drive an anodic current density (J(anodic)) of 10 mA cm(-2) is 0.22 V, a value much lower than those of Co3O4 nano-clusters (0.42 V), of bare SiC NWs (1.27 V) electrodes and of Pt foil (0.56 V). The overpotential value of 0.22 V is among the most active for the noble metal-free electro-catalytic electrode to produce J(anodic) of 10 mA cm(-2). The deposition of Co3O4 on the SiC NW substrate produces an extremely hydrophilic surface, which improves the charge transfer characteristics at the interface between the electrode and the aqueous electrolyte. Moreover, the vertically-aligned SiC NWs provide a directional charge transport route along the nanowire length, as seen from a lower charge transfer resistance (R-ct) in the Co3O4-functionalized SiC NW electrode compared to the Co3O4-functionalized SiC electrode under the same OER operating conditions. Finally, the Co3O4-functionalized SiC NW electrode maintains stable performance in an alkaline electrolyte (i.e., 1 M KOH aqueous solution) during continuous electrolysis testing over 16 h. The outstanding electro-catalytic performance and stability make the Co3O4-functionalized SiC NW electrode a promising noble metal-free electro-catalytic electrode for the OER and other renewable energy applications. (C) 2017 Elsevier Ltd. All rights reserved.

Graphene dots (GDs) are used for enhancing the performance of the poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS)-based counter electrodes in Pt-free dye-sensitized solar cells (DSSCs). As compared to PEDOT:PSS CEs, GD–PEDOT:PSS films possess a rough surface morphology, high conductivity and electrocatalytic activity, and low charge-transfer resistance toward I − /I 3 − redox reaction, pushing cell efficiency to 7.36%, which is 43% higher than that of the cell with PEDOT:PSS CEs (5.14%). Without much impact on efficiency, the DSSCs with GD–PEDOT:PSS CEs work well under low-light conditions (light intensity −2 and angle of incidence >60°), such as indoor and low-level outdoor lighting and of the sun while the other traditional cells would fail to work. The concurrent advantage in low cost in Pt-free materials, simple fabrication processes, comparable efficiency with Pt CEs, and high performance under low-light conditions makes the DSSC with GD–PEDOT:PSS CEs suitable to harvest light for a diverse range of indoor and low-level outdoor lighting locations.

A honeycomb-like composite film of nitrogen-doped graphene and poly(3,4-ethylenedioxythiophene) (NGr/PEDOT) was prepared as a highly-efficient catalytic material for the counter electrode (CE) of a dye-sensitized solar cell (DSSC). The NGr was intended for increasing the conductivity and electrocatalytic ability of the composite film, and the PEDOT was used for a strong adhesion of the composite film to the substrate and for large surface area. The DSSC with the NGr/PEDOT composite CE exhibited a power conversion efficiency ( η ) of 8.30±0.03% for front-side illumination and 6.10±0.02% for back-side illumination. The DSSC with a Pt CE showed an η of 8.17±0.01% for front-side illumination and 5.76±0.05% for back-side illumination. The composite catalytic film of NGr/PEDOT is a low-cost alternative for replacing the conventional and expensive Pt film. Another DSSC was fabricated, in which its counter electrode contained a flexible Ti foil as the substrate and the NGr/PEDOT film as the catalytic film. This DSSC with its flexible CE exhibited an η of 8.53±0.02%.

Mesoporous TiO2 spheres (hereafter, MSs) were synthesized and incorporated into the photoanode of a quasi-solid state dye-sensitized solar cell (QSS-DSSC) containing an air stable ionic liquid electrolyte, namely 1-propyl-3-methylimidazolium iodide (PMII) along with triethylmethylammonium methyl sulfate (TEMAMS) (65 : 35 = v/v), in order to improve its performance. The presence of large pores in the MS, as confirmed using a high resolution scanning electron microscope (HR-SEM) and a mercury porosimeter, facilitates the penetration of QSS-electrolytes into the thin film, whereas their high surface area (108.1 m2 g−1) helps for high dye loading. Further, the large particle size increases the scattering ability of incident light leading to an excellent increment in the number of photons. The performance of DSSCs containing bi-ionic liquid (bi-IL) based electrolytes, namely, PMII/TEMAMS and PMII/1-ethyl-3-methylimidazolium tetrafluoborate (EMIBF4), with the addition of 0.2 M iodine, 0.4 M N-methylbenzimidazole (NMBI), and 0.15 M guanidiniumthiocyanate (GuSCN), was compared, where the DSSC based on PMII/TEMAMS bi-ILs demonstrates superior efficiency (6.18%) than that of PMII/EMIBF4 based one (4.53%). The DSSC with PMII/TEMAMS shows extraordinary durability and unfailing stability for 1200 h even though it was stored in the dark at 50 °C. Further, the PMII/TEMAMS bi-IL electrolyte shows a gel-state at room temperature naturally without adding any gelators or polymers.

Efficient titanium nitride/titanium oxide (TiN/TiO2) composite photoanodes have been proposed for the use not only in dye-sensitized solar cells (DSSCs) but also for water splitting. When the TiN precursor films were sintered at 500 °C for 0.5 to 4 h, they were partially converted to crystalline TiO2 containing both rutile and anatase phases. For the DSSCs, higher TiN content in the photoanodes resulted in a more negative flat-band potential and higher conductivity but lower surface area for the dye adsorption; therefore, the increase in VOC and FF but the decrease in JSC value were observed. The best DSSC, with TiN/TiO2 composite photoanode annealed for 1 h, exhibited a power conversion efficiency of 7.27%, while the cell without TiN, i.e., the cell with a standard P25 photoanode, showed an efficiency of 7.02%. For the water splitting, higher TiN content in the photoanodes resulted in better triggering of the H2O electrolysis, but less photo-induced current response at UV light illumination. Considering the water splitting performance measured at AM 1.5G, the TiN/TiO2 composite photoanode annealed for 1 h showed the best photo-induced current density (Jpho) of 0.12 mA cm−2, as compared with that of the standard P25 film. With the TiN/TiO2 composite photoanode annealed for 1 h, both DSSCs and water splitting electrochemical devices achieved their best performance independently.

Dye-sensitized solar cells (DSSCs) are fabricated using low-cost materials and a simple fabrication process; these advantages make them attractive candidates for research on next generation solar cells. In this type of solar cell, dye-sensitized metal oxide electrodes play an important role for achieving high performance since the porous metal oxide films provide large specific surface area for dye loading and the dye molecule possesses broad absorption covering the visible region or even part of the near-infrared (NIR). Recently, metal-free sensitizers have made great progress and become the most potential alternatives. This review mainly focuses on recent progress in metal-free sensitizers for applications in DSSCs. Besides, we also briefly report DSSCs with near-infrared (NIR) organic sensitizers, which provide the possibility to extend the absorption threshold of the sensitizers in the NIR region. Finally, special consideration has been paid to panchromatic engineering, co-sensitization, a key technique to achieve whole light absorption for improving the performance of DSSCs.

In this study, we report a novel, one-step synthesis method to fabricate multilayer graphene (MLG)-wrapped copper nanoparticles (CuNPs) directly on various substrates (e.g., polyimide film (PI), carbon cloth (CC), or Si wafer (Si)). The electrical resistivities of the pristine MLG-CuNPs/PI and MLG-CuNPs/Si were measured 1.7 × 10–6 and 1.4 × 10–6 Ω·m, respectively, of which both values are ∼100-fold lower than earlier reports. The MLG shell could remarkably prevent the Cu nanocore from serious damages after MLG-CuNPs being exposed to various harsh conditions. Both MLG-CuNPs/PI and MLG-CuNPs/Si retained almost their conductivities after ambient annealing at 150 °C. Furthermore, the flexible MLG-CuNPs/PI exhibits excellent mechanical durability after 1000 bending cycles. We also demonstrate that the MLG-CuNPs/PI can be used as promising source-drain electrodes in fabricating flexible graphene-based field-effect transistor (G-FET) devices. Finally, the MLG-CuNPs/CC was shown to possess high performance and du...

In the last two decades, dye-sensitized solar cells (DSSCs) have attracted more attention as an efficient alternative to economical photovoltaic devices, and the highest efficiency record has increased from ∼7% to ∼14%. To be more competitive in the solar cell markets, various organic materials are investigated and used in DSSCs to improve the cell efficiency, enhance the cell durability, and reduce the cost of production. In this review article, we provide a short review on the organic materials used for the preparation of photoanodes (including metal element-free organic dye sensitizers), quasi/all-solid-state electrolytes, and metal element-free electrocatalytic films in DSSCs with the cell efficiencies of >5%. Finally, the future perspectives for DSSCs are also briefly discussed.

Nitrogen-doped graphene (NGR) was utilized in dye-sensitized solar cells for energy harvesting. NGR on a Pt-sputtered fluorine-doped tin oxide substrate (NGR/Pt/FTO) as counter electrodes (CEs) achieves the high efficiency of 9.38% via the nitrogen doping into graphene. This is due to (i) the hole-cascading transport at the interface of electrolyte/CEs via controlling the valence band maximum of NGR located between the redox potential of the I–/I– redox couple and the Fermi level of Pt by nitrogen doping, (ii) the extended electron transfer surface effect provided by large-surface-area NGR, (iii) the high charge transfer efficiency due to superior catalytic characteristics of NGR via nitrogen doping, and (iv) the superior light-reflection effect of NGR/Pt/FTO CEs, facilitating the electron transfer from CEs to I3– ions of the electrolyte and light absorption of dye. The result demonstrated that the NGR/Pt hybrid structure is promising in the catalysis field.

As the catalytic material for the counter electrode (CE) of a dye-sensitized solar cell (DSSC), a composite film of nickel nanoparticles (Ni-NPs) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was deposited on an FTO glass substrate, by using a home-made polymeric dispersant, poly(oxyethylene)-segmented imide (POEM). Scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy dispersive X-ray spectroscopy (EDX) were used to characterize the films. A solar-to-electricity conversion efficiency (η) of 7.81% was achieved for the DSSC using Ni-NPs/PEDOT: PSS, while the DSSC with the Pt CE showed a ηof 7.63%. The best composite film showed a high stability, when it was subjected to potential cycling for 100 cycles in an electrolyte containing the redox couple, iodide/triiodide (I-/I3−), while the Pt film showed a considerable decrease in its stability. In replacing the conventional sputtered Pt film as the CE in a DSSC, the Ni-NPs/PEDOT: PSS film exhibited multiple advantages of higher power conversion efficiency, higher stability of the catalytic film, and less expensive material cost. The photovoltaic parameters of the cells were substantiated by incident photon-to-current conversion efficiency (IPCE) spectra, electrochemical impedance spectroscopy (EIS), Tafel polarization plots, and cyclic voltammetry (CV).

An improved light-harvesting ruthenium dye with an alkyl bithiophene group, designated as CYC-B1, is employed as the photosensitizer for a zinc oxide (ZnO)-based dye-sensitized solar cell (DSSC). ZnO films with N3 and CYC-B1 dyes exhibit different surface appearances. Interestingly, the ZnO nanocrystal electrode surface with CYC-B1 dye is found to be almost free from Zn 2+ /dye-agglomerations, usually observed in the case of other commercial ruthenium dyes for such an electrode surface, e.g., N3 dye. Owing to this favorable effect of the CYC-B1 dye, the DSSC with a ZnO film (designated as ZN20) sensitized with this dye exhibited an average efficiency ( η ) of 4.85 ± 0.03%, which is about 94% higher than the η of the cell with N3 dye (2.50 ± 0.12%). The enhancements of the cell with CYC-B1 dye are explained by analyzing the electrochemical impedance spectra (EIS) and laser-induced photocurrent transients. Further, polymethylmethacrylate (PMMA) spheres with uniform sizes of ca. 300 nm are synthesized and incorporated to template the ZN20 film (designated as PMMA-ZN20); this PMMA-ZN20 film is used as the scattering layer and it is coated on the underlayer ZN20 film to make the photoanode film (ZN20/PMMA-ZN20) of a DSSC. The thus fabricated DSSC shows an η of 5.40 ± 0.03%.

High-surface-area (118 m2 g−1) microflower-like TiO2 (MF-TiO2), consisting of TiO2 nanopetals, is synthesized for the photoanode of a quasi-solid-state dye-sensitized solar cell (QSSDSSC). The QSSDSSC with the MF-TiO2 film scattering layer (SL) shows an efficiency (η) of 5.30 %, whereas its counterpart with a commercial SL shows an η of 3.90 %.

The chemical stability of ZnO against acidic dye molecules is an important issue to be improved in a dye-sensitized solar cell (DSSC). In this study, ZnO nanowires (ZnO-NWs) are prepared on a FTO glass through chemical bath deposition, and then the surface of ZnO-NWs are precisely coated with a thin TiO 2 layer step by step using a simple dipping–rinse–hydrolyzation (DRH) process to create the core–shell structure of ZnO@TiO 2 nanowires (ZnO@TiO 2 -NWs) for improving the chemical stability of ZnO. This core–shell structure of ZnO@TiO 2 -NWs on a FTO glass is further used as the photoanode of a DSSC with an acidic N3 dye as sensitizer. The TiO 2 shell acts not only as a protective layer to avoid the formation of Zn 2+ /dye complexes on the surface of ZnO-NWs, but also as a barrier against the recombination of injected electrons with the triiodide ions at the interface of ZnO-NWs and the electrolyte. A higher efficiency of 1.17% is achieved for the core–shell ZnO@TiO 2 -NWs based DSSC with optimized dye sensitization time and DRH cycles, when compared to the optimized cell with pristine ZnO-NWs (0.75%).

A quantum dot-sensitized solar cell (QDSSC) is fabricated using a composite layer, consisting of ZnO nanowires and ZnO nanoparticles (CL-ZnO) as its semiconductor film. The diameter and the thickness of each ZnO nanowire (ZNW) are ∼100 nm and ∼6 μm, respectively. The structure and morphology of the films with ZnO nanoparticles (ZNPs), ZNWs, and CL-ZnO are characterized by X-ray diffraction (XRD) patterns and scanning electron microscopic (SEM) images. Cadmium sulfide quantum dots (CdS QDs) are deposited on the ZNWs, ZNPs, and CL-ZnO by a successive ionic layer adsorption and reaction (SILAR) cycle. The highest efficiency (η) for the QDSSC sensitized by CdS (CdS-QDSSC) is obtained in the case of CL-ZnO photoanode, and this is attributed to significant improvement in the short-circuit photocurrent density (JSC) of the pertinent cell, which is 2.81- fold higher than that of the cell with ZNWs. Moreover, cadmium selenide quantum dots (CdSe QDs) are used as co-sensitizer along with the CdS QDs for the CL-ZnO semiconductor layer (film designated as CL-ZnO/CdS/CdSe), and the pertinent QDSSC showed much higher efficiency than the one obtained in the case of the cell using only CdS QDs as the sensitizer. Finally, a passivation layer of ZnS was deposited on the film of CL-ZnO/CdS/CdSe, and the cell with this film (CL-ZnO/CdS/CdSe/ZnS) showed an efficiency of 0.55%, the highest in this research. Electrochemical impedance spectra (EIS), UV–vis absorbance spectra, transmission electron microscopy (TEM), and incident photon-to-current conversion efficiency (IPCE) curves are used to substantiate the explanations.

A novel 2,7-diaminofluorene-based organic dye (coded as JD2) with the diarylaminofluorene unit as the electron donor and the cyanoacrylic acid as the acceptor as well as anchoring group in a donor-π–donor-π–acceptor architecture is used in a dye-sensitized solar cell (DSSC). The TiO 2 film thickness and the dye soaking time are optimized, and a coadsorbate of bis-(3,3-dimethyl-butyl)-phosphinic acid (DINHOP) is added to the dye solution to reform the cell performance. Effects of the additives, N -methylbenzimidazole (NMBI), guanidinium thiocyanate (GuSCN) or 4-tert-butylpyridine (TBP) in the electrolyte on the photovoltaic performance of the DSSC are studied. Effects of change of DINHOP concentration in JD2 dye solution, change of ratio of LiI to 1,2-dimethyl-3-propylimidazolium iodide (DMPII), and change of concentration of I 2 in the electrolyte on the photovoltaic performance of the DSSC are studied. A light-to-electricity conversion efficiency ( η ) of 6.31% is achieved for the JD2 dye-based DSSC, which is one of the best efficiencies for a cell with an organic dye. Explanations are made with electrochemical impedance spectra (EIS), laser-induced photo–voltage transients, and incident photo-to-current conversion efficiency (IPCE) curves.

Carbon black (CB), multi-walled carbon nanotube (MWCNT), and graphene (GN) were examined as catalytic films on the counter electrodes (CEs) of dye-sensitized solar cells (DSSCs). GN exhibits the best performance among these materials for the corresponding cell. A composite film of GN/Nafion® was next used as the catalytic film on the CE of a DSSC. Nafion® is demonstrated to be an excellent dispersant for inhibiting the aggregation of GN. A solar-to-electricity conversion efficiency (η) of 8.19% was achieved for the DSSC sensitized by TBA(Ru[(4-carboxylic acid-4′-carboxylate-2,2′-bipyridine)(4,4′-bis(5-(hexylthio)-2,2′-bithien-5′-yl)-2,2′-bipyridine)(NCS)2]), i.e., CYC-B11 dye, which was synthesized by our group, after the optimization of the composition of GN/Nafion®, and an η of 8.89% was exhibited for the cell with a sputtered-Pt (s-Pt) film on its CE under the same conditions. The significance of the cell with the composite film of GN/Nafion® lies in the fact that the expensive Pt is avoided in this case, thereby the cost of the pertinent DSSC was greatly reduced, even though its η (8.19%) is slightly smaller than that of the cell with the s-Pt film (8.89%).

A composite thin film of only 6 μm, consisting of a first layer of ZnO nanorods (ZNRs) and a second layer of ZnO nanoparticles (ZNPs), was deposited on a flexible Ti foil. The structures and morphologies of the films of ZNRs, ZNPs, and their composite (hereafter ZNRs/ZNPs) were studied by X-ray diffraction (XRD) patterns, scanning electron microscopic (SEM) and transmission electron microscopy (TEM) images. The Ti foil with the composite film was used as the photoanode of a flexible dye-sensitized solar cell (DSSC); an indium doped tin oxide/polyethylene naphthalate (ITO/PEN) substrate with a thin layer of platinum was used as the counter electrode. A power conversion efficiency (η) of 2.19% was achieved for the DSSC with ZNRs/ZNPs, through back-illumination, which is higher than that of the cell with only ZNPs (1.80%); the DSSC with bare ZNRs showed a very poor efficiency of 0.90%. Explanations are substantiated by electrochemical impedance spectra (EIS), laser-induced photo-voltage transients, and incident photon-to-electron conversion efficiency (IPCE) curves.

This communication demonstrated the technique of using microemulsion to synthesize ZnO crystals with a variety of morphologies. A nearly 30% improved efficiency of a dye-sensitized solar cell can be obtained by using one of the synthesized crystals with coral-like structure, as compared to the commercially available ZnO particles.

a b s t r a c t Conducting polymer materials, i.e., polythiophene (PT), polypyrrole (PPy), and poly(3,4- ethylenedioxythiophene) (PEDOT) were used to prepare counter electrodes (CEs) for quantum-dot-sensitized solar cells (QDSSCs). The QDSSC with PEDOT-CE exhibited the highest solar-to-electricity conversion efficiency (� ) of 1.35%, which is remarkably higher than those of the cells with PT-CE (0.09%) and PPy-CE (0.41%) and very slightly higher than that of the cell with sputtered- gold-CE (1.33%). Electrochemical impedance spectra (EIS) show that this highest conversion efficiency of the PEDOT-based cell is due to higher electrocatalytic activity and reduced charge transfer resistance at the interface of the CE and the electrolyte, compared to those in the case of the cells with other conducting polymers and bare Au. Furthermore, the influences of morphology of the PEDOT film and the charge passed for its electropolymerization on the performance of its QDSSC were also studied. The higher porosity and surface roughness of the PEDOT matrix, with reference to those of other polymers are understood to be the reason for PEDOT to possess higher electrocatalytic activity at its interface with electrolyte.

A flexible photoanode was prepared for a dye-sensitized solar cell (DSSC), using a titanium (Ti) foil as the substrate, titanium oxide nanotubes (TNTs) as the underlayer, and TiO 2 nanoparticles (TNPs) as the overlayer; the TNTs were intended to provide one-dimensional (1-D) electron transfer paths at the interface of the Ti foil and the TNPs. The Ti foil was subjected to anodization at a constant applied potential to obtain the TNTs. Scanning electron microscopic (SEM) images show a steady increase in the diameters of the TNTs with the increase of the anodization potential from 20 to 50 V. X-ray diffraction (XRD) patterns indicate anatase (1 0 1) crystal plane for all the TNTs. The DSSCs with the TNTs as the underlayer show higher short-circuit current density ( j SC ) and higher light-to-electricity conversion efficiency ( η ), compared to those of a DSSC without TNTs. An efficiency of 6.68% was achieved for the DSSC with TNTs as the underlayer, which is 20.4% higher than that obtained for a cell with only a film of TNPs. This efficiency is also one of the best for a back-illuminated DSSC with Ti foil as the substrate. Charge transfer resistances of the cells were investigated by electrochemical impedance spectroscopy (EIS). Laser-induced photo-potential transient and photo-current transient techniques were respectively used to calculate the electron lifetime and electron diffusion coefficient in Ti/TNTs/TNPs films.

Monodispersed polystyrene (PS, ca. 300 nm) latex particles are incorporated into a TiO2 film. A polystyrene-modified TiO2 film (M-TiO2) with micro-cluster structure, containing micro/nano-composite pores is thus obtained after sintering. Cadmium sulfide (CdS) quantum dots (CdS-QDs) are accumulated over M-TiO2 and bare TiO2 films (B-TiO2) by successive ionic layer adsorption and reaction (SILAR); we designate these films as M-TiO2/CdS and B-TiO2/CdS, respectively. Influence of SILAR cycles used for depositing CdS on B-TiO2 and M-TiO2 films on the performance of the pertinent quantum dot-sensitized solar cells (QDSSCs) is studied. The QDSSC with 6 SILAR cycles of M-TiO2/CdS (M-TiO2/CdS6) exhibited a solar-to-electricity conversion efficiency (η) of 1.79%, while the cell with B-TiO2/CdS5 shows an η of 1.35%, under the illumination of one sun. Moreover, guanidine thiocyanate (GuSCN) is found to be a promising additive to the polysulfide electrolyte. The additive renders higher conversion efficiency (2.01%) to its QDSSC. Durability of the CdS-QDSSC is also tested. Scanning electron microscopy (SEM) is used to obtain the images of TiO2 films and energy-dispersive X-ray spectroscopy (EDX) is employed to study the stoichiometric ratios of M-TiO2/CdS and B-TiO2/CdS. Incident photon-to-current conversion efficiencies (IPCE) of the QDSSCs are obtained to confirm the JSC behaviors of the cells.

A composite poly(3,3-diethyl-3,4-dihydro-2H-thieno-[3,4-b][1,4]-dioxepine) and platinum (PProDOT-Et 2 /Pt) film was prepared for using as a counter electrode (CE) catalyst in a dye-sensitized solar cell (DSSC). Four composite films were prepared by electropolymerization of ProDOT-Et 2 on indium tin oxide (ITO) conducting glass, followed by Pt sputtering for 10, 30, 120, and 720 s. The Pt content in the composite film was verified by energy dispersive X-ray spectroscopy (EDX). The composite films possessed three-dimensional (3D) porous structures, as determined by scanning electron microscopy (SEM). The DSSC with the composite film that was subject to 10 s of Pt deposition (PProDOT-Et 2 /Pt-10 s) exhibited the highest solar to electricity conversion efficiency ( η ) of 6.68%, while the cells with the bare polymer film (PProDOT-Et 2 ) and Pt that was sputtered for 720 s (s-Pt-720 s) demonstrated efficiencies of 4.76% and 6.43%, respectively. The cell photovoltaic parameters were substantiated through dark current, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) analyses. Incident photon-to-current conversion efficiency (IPCE) curves were used to explain the cell photocurrent behaviors.

An energy-economical dye-sensitized solar cell (DSSC) with highly flexible Ti/TiO2 photoanode was developed through a low-temperature process, using a binder-free TiO2 paste. Ti foils, coated with the binder-free TiO2 films were annealed at various temperature. Scanning electron microscopic (SEM) images of the films show uniform, mesoporous and crack-free surface morphologies as well as interpenetrated TiO2 network. DSSCs with binder-free TiO2 films annealed at 450, 350, 250 and 120°C show solar-to-electricity conversion efficiencies (η) of 4.33, 4.34, 3.72 and 3.40%, respectively, which are comparable to the efficiency of 4.56% obtained by using a paste with binder and annealing it at 450°C; this observation demonstrates the benefits of a binder-free TiO2 paste for the fabrication of energy-fugal DSSCs. On the other hand, when organic binder was used in the TiO2 paste for film preparation, a drastic deterioration in the cell performance with decreasing annealing temperature is noticed. Laser-induced photo-voltage transient technique is used to estimate the electron lifetime in various Ti/TiO2 films. Electrochemical impedance spectroscopic (EIS) analysis shows that the lower the annealing temperature of the TiO2 coated Ti foil, the larger the charge transfer resistance at the TiO2/dye/electrolyte interface (Rct2). Copyright © 2011 John Wiley & Sons, Ltd.

Titanium nitride (TiN) or its thermally treated version is incorporated into the gel electrolyte of a dye-sensitized solar cell (DSSC) and the consequent effects are investigated in terms of photovoltaic performance of the cell. The gel electrolyte is essentially prepared by using poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP). With an addition of 3 wt% TiN, the solar-to-electricity conversion efficiency ( η ) of the DSSC reaches 5.33% from 4.15% of the cell without TiN. X-ray diffraction (XRD) spectra of thermally treated-TiN (tt-TiN) clearly shows the partial conversion of TiN into TiO 2 with both anatase and rutile crystal phases. The DSSC with the incorporation of 3 wt% of tt-TiN into its electrolyte shows a further improved efficiency of 5.68%, with reference to the efficiency of TiN-incorporated DSSC. The cell with 3 wt% of tt-TiN also shows unfailing at-rest stability after more than 1000 h. Electrochemical impedance spectroscopy (EIS) is used to obtain charge transfer properties of the cells. Crystallinity and crystalline phases are analyzed by X-ray diffraction (XRD) spectra. Surface morphologies are observed with scanning electron microscopy (SEM). IPCE curves substantiate the variations in short circuit photocurrents.

Highly efficient and stable back illumination dye-sensitized solar cell (BIL-DSSC) is developed using its Pt-counter electrode (Pt-CE) as the light-irradiating surface. Photovoltaic parameters are measured for DSSCs with Pt-CEs obtained with different sputtering periods of platinum layer. By optimizing the transmittance and catalytic property of the platinum layer on the counter electrode, a light-to-electricity conversion efficiency (η) of 7.54% is achieved with back illumination at 100 mW cm−2, when the platinum deposition time is 30 s. The effects of platinum layers with different sputtering periods on the photovoltaic characteristics of the respective DSSCs are explained in terms of transmittance and catalytic activity of the layers. A comparative study is also made on the durability of the DSSCs with BIL and front illumination (FIL), in which the respective DSSCs are previously subjected to UV-soaking for different periods of time under simulated conditions of back and front illuminations; at-rest stability tests for such UV-soaked DSSCs carried out through BIL and FIL suggest a far higher stability in favor of the BIL-DSSC, compared to that of the FIL-DSSC. Explanations are substantiated with transmittance spectra, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and absorption spectra.

Back-illuminated dye-sensitized solar cell (DSSC) based on a flexible TiO2/Ti foil photoanode and a high transparent platinum counter electrode (Pt-CE) has been developed by using a net-like Pt-CE ...

The effects of four factors, i.e., (i) sputter-deposition time of platinum (Pt) film, (ii) sintering temperature of TiO2-coated Ti foil (Ti/TiO2), (iii) thickness of Ti foil, and (iv) concentration of iodine are reported for the photovoltaic performance of a back-illuminated flexible dye-sensitized solar cell (DSSC) with Ti foil substrate for the TiO2 layer. Optimization of these four factors yields a solar-to-electricity conversion efficiency (� ) of 5.95%. Transmittance spectra, cyclic voltammetry (CV), electrochemical impedance spectra (EIS), X-ray diffraction (XRD), scanning electron micrographs (SEM), and laser-induced photovoltage transient technique are used to substantiate the explanations. © 2010 Elsevier B.V. All rights reserved.

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 TiO 2 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-Et 2 ) 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.

We have fabricated organic photovoltaic devices with blends of poly[9,9′-dioctyl-fluorene- co -bithiophene] (F8T2) and fullerene as an electron donor and electron acceptor, respectively. A significant improvement of the photovoltaic efficiency was found in device by using active materials with complementary spectra. The different weight ratios of composite film were also performed to correlate between morphology and the device performance. A power conversion efficiency (PCE) up to 2.0% with an open-circuit voltage of 0.85 V and a short-circuit current ( J SC ) of 5.3 mA/cm 2 , was achieved by blending the F8T2 with [6,6]-phenyl-C71-butyric acid methyl ester (PC[70]BM).

Dye-sensitized solar cells (DSSCs) are fabricated using low-cost materials and a simple fabrication process; these advantages make them attractive candidates for research on next generation solar cells. In this type of solar cell, dye-sensitized metal oxide electrodes play an important role for achieving high performance since the porous metal oxide films provide large specific surface area for dye loading and the dye molecule possesses broad absorption covering the visible region or even part of the near-infrared (NIR). Recently, metal-free sensitizers have made great progress and become the most potential alternatives. This review mainly focuses on recent progress in metal-free sensitizers for applications in DSSCs. Besides, we also briefly report DSSCs with near-infrared (NIR) organic sensitizers, which provide the possibility to extend the absorption threshold of the sensitizers in the NIR region. Finally, special consideration has been paid to panchromatic engineering, co-sensitization, a key technique to achieve whole light absorption for improving the performance of DSSCs.

Inspired by geogrids commonly applied in construction engineering to reinforce side slopes and retaining walls, the use of a “nano-geogrid” to reinforce a CuxZnySnzS (CZTS) nanowall electrode for application in electrochemical reactions is demonstrated. The CZTS nanowall electrode reinforced by the nano-geogrid (denoted as NWD) shows not only remarkable mechanical and electrochemical stability but also considerable electrochemical performances. The NWD demonstrated as a counter electrode in a dye-sensitized solar cell shows a power conversion efficiency of 7.44 ± 0.04%, comparable with the device using Pt as electrode, and also significantly improves device stability as compared with that afforded by an electrode comprising a CZTS nanowall without the nano-geogrid (denoted as NOD). In addition, applying the NWD electrode as a cathode in photo-electrochemical hydrogen evolution reactions (HERs) yields a photocurrent density of −10 mA cm−2 at −0.162 V (vs RHE) under AM 1.5 illumination. Moreover, when HERs are conducted under extreme conditions, the NWD electrode remains intact, whereas the NOD electrode is completely peeled off after 10 min of reaction. Therefore, the concept of using a mimetic rational nanostructure could pave the way for the possibility of improving the performance and stability of various devices.

The increasing global need for energy coupled with the depletion of easily accessible, hence cheap, fossil fuel reserves, poses a serious threat to the human global economy in the near future [1]. Considering in addition the harmful ecological impact of conventional energy sources, it becomes obvious that development of clean alternative energy sources is a neces‐ sity [2, 3]. Best renewable energy options must rely on a reliable input of energy onto the earth. Since the sun is our only external energy source, harnessing its energy, which is clean, non-hazardous and infinite, satisfies the main objectives of all alternative energy strategies. Mastering the conversion of sunlight to electricity or to a nonfossil fuel like hydrogen is without any doubt the most promising solution to the energy challenge. It is remarkable that a mere 10 min of solar irradiation onto the Earth’s surface is equal to the total yearly human energy consumption [4]. Therefore, solar power is considered to be one of the best sustaina‐ ble energies for future generations. To date photovoltaics has been dominated by solid-state junction devices, usually in silicon, crystalline or amorphous, and profiting from the experi‐ ence and materials availability resulting from the semiconductor industry. However, the ex‐ pensive and energy-intensive high-temperature and high-vacuum processes is needed for the silicon based solar cells. Therefore, the dominance of the photovoltatic field by such kind of inorganic solid-state junction devices is now being challenged by the emergence of a third generation solar cell based on interpenetrating network structures, such as dye-sensitized solar cells (DSSCs) [5].

Electrophoretic deposition (EPD) method is employed to obtain mesoporous TiO 2 film on a titanium (Ti) foil; the film is then mechanically compressed and sintered at 350 °C before being subjected to dyeing. A comprehensive study was made on the mechanistic aspects of the EPD process. The dye-sensitized solar cell (DSSC) using the thus formed TiO 2 film rendered a power conversion efficiency (Eff.) of 6.5%. Effects of various compression pressures on the photovoltaic parameters and on other characteristic parameters of the pertinent DSSCs are studied. Electrochemical impedance spectroscopy (EIS) is applied for the first time, using a novel equivalent model, to study the impedance behavior of the DSSC with this type of TiO 2 film. We also obtain characteristic parameters of the TiO 2 photoanode by using EIS. The coordination number of the TiO 2 film, and the ratio of charge transfer resistances of electron recombination and electron transport are also obtained and analyzed. Moreover, we employ a multilayer approach and increase the film thickness to prepare TiO 2 films with the same coordination number and porosity; DSSCs using such TiO 2 films obtained from P90 and P25 rendered efficiencies of 6.5% and 5.24%, respectively. Scanning electron microscopy (SEM) micrographs are obtained to characterize the TiO 2 films formed by the EPD technique and laser-induced transient technique is used to estimate the electron lifetime in the TiO 2 films.

A novel amphiphilic copolymer, poly(oxyethylene)-amide–imide (POEM), was synthesized and utilized for gelling an ionic liquid electrolyte. The polymer-gelled ionic liquid (PG-IL) electrolyte containing 1-methyl-3-propylimidazolium iodide (PMII), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) and POEM has been employed as a quasi-solid-state electrolyte in DSSCs. By adding the POEM to a room temperature ionic liquid (RTIL) electrolyte up to 5 wt%, the binary electrolyte exhibited a quasi-solid-state. The structure of the PG-IL electrolyte with POE segments, which have lone pair electrons, could cause the ionic pair separation and enhance mobility of the counter I− ions. When fabricated into a quasi-solid-state dye-sensitized solar cell, the cell performance exhibited a high power conversion efficiency of 6.28% and long-term durability over 1000 h.

A platinum nanoparticle/multi-wall carbon nanotube (PtNP/MWCNT) hybrid counter electrode (CE) based on a flexible substrate, Ti foil, was prepared for a high performance dye-sensitized solar cell (DSSC) via a facile fabricating route. This flexible nanohybrid CE was established by using a requisite homemade dispersant, consisting of poly(oxyethylene) segment and imide linkage functionalities. MWCNTs were well suspended in an ethanol/water solution in the presence of copolymer dispersant and PtNPs. The solution containing the PtNP/MWCNT (2/1 weight ratio) hybrid was further coated into a thin film on the Ti foil by the doctor blade technique, followed by annealing at 390 °C to obtain the flexible PtNP/MWCNT hybrid CE. The solar-to-electricity conversion efficiency (η) of a DSSC with the flexible PtNP/MWCNT hybrid CE gave a higher value of 9.04% in comparison to that of the cell with a conventional Pt CE (η = 7.47%). A rougher surface morphology of the nanohybrid film precisely controlled by the configuration of MWCNT was obtained, with reference to that of a Pt-sputtered film. The PtNP/MWCNT hybrid film was physically characterized by scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. Cyclic voltammetry, incident-photon-to-current efficiency, and electrochemical impedance spectra were examined for confirming the high electro-catalytic ability of this flexible PtNP/MWCNT hybrid CE.

A composite film of PEDOT:PSS/TiN–NPs, containing poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and titanium nitride nanoparticles (TiN–NPs), was deposited on a Ti foil by a doctor blade technique. Various weight percentages of TiN–NPs (5, 10, 20, 30 wt%) were used to prepare different composite films. This Ti foil with the composite film was used as the flexible counter-electrode (CE) for a dye-sensitized solar cell (DSSC). Performances of the DSSCs with the platinum-free CEs containing PEDOT:PSS/TiN–NPs with various contents of TiN–NPs were investigated. After the optimization of composition and thickness of the composite film PEDOT:PSS/TiN–NPs, a light-to-electricity conversion efficiency (η) of 6.67% was achieved for the pertinent DSSC, using our synthesized CYC-B1 dye, which was found to be higher than that of a cell with a sputtered-Pt film on its CE (6.57%). The homogeneous nature of the composite film PEDOT:PSS/TiN–NPs, the uniform distribution of TiN–NPs in its polymer matrix, and the large electrochemical surface area of the composite film are seen to be the factors for the best performance of the pertinent DSSC. Scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy dispersive X-ray spectroscopy (EDX) were used to characterize the films. The high efficiency of the cell with PEDOT:PSS/TiN–NPs is explained by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and incident photon-to-current conversion efficiency (IPCE) curves.

A solid-state composite electrolyte, comprising two ionic liquids and a carbon material, was sandwiched between a dye-sensitized porous TiO2 working electrode and its counter electrode to fabricate a solid-state dye-sensitized solar cell (DSSC); the ionic liquids were 1-ethyl-3-methylimidazolium iodide (EMII, ionic liquid crystal) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4, room temperature ionic liquid), and the carbon materials were carbon black (CB), multi-wall carbon nanotubes (MWCNT), and single-wall carbon nanotubes (SWCNT). A cell efficiency (η) of 0.41% was achieved by using the bare 1-ethyl-3-methylimidazolium iodide (EMII) as the charge transfer intermediate (CTI); an efficiency of 2.52% was achieved for a solid-state DSSC by the incorporation of carbon black (CB) in the same composite electrolyte. To further improve the cell efficiency, we utilized 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4), a crystal growth inhibitor, as an additive to the electrolyte. The binary CTI (EMII plus EMIBF4) was in the form of a solid, until the weight percentage of EMIBF4 in the binary CTI exceeded the level of 60%. A cell efficiency of 3.09% was obtained using an electrolyte containing the CB and the binary CTI; the binary CTI for this cell contained EMII and EMIBF4 in the ratio of 8/2. When the CB was replaced with MWCNT and SWCNT, the cell efficiency could be improved to 3.53% and 4.01%, respectively. Long-term durability of the DSSC with SWCNT–binary CTI was found to be far superior to that of the cell with an organic solvent electrolyte, and in fact the durability was uninterrupted for at least 1000 h. Scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), differential scanning calorimetry (DSC), and laser-induced photo-voltage transients were used to substantiate the results.

A solid organic ionic crystal, 1-ethyl-3-methylimidazolium iodide (EMII), was employed as a charge transfer intermediate (CTI) to fabricate all-solid-state dye-sensitized solar cells (DSSCs). In addition, single wall carbon nanotubes (SWCNTs) were incorporated into the CTI as the extended electron transfer materials (EETM), which can reduce charge diffusion length and serve simultaneously as catalyst for the electrochemical reduction of I3−. An all-solid-state DSSC with this hybrid SWCNT-EMII achieved a higher cell efficiency (1.88%), as compared to that containing bare EMII (0.41%). To further improve the cell efficiency, we utilized 1-methyl-3-propylimidazolium iodine (PMII), which acts simultaneously as a co-charge transfer intermediate and crystal growth inhibitor. The binary CTI (EMII mix with PMII) is in the form of solid as the weight percentage of PMII reaches 60%, at which a smoother surface morphology for the binary CTI is observed. The highest cell efficiency (3.49%) was obtained using a hybrid SWCNT-binary CTI. At-rest durability of the DSSC with the hybrid SWCNT-binary CTI was also studied and found to be far superior to that of a cell with an organic solvent electrolyte. Electrochemical impedance spectroscopy (EIS) and laser-induced photo-voltage transient were used to substantiate the results.