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Transparent conductive oxide-less (TCO-less) dye-sensitized solar cells (DSSCs) have been fabricated and characterized using nanoporous TiO2-coated stainless steel metal mesh as flexible photoanode and cobalt bipyridyl complex (Co(bpy))-based one electron redox shuttle electrolyte. Attempts have been made towards enhancing the efficiency of TCO-less DSSCs to match with their TCO-based DSSC counterparts. It has been found that surface protection of metal mesh is highly required for enhancing the efficiency of TCO-less DSSCs specially using cobalt electrolytes as confirmed by dark current-voltage characteristics. Photocurrent action spectra clearly reveal that TCO-based DSSCs using (Co(bpy)) electrolyte exhibits photon harvesting (incident photon to current conversion efficiency (IPCE) 52%) in the 370-450 nm wavelength region as compared to photon harvesting at peak absorption of the dye (IPCE 56% at 550 nm), which is almost the same (IPCE 47%) in the 400-610 nm wavelength region for TCO-less DSSCs. Under similar experimental conditions, replacing indoline dye D-205 to porphyrin-based dye YD2-o-C8 led to the enhancement in the photoconversion efficiency from 3.33% to 4.84% under simulated solar irradiation. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Dye-sensitized solar cells with sub-5 μm-thick Pt/SiC-P (1.79 at. % Pt), Pt/SiC-M (0.45 at. % Pt), and Pt/SiC-R (0.39 at. % Pt) counter electrode (CE) films fabricated by using three different processes produced power conversion efficiencies of 6.82, 7.64, and 7.04 % that reached 86.5, 97.0, and 89.3 %, respectively, of the level obtained by using a print-Pt CE (7.88 %). These materials can reduce the cost of CEs and solve challenges involving Pt. [ABSTRACT FROM AUTHOR]

Mesoporous-graphitic-carbon-supported HfO2 (HfO2-MGC) nanohybrids were synthesized by using a soft-template route. Characterization and a systematic investigation of the catalytic properties, stability, and catalytic mechanism were performed for HfO2-MGC counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). The new HfO2-MGC as a CE in DSSCs showed a surprisingly high efficiency of 7.75 % for the triiodide/iodide redox couple and 3.69 % for the disulfide/thiolate redox couple, greater than the Pt electrode in the corresponding electrolyte system, which opens up a possibility for its practical application. [ABSTRACT FROM AUTHOR]

The article focuses on the dye-sensitized solar cells (DSCs) which features a moderate power conversion efficiency (PCE), low cost and plasticity. It mentions that the introduction of nanocrystalline semiconductor (metal oxide) mesoporous films is the major break through in the development of DSCs. It further mentions that titanium oxide-based DSCs performance level is low due to the fast recombination dynamics, low voltage value and poor adsorption capacity of sensitizer.

The effects of the thickness of Pt film on the property of platinized counter electrode and the performance of the dye-sensitized solar cell (DSC) were investigated. The Pt film sputtered on an FTO glass is constructed of Pt particles, and the grain size of the Pt particles gradually increased with the increase in the Pt film thickness. When the Pt film thickness exceeds 100 nm, further Pt deposition has no significant effect on the conductivity improvement. In the range between 10 and 415 nm, the Pt film thickness has no significant influence on the performance of the DSC. A high conversion efficiency of ca. 5% was obtained by the DSC composed of the counter electrode with Pt film of 10 nm thickness. These results are important for reducing the production cost by reducing the required amount of expensive platinum. [Copyright &y& Elsevier]

A composite catalyst of rosin carbon/Fe3O4 with marvellous morphology was synthesized and applied as a counter electrode (CE) in dye-sensitized solar cells (DSCs), demonstrating notable electrocatalytic activity for the reduction of I3−. Based on this CE, a high power conversion efficiency of 8.11% was achieved, comparable to that of the traditional Pt CE. [ABSTRACT FROM AUTHOR]

Pyridyl iodides were synthesized to serve as effective, economical, green and dual function additives for high efficiency and stable DSCs. Using commercial P25 as the photoanode, a high PCE of 7.81% was achieved with a pyridyl iodide-containing electrolyte. Meanwhile, DSCs based on our novel electrolytes demonstrated better stability. [ABSTRACT FROM AUTHOR]

The dye-sensitized solar cells (DSCs) using SnO2 and Nb2O5 counter electrodes (CEs) prepared in N2 atmosphere yielded power conversion efficiencies (PCE) of 6.09% and 4.65%, much higher than the PCE values (1.84%, 0.97%) of the DSCs using the same SnO2 and Nb2O5 CEs prepared in air. [ABSTRACT FROM AUTHOR]

Synthesized niobium oxides (Nb2O5and NbO2) were applied for the first time as counter electrodes (CEs) in dye-sensitized solar cells (DSCs). The DSC using NbO2CE showed a higher power conversion efficiency of 7.88%, compared with that of the DSC using Pt CE (7.65%). [ABSTRACT FROM AUTHOR]

Tungsten dioxide (WO2) nanorods were synthesized, which showed excellent catalytic activity for the reduction of triiodide to iodide. The dye-sensitized solar cell (DSC) using WO2as a counter electrode (CE) reached a high energy conversion efficiency of 7.25%, which can match the performance of the DSC based on a Pt CE. [ABSTRACT FROM AUTHOR]

Developing highly effective and stable counter electrode (CE) materials to replace rare and expensive noble metals for dye‐sensitized and perovskite solar cells (DSC and PSC) is a research hotspot. Carbon materials are identified as the most qualified noble metal‐free CEs for the commercialization of the two photovoltaic devices due to their merits of low cost, excellent activity, and superior stability. Herein, carbonaceous CE materials are reviewed extensively with respect to the two devices. For DSC, a classified discussion according to the morphology is presented because electrode properties are closely related to the specific porosity or nanostructure of carbon materials. The pivotal factors influencing the catalytic behavior of carbon CEs are also discussed. For PSC, an overview of the new carbon CE materials is addressed comprehensively. Moreover, the modification techniques to improve the interfacial contact between the perovskite and carbon layers, aiming to enhance the photovoltaic performance, are also demonstrated. Finally, the development directions, main challenges, and coping approaches with respect to the carbon CE in DSC and PSC are stated. [ABSTRACT FROM AUTHOR]

As a hole transport materials (HTMs) and noble-metal free perovskite solar cells (PSCs), carbon-based PSCs (C-PSCs) have drawn much attention due to its low cost and excellent stability. The interfacial engineering, between perovskite and counter electrodes (CEs), played a crucial role in charge collection and affected the performance of C-PSCs. Herein, the systematic investigation of interfacial bridging carbon materials has been carried out to improve the interfacial contact. Results demonstrated that the morphology of interfacial bridging carbon materials played more important role than their energy band and conductivity, where carbon nanotube (CN) showed much better interfacial bridging effect and energy level alignment than other carbon materials. We achieved both the high power conversion efficiency (PCE) (15.09%) and stability in C-PSCs without HTMs due to the optimal interfacial bridging carbon material. It could retain 67% of their initial PCE after storing for 340 h under the rigorous environmental condition without any encapsulation (air atmosphere, 85 °C, 65% RH). [ABSTRACT FROM AUTHOR]

Novel composites made of two dimensional (2D) MoS 2 nanosheets and graphene (G) have been fabricated by a combined approach of chemical vapor deposition and hydrothermal technique. The G film helps to mediate the growth and dispersion of MoS 2 nanosheets, of which the unique role of G in the MoS 2 growth is revealed by density functional theory study. The results show that the hexagonal lattice carbon of the G film can easily interact with sulfur species derived from reaction precursors, which favors the uniform growth of 2D MoS 2 . The unique function of the G film demonstrated here can be extended to other carbon substrates for growing 2D MoS 2 nanosheets. The G-MoS 2 composites consisting of two types of 2D materials are tested as the binder-free counter electrodes (CEs) for dye-sensitized solar cells, showing a high power conversion efficiency of 7.1% that is comparable to the expensive Pt CEs. The 2D G film in the hybrids has two functions: the active sites for dispersing the electrochemically active MoS 2 crystals and the high electrical conducting matrix for fast charge transfer. This synergistic effect may help to shed a light on the functionalization of other inorganic materials to G for advanced energy applications. [ABSTRACT FROM AUTHOR]

This paper reports a comparative study of the photovoltaic characteristics of titanium (Ti) metal wires with different diameter and surface treatments towards their utilization as photoanodes for coil-based dye-sensitized solar cells. The surface property of the Ti wire, especially oxidized overlayer and surface treatments have been found to greatly influence the adhesion as well as optimum electrical contact between coated nanoporous titanium oxide (TiO 2 ) and Ti-wires. Implication of adhesion of nanoporous TiO 2 on the titanium wire and its influence on photovoltaic performance was analyzed using electrochemical impedance spectroscopy. Results of X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy reveals the formation of anatase TiO 2 nanosheets after the H 2 O 2 surface treatment on the titanium wire resulting into enhancement in the extent of dye loading leading to enhanced photoconversion efficiency of 4.71% under simulated solar irradiation. [ABSTRACT FROM AUTHOR]

Abstract: MoSi2 is introduced into dye-sensitized solar cell (DSC) as counter electrode (CE) catalyst for the first time, and the DSC produces power conversion efficiency (PCE) of 4.87%. To improve the catalytic activity, Pt/MoSi2 composite catalyst is synthesized and it is found that 1.13 wt% of Pt loading is enough for achieving high catalytic activity. After optimization, the DSC using the Pt/MoSi2 composite CE shows high PCE of 7.68%, close to the Pt CE based DSC (7.94%). [Copyright &y& Elsevier]

Abstract: New metal-free organic sensitizers containing a fluorene unit as a π-conjugated system, a diphenylamine as an electron donor, and a cyanoacrylic acid moiety as an electron acceptor were synthesized and used for dye-sensitized solar cells. The photophysical and electrochemical properties of these dyes were investigated, and their performances as sensitizers in solar cells were measured. One solar cell containing the n-hexyl group in the fluorene unit produced an η of 5.15% (J sc = 9.69 mA cm−2, V oc = 0.77 V, and ff = 0.70) under 100 mW cm−2 simulated AM 1.5 G solar irradiation (100 mW cm−2). [Copyright &y& Elsevier]

Abstract: Five kinds of triphenylamine-based organic dyes with different electron acceptors were designed and synthesized as sensitizers for dye-sensitized solar cells (DSSCs). The photophysical and electrochemical properties of these dyes were investigated and their performance as sensitizers in DSSCs was measured. The dye with cyanoacrylic acid electron acceptor exhibits the highest solar-to-electrical energy conversion efficiency of 4.93% (short-circuit photocurrent density J sc = 8.59 mA cm−2, open-circuit photovoltage V oc = 0.77 V, and fill factor ff = 0.75) under 100 mW cm−2-simulated AM 1.5 G solar irradiation. [Copyright &y& Elsevier]

Abstract: A novel method for the preparation of monolithic coal-based porous carbon counter electrodes (CEs) for high performance dye-sensitized solar cells has been reported. Rigid monolithic coal-based carbon CE has been synthesized by preferential densification of one side of porous carbon plate formulated by caking bituminous coal powder. The phase, surface composition, and surface micro&nanotexture of the monolithic porous carbon plates have been characterized by X-ray diffraction, X-ray photoelectron energy spectroscopy, nitrogen sorption, scanning electron microscopy, and transmission electron microscopy. The coal-based carbon monolithic CEs exhibit a low internal resistance and high energy conversion efficiency (up to 6.38%). When the surface of the porous substrate was modified with mesoporous carbon as catalytic layer, the energy conversion efficiency can be further enhanced up to 8.73%, which is comparable to that of the platinized fluorine-doped tin oxide glass based device. [Copyright &y& Elsevier]

Abstract: Binary composite of Pt decorated transition metal compounds (WO2, TiC, and VN) were introduced into dye-sensitized solar cells and excellent performance were obtained, almost 20% better than unitary materials. Ternary composite of Pt/WO2/TiO2 was also prepared to further improve the photovoltaic performance. [Copyright &y& Elsevier]

Titanium films have been deposited on stainless steel metal sheets using dc magnetron sputtering technique at different substrate temperatures. The structure of the titanium films strongly depend on the substrate temperature. The titanium film deposited at the substrate temperature lower than 300°C has a loose flat sheet grains structure and the titanium film prepared at the substrate temperature higher than 500°C has a dense nubby grains structure. The DSSC assembled using stainless steel sheet coated with titanium film deposited at high substrate temperature has a low charge transfer resistance in the TiO2/Ti interface and results in a high conversion efficiency. The DSSC assembled using stainless steel sheet coated with titanium film deposited at temperature higher than 500°C has higher conversion efficiency than that assembled using titanium metal sheet as the substrate. The maximum conversion efficiency, 2.26% is obtained for DSSC assembled using stainless steel sheet coated with titanium film deposited at 700°C substrate temperature, which is about 70% of the conversion efficiency of the FTO reference cell used in this study. [ABSTRACT FROM AUTHOR]

Abstract: New metal-free organic sensitizers containing a benzo[d]thiazole or phenyl unit as the π-conjugated system, a triphenylamine as an electron donor, and a cyanoacrylic acid moiety as an electron acceptor were synthesized and used for dye-sensitized solar cells. Photophysical and electrochemical properties of these dyes were investigated, and their performances as sensitizers in solar cells were measured. The introduction of a benzo[d]thiazole unit into the molecular structure resulted in a high incident photon-to-current conversion efficiency (more than 70%) from 340 nm to 600 nm. One solar cell containing a benzo[d]thiazole unit, produced a η of 5.85% (J SC = 10.63 mA cm−2, V OC = 0.72 V, and ff = 0.77) under 100 mW cm−2 simulated AM 1.5 G solar irradiation. [Copyright &y& Elsevier]

Abstract: Novel polymer gel electrolytes (PGEs) with high ionic conductivity based on polyvinyl (acetate-co-methyl methacrylate) [P(VA-co-MMA)] were prepared by soaking porous copolymers in an organic electrolyte solution [acetonitrile (ACN) or 3-Methoxypropionitrile (MPN)] that contained an I3 −/I− as redox couple. Quasi-solid-state dye-sensitized solar cells (QS-DSSCs) were fabricated with the PGEs, and the best PGE was selected and optimized. Using the best PGE and under 100mWcm−2 light illumination (AM1.5), the QS-DSSC achieved a high photovoltaic conversion efficiency of 9.10%, nearly the same as that for the DSSC based on the original liquid electrolyte. Introduction of TiO2 nanoparticles into the PGEs further enhanced PGEs ionic conductivity and the conversion efficiency to 9.40%. Subsequent results revealed that our QS-DSSC had a better stability because it could maintain 96.7% of its initial efficiency after long-time (1000h) exposure to simulative sunlight. Besides, for the first time, large-area QS-DSSCs were fabricated by screen printing of PGE, other than the traditional vacuum injection that was infeasible for the viscous gel electrolyte. Finally, our 5cm×7cm QS-DSSC sub-module exhibited a conversion efficiency higher than 4%. [Copyright &y& Elsevier]

Abstract: The Pt-like electrocatalytic activity of counter electrodes (CEs) prepared from tantalum oxides for dye-sensitized solar cells (DSCs) is demonstrated. The low ratio of oxygen to metal atom of the oxide favors the electrocatalytic activity of these CE materials for I3 − reduction in DSCs. TaO, used as a CE in DSCs, shows superior electrocatalytic activity and a high power conversion efficiency of 6.48%, up to 90.5% of the level obtained using Pt as a CE (7.16%). This work develops the use of novel tantalum oxide CE materials for low cost and high efficiency DSCs. [Copyright &y& Elsevier]

Abstract: We fabricated low-cost carbon and carbides counter electrodes (CEs) with excellent adhesion by adding an industrial conductive carbon paste (CC) as a binder for dye-sensitized solar cells (DSSCs). We compared the electrochemical catalytic activity of CC and carbon dye (Cd)/CC in the reduction of triiodide to iodide using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). CC and Cd/CC electrodes both exhibit electrochemical catalytic activity for triiodide reduction. After investigating the influence of CC on the performance of DSSCs, we also chose several transition metal carbides, including molybdenum carbide (MoC), tungsten carbide (WC), ordered mesoporous carbon (OMC), MoC embedded in OMC (MoC-OMC), and WC embedded in OMC (WC-OMC) as catalytic materials of CEs. DSSCs based on the carbon and carbides CEs reached efficiencies of 4.50–6.81%. The results indicate that CC is a superior binder for Pt-free catalysts in DSSCs. [Copyright &y& Elsevier]

Abstract: Several nickel bis(dithiolene) complexes with strong and broad absorptions in the Near-IR (NIR) region (700–1100nm) were synthesized by using green and simple synthetic routes. The physical and chemical properties of these dyes were systematically studied, including structure, optical spectroscopy and electrochemical behavior, etc. These NIR dyes were first applied to dye-sensitized solar cells (DSCs) and the photoelectrochemical performances were also investigated. The effects of different substituent groups on the properties of the dyes and photovoltaic performances of DSCs were discussed. Furthermore, we also applied the synthesized NIR dyes for constructing NIR absorbing filter. With their particular photoelectrochemical properties, the nickel bis(dithiolene) complexes exhibit promising prospects for future application. [Copyright &y& Elsevier]

Abstract: Three different types of nanocrystalline, N-doped TiO2 electrodes were synthesized using several nitrogen dopants through wet methods. The obtained nanocrystalline, N-doped TiO2 electrodes possessed different crystallite sizes, surface areas, and N-doping amounts. Characterizations were performed to reveal the nitrogen-doping processes for the wet methods using ammonia, urea, and triethylamine as the nitrogen dopants. Additionally, a high conversion efficiency of 8.32% was achieved by the dye-sensitized solar cells, based on the N-doped TiO2 electrodes. For instance, in comparison with the commercial P25 (5.76%) and pure anatase TiO2 electrodes (7.14%), significant improvements (44% and 17%, respectively) in the efficiencies were obtained. The findings also indicated that the ammonia nitrogen dopant was more efficient than other two nitrogen dopants. The electron transports, electron lifetimes, and charge recombination in the dye-sensitized N-doped TiO2 solar cells also differed from those in the pure TiO2-based dye-sensitized solar cells (DSCs). Specifically, an enhanced photocurrent of ca. 36% in N-doped DSCs resulted from the synergistic effects of the high dye uptake and the efficient electron transport. Moreover, the relationship between charge and voltage revealed that less charge was needed to get a high open-circuit voltage in the N-doping films. [Copyright &y& Elsevier]

Abstract: Twenty natural dyes, extracted from natural materials such as flowers, leaves, fruits, traditional Chinese medicines, and beverages, were used as sensitizers to fabricate dye-sensitized solar cells (DSCs). The photoelectrochemical performance of the DSCs based on these dyes showed that the open circuit voltages (Voc) varied from 0.337 to 0.689V, and the short circuit photocurrent densities (Jsc) ranged from 0.14 to 2.69mAcm−2. Specifically, a high Voc of 0.686V was obtained from the dye extracted from mangosteen pericarp sensitizer. The photo-to-electric conversion efficiency of the DSC sensitized by the ethanol extract of mangosteen pericarp without purification reached 1.17%. Moreover, various components of the ethanol extract were extracted using different organic solvents. The photoelectrochemical performance of these extracts demonstrated that rutin was the most effectual component of the sensitizer for DSC. [Copyright &y& Elsevier]

Abstract: A series of nitrogen-doped and undoped TiO2 nanocrystals was prepared by several simple methods. Needle-like N-doped TiO2 nanocrystals and nanoparticles were obtained from commercial TiO2 powders. Several dye-sensitized solar cells (DSCs) were fabricated based on N-doped and undoped TiO2 electrodes. The N-doped DSCs achieved a high conversion efficiency of 10.1% and 4.8% using an organic electrolyte and an ionic liquid electrolyte, respectively. Systemic investigations were carried out on the properties of N-doped and undoped TiO2 powders, films, and DSCs. The electron transport time and electron lifetime were investigated by intensity-modulated photocurrent and photovoltage spectroscopy (IMPS/IMVS). Moreover, the electron injection of N-doped DSCs was studied by surface photovoltage spectroscopy (SPS). The synergetic effect of higher dye uptake, faster electron transport and higher photovoltage contributes to a higher conversion efficiency of N-doped DSCs. The stability test also demonstrated that the photodegradation of the DSCs was not accelerated and the DSC system was stabilized by the introduction of nitrogen into the TiO2 photoelectrode. These results indicate that the N-doped TiO2 nanocrystals prepared by our approach from commercial TiO2 are ideal semiconductor materials for DSCs. [Copyright &y& Elsevier]

Abstract: Surface treatment of ruthenium dye (Bu4N)2[Ru(dcbpyH)2(NCS)2]-sensitized TiO2 films using diethyl 4-methylphenylphosphonate as a coadsorbent results in large improvements in DSC performance, 24% larger overall conversion efficiency and 55mV higher open-circuit voltage without current penalty. Introducing another two coadsorbents ethyl 4-methylphenylphosphonate and 4-methoxyphenylphosphonic acid brings in negative effects. Analysis by impedance spectroscopy indicated that this was attributed to different numbers of proton-releasing hydroxyl groups of the coadsorbents and consequently different proton-adsorbing chemical environments on the surface of TiO2 photoanodes. [Copyright &y& Elsevier]

Abstract: All-transparent and all-flexible dye-sensitized solar cells (DSCs) were fabricated using a novel, facile, and low-lost friction-transfer technique, which involved assembling TiO2 films on flexible substrates via high-temperature sintering. This friction-transfer technique led to a 25% enhancement in conversion efficiency compared with the compression method. The efficiency of the optimized all-flexible DSC reached 5.7%, which is approximately 73% higher than that of the all-flexible DSC prepared by the low-temperature sintering method (3.3%). [Copyright &y& Elsevier]

Abstract: A new class of organic dyes based on acenaphthopyrazine derivatives, containing pyrazine group as the electron acceptor and o-dicarboxyl acids as the anchoring groups were designed and synthesized for application in dye-sensitized solar cells (DSCs). These dyes have short synthesis routes and are easily adsorbed on the surface of TiO2. Under illumination of simulated AM1.5 solar light (100mWcm−2), a total solar energy conversion efficiency (η) of 4.04% was obtained for the 3-(diphenylamino)acenaphtho[1,2-b] pyrazine-8,9-dicarboxylic acid (AP-1) in the preliminary tests, in comparison with the conventional N719 dye (η =7.05%) under the same conditions. [Copyright &y& Elsevier]