High-performance Dye-sensitized Solar Cells Research Articles

Enhancing the performance of dye-sensitized solar cells: doping SnO2photoanodes with Al to simultaneously improve conduction band and electron lifetime

Al-doping of SnO2photoanodes can simultaneously improve conduction band and electron lifetime of high-performance dye-sensitized solar cells.

Engineering of the electron donor of triarylamine sensitizers for high-performance dye-sensitized solar cells

Triphenylamine (TPA) and their derivatives are well-known electron-rich compounds that are widely used in various optical and electronic fields. Here, two new organic dyes (M40 and M41) featuring TPA or dihexyloxy-substituted triphenylamine (DHO–TPA) electron donor have been designed and synthesized. M40 sensitized DSCs employing the Co(II/III)tris(1,10-phenanthroline)-based redox electrolyte affords a short circuit photocurrent of 14.32mAcm−2, an open circuit voltage of 907mV, and a fill factor of 0.68, corresponding to an overall conversion efficiency of 8.83% under standard AM 1.5 sunlight. This efficiency is much higher than those of the M41 sensitized DSCs, being 7.81% under the same conditions. Absorption spectra, electrochemical measurements, theoretical calculations, and photovoltaic measurements are used to compare the light absorptions, energy-levels, and charge transfer dynamics that contribute to the photovoltaic behavior.

Microwave-Assisted Topochemical Conversion of Layered Titanate Nanosheets to {010}-Faceted Anatase Nanocrystals for High Performance Photocatalysts and Dye-Sensitized Solar Cells

The {010}-faceted anatase nanocrystals with controllable crystal size and morphology were synthesized by microwave hydrothermal treatment of layered titanate nanosheet solutions. The nanostructures and formation reaction mechanism of TiO2 nanocrystals were investigated using X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and selected-area electron diffraction. Their photocatalytic behavior and dye-sensitized solar cell (DSSC) performance were studied and compared with [111]-faceted anatase nanocrystals and anatase nanocrystals without a specific facet on the surface. There are two kinds of reactions in the formation process of the anatase nanocrystals. One is an in situ topochemical conversion reaction of layered titanate structure to anatase structure, and another is the dissolution–deposition reaction on the particle surface. The microwave hydrothermal process is suitable to control the structural conversion reaction for uniform the crystal size and morphology due to its uniform heating mechanism. The UV–visible spectrum results revealed that the bandgap of the TiO2 nanocrystals was enhanced in the order of nanocrystal without specific facet < [111]-faceted nanocrystal < {010}-faceted nanocrystal, which corresponded to their photocatalytic activities. The DSSC performance also was enhanced in the same order, suggesting that the {010}-faceted nanocrystals are promising for the high performance DSSCs.

Rational modifications on champion porphyrin dye using different electron-withdrawing moieties toward high performance dye-sensitized solar cells.

Ten porphyrin sensitizers with different electron-withdrawing groups derived from the best sensitizer SM315 were investigated by means of the density functional theory (DFT) and time-dependent DFT calculations. To this end, major factors affecting the performance of the cell, including light harvesting, electron injection, dye regeneration, and conduction band energy shift are taken into consideration. Especially, the calculated distance (r) from the electron recapture center to the semiconductor surface is used to probe the charge recombination process. In addition, considering the complexity of the porphyrin sensitizers' absorption, the maximum short circuit current density (J(max)sc) is determined for investigating the light harvesting ability quantitatively. We find that when compared to SM315 with 2,1,3-benzothiadiazole, 1 with naphtho[1,2-c:5,6-c]bis[1,2,5]thiadiazole shows better performance due to both larger J(max)sc and r, and 7 with diketopyrrolopyrrole could also be a promising candidate due to the much larger J(max)sc and comparable r.

Integrating a triplet-triplet annihilation up-conversion system to enhance dye-sensitized solar cell response to sub-bandgap light.

The poor response of dye-sensitized solar cells (DSCs) to red and infrared light is a significant impediment to the realization of higher photocurrents and hence higher efficiencies. Photon up-conversion by way of triplet-triplet annihilation (TTA-UC) is an attractive technique for using these otherwise wasted low energy photons to produce photocurrent, while not interfering with the photoanodic performance in a deleterious manner. Further to this, TTA-UC has a number of features, distinct from other reported photon up-conversion technologies, which renders it particularly suitable for coupling with DSC technology. In this work, a proven high performance TTA-UC system, comprising a palladium porphyrin sensitizer and rubrene emitter, is combined with a high performance DSC (utilizing the organic dye D149) in an integrated device. The device shows an enhanced response to sub-bandgap light over the absorption range of the TTA-UC sub-unit resulting in the highest figure of merit for up-conversion assisted DSC performance to date.

High performance dye-sensitized solar cell by using porous polyaniline nanotubes as counter electrode

High efficiency and low cost dye-sensitized solar cells (DSSCs) have attracted much attention very recently in the context of our need for an affordable renewable energy source. Inexpensive porous polyaniline nanotubes (PPNT-1) have been synthesized through a simple method via controlled polymerization of aniline with ammonium persulfate in the presence of concentrated orthophosphoric acid. PPNT-1 has been used as a substitute for platinum to construct the counter electrode (CE) in a DSSC, which showed lower charge transfer resistance and higher electrocatalytic activity for reduction of I3- into I− than that of Pt electrode. PPNT-1-10T CE achieved a high conversion efficiency of 5.57%, matching the performance of otherwise identical DSSCs with Pt CE (5.20%).

Molecular gelation of ionic liquid–sulfolane mixtures, a solid electrolyte for high performance dye-sensitized solar cells

Cyclohexanecarboxylic acid-[4-(3-tetradecylureido)phenyl]amide is an efficient gelator to solidify ionic liquid electrolytes. In this paper we apply this low molecular weight gelator to solidify the newly prepared sulfolane based ionic liquid electrolyte. This solid electrolyte is successfully applied as an electrolyte for dye sensitized solar cells. This solid electrolyte is thermo-reversible, upon heating it will become a liquid and at room temperature it will solidify, facilitating the cell filling by the electrolyte. Applying this solid electrolyte we obtained 7.8% power conversion efficiency under simulated AM 1.5 full sunlight intensity. The devices with liquid and solid electrolytes were analysed by electrochemical impedance spectroscopy to explain the differences in the photovoltaic performance. These cells were also measured under outdoor conditions at Jeddah, Saudi Arabia to explore the feasibility of practical applications of this electrolyte.

Synthesis of {010}-faceted anatase TiO2nanoparticles from layered titanate for dye-sensitized solar cells

Crystal facets exposed on TiO2 nanoparticles strongly affect dye molecule adsorption and cell performance in dye-sensitized solar cells (DSSCs). In this study, size- and morphology-controllable {010}-faceted anatase-type TiO2 nanocrystals, including rhombic, tetragonal, and leaflike nanocrystals and platelike mesocrystals, were synthesized via hydrothermal treatment of layered titanate (HTO) nanosheet colloidal solutions. The formation reactions and nanostructures of the anatase nanocrystals were investigated using XRD, FE-SEM, and TEM. There are two kinds of reactions in the formation process of the anatase nanocrystals from the HTO nanosheets. One is an in situ topotactic structural transformation reaction and another is a dissolution–deposition reaction. The DSSC performance of the {010}-faceted anatase nanocrystals was investigated by measurements of I–V characteristics, electrochemical impedance spectra, and dye adsorptions and compared with [111]-faceted P25 nanocrystals and spherical ST20 nanocrystals without a specific facet on the surface. The DSSC results suggested that the Jsc and η values increase in the order of spherical nanocrystals without a specific facet < [111]-faceted nanocrystals < {010}-faceted nanocrystals, which concludes that the facet on the nanoparticle surface significantly impacts on the DSSC performance and the {010}-faceted nanocrystals are promising for the high-performance DSSCs.

Synthesis of Single-Crystalline Anatase TiO2 Nanorods With High-Performance Dye-Sensitized Solar Cells

Single-crystalline anatase TiO2 nanorods have been prepared by solvothermal method using tetrabutylammonium hydroxide (TBAH) as a morphology controlling agent. The obtained TiO2 nanorods are dominated by a large percentage of {010} facets. The power conversion efficiency of dye-sensitized solar cell (DSSC) based on anatase TiO2 nanorods (8.66%) exhibits a significant improvement (35%) compared to that of P25 TiO2 (5.66%). The high performance of the anatase TiO2 nanorods solar cell is ascribed to their large percent of exposed {010} facets as well as balancing their surface areas and sizes.

DFT and TD-DFT studies on osmacycle dyes with tunable photoelectronic properties for solar cells

B3LYP and CAM-B3LYP functionals have been used to determine structures, electronic and optical properties of osmium-bridged tricyclic aromatic compounds. Calculations show that the optical properties and charge separation features of these osmacycle derivatives can be well modified by incorporating different π-bridge groups. In particular, the newly designed osmacycle dyes 5 and 6 by embedding thiophene and thienothiophene bridge units to osmium polycyclic aromatic system show very strong and broad adsorptions in the whole visible region and excellent charge separation in the first excited state of 1(ππ*) from the hightest occupied molecular orbital to the lowest unoccupied molecular orbital excitation. Furthermore, the predicted relatively high light harvesting efficiency and large driving force for electron injection suggest that they are quite promising for design of high-performance dye-sensitized solar cells.

All-nano-TiO2 compact film for high-performance dye-sensitized solar cells.

An innovative all-nano-TiO2 thin film capable of enhancing dye-sensitized solar cell (DSC) photoefficiencies was prepared by a layer-by-layer method beneath the meso-TiO2 film, employing acid and basic nano-TiO2 sols as cations and anions, respectively. TiO2 syntheses were performed under absolute control to lead to appropriate morphological and optical properties to yield high-quality compact films using profilometry, tuning, and scanning electron microscopy. A detailed study by photoelectrochemical parameters, incident photon-to-current efficiency, electron lifetime, and electrochemical impedance spectroscopy demonstrates that the physical contact between FTO and the electrolyte is prevented and the role of the compact film has been elucidated. DSCs with TiO2 bilayers on top of FTO improved the conversion efficiency up to 62%, mainly because of the prevention of FTO/I3(-) charge recombination and an improved contact between FTO and TiO2.

2,6-Conjugated Bodipy sensitizers for high-performance dye-sensitized solar cells

A series of novel 2,6-conjugated Bodipy metal-free organic dyes (UY5–8) with phenothiazine (PTZ) moiety as electron donor for the dye-sensitized solar cells (DSSCs) have been designed and synthesized. The optical, electrochemical properties and photovoltaic performances are extensively investigated. The structure–property relationship shows that the introduction of various auxiliary conjugated spacers and anchoring groups are favorable to changing the efficiency of DSSCs. Among these dyes, UY7 comprised of furan with lower resonance energy as linker and cyanoacetic acid unit as electron acceptor possesses a flatter structure and longer electron recombination lifetime. Hence, a DSSCs using UY7 showing best photovoltaic performance with a short-circuit photocurrent density (Jsc) of 13.64mAcm−2, an open-circuit photovoltage (Voc) of 590mV and a fill factor (ff) of 0.66, corresponding to an overall conversion efficiency (η) of 5.31% under 100mWcm−2 simulated AM 1.5 G solar irradiation. This is the best reported result in the solar cell with a Bodipy dye as photosensitizer.

Flexible counter electrodes based on nitrogen-doped carbon aerogels with tunable pore structure for high-performance dye-sensitized solar cells

Nitrogen-doped carbon aerogels (NCAs) were prepared by introducing tripolycyanamide during the synthesis of organic aerogel precursors, and the effects of the nitrogen content on the pore structure of NCAs and the photovoltaic properties of dye-sensitized solar cells (DSSCs) based on NCA counter electrodes (CEs) were studied. With the increase of nitrogen-doped concentration, the pore size of NCAs decreases, and the mesoporous volume fraction increases, which lead to lower charge-transfer resistance and better electrocatalytic activity. The NCA CE based on polyvinylidene fluoride as binder shows a greater electrocatalytic activity than that based on polytetrafluorethylene because its higher polarity leads to better bonding capacity. Under optimized experimental conditions, the DSSC based on NCA8 flexible CE achieved a photoelectric conversion efficiency of 8.83%, which is 102.6% of that based on platinum CE (8.61%) under the same experimental conditions (AM 1.5, 100mWcm−2).

High performance dye-sensitized solar cells using graphene modified fluorine-doped tin oxide glass by Langmuir–Blodgett technique

Since the introduction of dye-sensitized solar cells (DSSCs) with low fabrication cost and high power conversion efficiency, extensive studies have been carried out to improve the charge transfer rate and performance of DSSCs. In this paper, we present DSSCs that use surface modified fluorine-doped tin oxide (FTO) substrates with reduced graphene oxide (r-GO) sheets prepared using the Langmuir–Blodgett (LB) technique to decrease the charge recombination at the TiO2/FTO interface. R-GO sheets were excellently attached on FTO surface without physical deformations such as wrinkles; effects of the surface coverage of r-GO on the DSSC performance were also investigated. By using graphene modified FTO substrates, the resistance at the interface of TiO2/FTO was reduced and the power conversion efficiency was increased to 8.44%.

Branched hierarchical photoanode of titanium dioxide nanoneedles on tin dioxide nanofiber network for high performance dye-sensitized solar cells

We report a branched hierarchical nanostructure of TiO2 nanoneedles on SnO2 nanofiber network (B-SnO2 NF) that serves as model architecture for highly efficient dye-sensitized solar cells (DSSCs). The nanostructure simultaneously offers a low degree of charge recombination, a fast electron transport and a large specific surface area. The power conversion efficiency for B-SnO2 NF52 (with SnO2 NF diameter ∼52 nm) is up to 7.06%, increased by 26% and 40% compared to B-SnO2 NF113 (5.57%, with SnO2 NF diameter ∼113 nm) and TiO2 nanoparticle (5.04%, P25), respectively, and more than five times as large as SnO2 NF52 (1.34%). The distinct photovoltaic behavior of the B-SnO2 NF52 is its large short-circuit current density (Jsc, 20.5 mA cm−2) as compared with the commonly used P25 photoanode (11.7 mA cm−2). Our results indicate that Jsc enhancement derived by the slower electron recombination associated with the SnO2–TiO2 core–shell heterojunction and faster electron transport in SnO2 NF network could synergistically contribute to high efficiency.

Improved anatase phase stability in small diameter TiO2 nanotube arrays for high performance dye-sensitized solar cells

Anatase is the preferred phase of TiO2 in dye-sensitized solar cells (DSSCs) because of its lower charge recombination than other phases. However, for small diameter nanotubes before detached from the Ti foil, rutile rather than anatase appears upon a pre-treatment annealing at 400°C or above. Here we have fabricated highly ordered free-standing small diameter (50nm) TiO2 nanotube membranes which were pre-treated at 300°C to maintain pure anatase phase. The free-standing nanotube membranes were used to fabricate the photoanodes and were further calcined at 500°C to achieve full crystallization of the nanotubes. It was shown that the electron lifetime is much longer in the 300°C-pre-treated nanotubes than those pre-treated at 400 or 500°C, leading to a significantly improved power conversion efficiency of 4.59% (enhanced by ∼50%).

Constructing hierarchical fastener-like spheres from anatase TiO2 nanosheets with exposed {001} facets for high-performance dye-sensitized solar cells

Hierarchical fastener-like spheres assembled from anatase TiO2 nanosheets with exposed {001} facets are successfully synthesized via a facile one-pot hydrothermal process. Compared with standard commercial P25, the as-obtained hierarchical fastener-like TiO2 spheres exhibit an improved light harvesting efficiency, owing to the excellent light scattering effect of layer-by-layer hierarchical structure and superior dye adsorption capacity of the dominant {001} facets. As a consequence, the photoanode composed of TiO2 fastener-like sphere scattering layer shows an improved DSSCs conversion efficiency of 7.01% compared to that of commercial P25 (5.78%). The remarkable electrochemical performances of hierarchical fastener-like TiO2 spheres indicate their promising application as scattering materials for DSSCs.

High Performance Dye-Sensitized Solar Cells Based on Vacuum-Assisted Thermal Deposition Pt Counter Electrodes

In this work, the vacuum-assisted thermal deposition platinum (Pt) film was prepared and used as a counter electrode (CE) in dye sensitized solar cell (DSC). The films were characterized by scanning electron microscopy (SEM). Electrochemical catalytic activities of the films were also characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The effects of the Pt loading amount on the fluorine-doped tin oxide (FTO) glass and titration time on the performance of the DSC were investigated. The optimal performance of the DSC was obtained when using the three-time titration with 1.69 mg/cm2 Pt loading amount vacuum-assisted thermal deposit CE. The DSC showed a high efficiency of 7.20%. The short-circuit current density (Jsc), open circuit voltage (Voc) and fill factor (FF) were 13.79 mA·cm-2, 0.73 V and 0.71, respectively.

Printable Highly Catalytic Pt- and TCO-Free Counter Electrode for Dye-Sensitized Solar Cells

Here we show that a counter electrode based on carbon network supported Cu2ZnSnS4 nanodots on Mo-coated soda-lime glass for dye-sensitized solar cells can outperform the conventional best electrode with Pt nanoparticles on the fluorine-doped SnO2 conducting glass. In the as-developed electrode, all of the elements are of high abundance ratios with low materials cost. The fabrication is scalable because it is conducted by a screen-printing based approach. Therefore, this research lays a solid ground for the large area fabrication of high-performance dye-sensitized solar cell at reduced material cost.

Dependence of the electrocatalytic performance of platinized counter electrodes on the redox mediator employed in dye-sensitized solar cells

The electrocatalytic properties of platinized counter electrodes (Pt CEs) prepared by various coating methods were investigated with respect to the redox mediator, including the widely used iodide/tri-iodide (I - / I3 ) and the more recently introduced cobalt(II/III)tris(2,2 0 - bipyridine) (Co(bpy)3?/3? ), for application in dye-sensi- tized solar cells (DSCs). The coating methods controlled Pt loading and the surface morphology of the Pt CEs. For a high-performance DSC with a fill factor (0.7, the charge- transfer resistance at the Pt CE/electrolyte interface should be \4.5 X cm 2 for both redox mediators. The I - /I3 -med- iated DSCs were insensitive to Pt loading as low as 0.001 mg cm -2 , while the Co(bpy)3?/3? -mediated DSCs required relatively large Pt loadings of ( 0.005 mg cm -2 . Our results indicated that care should be taken in the preparation of Pt CEs with high transparency and low loading to obtain high-performance DSCs employing cobalt-ligand redox electrolyte.