Dye Solar Cells Research Articles

Effect of Metal Doped-TiO<sub>2</sub> on the Performance of Dye Solar Cells (DSCs)

Doping of TiO2 with metal or non-metal elements draws much attention in tailoring the properties of photoanode in Dye Solar Cells (DSCs). In this study, liquid impregnation method was implemented in synthesizing metal-doped TiO2 of Al, Fe, Ni and Zn in order to study the effect of doping of metals in TiO2 photoelectrode materials on the performance of integrated DSCs. The synthesized samples were then screen printed onto FTO glass, sensitized with N719 and assembled in sandwich layer with Pt counter electrode. The performance of integrated DSCs was verified using I-V characteristics under illumination of simulated AM 1.5 solar radiance. EIS characterization was done to further understand the electrochemical properties of metal-doped TiO2 photoelectrode of a DSC. The results show that doping with Al at concentration of 0.5 moles metal ion over 100 moles of Ti4+ ions can improve the overall performance efficiency of a DSC from 3.656% to 4.540%. However, Ni and Zn-doped TiO2 photoelectrode were found to improve the Voc whilst DSC with Al-doped TiO2 exhibits the highest Isc and the lowest Rdc resulting in the highest efficiency compared to other metal doped TiO2 DSCs. The doping could influence the electron transport in the photoelectrode materials and interface charge recombination between the photoelectrode materials and the redox electrolyte.

Effect of Reflective Platinum Film on the Performance of Flexible Dye Solar Cell (DSC)

Robust and flexible dye solar cell (DSC) made up of nanocrystalline TiO2 encapsulated in polyethylene naphthalate (PEN) substrate will be able to fulfill the demand for indoor power applications as it has lower energy and manufacturing cost, produces electricity in low light conditions even under artificial light. The fabrication using PEN substrate has the advantage of scalability and compatible with the roll to roll manufacturing method. This paper reports the study on the effect of platinum film reflectance on the counter electrode to the DSC performance and efficiency. The reflective counter electrode uses the commercially available Pt/Ti PEN film with 100% reflectance properties. The transparent counter electrode with 20.9% reflectance is prepared using pre-treated indium doped tin oxide (ITO). The platinum film is sintered at 170°C followed by direct heat of 150°C to achieve a good bonding between the ITO and the deposited platinum film. Both cells uses TiO2 coated ITO PEN as the working electrode. The DSC test cell with reflective counter electrode increases the cell efficiency compared to the non-reflective counter electrode as there is a higher light spectrum response on the reflective DSC cell.

Modified Polyol-Mediated Synthesis of Doped TiO<sub>2</sub> Nanoparticles as the Photoanode in Dye Solar Cells (DSCs)

Synthesis of nanoscale TiO2 exhibiting specific properties of electron or ion conductivity is critical to improve the performance of dye solar cells (DSC). This paper presents the modified polyol-mediated synthesis of doped TiO2 nanoparticles. TiO2 samples were doped with cobalt (Co) and nickel (Ni) and the effects of calcination temperature (550 °C and 650 °C) on the crystallinity of pure samples were investigated. X-ray diffraction (XRD) analysis was used to determine the effect of dopant in lattice structure. The morphology and Crystal structure of TiO2 samples and their chemical analysis was conducted using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectrometer respectively. Results show agglomeration of spherical particles in all doped samples. Crystal structure in the doped samples reveals modified phases and major crystal phase identical to anatase. It is observed that the molar ratio of water to metal can control the nucleation and growth and prevents significant agglomeration of nanoparticles. More effective doping was recorded for samples with 0.5 % concentration. Effective hydroxyl group is detected in both 0.5% Ni and Co promising good photocatalytic material. SEM images of 0.2% Ni-doped sample shows smallest average particle size.

Combined Strategy to Realize Efficient Photoelectrodes for Low Temperature Fabrication of Dye Solar Cells

We implemented a low-temperature approach to fabricate efficient photoanodes for dye-sensitized solar cells, which combines three different nanoarchitectures, namely, a highly conductive and highly transparent AZO film, a thin TiO2-blocking layer, and a mesoporous TiO2 nanorod-based working electrode. All the components were processed at T≤200°C. Both the AZO and the TiO2 blocking layers were deposited by reactive sputtering, whereas the TiO2 nanorods were synthesized by surfactant-assisted wet-chemical routes and processed into photoelectrodes in which the native geometric features assured uniform mesoporous structure with effective nanocrystal interconnectivity suitable to maximize light harvesting and electron diffusion. Because of the optimized structure of the TiO2-blocking/AZO bilayer, and thanks to the good adhesion of the TiO2 nanorods over it, a significant enhancement of the charge recombination resistance was demonstrated, this laying on the basis of the outstanding power conversion efficiency achievable through the use of this photoanode's architecture: a value of 4.6% (N719) was achieved with a 4-μm-thick electrode processed at T=200°C. This value noticeably overcomes the current literature limit got on AZO-based cells (N719), which instead use Nb-doped and thicker blocking layers, and thicker nanostructured photoanodes, which have been even sintered at higher temperatures (450-500°C).

A metallocene molecular complex as visible-light absorber for high-voltage organic-inorganic hybrid photovoltaic cells.

A thin solid-state dye-sensitized photovoltaic cell is fabricated by composing organic and inorganic heterojunctions in which the visible-light sensitizers are cyclopentadiene derivatives (Cp*) coordinated to a metal oxide, typically TiO2. The coordination bonds of the metallocene molecular complex (Ti-Cp*) create a new LMCT (ligand-to-metal charge transfer) absorption band and induce a rectified charge transfer from the organic ligands to TiO2, leading to photocurrent generation. Photovoltaic junctions are completed by coating crystalline organic molecules (perylene) as a hole-transport layer on the Cp*-coordinated TiO2 surface by using the vapor deposition method. The molecular plane of Cp* on the TiO2 surfaces seems to help the hole-transport layer to form ordered structures, which effectively improve carrier conductivities and minimize interfacial resistance. The organic-inorganic hybrid thin-film photocell with metallocene molecular complexes is capable of generating high open-circuit voltages exceeding 1.2 V.

Atomistic Simulation Studies of TiO2 Nanosheets

Studies on TiO2 nanosheets for energy storage and conversion, including anode in lithium ion batteries (LIB) and electrodes in dye solar cells respectively, are not as abundant as those of nanoparticle and nanoporous structures [1]. Such nanosheets are ideal owing to exposure of highly reactive surfaces, such as the anatase {001}facets, which can now be stabilised [2]. Electrochemical investigations reveal that the exposed (001) high-energy facets of the nanosheet result in enhanced rate capability which originates from both the shortened diffusion path and lowered insertion energy barriers on the active surface for Li+ ions [3]. Furthermore, the electrolyte/electrode contact is enhanced via hollow structures; and such features collectively allow for more efficient lithium diffusion in anodes of LIB. In addition to the anatase polymorph [4], TiO2–B [5] nanosheets have also been observed.Generally, studies of nanostructures with the brookite structure are scarce since this polymorph is difficult to grow. Aggregations of nanoparticles with the brookite structure have been reported [6]. However, TiO2 nanosheets with the brookite and rutile components have been recently observed [7]. In order to understand such nano-architecture better, we present results of TiO2 simulated nanosheets, which were generated by amorphisation recrystallisation method [8]. Simulated X-ray diffractions of such structures allude to the presence of the brookite and rutile polymorphs. In addition analysis of their microstructures clearly show zigzag patterns associated with the brookite and straight tunnels related to twinned rutile polymorphs. The lithiated nanosheets of TiO2 were also investigated, and lithium ions were located well within the observed tunnels. The suitability of this TiO2polymorph and nano-architecture for lithium ion batteries electrodes, as compared to the bulk form, will be discussed.

Effect of self-assembly on triiodide diffusion in water based polymer gel electrolytes: An application in dye solar cell

The preparation of ordered polymer gels from the amphiphilic block copolymers, Pluronic® F77, P123 and polyethylene glycol in the presence of ionic liquid, iodine and organic additives is presented. At 35%(w/w) concentration these copolymers (F77 and P123) self-assembled into cubic liquid crystalline phase in aqueous solution and characterized by using SAXS and AFM measurements. The effects of micellar aggregation formed by polymers on the ionic transport and triiodide diffusion have been studied by electrochemistry and SANS experiments. The ionic migration or triiodide diffusion through these polymer gels is found to be affected by the PEO/PPO content in the polymer backbone. These gels were successfully employed as an electrolyte in a dye sensitized solar cell. A remarkable solar to electricity conversion efficiency and good stability was obtained using Pluronic® F77 based gel, which is attributed to its thermoreversible sol to gel transition.

High-performance/low-temperature-processed dye solar cell counter electrodes based on chromium substrates with cube-like morphology

There is still an open question of how to prepare high-performance counter electrodes for dye solar cells (DSCs) at room temperature; a requirement for flexible DSCs. Here, we introduce Pt deposited cube-like chromium coating as a low-temperature highly-efficient counter electrode for DSCs. Cr is a chemically stable metal and can be easily electroplated on conductive substrates with high roughness (here ∼160 nm) and cube-like appearance. A cyclic electrochemical deposition method with optimized temperature and number of cycles is used to grow Pt nanoparticles on this surface and charge transfer resistance as low as 0.54 Ω cm2 and 0.27 Ω cm2 were obtained at 40 °C and 55 °C solution temperatures, respectively. More surface defects (kinks, terraces and ledges) on the cube-like chromium film, as well as the electric field enhancement near the cube edges produces more dispersed Pt nanoparticles on this substrate compared to FTO (fluorine doped tin oxide) substrate. By replacing the conventional DSC counter electrode (thermal Pt on FTO) with this new electrode, filling factor and efficiency increase from 0.63–6.6% to 0.68–8.77%, without a scattering film. The efficiency can be as high as 9.52% by using a scattering film.

Status of Dye Solar Cell Technology as a Guideline for Further Research

Recently, the first commercial dye solar cell (DSC) products based on the mesoscopic principle were successfully launched. Introduction to the market has been accompanied by a strong increase in patent applications in the field during the last four years, which is a good indication of further commercialization activity. Materials and cell concepts have been developed to such extent that easy uptake by industrial manufacturers is possible. The critical phase for broad market acceptance has therefore been reached, which implies focusing on standardization-related research topics. In parallel the number of scientific publications on DSC is growing further (>3500 since 2012), and the range of new or renewed fundamental topics is broadening. A recent example is the introduction of the perovskite mesoscopic cell, for which an efficiency of 14.1% has been certified. Thus, a growing divergence between market introduction and research could be the consequence. Herein, an attempt is made to show that such an unwanted divergence can be prevented, for example, by developing suitable reference-type cell and module concepts as well as manufacturing routes. An in situ cell manufacturing concept that can be applied to mesoscopic-based solar cells in a broader sense is proposed. As a guideline for future module concepts, recent results for large-area, glass-frit-sealed DSC modules from efficiency studies (6.6% active-area efficiency) and outdoor analysis are discussed. Electroluminescence measurements are introduced as a quality tool. Another important point that is addressed is sustainability, which affects both market introduction and the direction of fundamental research.

Influence of Fluorine Plasma Treatment of TiO2Films on the Behavior of Dye Solar Cells Employing the Co(II)/(III) Redox Couple

Fluorine plasma treatment was investigated as an appropriate means for the surface modification of TiO2 thin film electrodes and the optimization of their performance as photoanodes in dye solar ce...

Performance of TiO<sub>2</sub> Nanoparticles Synthesized at pH 2 as Photoelectrode in Dye Solar Cell

Nanocrystalline TiO2 was prepared using sol-gel hydrothermal method to be used as photoelectrode material for dye solar cells (DSC) employing continuous stirring of titanium tetrachloride (TiCl4) with hydrochloric acid (HCl) and deionized water at 70 oC for 6 hours. TiO2 nanopowder was obtained after calcinations in air at 400 oC. The samples were characterized using FESEM, TEM, XRD, BET and UV-Vis optical absorption. This paper discusses the effect of surfactant on the physicochemical properties and the efficiency of the synthesized TiO2 photoelectrode to convert light into electricity.

Improved performance of dye solar cells using nanocarbon as support for platinum nanoparticles in counter electrode

Carbon nanoparticles (CNPs) were used to support platinum nanoparticles as counter electrodes in dye-sensitized solar cells (DSCs). Carbon nanoparticles provided larger effective surface area and better exposure of Pt nanoparticles resulting in very efficient electrocatalytic performance as counter electrode. DSCs fabricated using such counter electrode showed enhanced efficiency owing to lower series resistance and higher fill factor as a result of reduced charge transfer resistance. The overall power conversion efficiency of the DSC devices using these CNP/Pt counter electrodes reached 8.12% as compared to 7.49% for reference platinum counter electrode DSCs under 1sun illumination.

Predicting Energy Conversion Efficiency of Dye Solar Cells from First Principles

In this work we target on accurately predicting energy conversion efficiency of dye-sensitized solar cells (DSC) using parameter-free first principles simulations. We present a set of algorithms, mostly based on solo first principles calculations within the framework of density functional theory, to accurately calculate key properties in energy conversion including sunlight absorption, electron injection, electron–hole recombination, open circuit voltages, and so on. We choose two series of donor-π-acceptor dyes with detailed experimental photovoltaic data as prototype examples to show how these algorithms work. Key parameters experimentally measured for DSC devices can be nicely reproduced by first-principles with as less empirical inputs as possible. For instance, short circuit current of model dyes can be well reproduced by precisely calculating their absorption spectra and charge separation/recombination rates. Open circuit voltages are evaluated through interface band offsets, namely, the difference between the Fermi level of electrons in TiO2 and the redox potential of the electrolyte, after modification with empirical formulas. In these procedures the critical photoelectron injection and recombination dynamics are calculated by real-time excited state electronic dynamics simulations. Estimated solar cell efficiency reproduces corresponding experimental values, with errors usually below 1–2%. Device characteristics such as light harvesting efficiency, incident photon-to-electron conversion efficiency, and the current–voltage characteristics can also be well reproduced and compared with experiment. Thus, we develop a systematic ab initio approach to predict solar cell efficiency and photovoltaic performance of DSC, which enables large-scale efficient dye screening and optimization through high-throughput first principles calculations with only a few parameters taken from experimental settings for electrode and electrolyte toward a renewable energy based society.

Effect of electrolyte bleaching on the stability and performance of dye solar cells

Degradation of dye solar cells (DSCs) under severe ageing conditions may lead to loss of the tri-iodide in the electrolyte - a phenomenon known as electrolyte bleaching. Monitoring changes in the tri-iodide concentration as a result of degradation mechanisms and understanding their causes and effects are fundamental for improving the long-term stability of DSCs. In this contribution a strongly accelerated ageing test (1 Sun visible light, 1.5 Suns UV light, T = 110 °C for 12 h) was performed on DSCs in a double-sealed masterplate configuration to purposely induce severe electrolyte bleaching, and its effects on the performance and stability of DSCs with different initial tri-iodide concentrations [I3(-)]0 were investigated. The cells with low [I3(-)]0 suffered a severe loss in short circuit current density JSC (up to 85%). Also a significant loss of open circuit voltage VOC was observed and this loss was proportional to [I3(-)]0 with the highest VOC drop observed with the highest [I3(-)]0. Non-destructive analysis techniques based on the limited current density, JSCvs. light intensity, and photographic image analysis, were used to quantify the [I3(-)] loss, which was found to be ca. 50 mM and independent of [I3(-)]0. Quantitative model based VOC analysis in terms of changing [I3(-)] revealed that the degradation responsible for the VOC drop was dominated by an unknown mechanism that is unrelated to [I3(-)]0. The methods and results reported here help separating and identifying different degradation mechanisms related to electrolyte bleaching in DSCs.

Nanosheet arrays of TiO2 synthesized by one step conversion of ZnO nanosheets: boosting of electron transport rate and application in dye solar cells

TiO2 replica of ZnO nanosheets were synthesized, showing exceptional e-transport properties in dye solar cells.

Dielectric core–shells with enhanced scattering efficiency as back-reflectors in dye sensitized solar cells

Particulate back-reflector films are conventionally used for the improvement of light harvesting in dye solar cells (DSC). The back-reflection of the films is directly related to the scattering efficiency of the individual particles. Inspired by the idea of multilayer optical thin films, here it is demonstrated theoretically and experimentally that putting a SiO2 shell around spherical rutile-TiO2 particles leads to improved light scattering by the particles. These dielectric core–shells not only enhance the overall diffuse reflection of the films, but they also cause a relative improvement in the red and near infrared regions. Back-reflector films of these core–shell particles employed in DSCs result in an enhanced device efficiency of up to 9.52%. Contrary to the general notion, the conventional DSC back-reflector films are far from ideal, i.e. they show less than a 50% reflection in real device conditions. This is due to the limited thickness of the films (a few micron), as well as the low “wet” reflection of the back-reflector films, i.e. the reflection of the scattering particles embedded in a liquid electrolyte. This fact reveals the need for more optimized scattering particles. We suggest dielectric core–shell particles as an alternative.

Study on Hydrogen Production System by Coupling with DSSCs

The consumption of dye-sensitized solar cells (DSSCs) used to produce hydrogen, compared with the traditional water-splitting energy, is much less. First of all it is because of DSSCs’ low cost, easy fabrication process, high conversion efficiency and good stability; secondly it also solves the problem of serious corrosion of the electrode, for the entire solar system is in the air. We use three tandem dye-sensitized photovoltaic cells as a source of power; the open circuit voltage of photoelectric unit shows the feasibility of using dye-sensitized photovoltaic cell decomposition of water to produce hydrogen.

Panchromatic porous specular back reflectors for efficient transparent dye solar cells

A panchromatic specular reflector based dye solar cell is presented herein. Photovoltaic performance of this novel design is compared to that of cells in which standard diffuse scattering layers are integrated. The capability of the proposed multilayer structures to both emulate the broad band reflection of diffuse scattering layers of standard thickness (around 5 microns) and give rise to similarly high light harvesting and power conversion efficiencies, yet preserving the transparency of the device, is demonstrated. Such white light reflectors are comprised of stacks of different porous optical multilayers, each one displaying a strong reflection in a complementary spectral range, and are designed to leave transmittance unaltered in a narrow red-frequency range in which the sensitized electrode shows negligible absorption, thus allowing us to see through the cell. The reflectance bandwidth achieved is three times as broad as the largest bandwidth previously achieved using any photonic structure integrated into a dye solar cell.

Low Cost Ferritic Stainless Steel in Dye Sensitized Solar Cells with Cobalt Complex Electrolyte

Cheap ferritic stainless steel is applied here as the counter electrode substrate in dye sensitized solar cells with cobalt complex electrolyte. A 5.0% efficiency was reached with these type of cells which is more than 2.5 times higher compared to previously reported devices with metal counter electrode and cobalt complex electrolyte. The electrochemical impedance spectra analysis showed that the best cells with the ferritic steel counter electrode had as low charge transfer resistance (3.6 Ωcm2) as the reference glass cells with the same electrolyte. While in previous studies many metals have corroded in the cobalt complex electrolyte, the stability analysis including scanning electron microscope imaging of the aged electrodes suggested that the ferritic stainless steel substrates did not corrode in the electrolyte. Hence ferritic stainless steel appears as a possible alternative counter electrode in dye solar cells with cobalt electrolyte in terms of cost, performance and stability.

Micro-Raman analysis of reverse bias stressed dye-sensitized solar cells

The degradation mechanisms of Reverse Bias (RB) stressed Dye Solar Cells (DSCs), sensitized with cis-bis(isothiocyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylato)-ruthenium(II)bis-tetrabutylammonium (N719, Red Dye) and with cis-dicyano-bis(2,2′-bipyridyl-4,4′-dicarboxylic acid) ruthenium(II) (Ru505, Orange Dye) have been studied by means of resonance micro-Raman and UV-Vis spectroscopy. For N719 sensitized devices, the visible degradation induced by the stress tests involves both electrolytic solution and the sensitizer: the electrolyte suffers gas bubble formation and loss of solvent, while the dye cannot be regenerated and undergoes irreversible chemical changes. Confocal Raman imaging and UV-Vis absorption spectra confirmed that in regions where the electrolyte was absent, the detachment of the thiocyanate ligand (SCN−) from the dye is favored. On the other hand, measurements carried out on DSCs realized with the bis-cyano dye (Ru505) do not show dye modifications during the RB stress. We also clarify that the apparent N719 dye bleaching in particular zones of the cell active area, is not related to dye desorption from the TiO2 layer, but to loss of solvent and to dye chemical changes, which are responsible for a characteristic blue shift in the absorption spectrum.