Characteristics Of Dye-sensitized Solar Cells Research Articles

Synthesis and characterization of UV-treated Fe-doped bismuth lanthanum titanate-doped TiO2 layers in dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) based on titanium dioxide (TiO2) have been extensively studied because they constitute promising low-cost alternatives to their conventional semiconductor-based counterparts. However, much of the effort aimed at achieving high conversion efficiencies has focused on dye and liquid electrolytes. In this work, we report the photovoltaic characteristics of DSSCs fabricated by mixing TiO2 with Fe-doped bismuth lanthanum titanate (Fe-BLT). These nanosized Fe-BLT powders were prepared by using a high-energy ball-milling process. In addition, we used a UV radiation-ozone (UV-O3) treatment to change the surface wettability of TiO2 from hydrophobic to hydrophilic and thereby prevented the easy separation of the Fe-BLT-mixed TiO2 from the fluorine-doped tin-oxide (FTO) coating glass.

Facile synthesis of Gd_2O_3:Ho^3+/Yb^3+ nanoparticles: an efficient upconverting material for enhanced photovoltaic performance of dye-sensitized solar cells

A series of Ho3+/Yb3+-codoped Gd2O3 nanoparticles were prepared by a facile urea-based homogeneous precipitation method. Under the excitation of 980 nm light, all the samples exhibited strong green and red upconversion (UC) emissions corresponding to the (5F4,5S2) → 5I8 and 5F5 → 5I8 transitions of Ho3+ ions, respectively. A gradual enhancement in the UC emission intensity was observed with increasing the Yb3+ ion concentration, achieving its optimum value when the doping concentration was 3 mol%. In addition, with the introduction of Ho3+/Yb3+-codoped Gd2O3 nanoparticles into the TiO2 porous film of dye-sensitized solar cells (DSSCs), the power conversion efficiency of the cells (7.403%) was ~10.47% higher than that of the DSSCs with pure TiO2 porous film (6.701%), which is mainly caused by increased short-circuit current density due to their enhanced light-harvesting properties via an efficient UC process. The result suggested that the incorporation of upconverting nanoparticles into the TiO2 porous film is an effective approach to improve the photovoltaic characteristics of DSSCs.

Dye-Sensitized Solar Cells in Humidity Environment: A Suitable Fabrication Procedure and Outdoor Test of Cell Stability

The performance of dye-sensitized solar cells (DSCs) fabricated by conventional procedure in humid environment have rapidly declined in outdoor testing. This fact may be caused due to the uptake of water into cells during the process of dye soaking (around 20 - 24 hours) and electrolyte filling under ambient air. In this work a new fabrication procedure, that proved to prevent the water uptake, was established for DSC assembling in high humidity environment. In the procedure, the sandwich cell, assembled from preparative FTO/TiO2 and FTO/Pt electrodes was filled with N719 (10 mM)/DMF solution for the dye adsorption on TiO2film in 4 hours. The dye adsorbing, electrolyte filling and cell sealing have been carried out in inert gas atmosphere using a glove box. By new fabrication procedure the energy conversion efficiency (η) of DSCs was improved on 10%. In addition, DSCs fabricated by new procedure were more stable under outdoor testing, the efficiency was even increased 9% at 14-day-outdoor-exposure. From 30thday of outdoor test the cell efficiency began slightly decrease, and reached the initial value after 100-day-exposure. The effect of co-adsorption with chenodeoxycholic acid (CDA) on DSC performance based on new fabrication procedure was investigated. By addition of 100 mM CDA the short circuit photocurrent has significantly increased, the open circuit voltage slightly increased, and the overall power conversion efficiency of as-prepared DSCs was improved by 8%. However the effect of CDA on cell performance was diminished during outdoor exposure. The change of DSC characteristics was discussed based on analysis of electrochemical impedance spectroscopy (EIS) data. The enhancement of photocurrent caused by the photo-activation of the cathode interface during first weeks of outdoors exposure, as well was the effect of co-adsorbate, were interpreted from impedance spectra.

Synthesis and Characterization of MgO by Microwave-Assisted Thermal Oxidation for Dye-Sensitized Solar Cells

Magnesium oxide (MgO) nanostructures were synthesized by microwave-assisted thermal oxidation at various amount of activated carbon additive. The MgO nanostructures were characterized by scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray diffractrometry (XRD) and UV-Visible spectroscopy, respectivly. It was observed that, the obtained MgO have nanocube shape. The MgO nanostructures were applied as a blocking layer in ZnO dye-sensitized solar cells (DSSC). The photovoltage, photocurrent, and power conversion efficiency characteristics of DSSCs were measured under illumination of simulated sunlight obtained from a solar simulator with the radiant power of 100 mW/cm2. The DSSCs with MgO layer exhibited higher current density, open circuit voltage and photoconversion efficiency than those without MgO layer The optimum power conversion efficiency (PCE) was 2.49 % with short circuit current (Jsc) of 6.61 mA/cm2, the open circuit voltage (Voc) of 0.66 V and the fill factor (FF) of 0.59, respectively.

Realizing omnidirectional light harvesting by employing hierarchical architecture for dye sensitized solar cells.

To improve the omnidirectional light-harvesting in dye-sensitized solar cells (DSSCs), here we present a dandelion-like structure composed of ZnO hemispherical shells and nanorods. Uniformly distributed hemispherical shells effectively suppress the reflection over the broadband region at incident angles up to 60°, greatly improving the optical absorption of the DSSCs. In addition, modulating the length of the ZnO nanorods controls the omnidirectional characteristics of DSSCs. This phenomenon is attributed to the degree of periodicity of the ZnO dandelion-like structures. Cells with shorter rods exhibit a high degree of periodicity, thus the conversion efficiencies of the cells show specific angle-independent features. On the other hand, the cells with longer lengths reveal angle-dependent photovoltaic performance. Along with the simulation, the cells with dandelion-like ZnO structures can couple incident photons efficiently to achieve excellent broadband and omnidirectional light-harvesting performances experimentally, and the DSSCs enhanced the conversion efficiency by 48% at large incident angles. All these findings not only provide further insight into the light-trapping mechanism in these complex three-dimensional nanostructures but also offer efficient omnidirectional and broadband nanostructured photovoltaics for advanced applications.

Application of non-covalent functionalized carbon nanotubes for the counter electrode of dye-sensitized solar cells

Multi-walled carbon nanotubes (MWCNTs) were functionalized noncovalently by lysozyme (LZ), cetyl pyridinium chloride (CPC), deoxycholate sodium (NaDC) and polyethylene glycol octylphenol ether (Triton X-100), respectively in this study. Four different kinds of functionalized MWCNTs were employed into dye-sensitized solar cell (DSSC) as the Pt-free counter electrode (CE). The correlation between the dispersion of MWCNTs and electrochemical active area of CE and the photovoltaic characteristic of DSSC were investigated. Among these four DSSCs, the one with Triton X-100 functionalized MWCNTs showed the best energy conversion efficiency of 2.69% which is 11.16% higher than the DSSC using pristine MWCNTs CE (2.42%), yet the efficiency is lower than the DSSC using Pt CE. While the DSSC with CPC, NaDC and LZ functionalized MWCNTs as the CE showed inferior the photovoltaic conversion efficiency than the DSSC using pristine MWCNTs CE. On analysis of the photovoltaic performance of DSSC and the dispersion of MWCNTs and electrochemical active area of CE, it is found that the high efficiency of the DSSC is associated with the good dispersion of MWCNTs and large electrochemical active area of the counter electrode material.

Spray‐deposited carbon‐nanotube counter‐electrodes for dye‐sensitized solar cells

Carbon nanotubes due to their catalytic properties are a promising alternative to platinum counter electrodes (CE) for dye‐sensitized solar cells (DSSC). In this study, counter electrodes were made from double‐walled carbon nanotube (DWCNT) ink using the spray printing technique and afterwards they were thermally treated at temperatures ranging from 120 to 300 °C. Morphology and structure was studied using scanning electron microscopy and Raman spectroscopy. DSSCs were constructed from titanium‐dioxide photoanodes and DWCNT counter electrodes cured at various temperatures. The current–voltage characteristics of DSSCs and their impedance spectra recorded under illumination have been studied and compared. The photoconversion efficiency (PCE) of the solar cell reached a maximum value of 4.59% when the carbon layer was thermally treated at 300 °C and is 16% higher than that registered for devices with a standard platinum counter electrode.

Effects of compression at elevated temperature for electrophorically deposited TiO2-based dye-sensitized solar cell

In this investigation, dye-sensitized solar cells (DSSCs) were prepared by electrophoretic deposition (EPD) of commercially available nanometer-sized titanium oxide (TiO2) nanoparticles (anatase, ST01) on fluorine-doped tin oxide (FTO) glass substrates. The rate of cathodic electrophoretic deposition of TiO2 nanoparticle agglomerates and the density of the obtained films were explored as a function of the applied electric field, keeping optimized suspension compositions, such as the particle concentration and the type of solvent. Optimized deposition conditions were found to result in homogeneous, well-controlled, mesoporous TiO2 thick-film photoanodes. Compression of the prepared glass substrate TiO2 photoanode at elevated temperature was commenced as a promising postdeposition surface treatment. The photovoltaic performance characteristics of DSSC prepared by this method were found to be considerably improved compared with those of DSSCs prepared by high-temperature postannealing and compression at room temperature. Surface morphologies were observed by scanning electron microscopy (SEM) and significant improvement was observed after compression as well as compression at elevated temperature.

High-Performance Platinum-Free Dye-Sensitized Solar Cells with Molybdenum Disulfide Films as Counter Electrodes.

By using a radio-frequency sputtering method, we synthesized large-area, uniform, and transparent molybdenum disulfide film electrodes (1, 3, 5, and 7 min) on transparent and conducting fluorine-doped tin oxide (FTO), as ecofriendly, cost-effective counter electrodes (CE) for dye-sensitized solar cells (DSSCs). These CEs were used in place of the routinely used expensive platinum CEs for the catalytic reduction of a triiodide electrolyte. The structure and morphology of the MoS2 was analyzed by using Raman spectroscopy, X-ray diffraction, and X-ray photoemission spectroscopy measurements and the DSSC characteristics were investigated. An unbroken film of MoS2 was identified on the FTO crystallites from field-emission scanning electron microscopy. Cyclic voltammetry, electrochemical impedance spectroscopy, and Tafel curve measurements reveal the promise of MoS2 as a CE with a low charge-transfer resistance, high electrocatalytic activity, and fast reaction kinetics for the reduction of triiodide to iodide. Finally, an optimized transparent MoS2 CE, obtained after 5 min synthesis time, showed a high power-conversion efficiency of 6.0 %, which comparable to the performance obtained with a Pt CE (6.6 %) when used in TiO2 -based DSCCs, thus signifying the importance of sputtering time on DSSC performance.

Enhancing the efficiency of flexible dye-sensitized solar cells utilizing natural dye extracted from Azadirachta indica

The natural dye extracted from Azadirechta indica (neem) was used as a sensitizer in flexible dye-sensitized solar cells (DSSCs). The fabricated DSSC exhibited open circuit voltage of 0.538 V with 2.81% power conversion efficiency (η) in back-illuminated mode which is higher than that reported in the literature. In order to understand the characteristics of DSSC, systematic study of solar cell component materials was carried out. Anatase TiO2 (30–40 nm) nanoparticles were synthesized by DC arc plasma method and deposited electrophoretically on a flexible titanium (Ti) substrate. A platinum-coated polyethylene terephthalate (PET) substrate was used as a counter electrode to construct flexible DSSC. The structural and optical behavior of neem-dye sensitized TiO2 thin film has been studied using x-ray diffraction, field emission scanning electron microscopy, high resolution transmission electron microscopy and UV-visible spectroscopy. We have observed that the neem dye gives a very good sensitization effect. In addition, the dye has good prospects as a low-cost and environmental friendly alternative to ruthenium-based sensitizers which are normally used in DSSCs.

Investigation of Coral-Like Cu2O Nano/Microstructures as Counter Electrodes for Dye-Sensitized Solar Cells.

In this study, a chemical oxidation method was employed to fabricate coral-like Cu2O nano/microstructures on Cu foils as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). The Cu2O nano/microstructures were prepared at various sintering temperatures (400, 500, 600 and 700 °C) to investigate the influences of the sintering temperature on the DSSC characteristics. First, the Cu foil substrates were immersed in an aqueous solution containing (NH4)2S2O8 and NaOH. After reacting at 25 °C for 30 min, the Cu substrates were converted to Cu(OH)2 nanostructures. Subsequently, the nanostructures were subjected to nitrogen sintering, leading to Cu(OH)2 being dehydrated into CuO, which was then deoxidized to form coral-like Cu2O nano/microstructures. The material properties of the Cu2O CEs were comprehensively determined using a scanning electron microscope, energy dispersive X-ray spectrometer, X-ray diffractometer, Raman spectrometer, X-ray photoelectron spectroscope, and cyclic voltameter. The Cu2O CEs sintered at various temperatures were used in DSSC devices and analyzed according to the current density–voltage characteristics, incident photon-to-current conversion efficiency, and electrochemical impedance characteristics. The Cu2O CEs sintered at 600 °C exhibited the optimal electrode properties and DSSC performance, yielding a power conversion efficiency of 3.62%. The Cu2O CEs fabricated on Cu foil were generally mechanically flexible and could therefore be applied to flexible DSSCs.

Effect of flower extracts on the photoconversion efficiency of dye sensitized solar cells fabricated with Sn-doped TiO2

Extensive efforts are being made in enhancing the photoconversion efficiency of TiO2 based dye sensi- tized solar cells (DSSC) using different approaches. In this work, the Sn-doped TiO2 nanopowder was sensitized with flower extracts of Dahlia Violet (DV), Rabbit flower (RF) and their mixed extract separately other than the com- mercial N719 dye and DSSC characteristics were studied. Hydrothermal method was used to synthesize Sn-doped TiO2 for 48 h at 150 C. X-ray diffraction, UV-Vis, FTIR and Raman scattering were used to characterize the syn- thesized powder. DSSCs of the synthesized powder was fabricated using conventional sandwich type technique sealed with Surlyn polymer film. The photocurrent-volt- age characteristics were measured under solar simulated light using source-meter. It is interesting to note that the flower extract resulted in comparable photoconversion ef- ficiency as that of N719 dye. When the powder was sen- sitized with N719, 1.66 % efficiency was achieved while mixed extract resulted in 1.28 %, DV in 0.99 % and RF in 0.52 % efficiency. The results of various analysis tech- niques and cell characteristics are correlated.

Dependence of ZnO-based dye-sensitized solar cell characteristics on the layer deposition method

The selection of a proper method for the semiconductor layer deposition is an important requirement towards a high efficiency for dye-sensitized solar cells (DSSCs). We compared three techniques for deposition of the semiconductor thin layer in ZnO-based DSSCs, in order to determine the dependence between the deposition method, the ZnO film properties and finally the DSSCs characteristics. For this purpose, we varied the method used for deposition of the semiconductor film and we replaced ZnO with Al-doped ZnO. The nanostructured films morphology was analysed by transmission electron microscopy, high-resolution transmission electron microscopy and selected area electron diffraction. The optical properties were examined by UV–visible spectroscopy and the bandgap energies were calculated using the Tauc equation. The higher fill factor value was registered for DSSCs based on the ZnO film obtained by electrochemical method, but the higher efficiency was registered for doctor-blading method.

TiO<sub>2</sub> Nanorods Prepared from Anodic Aluminum Oxide Template and their Applications in Dye-Sensitized Solar Cells

Anodic aluminum oxide (AAO) was used as a template coupled with liquid process for synthesis of TiO2 nanorods. Immersion setting (IS) was carried out to insert a TiO2 precursor solution into AAO pore. With the calcination and NaOH treatment to remove AAO, SEM characterization revealed that TiO2 nanorods with diameter around 100-200 nm were successfully fabricated from AAO commercial templates. The synthesized nanorods mixed with commercial TiO2 nanoparticles (P-25) with a mixing ratio of 5:95 (by mass) were used as an electrode in a dye-sensitized solar cell (DSSC), The photoelectrodes made with nanorods showed a better performance than the cells used of only pristine TiO2 nanoparticles. The results from current density-voltage (J-V) characteristics of DSSCs showed that short-circuit current density (JSC), open-circuit voltage (VOC), fill factor (FF), and power conversion efficiency (PCE) are 11.78 mA/cm2, 0.72 V, 0.55, and 4.68%, respectively. Due to the effects of one-dimensional (1-D) nanostructure, the electron expressway concept was achieved in this research.

TiO<sub>2</sub> Nanorods Prepared from Anodic Aluminum Oxide Template and their Applications in Dye-Sensitized Solar Cells

Anodic aluminum oxide (AAO) was used as a template coupled with liquid process for synthesis of TiO2 nanorods. Immersion setting (IS) was carried out to insert a TiO2 precursor solution into AAO pore. With the calcination and NaOH treatment to remove AAO, SEM characterization revealed that TiO2 nanorods with diameter around 100-200 nm were successfully fabricated from AAO commercial templates. The synthesized nanorods mixed with commercial TiO2 nanoparticles (P-25) with a mixing ratio of 5:95 (by mass) were used as an electrode in a dye-sensitized solar cell (DSSC), The photoelectrodes made with nanorods showed a better performance than the cells used of only pristine TiO2 nanoparticles. The results from current density-voltage (J-V) characteristics of DSSCs showed that short-circuit current density (JSC), open-circuit voltage (VOC), fill factor (FF), and power conversion efficiency (PCE) are 11.78 mA/cm2, 0.72 V, 0.55, and 4.68%, respectively. Due to the effects of one-dimensional (1-D) nanostructure, the electron expressway concept was achieved in this research.

Sea‐Urchin‐Like ZnO Nanoparticle Film for Dye‐Sensitized Solar Cells

We present novel sea‐urchin‐like ZnO nanoparticles synthesized using a chemical solution method. Solution approaches to synthesizing ZnO nanostructures have several advantages including low growth temperatures and high potential for scaling up. We investigated the influence of reaction times on the thickness and morphology of sea‐urchin‐like ZnO nanoparticles, and XRD patterns show strong intensity in every direction. Dye‐sensitized solar cells (DSSCs) were developed using the synthesized ZnO nanostructures as photoanodes. The DSSCs comprised a fluorine‐doped tin oxide (FTO) glass with dense ZnO nanostructures as the working electrode, a platinized FTO glass as the counter electrode, N719‐based dye, and I‐/I3‐liquid electrolyte. The DSSC fabricated using such nanostructures yielded a high power conversion efficiency of 1.16% with an incident photo‐to‐current efficiency (IPCE) as high as 15.32%. Electrochemical impedance spectroscopy was applied to investigate the characteristics of DSSCs. An improvement in the electron transport in the ZnO photoanode was also observed.

Effect of neodymium on the photoconversion efficiency of TiO2 based dye sensitized solar cells

Extensive efforts are being made in enhancing the photoconversion efficiency of TiO2 based dye sensitized solar cells (DSSC) using different approaches. In this work, the TiO2 nanopowder was sensitized with rare earth metal and DSSC characteristics were studied. Commercial powder (P25) was calcined at 450 °C and sensitized with Nd. X-ray diffraction, UV–Vis, FTIR and Raman scattering were used to characterize nanopowder and found that Nd-sensitization resulted in formation of additional absorption/vibrational bands. The photocurrent–voltage characteristics were measured under simulated light using source-meter. It is interesting to note that the photoconversion efficiency has doubled when commercial powder was just calcined. When the powder was sensitized with Nd, efficiency has tremendously increased to 4.51 % for commercial powder and 9.10 % for calcined powder indicating the effect of Nd-sensitization. The results of various analysis techniques and cell characteristics are correlated.

Incorporation of 3D crumpled graphene in nanostructured TiO2 films for dye-sensitized solar cells

The characteristics of three-dimensional crumpled graphene (3D CGR) incorporated into TiO2 photoanode film for dye-sensitized solar cells (DSSCs) were investigated. The 3D CGR was prepared from a colloidal solution of graphene oxide (GO) via an aerosol spray-drying process. The morphological and optical properties of the as-fabricated 3D CGR/TiO2 photoanodes were systematically investigated. Furthermore, the photovoltaic characteristics of DSSCs fabricated with 3D CGR/TiO2 photoanodes with different amounts of 3D CGR were investigated. The DSSCs fabricated with the 3D CGR/TiO2 photoanode (3D CGR/TiO2=0.01) showed the highest conversion efficiency of 6.3%, which was approximately 47% higher than that of a DSSC fabricated with a pure TiO2 photoanode.

Effects of polymer chemistry on polymer-electrolyte dye sensitized solar cell performance: A theoretical and experimental investigation

The effects of polymer chemistry on interfacial properties and overall performance in polymer-electrolyte dye sensitized solar cells (DSSCs) are investigated theoretically and experimentally. Specifically, polymer electrolytes based on poly(2-hydroxyethyl methacrylate) (PHEMA), poly(glycidyl methacrylate) (PGMA), and poly(4-vinylpyridine) (P4VP) are considered. These polymers are grown directly within the mesoporous TiO2 photoanode via a single step polymerization and coating using initiated chemical vapor deposition (iCVD) to maximize pore filling. The experimental study coupled with a 1-D first-principles macroscopic DSSC mathematical model provides insight into the cell interfacial processes and overall performance. Parameter estimation using the macroscopic model indicates that the pendant groups on the polymers strongly affect the conduction band position of TiO2, the back electron transfer at the photoanode-electrolyte interface, and the exchange current density at the platinum cathode. The estimated difference between the TiO2 conduction band edge and the redox potential of the electrolyte are 0.87, 0.99 and 1.06 eV for P4VP, PGMA, and PHEMA, respectively. Estimated recombination rate constants for P4VP and PGMA are respectively 54% and 19% lower than that of PHEMA. This study indicates that by varying polymer electrolyte chemistry, DSSC characteristics including open-circuit voltage, short-circuit current density, and fill factor can be tuned.

Recent developments in dye-sensitized solar cells.

The knowledge of dye-sensitized solar cells (DSCs) has expanded considerably in recent years. They are multiparameter and complex systems that work only if various parameters are tuned simultaneously. This makes it difficult to target to a single parameter to improve the efficiency. There is a wealth of knowledge concerning different DSC structures and characteristics. In this review, the present knowledge and recent achievements are surveyed with emphasis on the more promising cell materials and designs.