Photovoltaic Characteristics Of Dye-sensitized Solar Cells Research Articles

Synthesis of Novel Triphenylamine-Based Organic Dyes with Dual Anchors for Efficient Dye-Sensitized Solar Cells

A new series of metal-free organic dyes (SM1-5) with dual anchors are synthesized for application in dye-sensitized solar cells (DSSC). Here, a simple triphenylamine (TPA) moiety serves as the electron donor, while di-cyanoacrylamide and di-thiazolidine-5-one units serve as the electron acceptors and anchoring groups. To understand the effect of dye structure on the photovoltaic characteristics of DSSCs, the photophysical and electrochemical properties, as well as molecular geometries calculated from density functional theory (DFT), are used for dyes SM1-5. The extinction coefficients of the organic dyes SM1-5 are high (5.36–9.54 104 M−1 cm−1), indicating a high aptitude for light harvesting. The photovoltaic studies indicated that using dye SM4 as a sensitizer showed a power conversion efficiency (PCE) of 6.09% (JSC = 14.13 mA cm−2, VOC = 0.624 V, FF = 68.89%). Interestingly, SM4 showed the highest values of VOC among all dyes, including N-719, due to its maximum dye coverage on the TiO2 surface, enhancing charge recombination resistance in the sensitized cell. The good agreement between the theoretically and experimentally obtained data indicates that the energy functional and basis set employed in this study can be successfully utilized to predict new photosensitizers' absorption spectra with great precision before synthesis. Also, these results show that bi-anchoring molecules have a lot of potentials to improve the overall performance of dye-sensitized solar cells.

Tuning the dye aerosol impaction and TiO2 nanoparticle stacking structures for High-Efficiency Dye-Sensitized solar cells

The rapid manufacturing of high-efficiency dye-sensitized solar cells (DSSCs) is limited by the slow dye adsorption on TiO2 nanoparticles (NPs)-accumulated photoelectrode using conventional dip-coating process. Therefore, we aim to accelerate the adsorption of dyes that are attached on TiO2 NPs by employing an aerosol impactor. Herein the aerosolized dyes are designed to get deposited rapidly on the TiO2 NPs-accumulated photoelectrode. In addition, to effectively trap the irradiated sunlight in DSSCs, we assemble the photoelectrodes incorporated with bilayered TiO2 thin films comprising small TiO2 NPs-based underlayer and large TiO2 NPs-based overlayer as dye-supporting and light-scattering mediums, respectively. Furthermore, the effects of dye aerosol impaction and TiO2 stacking structures on the efficiency of DSSCs are examined. The power conversion efficiency (PCE) of DSSCs comprising a N719 dye-supporting layer treated with dip-coating process was determined as ∼ 5.67%; however, when the bilayered TiO2 thin films with an optimized thickness ratio of light-scattering overlayer and dye-supporting underlayer were coated with N719 dyes using dye aerosol impactor, the resulting PCE increased to ∼ 7.46%. This suggests that the photovoltaic characteristics of DSSCs can be enhanced considerably using the effective TiO2 NP stacking structures coated with rapid, uniform, and strong aerosol dye adsorption throughout the TiO2-based photoelectrodes.

Chemical bath deposited WS2 quantum dots on TiO2 for dye sensitized solar cell applications

Tungsten disulphide (WS2) quantum dots, coated on titanium dioxide (TiO2) by chemical bath deposition, increased the photovoltaic performance of dye sensitized solar cells (DSSCs) by ~ 11%. WS2 quantum dots exhibited a dominant optical absorption in a spectral range of 350–800 nm with its characteristics peaks at 550 nm and 620 nm corresponding to the direct bandgap optical transition at the K-point. X-ray photoelectron spectroscopic measurement was performed to study W 4f and S 2p peaks assured the presence of phase-pure WS2 quantum dots. Further, transmission electron microscopic studies showed a distribution of 8.5–20 nm quantum dots with d-spacing of 0.33 nm confirming the WS2. Photovoltaic characteristics of DSSCs with WS2 quantum dots asserted the additional photo-electrons generated by WS2 via the increment in photocurrent density and overall performance. This study demonstrated the possibility of integrating 2D-layered quantum dots into DSSCs as an additional photo-absorbing material candidate along with organic photo-sensitizer such as Ruthenium based N719.

Charge transfer improvement of ZnO-based dye-sensitized solar cells modified with graphite nanosheets and bilayer photoelectrode structures

In this work, dye-sensitized solar cells (DSSCs) were fabricated with different photoelectrode structures consisting of a ZnO-based photoelectrode, a ZnO/Au Schottky barrier-based photoelectrode, graphite nanosheets loaded on a ZnO (GZnO)-based photoelectrode, graphite nanosheets loaded on a ZnO nanoparticles (GZnO NPs)-based photoelectrode and graphite nanosheets loaded on a ZnO nanoparticles/ZnO (GZnO NPs/ZnO) as a bilayer-based photoelectrode. The photovoltaic characteristics of DSSCs were investigated based on: the power conversion efficiency (PCE), short-circuit current density (Jsc), open-circuit voltage and fill factor. The kinetics electron transport of DSSCs was carried out using electrochemical impedance spectroscopy (EIS). The semi-circle in the Nyquist plot was calculated to represent the charge transfer resistance (Rct). It was found that the GZnO NPs/ZnO bilayer-based photoelectrode exhibited the maximum Jsc (9.185 mA/cm2) and maximum PCE (2.37%), which resulted by the minimum Rct in the device. The result can be interpreted as showing that a graphite nanosheet structure improves the electron transport property which produces an excellent charge transfer mechanism in the photoelectrode. Accordingly, enhanced performance of ZnO-based dye-sensitized solar cells with graphite nanosheets loaded on a ZnO nanoparticles layer could be simply explained in terms of the charge transfer mechanism.

Dye-sensitized solar cells using carbon nanotube-based counter electrodes in planar and micro-array patterned configurations

Dye-sensitized solar cells (DSSCs) have been substantially researched as a prospective candidate for renewable energy technology, and a variety of materials alternative to corroding and high-cost Pt have been utilized as counter electrodes for these cells. In this article, we report on the fabrication and photovoltaic characteristics of DSSCs with vertically aligned carbon nanotube (CNT)-based DSSC counter electrodes. Our DSSCs utilized three different counter electrodes with CNTs in planar (P-CNT) and micro-array patterned (MA-CNT) configurations and platinum (Pt)-film coated Si as the control sample. The CNTs were grown in planar and micro-array patterned configurations directly on highly doped n-type silicon substrates by a hot-filament chemical vapor deposition process. In combination with an N-719 dye-sensitized titanium dioxide (TiO2) coated onto a fluorine doped tin oxide coated glass substrate as the photoanode and an iodide-based electrolyte, our P-CNT as the counter electrode showed a very high photocurrent density (Jsc) of 26.3 mA/cm2 and a power conversion efficiency (η) of 7.13% when compared to platinum's JSC of 20.6 mA/cm2 and η of 6.29%. The photovoltaic behavior of the micro-array patterned CNTs was also characterized, providing a better understanding of their electrocatalytic performance for the DSSCs. Overall, this work demonstrates the superior and improved photovoltaic performance of the vertically-aligned CNTs as the DSSC counter electrode, which makes them a stronger alternative to platinum counter electrodes.

Structural and chemical analysis of TiO2 nanotube surface for dye-sensitized solar cells

One-dimensional TiO2 nanotube (TNT) arrays were fabricated on fluorine-doped tin oxide glass substrate as the photoanodes for dye-sensitized solar cells (DSCs) using one-step ZnO nanorods template method. The depth profile analysis using X-ray photoelectron spectroscopy and ion sputtering indicated that a small amount of Zn species was attached on the TNT surface. Relationship of the properties of the TNT surface with the Zn residue and the photovoltaic characteristics of DSCs were investigated. Residual Zn species on TNT improve the open circuit voltage of the DSCs. A maximum open circuit voltage of 0.876 V was achieved, which is close to the theoretical maximum of the TiO2-based DSCs. However, photocurrent density was decreased significantly for the high-Zn-amount sample. It was revealed that the surface Zn species were divalent oxides and the amount of surface hydroxyl group was increased in conjunction with the Zn amount. Slight increase of the dye amount was found for the high Zn amount sample. It was expected that decrease in injection probability of the photo-excited electrons into TNT was the dominant reason for the photocurrent decrease.

Influence of thin film thickness of working electrodes on photovoltaic characteristics of dye-sensitized solar cells

This paper presents the study of the influence of thin film thickness of working electrodes on the photovoltaic characteristics of dye-sensitized solar cells. Titanium dioxide (TiO2) thin films, with the thickness from 7.67 to 24.3 μ m, were used to fabricate the working electrodes of dye-sensitized solar cells (DSSCs). A TiO2 film was coated on a fluorine-doped tin oxide (FTO) conductive glass substrate and then sintered in a high-temperature furnace. On the other hand, platinum (Pt) solution was coated onto an FTO substrate for the fabrication of the counter electrode of a DSSC. The working electrode immersed in a dye, the counter electrode, and the electrolyte were assembled to complete a sandwich-structure DSSC. The material analysis of the TiO2 films of DSSCs was carried out by scanning electron microscopy (SEM) and ultraviolet-visible (UV-Vis) spectroscopy, while the photovoltaic characteristics of DSSCs were measured by an AM-1.5 sunlight simulator. The light transmittance characteristics of the TiO2 working electrode depend on the TiO2 film thickness. The thin film thickness of the working electrode also affects the light absorption of a dye and results in the photovoltaic characteristics of the DSSC, including open-circuited voltage ( V OC), short-circuited current density ( J SC), fill factor, and photovoltaic conversion efficiency.

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.

Al2O3 Doping of TiO2 electrodes and applications in dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) have been intensively studied since their discovery in 1991. DSSCs have been extensively researched over the past decades as cheaper alternatives to silicon solar cells due to their high energy-conversion efficiency and their low production cost. However, some problems need to be solved in order to enhance the efficiency of DSSCs. In particular, the electron recombination that occurs due to the contact between the transparent conductive oxide (TCO) and a redox electrolyte is one of the main limiting factors of efficiency. In this work, we report for the first time the improvement of the photovoltaic characteristics of DSSCs by doping TiO2 with Al2O3. DSSCs were constructed using composite particles of Al2O3-doped TiO2 and TiO2 nanoparticles. The DSSCs using Al2O3 showed the maximum conversion efficiency of 6.29% due to effective electron transport. DSSCs based on Al2O3-doped TiO2 films showed better photovoltaic performance than cells fabricated with only TiO2 nanoparticles. This result is attributed to the prevention of electron recombination between electrons in the TiO2 conduction band with holes in the dye or the electrolyte. There mechanism is suggested based on impedance results, which indicated improved electron transport at the TiO2/dye/electrolyte interface.

Improved performance of metal foil-based dye-sensitized solar cells with low porosity and short length of TiO2 nanotube underlayer

In the present study, we propose low porosity and short length of TiO2 nanotubes (NTs) as underlayer in dye-sensitized solar cells (DSSCs). Photovoltaic characteristics of DSSCs with and without TiO2 NT underlayer are compared using various electrochemical analyses. Low porosity by small pore diameter, thick walled NT geometry and short length of NT underlayer help efficient charge transfer and reduced recombination at the interface of TiO2 nanoparticles (NPs)/Ti substrate. As a result, we can achieve a conversion efficiency of 6.89% for DSSCs with TiO2 NT underlayer, which is about 20% higher than that obtained from DSSCs with only a TiO2 NPs layer.

Effect of the Geometry of the Anodized Titania Nanotube Array on the Performance of Dye-Sensitized Solar Cells

Highly ordered TiO2 nanotube arrays are superior photoanodes for dye-sensitized solar cells (DSSCs) due to reduced intertube connections, vectorial electron transport, suppressed electron recombination, and enhanced light scattering. Performance of the cells is greatly affected by tube geometry, such as wall thickness, length, inner diameter and intertube spacing. In this paper, effect of geometry on the photovoltaic characteristics of DSSCs is reviewed. The nanotube wall has to be thick enough for a space charge layer to form for faster electron transportation and reduced recombination. When the tube wall is too thin to support the space charge layer, electron transport in the nanotubes will be hindered and reduced to that similar in a typical nanoparticle photoanode, and recombination will easily take place. Length of the nanotubes also plays a role: longer tube length is desired because of more dye loading, however, tube length longer than the electron diffusion length results in low collecting efficiency, which in turn, results in low short-circuit current density and thus low overall conversion efficiency. The tube inner diameter (pore size) affects the conversion efficiency through effective surface area, i.e., larger pore size gives rise to smaller surface area for dye adsorption, which results in low short-circuit current density under the same light soaking. Another issue that may seriously affect the conversion efficiency is whether each of the tube stands alone (free from connecting to the neighboring tubes) to facilitate infiltration of dye and fully use the outer surface area.

Energetic surface heterogeneity of nanocrystalline TiO2 films for dye-sensitized solar cells

Dye sensitized solar cells (DSSCs) have been receiving significant attention because they have many advantages compared to conventional organic solar cells. It has been known that the photovoltaic characteristics of DSSC are highly dependent on the adsorption properties of dyes on TiO2 films. To analyze the surface heterogeneity of TiO2 surfaces, single-phase anatase nanocrystallite titanium films were prepared by sol-gel method using the hydrolysis reaction of titanium tetraisopropoxide under acidic condition and characterized by XRD, FE-SEM and BET analysis. The adsorption energy distribution functions were calculated by the generalized nonlinear regularization method. It was found that the shape and the intensity of the adsorption energy distribution curve determined were highly related with the physical properties (i.e., geometrical heterogeneity) and chemical characteristics (i.e., energetic heterogeneity) of nanocrystalline TiO2 for DSSC.