Charge recombination reduction in dye-sensitized solar cells by depositing ultrapure TiO2 nanoparticles on “inert” BaTiO3 films

Ultrapure TiO₂ nanoparticles (∼5 nm in size) were supported on “inert” BaTiO₃ films by TiCl₄ treatment, which was used to fabricate dye-sensitized solar cells (DSSCs). The optimized electrode, designated as BaTiO₃/TiO₂(4), was obtained upon four cycles of TiCl₄ treatment. DSSC with BaTiO₃/TiO₂(4) electrode exhibits superior power conversion efficiency (PCE) compared to that with conventional anatase TiO₂ (∼25 nm in size) electrode. The interfacial charge recombination kinetics was investigated by electrochemical impedance spectroscopy (EIS) and intensity-modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS). In contrast to DSSC with anatase TiO₂ electrode, the dramatically enhanced electron lifetime for DSSC with BaTiO₃/TiO₂(4) electrode could be attributed to the decrease of recombination reaction at the TiO₂ photoelectrode/electrolyte interface. It is proposed that the lower interfacial charge recombination can be related to the relatively shallower trap distributions in DSSC with BaTiO₃/TiO₂(4) electrode.     

Preparation of TiO2/NiO composite particles and their applications in dye-sensitized solar cells

This study investigates the applicability of n-type TiO₂ and p-type NiO on the FTO-glass (Fluorine doped tin oxide, SnO₂:F) substrate of the working electrode in a dye-sensitized solar cell (DSSC). The working electrode was designed and fabricated by depositing a film of TiO₂/NiO composite particles, which were prepared by mixing the Ni powder with TiO₂ particles using dry mixing method, on a FTO-glass substrate using a spin coating process. The working electrode was then immersed in the solution of N-719 (Ruthenium) dye at a temperature of 70 °C for 6 h. Moreover, a thin film of platinum (Pt) was deposited on the FTO-glass substrate of the counter electrode using an E-beam evaporator. Finally, the DSSC was assembled, and the short-circuit photocurrent, the open-circuit photovoltage and the power conversion efficiency of DSSC were measured using an I–V measurement system. This study also examined the effects of the mass ratio of TiO₂ to Ni and the number of coating of TiO₂ particles (or TiO₂/NiO composite particles) colloid on the power conversion efficiency of the DSSC. Most importantly, this study shows that the power conversion efficiency of the DSSC with TiO₂/NiO composite particles (3.80%) substantially exceeds that of the conventional DSSC (3.27%) due to the effects of the NiO barrier and the n–p junction.     

The optical properties of nanoporous structured titanium dioxide and the photovoltaic efficiency on DSSC

This study examined the characterization of nanoporous structured titanium dioxide and its application to dye-sensitized solar cells (DSSCs). TEM revealed nanopore sizes of 10.0 nm with a regular hexagonal form. When nanoporous structured TiO₂ was applied to DSSC, the energy conversion efficiency was enhanced considerably compared with that using nanometer sized TiO₂ prepared using a hydrothermal method. The energy conversion efficiency of the DSSC prepared from nanoporous structured TiO₂ was approximately 8.71% with the N719 dye under 100 mW cm⁻² simulated light. FT-IR spectroscopy showed that the dye molecules were attached perfectly to the surface and more dye molecules were absorbed on the nanoporous structured TiO₂ than on the nano-sized TiO₂ particles prepared using a conventional hydrothermal method. Electrostatic force microscopy (EFM) showed that the electrons were transferred rapidly to the surface of the nanoporous structured TiO₂ film.     

TiO2/PEN表面改性对柔性DSSC性能的影响

对于柔性DSSC的透明光阳极而言,在低温下制备出结晶性高、颗粒间结合性能良好的TiO₂薄膜是其获得优异光电性能的关键。本文通过对比三种不同浆料添加剂(盐酸、乙二醇乙醚、小颗粒凝胶)对DSSC光电性能的影响,发现小颗粒凝胶的加入可以显著提高器件的光电性能。在此基础上,优化了小颗粒凝胶添加量及退火工艺,得出了最佳制备工艺条件,最终获得短路电流密度为8.14 mA/cm²、填充因子为67.9%、光电转化效率为4.1%的DSSC。进一步研究表明,小颗粒凝胶的加入一方面可以增强TiO₂颗粒之间的连接,从而提高TiO₂的成膜质量;另一方面可以增加TiO₂薄膜对光的散射,从而提高电池的吸光率。     

The effects of the thickness of TiO2 films on the performance of dye-sensitized solar cells

Nanocrystalline anatase TiO₂ thin films with different thicknesses (0.5-2.0 μm) have been deposited on ITO-coated glass substrates by a sol-gel method and rapid thermal annealing for application as the work electrode for dye-sensitized solar cells (DSSC). From the results, the increases in thickness of TiO₂ films can increase adsorption of the N3 dye through TiO₂ layers to improve the short-circuit photocurrent (J_sc) and open-circuit voltage (V_oc), respectively. However, the J_sc and V_oc of DSSC with a TiO₂ film thickness of 2.0 μm (8.5 mA/cm² and 0.61 V) are smaller than those of DSSC with a TiO₂ film thickness of 1.5 μm (9.2 mA/cm² and 0.62 V). It could be due to the fact that the increased thickness of TiO₂ thin films also resulted in a decrease in the transmittance of TiO₂ thin films thus reducing the incident light intensity on the N3 dye. An optimum power conversion efficiency (η) of 2.9% was obtained in a DSSC with the TiO₂ film thickness of 1.5 μm.     

Synthesis of cluster like TiO<Subscript>2</Subscript> mesoporous spheres and nanorods and their applications in dye-sensitized solar cells

Cluster like mesoporous TiO₂ spheres, nanorods and nanoparticles were synthesized by simple wet chemical method. The TiO₂ mesoporous spheres, nanorods and nanoparticles were characterized by powder X-ray diffraction, Raman spectroscopy, ultraviolet visible spectroscopy, Fourier transform infrared spectroscopy, field emission scanning electron microscopy and transmission electron microscopy. Accordingly, a possible growth mechanism of mesoporous spheres, nanorods and nanoparticles were discussed. The changes of the dye-sensitized solar cell (DSSC) performance with the variation of the nanostructures of TiO₂ which were used in photoanodes have been investigated. The TiO₂ mesoporous sphere based DSSC with the film thickness of 20 μm was assembled and a conversion efficiency of 6.69% was obtained.     

Effects of HNO3 treatment of TiO2 nanoparticles on the photovoltaic properties of dye-sensitized solar cells

The effects of the nitric acid (HNO₃) treatment of TiO₂ nanoparticles on the photovoltaic properties of the dye-sensitized solar cell (DSSC) were investigated. The HNO₃ treatment enhanced the dispersion of TiO₂ particles, increased the surface area and porosity of the sintered TiO₂ films, increased the relative proportion of the Ti³⁺ state in the Ti 2p X-ray photoelectron spectroscopy spectrum, significantly increased the amount of adsorbed dye molecules on the TiO₂ electrode, and reduced the charge-transfer resistance at the TiO₂/dye/electrolyte interface. The short circuit photocurrent density (I_sc) was increased due to the increased amount of adsorbed dye molecules and the reduced charge-transfer resistance. The HNO₃ pre-treatment of TiO₂ particles improved the overall conversion efficiency of the DSSC by about 14%.     

The effect of SWCNT with the functional group deposited on the counter electrode on the dye-sensitized solar cell

This study investigated the applicability of single wall carbon nanotubes (SWCNT) with the functional group deposited on the FTO-glass (Fluorine doped tin oxide, SnO₂:F) substrate of the counter electrode for a dye-sensitized solar cell (DSSC). A nanocrystalline TiO₂ layer was fabricated on the FTO-glass substrate of the working electrode, and then sintered in a high-temperature furnace. The working electrode with a TiO₂ thin film was immersed in the solution of N-719 (Ruthenium) dye for 12 h. Moreover, the counter electrode with a layer of Ag (or without a layer of Ag) and a layer of SWCNT, which were (or was) fabricated in that order on the FTO-glass substrate, was subsequently prepared. Finally, the DSSC was assembled, the power conversion efficiency of the DSSC was measured using an I–V measurement system, and the incident photo conversion efficiency (IPCE) of the DSSC was obtained using the phase-locked loop optical chopper. This study also examined the effects of a layer of Ag deposited on the FTO-glass substrate, the type of organic solvent (such as DMAC and acetylacetone), and the sintering temperature on the performance of the DSSC. This film of SWCNT/Ag markedly increased the IPCE from 3.9% (conventional DSSC with a thin film of platinum on the FTO-glass substrate of the counter electrode) to 15.3% (DSSC with SWCNT/Ag/acetylacetone), as the wavelength of the light was 380 nm. Furthermore, as the wavelength of the light is 550 nm, the IPCE of the DSSC with SWCNT/Ag/acetylacetone (6.8%) becomes nearly equal to that of conventional DSSC (7.2%). Most interestingly, this study shows that the power conversion efficiency of the DSSC with SWCNT/Ag/acetylacetone (1.3037%) is not inferior to that of DSSC with a thin film of platinum on the counter electrode (1.25%).     

Preparation of a working electrode with a conducting PEDOT:PSS film and its applications in a dye-sensitized solar cell

This study investigates the applicability of a working electrode with a poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) film on a dye-sensitized solar cell (DSSC). This working electrode was designed and fabricated by inserting a PEDOT:PSS film between a fluorine-doped tin oxide (FTO) glass substrate and a layer of nanocrystalline TiO₂ particles (P-25). This study also examines the effects of annealing temperature and duration on the transmittance and microstructure of a PEDOT:PSS film as well as the power conversion efficiency of DSSC with this film. The power conversion efficiency of a DSSC with a PEDOT:PSS film (6.37%) substantially exceeds that of a conventional DSSC (4.24%). This result is attributed to the fact that this transparent and conductive PEDOT:PSS film deposited on the FTO glass substrate using a simple spin coating method substantially improves the short-circuit photocurrent per unit area and the fill factor of DSSC.     

Synthesis of hierarchical nanoparticles-based ZnO spheres for their application as the light blocking layers in dye-sensitized solar cells

Three-dimensional nanoparticles-based ZnO hierarchical spheres (ZnO-HS) with strong light harvesting and dye loading abilities have been fabricated by a simple hydrothermal method in this paper. These ZnO-HS were designed as the overlayer for light blocking and applied to the dye-sensitized solar cells (DSSCs) based on bare ZnO nanoparticles (ZnO-NP) or TiO₂ nanoparticles (TiO₂-NP). The results show that the values of the short-circuit current density (J _sc) and the power conversion efficiency (η) have been heightened up to 12.6 mA cm^?2 and 3.40 % for the ZnO-NP/ZnO-HS double-layered DSSC, far higher than the bare ZnO-NP DSSC. However, another DSSC assembled by the TiO₂-NP/ZnO-HS double-layered film displays an adverse result for the decreasing of J _sc and η even though the ZnO-HS light blocking layer has been established on the TiO₂-NP film. According to the electrochemical impedance data compared between the ZnO-NP/ZnO-HS double-layered and TiO₂-NP/ZnO-HS double-layered DSSC, it is found that the former possesses less possibility for the occurrence of charge recombination and electronic loss, which is responsible for its better photovoltaic response.     

The fabrication of the antibacterial paste based on TiO2 nanotubes and Ag nanoparticles-loaded TiO2 nanotubes powders

ABSTRACT

We successfully synthesised TiO₂ nanotubes (TNTs) and silver nanoparticles (Ag NPs)-loaded TiO₂ nanotubes paste. These were coated on a glass substrate by spin coating method, and their antibacterial activities were surveyed. The morphology of materials was defined by transmission electron microscopy (TEM) image; the crystalline structure and the composition of the materials were determined by X-ray diffraction (XRD) pattern and X-ray photoelectron spectroscopy (XPS). Vibrational properties of the molecules existing in the sample were investigated by Fourier transform infrared (FTIR) spectroscopy, and the transmittances of films were determined by UV–Vis transmittance spectroscopy. This research shows that the structure and morphology of TNTs did not change after they underwent the processes of paste preparing and film coating on a glass substrate. Furthermore, the transmittance of TNTs film (about 75%) is higher than Ag NPs-loaded TiO₂ nanotubes (Ag/TNTs) film (about 65%) in the visible region. Moreover, the antibacterial property of Ag/TNTs film shows its effectiveness against Escherichia coli bacteria, and the antibacterial efficiency is 99.06% for 24 h-incubation period in the dark condition.     

Multi-layered TiO2 nanostructured films for dye-sensitized solar cells

Multi-layered TiO₂ nanostructured films were fabricated to improve the light harvest efficiency of the dye-adsorbed TiO₂ electrode in dye-sensitized solar cells (DSSCs) by light scattering. Three different structures of TiO₂ electrodes, with layers consisting of TiO₂ pastes with average diameters of 9, 20, and 300 nm, respectively, were fabricated and their photovoltaic effects on the DSSC devices were investigated. By utilizing the multi-layered TiO₂ electrode constructed using the three different TiO₂ pastes, the overall power conversion efficiency of the DSSC devices in the PEG-based electrolyte was increased to 5.24% under irradiation of 100 mW/cm² at AM 1.5.     

Rapid thermal melted TiO2 nano-particles into ZnO nano-rod and its application for dye sensitized solar cells

TiO₂ nano-particles with an anchored ZnO nano-rod structure were synthesized using the hydrothermal method to grow ZnO nano-rods and coated TiO₂ nano-particles on ZnO nano-rods using the rapid thermal annealing method on ITO conducting glass pre-coated with nano porous TiO₂ film. The XRD study showed that there was little difference in crystal composition for various types of TiO₂ nano-particles anchored to ZnO nano-rods. The as-prepared architecture was characterized using field-emission scanning electron microscopy (FE-SEM). Films with TiO₂ nano-particles anchored to ZnO nano-rods were used as electrode materials to fabricate dye sensitized solar cells (DSSCs). The best solar energy conversion efficiency of 2.397% was obtained by modified electrode material, under AM 1.5 illumination, achieved up to J_sc = 15.382 mA/cm², V_oc = 0.479 V and fill factor = 32.8%.     

Optimization of the cutting process of multi-wall carbon nanotubes for enhanced dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) were fabricated based on multi-wall carbon nanotube (MWCNT)-TiO₂ photo-anodes, which were prepared by the procedures of cutting MWCNTs and subsequent immobilization TiO₂ on MWCNTs. Through a detailed study, we found that cut-MWCNTs with proper ultrasonication time (2 h) and proper content (0.075%) resulted in 58 and 40% increase in short-circuit photocurrent and overall energy conversion efficiency, respectively, compared with that of a DSSC using only TiO₂ photo-anode. The enhancement of cut-MWCNTs for DSSC was attributed to the introduction of percolative conductive paths which facilitate the rapid electron transfer.     

Design and development of electronic- and micro-structures for multi-functional working electrodes in dye-sensitized solar cells

This paper outlines a new strategy to optimize the performance of electrodes in dye-sensitized solar cells (DSSCs), through the engineering of electronic structures in conjunction with the micro-structures of the devices. We propose a simple hydrolysis method for the fabrication of a family of quasi-core–shell TiO₂ (hydrolysis)/PbS composites for working electrodes. Measurements confirm a shift in absorption from the UV to visible range. We also measured cell performance, including short-circuit photocurrent, open-circuit photovoltage, and the power conversion efficiency (η) of DSSCs. The obtained η of DSSC (6.05%) with a TiO₂ (P-25)/TiO₂ (hydrolysis) + 0.005 M PbS electrode is substantially higher than that of the conventional DSSC (5.11%) with a TiO₂ (P-25) electrode, due to improved p–n junctions, light-scattering, and light absorption. Finally, the shell of TiO₂ (hydrolysis) protected the core of PbS from the corrosive effects of electrolytes, thereby prolonging the life span of the DSSC. This novel approach to electrode design could lead to advances in DSSC as well as other energy applications including photo-catalysis technology.     

Effects of light scattering TiO2 surface-modified by dual oxide coating in dye-sensitized solar cells

The surface of light scattering TiO₂ particles in the dye-sensitized solar cell (DSSC) was dual-coated with Al₂O₃ and SiO₂ nanoparticles. The surface modification of the light scattering TiO₂ particles was performed by a modified sol–gel method using the colloidal alumina and the colloidal silica as surface coating precursors. It was revealed that the dual-coated light scattering TiO₂ particles leads to an increase in short-circuit photocurrent of DSSC device, resulting in an increase in energy conversion efficiency. This seems to be due to the increase of the light scattering by a combination of the light scattering TiO₂ particles and the oxide nanoparticles such as Al₂O₃ and SiO₂.     

Improving conversion efficiency of dye-sensitized solar cells by metal plasma ion implantation of ruthenium ions

Dye-sensitized solar cells (DSSC) are based on the concept of photosensitization of wide-band-gap mesoporous oxide semiconductors. At present, DSSC have ventured into advanced development and pilot production. Our current research emphasizes on improvements on titanium dioxide (TiO₂) photosensitivity under visible light irradiation by using metal plasma ion implantation (MPII). The anatase TiO₂ electrode was prepared via a sol-gel process and deposited onto indium-tin oxide glass substrates. Subsequently, the as-deposited TiO₂ films were subjected to MPII at 20 keV in order to incorporate ruthenium (Ru) atoms onto the TiO₂ surface layer. The Ru-implanted TiO₂ thin film possessed nanocrystalline Ru clusters of 20 nm in diameter and distributed in near surface layer of TiO₂ films. The Ru clusters showed effective in both prohibiting electron-hole recombination and generating additional Ru-O impurity levels for the TiO₂ band gap structure. A significant reduction of TiO₂ band gap energy from 3.22 to 3.11 eV was achieved, which resulted in the extension of photocatalysis of TiO₂ from UV to Vis regime. A small drop of photoelectric performance of 8% was obtained due to the incorporation of Ru atoms in the surface layer of TiO₂, a similar side effect as observed in the Fe-implanted TiO₂. However, the overall retention of the photocatalysis capability is as high as 92% when switch from UV to Vis irradiation. The improvement of the photosensitivity of TiO₂ DSSC by means of metal plasma ion implantation is promising.     

Effect on interfacial charge transfer resistance by hybrid co-sensitization in DSSC applications

TiO₂ nanoparticles were synthesized by hydrothermal process to prepare metal oxide based photoanode for dye sensitized solar cell (DSSC) fabrication. X-ray diffraction analysis indicates the formation of tetragonal TiO₂. High resolution transmission electron microscopy reveals the presence of agglomerated TiO₂ particles and the average particle size is found to be 14 nm. The UV–Visible absorption spectrum ensures the absorption maximum at 268 nm. The band gap energy of TiO₂ nanoparticles was found to be 3.3 eV which lies in the ultra-violet (UV) region. Impedance studies of TiO₂ nanoparticles show an increase in conductivity with an increase in bias voltage. In the present work, the UV active TiO₂ nanoparticles are employed for the fabrication of DSSC based on the hybrid co-sensitization of natural dye (Eugenia Jambolana) and organic dye (Eosin). The interfacial charge transfer resistance phenomena of the DSSC determined by electrochemical impedance spectroscopy is discussed in detail. Photovoltaic efficiency of 0.1377 % is achieved for the fabricated DSSC with co-sensitization of natural and organic dyes.     

Optimization of titanium dioxide film prepared by electrophoretic deposition for dye-sensitized solar cell application

Nanocrystalline TiO₂ films were deposited on a conducting glass substrate by the electrophoretic deposition technique. It was found that the thickness of TiO₂ film increased proportionally with an increase in deposition time and deposition voltage. However, as the deposition duration or deposition voltage increased, the film surface was more discontinuous, and microcracks became more evident. The characteristic of the dye-sensitized solar cell using TiO₂ film as a working electrode was analyzed. The results of the energy conversion efficiency and the photocurrent density exhibited a relationship dependent on the TiO₂ thickness. Curve fitting of energy conversion efficiency vs. TiO₂ thickness revealed the optimum solar cell efficiency ~ 2.8% at the film thickness of ~ 14 μm.     

Fabrication of thin film dye sensitized solar cells with solar to electric power conversion efficiency over 10%

Techniques of TiO₂ film fabrication for dye-sensitized solar cells having a conversion efficiency of global air mass 1.5 (AM 1.5, 1000 W/m²) solar light to electric power over 10% are reported. Newly implemented fabrication technologies consist of pre-treatment of the working photoelectrode by TiCl₄, variations in layer thickness of the transparent nanocrystalline-TiO₂ and applying a topcoat light-scattering layer as well as the adhesion of an anti-reflecting film to the electrode's surface. TiCl₄ treatments induce improvements in the adhesion and mechanical strength of the nanocrystalline TiO₂ layer. Optimization of the thickness of the TiO₂ layer, acting as the working electrode, affects both the photocurrent and the photovoltage of the devices. Covering of the TiO₂ photoanode by an anti-reflecting film results in enhancement of the photocurrent. Each of these components of film fabrication exerts a significant influence on the overall photovoltaic parameters of the devices resulting in improvements in the net energy conversion performance.