High efficiency dye-sensitized solar cells based on hierarchically structured nanotubes

Dye-sensitized solar cells (DSSCs) based on hierarchically structured TiO(2) nanotubes prepared by a facile combination of two-step electrochemical anodization with a hydrothermal process exhibited remarkable performance. Vertically oriented, smooth TiO(2) nanotube arrays fabricated by a two-step anodic oxidation were subjected to hydrothermal treatment, thereby creating advantageous roughness on the TiO(2) nanotube surface (i.e., forming hierarchically structured nanotube arrays-nanoscopic tubes composed of a large number of nanoparticles on the surface) that led to an increased dye loading. Subsequently, these nanotubes were exploited to produce DSSCs in a backside illumination mode, yielding a significantly high power conversion efficiency, of 7.12%, which was further increased to 7.75% upon exposure to O(2) plasma.     

Analysis of the electron transport properties in dye-sensitized solar cells using highly ordered TiO2 nanotubes and TiO2 nanoparticles

This study uses TiO2 nanoparticles and highly ordered anatase TiO2 nanotubes (AOTnt) as thin film photoanodes for dye-sensitized solar cells (DSSCs). DSSCs are assembled by single-layer and double-layer films of photoanodes and their electron transfer performance is compared. TiO2 nanoparticles were fabricated by the sol-gel method, and AOTnts were grown on titanium foil. This study uses TiO2 nanoparticles or AOTnts to prepare single-layer photoanodes and TiO2 nanoparticles coated on an AOTnt film to fabricate double-layer photoanodes. These three different photoanodes are soaked in dye and assembled into DSSCs, and their open-loop voltage recession, electrochemical impedance, lifetime, life cycle, and effective diffusion coefficient are measured. Electron transfer efficiency of the photoanodes and light harvesting efficiency are further analyzed. The results show that the electron transfer efficiency, open-loop voltage recession, lifetime, life cycle, and effective diffusion coefficient of the DSSCs assembled using double-layer photoanodes (AOTnt-TiO2) are superior to those of single-layer photoanodes (TiO2 or AOTnt).     

TiO2-grafted multi-walled carbon nanotubes for dye-sensitized solar cells

Dye-Sensitized Solar Cells (DSSCs) comprised of TiO2 porous films with multi-walled carbon nanotubes (MWNT) were prepared at low temperature (150 degrees C). MWNT were incorporated to facilitate the fast electron transport resulting from metallic properties of carbon nanotubes. In order to enhance the effect of MWNT incorporation, TiO2-grafted MWNT (TiO2-MWNT) was synthesized which can increase the electron transport rate further due to proximity of TiO2 to MWNT The presence of TiO2 nanoparticles on the surface of MWNT was confirmed by electron microscopy and energy dispersive X-ray spectroscopy. As in the DSSCs prepared through high temperature sintering of photoanodes, the maximum content of MWNT incorporated into TiO2 was limited to 0.01 wt% relative to TiO2. TiO2 photoanodes including TiO2-grafted MWNT (TiO2-MWNT/P25) enhanced the cell efficiencies by ca. 28% and 14%, relative to TiO2 photoanodes without and with MWNT respectively, reaching the efficiency of 5.0%. Electrochemical impedance spectroscopy (EIS) was utilized to examine the effect of incorporation of TiO2 nanoparticles grafted to MWNT on the cell performance.     

Fabrication and characterization of photoelectrode thin films with different morphologies of TiO2 nanoparticles for dye-sensitized solar cells

This study deals with the fabrication of three different morphologies of TiO2 nanoparticles to fabricate two-layer photoelectrode thin film for dye-sensitized solar cells (DSSC). The four different TiO2 morphologies are titania nanotubes (Tnt), TiO2 nanoparticles (H220), TiO2 nanoparticle (SP) and commercial DP-25 nanoparticles (P-25). To prepare the thin films of the photoelectrodes, the first layer is coated by H220 TiO2 nanoparticles, and the second is coated by 3 kinds of materials optimally proportionally mixed - P25, SP and Tnt. The photoelectric conversion efficiency of DSSCs with photoelectrodes fabricated using H220 reached 6.31%. Finally, the TiO2 nanaomaterials with four different morphologies were used to prepare a two layer photoelectrode with the structure of H220/P25-Tnt-SP which was combined with a Pt counter electrode to assemble DSSCs. These DSSCs had photoelectric conversion efficiencies of as high as 7.47%.     

Enhancement of photovoltaic performance in dye-sensitized solar cells with the spin-coated TiO2 blocking layer

The TiO2 thin film layers were introduced with the spin-coating method between FTO electrode and TiO2 photoanode in dye sensitized solar cell (DSSC) to prevent electron back migration from the FTO electrode to electrolyte. The DSSC containg different thickness of TiO2 thin film (10-30, 40-60 and 120-150 nm) were prepared and photovoltaic performances were analysed with /-Vcurves and electrochemical impedance spectroscopy. The maximum cell performance was observed in DSSC with 10-30 nm of TiO2 thin film thickness (11.92 mA/cm2, 0.74 V, 64%, and 5.62%) to compare with that of pristine DSSC (11.09 mA/cm2, 0.65 V, 62%, and 4.43%). The variation of photoelectric conversion efficiency of the DSSCs with different TiO2 thin film thickness was discussed with the analysis of crystallographic and microstructural properties of TiO2 thin films.     

上转换发光材料La(OH)3∶Er3+/Yb3+的制备及在染料敏化太阳能电池中的应用

针对N719染料仅可吸收可见光这一局限,本研究旨在通过引入上转换发光材料并将其应用于染料敏化太阳能电池的光阳极来拓宽光谱吸收范围,提高光的捕获率,进而达到提高电池光电转换效率的目的。首先,采用水热合成法以不同pH值的先驱体溶液,成功制备了Yb~(3+)/Er~(3+)双掺杂La(OH)_3粉末,然后将适量合成的稀土发光粉掺入TiO_2纳米浆料中,采用刮涂法成膜制备光阳极,并将其组装成染料敏化太阳能电池。研究结果表明,稀土发光粉的加入拓宽了光谱吸收范围,在其掺杂量达到3%时,电池的短路电流密度Jsc提高到17.72mA·cm-2,最终获得了8.3%的光电转换效率。     

Highly efficient solar cells using TiO(2) nanotube arrays sensitized with a donor-antenna dye

Donor antenna dyes provide an exciting route to improving the efficiency of dye sensitized solar cells owing to their high molar extinction coefficients and the effective spatial separation of charges in the charge-separated state, which decelerates the recombination of photogenerated charges. Vertically oriented TiO(2) nanotube arrays provide an optimal material architecture for photoelectrochemical devices because of their large internal surface area, lower recombination losses, and vectorial charge transport along the nanotube axis. In this study, the results obtained by sensitizing TiO(2) nanotube arrays with the donor antenna dye Ru-TPA-NCS are presented. Solar cells fabricated using an antenna dye-sensitized array of 14.4 microm long TiO(2) nanotubes on Ti foil subjected to AM 1.5 one sun illumination in the backside geometry exhibited an overall conversion efficiency of 6.1%. An efficiency of 4.1% was obtained in the frontside illumination geometry using a 1 microm long array of transparent TiO(2) nanotubes subjected to a TiCl(4) treatment and then sensitized with the Ru-TPA-NCS dye. Open circuit voltage decay measurements give insight into the recombination behavior in antenna-dye sensitized nanotube photoelectrodes, demonstrating outstanding properties likely due to a reduction in the influence of the surface traps and reduced electron transfer from TiO(2) to ions in solution.     

Efficient inverted solar cells using TiO(2) nanotube arrays

Using a vertical titania (TiO(2)) nanotube array, an inverted polymer solar cell was constructed with power conversion efficiency up to 2.71%. In this study, self-organized TiO(2) nanotubes arrays were grown by anodizing Ti metal in glycerol electrolyte containing 0.5?wt% NH(4)F and 1.0?wt% H(2)O with 20?V potential. The tube length (～100?nm) was controlled by the thickness of the sputtered titanium layer on the indium-tin oxide (ITO) substrate. The diameter of the tube was approximately 15-25?nm. After annealing in air at 500?°C for 1?h, nanotubes arrays were crystallized to the anatase phase from the initial amorphous state. Following the infiltration of polymeric semiconductor (poly(3-hexylthiophene) and (6,6)-phenyl C(60) butyric acid methyl ester, P3HT:PCBM), the filled TiO(2) layer had an optical absorption over a range from UV to visible light. The high surface-to-volume ratio of the nanotube arrays structure increased the effective area of the active region. The high efficiency of our solar cell is attributed to the vertical TiO(2) nanotube array's enhanced conduction of photo-induced current due to its charge transport capability.     

TiO2 nanotubes infiltrated with nanoparticles for dye sensitized solar cells

We present a detailed study of the infiltration of titanium dioxide (TiO(2)) nanotubes (NTs) with TiO(2) nanoparticles (NPs) for dye sensitized solar cells (DSSCs). The aim is to combine the merits of the NP's high dye loading and high light harvesting capability with the NT's straight carrier transport path and high electron collection efficiency to improve the DSSC performance. On infiltrating NTs with TiCl(4) solution followed by hydrothermal synthesis, 10 nm size NPs were observed to form a conformal and dense layer on the NT walls. Compared with the bare NT structure, dye loading of this mixed NT and NP structure is more than doubled. The overall photon conversion efficiencies of the fabricated DSSCs are improved by 152%, 107%, and 49% for 8, 13, and 20 μm long NTs, respectively. Electron transport and recombination parameters were extracted based on electrochemical impedance spectroscopy measurements. Although a slight reduction of electron lifetime was observed in the mixed structures due to enhanced recombination with a larger surface area, the diffusion length is still significantly longer than the NT length used, suggesting that most electrons are collected. In addition to dye loading and hence photocurrent increment, the photovoltage and filling factor were also improved in the mixed structure due to a low serial resistance, leading to the enhancement of the overall efficiency.     

Highly flexible frontside-illuminated dye-sensitized solar cells using three-dimensional network TiO2 nanowires

Here we report a highly flexible frontside-illuminated dye-sensitized solar cell (FIDSSC) using Ti foils as the substrates. The laser-drilled microhole arrays (LDMAs) on Ti foil substrates as the photoanode provided an efficient pathway for the diffusion of liquid electrolyte, which would be particularly favorable for frontside illumination of FIDSSC designs. The three-dimensional (3D) network TiO2 nanowires (NWs) were directly grown on the Ti substrate with LDMAs via a simple hydrothermal method. Platinized Ti sheet was used as the counter electrode in the FIDSSC. The mechanical properties of the novel structured device were measured. It was shown that as-synthesized large-scale 3D network TiO2 NWs with a diameter of about 20-30 nm and a length of about 6 microm can prevent crack from generating efficiently when bended to an extreme angle of 120 degree. Furthermore, we demonstrated that the effects of the different bending angles on the performance of the 3D network TiO2 NWs-based FIDSSCs were slight, indicating NWs preferable advantages for the fabrication of flexible DSSCs. The results showed that the FIDSSC achieved an efficiency of 0.72% under front illumination of AM 1.5 simulated one sun light (100 mWcm(-2)).     

Effect of TiO2 nanotube length and lateral tubular spacing on photovoltaic properties of back illuminated dye sensitized solar cell

The main objective of this study is to show the effect of TiO₂ nanotube length, diameter and intertubular lateral spacings on the performance of back illuminated dye sensitized solar cells (DSSCs). The present study shows that processing short TiO₂ nanotubes with good lateral spacings could significantly improve the performance of back illuminated DSSCs. Vertically aligned, uniform sized diameter TiO₂ nanotube arrays of different tube lengths have been fabricated on Ti plates by a controlled anodization technique at different times of 24, 36, 48 and 72?h using ethylene glycol and ammonium fluoride as an electrolyte medium. Scanning electron microscopy (SEM) showed formation of nanotube arrays spread uniformly over a large area. X-ray diffraction (XRD) of TiO₂ nanotube layer revealed the presence of crystalline anatase phases. By employing the TiO₂ nanotube array anodized at 24?h showing a diameter ??80?nm and length ??1·5???m as the photo-anode for back illuminated DSSCs, a full-sun conversion efficiency (??) of 3·5 % was achieved, the highest value reported for this length of nanotubes.     

Enhanced electron transport in mesoporous TiO2 films modified by sol-gel necking for dye-sensitized solar cells

Mesoporous TiO2 films modified via sol-gel necking were fabricated by dispersing Ti tetra-isopropoxide (TTIP; 8 to 16 wt% over TiO2) with TiO2 nanoparticles in isopropyl alcohol. The dye-sensitized solar cells (DSSCs) with 13 wt% TTIP-modified TiO2 film exhibited significantly improved overall energy conversion efficiency, despite having less adsorbed dye when compared with DSSCs with untreated and TiCl4 post-treated TiO2 films. The improvement can be attributed to the sol-gel necking (or interconnection) between the nanoparticles which leads to a much faster electron transport and a suppression of the recombination (or back electron transfer) between the TiO2 and electrolyte.     

Electrodeposition of lead zirconate titanate nanotubes

Lead zirconate titanate (PZT) nanotubes have been grown using porous anodic alumina templates. Sol–gel electrophoretic deposition method was utilized to form the nanotubes on pore walls. The templates were prepared using various anodizing voltages to achieve different pore diameters. Phosphoric acid solution was employed as the electrolyte. Stabilized PZT sols were prepared using lead acetate trihydrate and modified precursors of zirconium and titanium with acetic acid. The filled templates were then sintered at 700 °C. Scanning electron microscopy (SEM) shows that tubular PZT arrays have been efficiently grown in the alumina templates. Transmission electron microscopy (TEM) further confirms the tubular form and polycrystalline nature of the tubes. Energy dispersive X-ray (EDX) analyses also confirm the composition of the tubes. X-ray diffraction (XRD) spectra indicate the presence of the perovskite PZT as the main phase.     

End-group functionalization of poly(3-hexylthiophene) as an efficient route to photosensitize nanocrystalline TiO2 films for photovoltaic applications

Bulk heterojunction (BHJ) and dye-sensitized solar cells (DSSCs) have seen increased popularity over recent years and each technology has experienced tremendous improvements in power conversion efficiencies (PCEs), reaching 8 and 12%, respectively. The two technologies have been on independent improvement pathways, and this work establishes a link between them by using the archetypical hole conductor (poly-3-hexylthiophene, P3HT) in BHJs as a sensitizer on TiO(2) for DSSC applications. Three polymers were synthesized and examined as potential TiO(2) sensitizers in DSSCs under AM1.5 solar radiation. Using Grignard metathesis, regioregular P3HT was synthesized then functionalized with either one or two cyanoacrylic acid linker moieties to bind to the TiO(2) surface. End-group modification resulted in minimal changes to the optical and electronic properties as compared to pristine P3HT. Cyclic voltammetry (CV) experiments at anodic potentials of adsorbed sensitizer quantified the amount of alkylthiophene adsorbed on the TiO(2), whereas under reductive sweeps, cyanoacrylic acid end-group binding was determined. CVs of each polymer indicated that loading was drastically different as compared to pristine P3HT with the lowest loading on TiO(2) and monofunctionalized P3HT exhibited the highest loading. The DSSCs showed power conversion efficiencies (PCEs) of 0.1%, 0.2 and 2.2% for the polymer-sensitized TiO(2) of the unfunctionalized, monofunctionalized and difunctionalized polymers, respectively. DSSCs were then subjected to electrochemical impedance spectroscopy (EIS) in the dark and under monochromatic light radiation. The large variance in performance for the functionalized-P3HT sensitizers is attributed to differences in the adsorption modes of sensitizer on the TiO(2) surface, which in the difunctionalized case limits electrolyte recombination and favors forward charge transfer reactions.     

Fabrication of dye-sensitized solar cell (DSSC) using different particle sizes of TiO2 deposited via nano-particle deposition system (NPDS)

TiO2 layers were fabricated using a nano-particle deposition system (NPDS) on transparent conductive oxide (TCO) glass for dye sensitized solar cells (DSSCs). Conventionally, TiO2 paste for working electrodes has been fabricated using paste type methods. The fabricated paste composed of a mixture of nano-sized TiO2 powders, binders and solutions is then painted on TCO glass. After drying, the TiO2 layer on TCO glass is sintered to make a path for electron transfer. TiO2 layers formed by this paste type method require numerous steps, which can be time consuming. In this study, TiO2 powders were sprayed directly on TCO glass using NPDS in order to simplify the fabrication steps. To improve porosity and produce scattering layers, commercial nanocrystalline TiO, powders with different sizes were alternately deposited. Moreover, powders with different sizes were mixed and deposited on the TCO glass. The results indicate that the DSSCs with a TiO2 layer composed of different particle sizes had better cell performance than the cells assembled with single-sized TiO2 particles. Therefore, this study shows that a dry TiO2 coating process is possible for DSSC fabrication to improve its cell efficiencies, and this method can easily be applied on flexible substrates since NPDS is a room-temperature deposition process.     

Self-assembled TiO₂ with increased photoelectron production, and improved conduction and transfer: enhancing photovoltaic performance of dye-sensitized solar cells

Highly crystalline mesoporous anatase TiO(2) is prepared through supramolecular self-assembly and by utilizing cetyltrimethylammonium bromide (CTAB) as templating material. Photoanodes of dye-sensitized solar cells (DSSCs) made from these TiO(2) nanoparticles are found to have a high specific surface area of 153 m(2)/g and high surface roughness. Optical absorption spectroscopy studies reveal that the photoanode films adsorb four times more dye than films made of commercial P25 TiO(2). Mercury porosimetry and field emission scanning electron microscope (FESEM) studies show hierarchical macro- and meso-porosity of the photoanode films leading to better dye and electrolyte percolation, combined with improved electron conduction pathways compared to P25 films. Electrochemical impedance studies confirm lower impedance and higher electron lifetime in the synthesized mesoporous TiO(2) films compared to P25 films. Higher photovoltaic efficiency was recorded of cells made from the synthesized mesoporous TiO(2) in comparison to the corresponding cells made from P25. Incident-photon-to-current efficiency data provided critical understanding of recombination kinetics, and provided proof of Mie scattering by the self-assembled submicrometer sized TiO(2) aggregates and the macropores in their structure. The scattering phenomenon was further corroborated by diffused reflectance studies. An in-depth analysis of CTAB-templated mesoporous TiO(2) has been conducted to show how it can be a good candidate photoanode material for enhancing the performance of DSSCs.     

High-efficiency, solid-state, dye-sensitized solar cells using hierarchically structured TiO₂ nanofibers

High-performance, room-temperature (RT), solid-state dye-sensitized solar cells (DSSCs) were fabricated using hierarchically structured TiO? nanofiber (HS-NF) electrodes and plastic crystal (PC)-based solid-state electrolytes. The electrospun HS-NF photoelectrodes possessed a unique morphology in which submicrometer-scale core fibers are interconnected and the nanorods are dendrited onto the fibers. This nanorod-in-nanofiber morphology yielded porosity at both the mesopore and macropore level. The macropores, steming from the interfiber space, afforded high pore volumes to facilitate the infiltration of the PC electrolytes, whereas the mesoporous nanorod dendrites offered high surface area for enhanced dye loading. The solid-state DSSCs using HS-NFs (DSSC-NF) demonstrated improved power conversion efficiency (PCE) compared to conventional TiO? nanoparticle (NP) based DSSCs (DSSC-NP). The improved performance (>2-fold) of the DSSC-NFs was due to the reduced internal series resistance (R(s)) and the enhanced charge recombination lifetime (τ(r)) determined by electrochemical impedance spectroscopy and intensity modulated photocurrent/photovoltage spectroscopy. The easy penetration of the PC electrolytes into HS-NF layers via the macropores reduces R(s) significantly, improving the fill factor (FF) of the resulting DSSC-NFs. The τ(r) difference between the DSSC-NF and DSSC-NP in the PC electrolytes was extraordinary (~14 times) compared to reported results in conventional organic liquid electrolytes. The optimized PCE of DSSC-NF using the PC electrolytes was 6.54, 7.69, and 7.93% at the light intensity of 100, 50, and 30 mW cm?2, respectively, with increased charge collection efficiency (>40%). This is the best performing RT solid-state DSSC using a PC electrolyte. Considering the fact that most reported quasi-solid state or nonvolatile electrolytes require higher iodine contents for efficient ion transport, our HS-NFs are a promising morphology for such electrolytes that have limited ion mass transport.     

Fabrication of 3D interconnected porous TiO2 nanotubes templated by poly(vinyl chloride-g-4-vinyl pyridine) for dye-sensitized solar cells

Porous TiO(2) nanotube arrays with three-dimensional (3D) interconnectivity were prepared using a sol-gel process assisted by poly(vinyl chloride-graft-4-vinyl pyridine), PVC-g-P4VP graft copolymer and a ZnO nanorod template. A 7 μm long ZnO nanorod array was grown from the fluorine-doped tin oxide (FTO) glass via a liquid phase deposition method. The TiO(2) sol-gel solution templated by the PVC-g-P4VP graft copolymer produced a random 3D interconnection between the adjacent ZnO nanorods during spin coating. Upon etching of ZnO, TiO(2) nanotubes consisting of 10-15 nm nanoparticles were generated, as confirmed by wide-angle x-ray scattering (WAXS), energy-filtering transmission electron microscopy (EF-TEM) and field-emission scanning electron microscopy (FE-SEM). The ordered and interconnected nanotube architecture showed an enhanced light scattering effect and increased penetration of polymer electrolytes in dye-sensitized solar cells (DSSC). The energy conversion efficiency reached 1.82% for liquid electrolyte, and 1.46% for low molecular weight (M(w)) and 0.74% for high M(w) polymer electrolytes.     

An innovative approach to synthesize highly-ordered TiO2 nanotubes

An innovative route to prepare highly-ordered and dimensionally controlled TiO2 nanotubes has been proposed using a mild sonication method. The nanotube arrays were prepared by the anodization of titanium in an electrolyte containing 3% NH4F and 5% H2O in glycerol. It is demonstrated that the TiO2 nanostructures has two layers: the top layer is TiO2 nanowire and underneath is well-ordered TiO2 nanotubes. The top layer can easily fall off and form nanowires bundles by implementing a mild sonication after a short annealing time. We found that the dimensions of the TiO2 nanotubes were only dependent on the anodizing condition. The proposed technique may be extended to fabricate reproducible well-ordered TiO2 nanotubes with large area on other metals.     

暴露高活性晶面的TiO2纳米管的制备及生物活性

采用多次阳极氧化技术,在金属钛表面制备(001)晶面族择优生长的TiO_2纳米管阵列,研究电解液成分对锐钛矿TiO_2不同晶面相对比例的影响并考察其生物学活性。采用扫描电镜(SEM)、X射线衍射(XRD)等方法分析纳米管阵列的形貌特征和晶体结构,通过生物矿化CaP盐的沉积和蛋白吸附实验评价样品晶面对生物活性的影响。结果表明:通过改变电解液中H_2O的含量,能够便捷调控锐钛矿TiO_2纳米管中不同晶面的相对比例。当H_2O含量为2%(体积分数)时,制备得到的TiO_2纳米管阵列(004)晶面的织构系数T_c(004)可达4.76。而具有(001)优势晶面族的TiO_2纳米管,在类人体环境中能够为生物矿化和蛋白吸附提供更多的活性位点,加速羟基磷灰石的沉积并增加蛋白吸附量,表现出更优异的生物学活性。