Partially nanowire-structured TiO2 electrode for dye-sensitized solar cells

Partially nanowire-structured TiO₂ was prepared by a hydrothermal processing followed by calcination in air. The hydrogen titanate powder as-synthesized was calcined at 300 °C for 4 h to obtain the partially nanowire-structured TiO₂. A dye-sensitized solar cell (DSC) with a film thickness of 5.6 μm, fabricated using the partially nanowire-structured TiO₂ showed better performance than using a fully nanowire-structured TiO₂ or a conventional equi-axed TiO₂ nanopowder. The short-circuit current density (J_SC), the open-circuit voltage (V_OC), the fill factor (FF) and the overall efficiency (η) are 11.9 mA/cm², 0.754 V, 0.673 and 6.01 %, respectively. The effects of one-dimensional nanostructure and electron expressway concept are discussed.     

Preparation of TiO2 nanocrystalline films controlled by acetylacetone/polyethylene glycol and their photoelectric properties

TiO₂ nanocrystalline films were prepared from titanium tetra-n-butoxide modified with double hydrolysis inhibitors, acetylacetone and polyethylene glycol (PEG), in mixture of methanol and ethanol. The correlation among surface structure of the TiO₂ films, preparation conditions, and photovoltaic properties of the solar cells using the TiO₂ films was investigated. The particle size of the obtained TiO₂ films was decreased as the PEG content increased. The nanostructured films with the narrow distribution of particle size could be prepared. The amounts of adsorbed dyes for these TiO₂ films were larger than that without PEG. The performance of the solar cell fabricated using the TiO₂ film improved as the amount of the PEG increased, and the solar cell using the TiO₂ film prepared from the solution with 30 wt% PEG exhibited the highest performance.     

Voltage enhancement in dye-sensitized solar cell using (001)-oriented anatase TiO2 nanosheets

A nanocrystalline TiO₂ (anatase) nanosheet exposing mainly the (001) crystal faces was tested as photoanode material in dye-sensitized solar cells. The nanosheets were prepared by hydrothermal growth in HF medium. Good-quality thin films were deposited on F-doped SnO₂ support from the TiO₂ suspension in ethanolic or aqueous media. The anatase (001) face adsorbs a smaller amount of the used dye sensitizer (C101) per unit area than the (101) face which was tested as a reference. The corresponding solar cell with sensitized (001)-nanosheet photoanode exhibits a larger open-circuit voltage than the reference cell with (101)-terminated anatase nanocrystals. The voltage enhancement is attributed to the negative shift of flatband potential for the (001) face. This conclusion rationalizes earlier works on similar systems, and it indicates that careful control of experimental conditions is needed to extract the effect of band energetic on the current/voltage characteristics of dye-sensitized solar cell.     

Efficiency enhancement of solid‐state dye sensitized solar cell by in situ deposition of CuI

Solid‐state dye‐sensitized solar cells based on nanocrystalline TiO₂ thin film with the structures TiO₂/dye/CuI/Pt and TiO₂/dye/In situ CuI/CuI/Pt were developed in order to compare the use of In situ deposited CuI (In situ CuI). Porosity of the screen‐printed nanoporous TiO₂ thin film was enhanced by the addition of polystyrene balls. Evidence of decrease in interfacial resistance was observed by electrochemical impedance measurement for the device with In situ deposited CuI as compared to that without In situ deposited CuI as hole conductor. This was attributed to good interfacial contacts and better charge transfer between CuI and dye‐sensitized TiO₂ nanoparticles, which resulted in the enhancement of power conversion efficiency from 0.058 to 1.01%. Copyright © 2008 John Wiley & Sons, Ltd.     

Extending spectrum response of squaraine-sensitized solar cell by Förster resonance energy transfer

To extend the spectral response region of squaraine dye (SQ)-sensitized solar cell, eosin Y (EY) is encapsulated in the SQ-sensitized nanocrystalline thin film. EY is first adsorbed on nanocrystalline TiO₂ thin film (n-TiO₂), then a thin layer of EY contained ZnO (EY-ZnO) is electrodeposited, and SQ dye is finally sensitized to form two dye-sensitized nanocrystalline thin film with a structure of n-TiO₂/EY/EY-ZnO/SQ. There is a perfect spectral overlap between the emission of EY and the absorption of SQ; EY as an energy donor simultaneously transfers both electron and hole to the energy acceptor SQ according to the Förster resonance energy transfer (FRET) process. EY shifts the spectral response edge of SQ-sensitized solar cell toward blue from 550 to 450 nm through the FRET process in this new structure. Two dye-sensitized nanocrystalline thin film demonstrates a significant enhancement in light harvesting and photocurrent generation due to the FRET process. The thickness of the EY-ZnO thin layer and spectral overlap between emission of donor dye and absorption of acceptor dye are two important factors that affect the FRET process between EY and SQ in the structure of n-TiO₂/EY/EY-ZnO/SQ.     

TiO2 Nanoparticles Produced by Electric-Discharge-Nanofluid-Process as Photoelectrode of DSSC

Self-made TiO₂ nanoparticles were used as photoelectrode material of dye sensitized solar cell. The TiO₂ thin film coats through spreading nanoparticles evenly onto the ITO glass via self-made spin-heat platform, and then TiO₂ thin film is soaked in the dye N-719 more than 12 h to prepare the photoelectrode device. The TiO₂ nanoparticles produced by electric-discharge-nanofluid-process have premium anatase crystal property, and its diameter can be controlled within a range of 20-50 nm. The surface energy zeta potential of nanofluid is from -22 mV to -28.8 mV, it is a stable particle suspension in the deionized water. A trace of surfactant Triton X-100 put upon the surface of ITO glass can produce a uniform and dense TiO₂ thin film and heating up the spin platform to 200 oC is able to eliminate mixed surfac-tant. Self-made TiO₂ film presents excellent dye absorption performance and even doesn't need heat treatment procedure to enhance essential property. Results of energy analysis show the thicker film structure will increase the short-circuit current density that causes higher conversion efficiency. But, as the film structure is large and thick, both the open-circuit voltage and fill factor will decline gradually to lead bad efficiency of dye-sensitized solar cell.     

Efficiency improvement of flexible dye-sensitized solar cells by introducing mesoporous TiO2 microsphere

Mesoporous TiO2microsphere(MTM)was synthesized via a simple solution route and then mixed with commercial TiO2(P25)to form highly homogeneous and stable TiO2colloid by simple hydrothermal treatment.The TiO2colloid was coated onto the plastic conductive substrate to prepare mesoporous TiO2film for flexible dye-sensitized solar cells(DSSCs)by low-temperature heat treatment.The influence of MTM content on the physicochemical properties of the flexible TiO2film was characterized by scanning electron microscope,transmission electron microscopy,X-ray diffraction,energy-dispersive X-ray spectrometer,N2adsorption-desorption isotherms,UV–vis absorption and diffuse reflectance spectra.It is revealed that with increasing the MTM content,the dye-loading capability of TiO2film and light-harvesting efficiency of flexible DSSCs are improved due to MTM having high surface area and acting as a light scattering center,respectively,resulting in the enhancement of photocurrent of flexible DSSCs.However,more and larger cracks having negative effect on the performances of flexible DSSCs are formed simultaneously.Under the optimal condition with MTM content of 20%,a flexible DSSC with overall light-to-electric energy conversion efficiency of 2.74%is achieved under a simulated solar light irradiation of 100 mW cm 2(AM 1.5),with 26%improvement in comparison with DSSCs based on P25 alone.     

Polyethylene glycol assisted direct deposition of rutile TiO2 nanocrystals on transparent conducting oxide substrate for dye-sensitized solar cell applications

Rutile TiO₂ nanocrystals having rectangular faces were directly deposited on fluorine-doped tin oxide coated glass substrates. Using polyethylene glycol-400 as the surfactant, we succeeded in growing a porous rutile layer having maximum thickness of 4.8 μm and containing nanocrystals with lateral dimensions of at least 30 nm. We observed that polyethylene glycol not only controlled the sizes of the nanocrystals but also enhanced the rate of deposition. The nanocrystals had rutile structure and the film was strongly textured with preferential orientation along {002} direction. The dye adsorption properties of the nanocrystalline films depended on their microscopic surface areas which were determined by the sizes of the nanocrystals. A dye-sensitized solar cell, fabricated with a 4.8 μm thick nanocrystalline rutile thin film photoanode, exhibited a light-to-electricity conversion efficiency of 5.02 % under 1.0 sun illumination. The internal resistance, interface capacitance and electron lifetime of dye sensitized solar cell were estimated by electrochemical impedance spectroscopy and an electron lifetime of 0.19 s was recorded.     

TiO2纳米棒和CdSe纳米棒复合膜与聚3-甲基噻吩杂化太阳能电池研究

采用水热法制备了TiO₂和CdSe两种纳米棒材料, 将两种纳米材料制备成TiO₂/CdSe复合纳米棒膜电极, 并在复合膜上电化学聚合生成聚3-甲基噻吩poly(3-methylthiophene) (PMeT), 研究了其光电化学性能. 实验表明, 当TiO₂与CdSe的物质的量复合比为2∶1, PMeT的聚合时间为40 s, 在电极电势为－0.2 V下ITO/TiO₂/CdSe/PMeT电极光电转换效率(IPCE)达到56%, 对比ITO/TiO₂/CdSe复合膜电极在长波方向的光电转换效率明显提高, 光吸收截止波长发生了明显的红移. 同时以ITO/TiO₂/CdSe/PMeT组装了简易的杂化太阳电池, 初步研究了光电池性能, 光电池总效率为0.08%, V_oc＝0.4 V, j_sc＝0.61 mA/cm², ff＝0.33.     

Morphology and photoelectrochemical properties of TiO2 electrodes prepared using functionalized plant oil binders

Chemically functionalized plant oils, viz. acrylated epoxidized soybean oil (AESO) and maleinized acrylated epoxidized soybean oil (MAESO), were used as bio-based binders for the TiO₂ electrodes of dye-sensitized solar cells (DSSC). The surface roughness and number of appropriate pores were increased in the TiO₂ films prepared using the plant oil binders in comparison with the film prepared using polyethylene glycol (PEG), due to the larger number of functionalities. The short circuit photocurrent (I_SC) and open circuit photovoltage (V_OC) were increased, and the conversion efficiency was significantly improved, in the cell using the plant oil binders.     

Room-temperature preparation of nanocrystalline TiO2 films and the influence of surface properties on dye-sensitized solar energy conversion

An extremely easy method is presented for producing surfactant-free films of nanocrystalline TiO2 at room temperature with excellent mechanical stability when deposited on glass or plastic electrodes for dye-sensitized solar energy conversion. Prolonged magnetic stirring of commercial TiO2 nanoparticles (Degussa P25) in either ethanol or water results in highly homogeneous dispersions which are used to prepare TiO2 films with surface properties which depend on the solvent used for dispersing the particles, even after sintering. The optical and mechanical properties of films cast from ethanol and water dispersions are compared, and differences in the extent of surface defects and dye binding are observed. Optical absorption, photoluminescence, and resonance Raman spectra of TiO2 films sensitized with Ru(4,4'-dicarboxylic acid-2,2'-bipyridine)2(NCS)2 ("N3") reveal that the electronic coupling of the dye and semiconductor depends on the surface structure of the film which varies with film preparation. Current-voltage data for illuminated and dark dye-sensitized solar cells are obtained as a function of film preparation, and results are compared to spectroscopic data in order to interpret the microscopic basis for variations in solar cell performance, especially with regard to sintered versus unsintered TiO2 films. The results suggest that surface traps associated with oxygen vacancies play a critical role in determining the efficiency of dye-sensitized solar energy conversion through their influence on the binding and electronic coupling of the dye to the semiconductor.     

表面活性剂对染料敏化太阳能电池光电性能的提高

在硝酸/醋酸(HNO₃/HAc)的水溶液中分别加入十二烷基苯磺酸钠(DBS)、十六烷基三甲基溴化铵(CTAB)、吐温20等不同类型的表面活性剂来水解钛酸四正丁酯制得前驱体溶液,通过水热法制备纳晶TiO₂,并组装成染料敏化太阳能电池(DSSC)。通过XRD、SEM和UV-Vis对纳晶TiO₂薄膜进行表征,并对DSSC进行光电流-光电压(I-V)曲线的测试,研究了不同类型的表面活性剂和不同浓度的CTAB对DSSC光电性能的影响。结果表明：加入阳离子表面活性剂CTAB时提高了DSSC的光电性能,而加入阴离子表面活性剂DBS和非离子表面活性剂吐温20时,DSSC的光电性能反而降低。随着CTAB浓度的增加,电池的光电性能先提高后下降,当c_CTAB=0.08 mol·L^-1时,DSSC的光电转化效率最高为5.76%,比不添加表面活性剂制备的纳晶TiO₂所组装的DSSC的光电转化效率提高了约18%。     

TiO2薄膜优化对染料敏化太阳电池性能的影响

纳米TiO2多孔薄膜微结构对染料敏化太阳电池(DSC)光伏性能有很大的影响。本文采用不同实验和测试方法研究和分析了溶胶-凝胶法制备纳米TiO2颗粒时的热处理温度、TiO2多孔薄膜厚度、纳米TiO2大颗粒光散射、TiCl4溶液处理和电沉积致密TiO2层对纳米多孔薄膜电极和染料敏化太阳电池光伏性能的影响,得到了最佳的优化条件,为纳米TiO2薄膜材料的批量化制作打下了良好基础。     

Comparison of low crystallinity TiO2 film with nanocrystalline anatase film for dye-sensitized solar cells

Dye adsorption and microstructure of TiO₂ film are important properties when it is used as photoelectrode of dye-sensitized solar cells (DSCs). This study investigated the application of a low crystallinity TiO₂ film in DSCs. The low crystallinity TiO₂ film is composed of interconnected spherical particles with an average size of 20 nm and has homogeneous mesoporous inner structure. A DSC based on the anatase nanocrystalline mesoporous film prepared by P25 was used for comparison purpose. It is shown that although loaded with much less dye, the DSC based on the low crystallinity TiO₂ film generated I_sc (short circuit photocurrent) as much as the one based on the conventional anatase nanocrystalline film does and obtained higher V_oc (open circuit photovoltage) as well as ff (fill factor). The overall light-to-electricity efficiency (η) of the DSC based on the low crystallinity TiO₂ film reached 5.37%, while the η of the DSC based on anatase nanocrystalline film was 4.69% in this work condition. It is suggested that a low crystallinity TiO₂ mesoporous film with a proper microstructure is as efficient as the anatase nanocrystalline mesoporous film when used in DSCs.     

Sponge-like TiO2 layers for dye-sensitized solar cells

A titanium oxide layer used in a dye-sensitized solar cell (DSSC) has to meet two opponent properties to enable high conversion efficiency: a large surface area (for high dye loading) and good connection between TiO₂ grains (for efficient extraction of electrons toward the front contact). In order to meet a trade-off between these criteria a preparation method for TiO₂ paste formulation based on Pechini sol–gel method and commercial nanocrystalline TiO₂ powder has been developed. A series of TiO₂ pastes with different molar ratios between titanium isopropoxide, citric acid and ethylene glycol (1:X:4X) in the paste have been examined. The structure and morphology as well as cross-cut tests of deposited and sintered TiO₂ layers have been analyzed. Results reveal that the paste with X = 8 exhibits the best properties, resulting in an overall conversion efficiency of DSSC under standard test conditions (100 mW/cm², 25 °C, AM 1.5G) up to 6.6% for ionic liquid based electrolyte.     

Effects of Metal Oxide Modifications on Photoelectrochemical Properties of Mesoporous TiO2 Nanoparticles Electrodes for Dye-Sensitized Solar Cells

Mesoporous TiO₂ (m-TiO₂) nanoparticles were used to prepare the porous film electrodes for dye-sensitized solar cells, and a second metal oxide (MgO, ZnO, Al₂O₃, or NiO) modifi-cation was carried out by dipping the m-TiO₂ electrode into their respective nitrate solution followed by annealing at 500 oC. Experimental results indicated that the above second metal oxide modifications on m-TiO₂ electrode are shown in all cases to act as barrier layer for the interfacial charge transfer processes, but film electron transport and interfacial charge recombination characteristics under applied bias voltage were dependent significantly on the existing states and kinds of these second metal oxides. Those changes based on sec-ond metal oxide modifications showed good correlation with the current-voltage analyses of dye-sensitized solar cell, and all modifications were found to increase the open-circuit photo-voltage in various degrees, while the MgO, ZnO, and NiO modifications result in 23%, 13%, and 6% improvement in cell conversion efficiency, respectively. The above observations indi-cate that controlling the charge transport and recombination is very important to improve the photovoltaic performance of TiO₂-based solar cell.     

Preparation and properties of nanostructured TiO2 electrode by a polymer organic-medium screen-printing technique

An organic-medium screen-printing technique was developed for making porous TiO₂ electrodes. The TiO₂ pastes were prepared by mixing only 100% polyalkylene glycol and commercial nanocrystalline TiO₂ powders. The obtained paste is highly printable and hard to evaporate during printing. The TiO₂ electrodes have a very porous structure with large cavities. The dye-sensitized solar cell based on these meso-macroporous TiO₂ electrodes exhibits high overall conversion efficiency of 4.3–5.8%, which is comparable to those of prepared by water or terpineol medium.     

Microwave processing of TiO2 blocking layers for dye-sensitized solar cells

The microwave heat treatment of blocking layers for dye-sensitized solar cells has been investigated. It has been found that the solar cell efficiencies achieved with microwave heating were considerably higher than those achieved with conventional heating at low temperatures (100°C). This was attributed to microwave heating providing better sintering of the blocking layer and better interfacial contact between the substrate and the TiO₂ layers. These results are promising with regard to the application of microwave heating to the production of dye-sensitized solar cells on flexible polymer substrates.     

A novel architecture of poly(tetrafluoroethylene)-framed TiO2 electrodes for dye-sensitized solar cells

A novel architecture of polytetrafluoroethylene (PTFE)-framed TiO₂ electrodes is developed for dye-sensitized solar cells. The PTFE-framed TiO₂ electrodes with various thicknesses have been successfully fabricated, ranging from 20 to 160 μm. The optimal energy conversion efficiency of 9.04% is achieved with a film thickness of 60 μm. The PTFE-framed structure not only provides tunable film thickness but a reliable and cost-effective way for the mass production of photo-electrodes.     

Photovoltaic Performance Enhancement in Dye-Sensitized Solar Cells with Periodic Surface Relief Structures

One-dimensional and two-dimensional periodic TiO₂ relief structures were incorporated in dye-sensitized solar cells. The periodic TiO₂ structures were fabricated using surface relief gratings photoinscribed on azobenzene functionalized polymer films as templates and TiO₂ sol-gel solution. Enhancement of power conversion of the solar cells made with the relief TiO₂ structures was achieved. This enhancement suggests that the relief TiO₂ structures can offer efficient light-trapping with the increased effective optical-path length in the solar cells.