Dye-sensitized solar cells based on multiwalled carbon nanotube-titania/titania bilayer structure photoelectrode

Dye-sensitized solar cells (DSSCs) were fabricated using multiwalled carbon nanotube (MWCNT)-TiO(2) nanocomposite as a light scattering layer. Morphology of the MWCNT-TiO(2) film was investigated by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). FESEM and TEM images demonstrate that MWCNTs and TiO(2) nanoparticles can be dispersed with chitosan. Internal resistance in the DSSC was characterized by electrochemical impedance spectroscopy (EIS). EIS results reveal a decrease in the charge resistance of electrolyte/dye/MWCNT-TiO(2)/TiO(2) interface with increasing MWCNT content up to 3 wt% which leads to an improvement in the photovoltaic performance. Compare with a nanocrystalline TiO(2) single-layer cell, the DSSC based on the MWCNT (3 wt%)-TiO(2)/TiO(2) bilayer structure photoelectrode shows ~100% increase in solar-to-electric energy conversion efficiency, which is attributed to the inclusion of MWCNTs in TiO(2) matrix.     

Correlation between dispersion properties of TiO2 colloidal sols and photoelectric characteristics of TiO2 films

TiO2 film for use as dye-sensitized solar cell was prepared using the TiO2 colloidal sols (unpeptized sol and peptized sol). The optical properties and photocurrent-voltage characteristics of the resultant films were investigated. The optical transmittance of TiO2 thin film prepared from the peptized colloidal sol was over 90%, while that of TiO2 film from the unpeptized sol was under 80%. The TiO2 photoelectrode prepared from the peptized colloidal sol showed low photoelectric conversion efficiency (eta), 1.30%, whereas the efficiency of photoelectrode from the unpeptized sol was 2.21%. The high optical transmittance and low conversion efficiency of TiO2 film from the peptized sol are discussed in terms of dense microstructure due to the drying nature of well-dispersed colloidal sol.     

Dye-sensitized solar cells based on TiO2-B nanobelt/TiO2 nanoparticle sandwich-type photoelectrodes with controllable nanobelt length

The TiO(2)-B nanobelt (NB)/TiO(2) nanoparticle (NP) sandwich-type structure photoelectrode, with controllable nanobelt length, has been used to fabricate high-efficiency dye-sensitized solar cells (DSSCs), which combine the advantages of the rapid electron transport in TiO(2)-B NBs and the high surface area of TiO(2) NPs. The results indicate that the sandwich-type photoelectrode achieves higher photoelectrical conversion efficiency when compared with the TiO(2) nanoparticulate electrode. Increasing the length of TiO(2)-B NBs has been demonstrated to improve the photoelectric conversion efficiency (η). DSSCs with the longest (10 μm) TiO(2)-B NBs yield the highest η of 7.94%. The interfacial electron transport of DSSCs with different lengths of TiO(2)-B NBs has been quantitatively investigated using the photovoltage transient and the electrochemical impedance spectra, which demonstrates that the DSSCs with longest TiO(2)-B NBs display the highest electron collection efficiency and the fastest interfacial electron transfer.     

Effective enhancement of the performance of black dye based dye-sensitized solar cells by metal oxide surface modification of the TiO2 photoelectrode

Effective enhancement of the performance of black dye based dye-sensitized solar cells has been achieved by MgO or Al(2)O(3) surface modification of the TiO(2) photoelectrode. The conversion efficiency was improved from 10.4% to 10.8% due to the blocking effect of the thin overlayer at the TiO(2) surface.     

Hierarchical TiO(2) flowers built from TiO(2) nanotubes for efficient Pt-free based flexible dye-sensitized solar cells

A novel hierarchical TiO(2) flower consisting of anatase TiO(2) nanotubes on a Ti foil substrate has been prepared via a mild hydrothermal reaction of TiO(2) nanoparticles/Ti foil. The photovoltaic performance of DSSC based on hierarchical TiO(2) flowers/Ti (7.2%) is much higher than that of TiO(2) nanoparticle/Ti (6.63%) because of its superior light scattering ability and fast electron transport. Moreover, full flexible DSSC based on the novel hierarchical TiO(2) flowers/Ti foil photoelectrode and electrodeposited poly(3,4-ethylenedioxythiophene) (PEDOT) on indium tin oxide-coated poly(ethylene terephthalate) (ITO-PET) counter electrode shows a significant power conversion efficiency of 6.26%, accompanying a short-circuit current density of 11.96 mA cm(-2), an open-circuit voltage of 761 mV and a fill factor of 0.69.     

Microstructure design of nanoporous TiO2 photoelectrodes for dye-sensitized solar cell modules

The optimization of dye-sensitized solar cells, especially the design of nanoporous TiO2 film microstructure, is an urgent problem for high efficiency and future commercial applications. However, up to now, little attention has been focused on the design of nanoporous TiO2 microstructure for a high efficiency of dye-sensitized solar cell modules. The optimization and design of TiO2 photoelectrode microstructure are discussed in this paper. TiO2 photoelectrodes with three different layers, including layers of small pore size films, larger pore size films, and light-scattering particles on the conducting glass with the desirable thickness, were designed and investigated. Moreover, the photovoltaic properties showed that the different porosities, pore size distribution, and BET surface area of each layer have a dramatic influence on short-circuit current, open-circuit voltage, and fill factor of the modules. The optimization and design of TiO2 photoelectrode microstructure contribute a high efficiency of DSC modules. The photoelectric conversion efficiency around 6% with 15 x 20 cm2 modules under illumination of simulated AM1.5 sunlight (100 mW/cm2) and 40 x 60 cm2 panels with the same performance tested outdoor have been achieved by our group.     

Hydrothermal fabrication of quasi-one-dimensional single-crystalline anatase TiO2 nanostructures on FTO glass and their applications in dye-sensitized solar cells

One-dimensional and quasi-one-dimensional semiconductor nanostructures are desirable for dye-sensitized solar cells (DSSCs), since they can provide direct pathways for the rapid collection of photogenerated electrons, which could improve the photovoltaic performance of the device. Quasi-1D single-crystalline anatase TiO(2) nanostructures have been successfully prepared on transparent, conductive fluorine-doped tin oxide (FTO) glass with a growth direction of [101] through a facile hydrothermal approach. The influences of the initial titanium n-butoxide (TBT) concentration, hydrothermal reaction temperature, and time on the length of quasi-1D anatase TiO(2) nanostructures and on the photovoltaic performance of DSSCs have been investigated in detail. A power conversion efficiency of 5.81% has been obtained based on the prepared TiO(2) nanostructure photoelectrode 6.7 μm thick and commercial N719 dye, with a short-circuit current density of 13.3 mA cm(-2) , an open-circuit voltage of 810 mV, and a fill factor of 0.54.     

Enhanced water photolysis with Pt metal nanoparticles on single crystal TiO2 surfaces

Two novel deposition methods were used to synthesize Pt-TiO(2) composite photoelectrodes: a tilt-target room temperature sputtering method and aerosol-chemical vapor deposition (ACVD). Pt nanoparticles (NPs) were sequentially deposited by the tilt-target room temperature sputtering method onto the as-synthesized nanostructured columnar TiO(2) films by ACVD. By varying the sputtering time of Pt deposition, the size of deposited Pt NPs on the TiO(2) film could be precisely controlled. The as-synthesized composite photoelectrodes with different sizes of Pt NPs were characterized by various methods, such as SEM, EDS, TEM, XRD, and UV-vis. The photocurrent measurements revealed that the modification of the TiO(2) surface with Pt NPs improved the photoelectrochemical properties of electrodes. Performance of the Pt-TiO(2) composite photoelectrodes with sparsely deposited 1.15 nm Pt NPs was compared to the pristine TiO(2) photoelectrode with higher saturated photocurrents (7.92 mA/cm(2) to 9.49 mA/cm(2)), enhanced photoconversion efficiency (16.2% to 21.2%), and increased fill factor (0.66 to 0.70). For larger size Pt NPs of 3.45 nm, the composite photoelectrode produced a lower photocurrent and reduced conversion efficiency compared to the pristine TiO(2) electrode. However, the surface modification by Pt NPs helped the composite electrode maintain higher fill factor values.     

Nanoparticle and nanorod TiO2 composite photoelectrodes with improved performance

A novel nanoparticle-nanorod composite TiO(2) photoelectrode is fabricated. A 3.20% efficiency is achieved by using a 2.1 μm-thick as-prepared photoelectrode, which is about 3 times of that obtained by a nanorod array electrode (1.05%). The results demonstrate that the composite nanostructure can take advantage of both fast electron transport (nanorod) and high surface area (nanoparticle).     

A flexible photoelectrode for CdS/CdSe quantum dot-sensitized solar cells (QDSSCs)

We, for the first time, prepared a flexible photoelectrode for CdS/CdSe quantum dot-sensitized solar cells (QDSSCs). A power conversion efficiency of 3.47% was achieved under AM 1.5G illumination for a sandwich type QDSSC consisting of this flexible photoelectrode, Cu(2)S counter electrode and polysulfide electrolyte between the electrodes.     

PbS quantum dot sensitized anatase TiO2 nanocorals for quantum dot-sensitized solar cell applications

Lead sulphide (PbS) quantum dot (QD) sensitized anatase TiO(2) nanocorals (TNC) were synthesized by SILAR and hydrothermal techniques. The TNC, PbS and PbS-TNC samples were characterized by optical absorption, XRD, FT-IR, FESEM and XPS. The results show that PbS QDs are coated on the TNCs, the optical absorption is found to be enhanced and the band edge is shifted to ~693 nm as compared with plain TNCs at 340 nm. The PbS-TNC sample exhibits an improved photoelectrochemical performance with a maximum short circuit current (J(sc)) of 3.84 mA cm(-2). The photocurrent density was found to be enhanced 2 fold, as compared with those of the bare PbS photoelectrode. The total power conversion efficiency of the PbS-TNC electrodes is 1.23%.     

Layer-by-layer assembled multilayer TiO(x) for efficient electron acceptor in polymer hybrid solar cells

We demonstrate that TiO(x) nanocomposite films fabricated using electrostatic layer-by-layer (LbL) assembly improve the power conversion efficiency of photovoltaic cells compared to conventional TiO(x) films fabricated via the sol-gel process. For this study, titanium precursor/poly(allylamine hydrochloride) (PAH) multilayer films were first deposited onto indium tin oxide-coated glass to produce TiO(x) nanocomposites (TiO(x)NC). The specific effect of the LbL processed TiO(x) on photovoltaic performance was investigated using the planar bilayer TiO(x)NC and highly regioregular poly(3-hexylthiophene) (P3HT) solar cells, and the P3HT/LbL TiO(x)NC solar cells showed a dramatic increase in power efficiency, particularly in terms of the short current density and fill factor. The improved efficiency of this device is mainly due to the difference in the chemical composition of the LbL TiO(x)NC films, including the much higher Ti(3+)/Ti(4+) ratio and the highly reactive facets of crystals as demonstrated by XPS and XRD measurement, thus enhancing the electron transfer between electron donors and acceptors. In addition, the grazing incidence wide-angle X-ray scattering (GIWAXS) study revealed the presence of more highly oriented P3HT stacks parallel to the substrate on the LbL TiO(x)NC film compared to those on the sol-gel TiO(x) films, possibly influencing the hole mobility of P3HT and the energy transfer near and at the interface between the P3HT and TiO(x) layers. The results of this study demonstrate that this approach is a promising one for the design of hybrid solar cells with improved efficiency.     

TiO2/SnO2复合空心球在染料敏化太阳能电池中的应用

采用模板辅助法制备了SnO2/TiO2复合空心球,样品直径为1.5~4.0μm,比表面积达到了92.9 m^2·g^-1,复合空心球表现出优越的光散射性能.以这种复合空心球作为染料敏化太阳能电池的光阳极,电池的光电转换效率可达到7.72%,高于SnO2微米球(2.70%)和TiO2微米球(6.26%).此外,以锐钛矿型TiO2纳米晶作为底层,SnO2/TiO2复合空心球作为光散射层制备的双层结构光阳极,电池光电转换效率进一步提升至8.43%.     

Organic photovoltaic devices with colloidal TiO2 nanorods as key functional components

We report on a novel approach to integrate colloidal anatase TiO(2) nanorods as key functional components into polymer bulk heterojunction (BHJ) photovoltaic devices by means of mild, all-solution-based processing techniques. The successful integration of colloidal nanoparticles in organic solar cells relies on the ability to remove the long chain insulating ligands, which indeed severely reduces the charge transport. To this aim we have exploited the concomitant mechanisms of UV-light-driven photocatalytic removal of adsorbed capping ligands and hydrophilicization of TiO(2) surfaces in both solid-state and liquid-phase conditions. We have demonstrated the successful integration of the UV-irradiated films and colloidal solutions of TiO(2) nanorods in inverted and conventional solar cell geometries, respectively. The inverted devices show a power conversion efficiency of 2.3% that is a ca. three times improvement over their corresponding cell counterparts incorporating untreated TiO(2), demonstrating the excellent electron-collecting property of the UV-irradiated TiO(2) films. The integration of UV-treated TiO(2) solutions in conventional devices results in doubled power conversion efficiency for the thinner active layer and in maximum power conversion efficiency of 2.8% for 110 nm thick devices. In addition, we have demonstrated, with the support of device characterizations and optical simulations, that the TiO(2) nanocrystal buffer layer acts both as electron-transporting/hole-blocking material and optical spacer.     

掺钴氧化钛电极的制备、表征及其光电性能

采用溶胶-凝胶法在纯钛片上制备了掺Co氧化钛薄膜光电极,运用扫描电子显微镜(SEM)、 X射线衍射(XRD)等分析手段对其进行表征,并对其结构和性能的相互关系进行了研究.结果表明,掺5%Co, 500℃热处理的TiO2电极具有最大的可见光响应.过量的Co掺入将析出新相CoTiO3,并促使TiO2由锐钛矿型转变为金红石型,使电极光电效应减低.而高温处理的掺钴TiO2也将析出CoTiO3,对电极光电性能有阻碍作用.     

TiO_2/CuPc/NiFe-LDH photoanode for efficient photoelectrochemical water splitting

Photoelectrochemical(PEC) water splitting is a promising approach for renewable hydrogen production.However,the practical PEC solar-to-fuel conversion efficiency is still low owing to poor light absorption and rapid recombination of charge carriers in photoelectrode.In this work,we report a ternary photoanode with simultaneously enhancement of light absorption and water oxidation efficiency by introducing copper phthalocyanine(CuPc) and nickel iron-laye red double hydroxide(NiFe-LDH) on TiO_2(denoted as TiO_2/CuPc/NiFe-LDH).An experimental study reveals that CuPc loading on TiO_2 bring strong visible light absorption;NiFe-LDH as an oxygen evolution reaction catalyst efficiently accelerates the surface water oxidation reaction.This synergistic effect of CuPc and NiFe-LDH gives enhanced photocurrent density(2.10 mA/cm2 at 0.6 V vs.SCE) and excellent stability in the ternary TiO_2/CuPc/NiFeLDH photoanode.     

Standing wave enhancement of red absorbance and photocurrent in dye-sensitized titanium dioxide photoelectrodes coupled to photonic crystals

The light harvesting efficiency of dye-sensitized photoelectrodes was enhanced by coupling a TiO(2) photonic crystal layer to a conventional film of TiO(2) nanoparticles. In addition to acting as a dielectric mirror, the inverse opal photonic crystal caused a significant change in dye absorbance which depended on the position of the stop band. Absorbance was suppressed at wavelengths shorter than the stop band maximum and was enhanced at longer wavelengths. This effect arises from the slow group velocity of light in the vicinity of the stop band, and the consequent localization of light intensity in the voids (to the blue) or in the dye-sensitized TiO(2) (to the red) portions of the photonic crystal. By coupling a photonic crystal to a film of TiO(2) nanoparticles, the short circuit photocurrent efficiency across the visible spectrum (400-750 nm) could be increased by about 26%, relative to an ordinary dye-sensitized nanocrystalline TiO(2) photoelectrode.     

光电化学分解水电池的电极性能提高方法及光阴极研究进展

光电化学水分解电池能够将太阳能直接转化为氢能,是一种理想的太阳能利用方式. p-n叠层电池具有理论转换效率高、成本低廉、材料选择灵活等优势,被认为是最有潜力的一类光电化学水分解电池. 然而,目前这类叠层电池的太阳能转化效率还不高,主要原因是单个电极的效率太低. 本文介绍了几种提高光电极分解水性能的方法--减小光生载流子的体相复合、表面复合以及抑制背反应等,同时综述了国内外关于几种p型半导体光阴极的研究进展,如Si、InP、CuIn_1-x GaxS(Se)₂、Cu₂ZnSnS₄等. 通过总结,作者提出一种p-Cu₂ZnSnS₄(CuIn_1-xGaxS(Se)₂)/n-Ta₃N₅(Fe₂O₃) 组装方式,有望获得高效低成本叠层光电化学水分解电池.     

Bifunctional single-crystalline rutile nanorod decorated heterostructural photoanodes for efficient dye-sensitized solar cells

A novel heterostructural TiO(2) nanocomposite, which consists of single-crystalline rutile TiO(2) nanorod decorated Degussa P25 nanoparticles, has been fabricated through a facile acidic hydrothermal method and successfully applied as the photoanodes for efficient dye-sensitized solar cells. The morphology, crystal structure, specific surface area and pore size distribution of the obtained nanocomposite were systematically investigated by X-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), high resolution transmission electron microscope (HRTEM), selected-area electron diffraction patterns (SAED) and nitrogen adsorption-desorption measurements. Under standard illumination conditions (AM 1.5, 100 mW cm(-2)), devices with these hybrid anodes exhibited considerably enhanced photocurrent density and overall conversion efficiency in comparison with that of the commercial Degussa P25 electrodes, which can be partially attributed to the light scattering effect in the long-wavelength region as evidenced from the incident photon-to-current conversion efficiency (IPCE) response and the diffuse reflectance spectroscopy. More importantly, devices employing these hybrid anodes have demonstrated extended electron lifetimes and larger electron diffusion coefficient as validated by the intensity-modulated photocurrent/photovoltage spectroscopy measurements, which can be mainly ascribed to the fast electron transport and collection superiority of the single-crystalline nanorods.     

水热法可控合成二氧化钛纳米晶及其在染料敏化太阳能电池中的应用

本文报道了水热法可控合成二氧化钛纳米晶及其在染料敏化太阳能电池中的应用.选择合适的有机碱胶化剂,能很好地控制二氧化钛纳米晶的生长,形成不同形貌和粒径的锐钛矿型二氧化钛纳米晶颗粒.染料敏化太阳能电池光电性能测试结果表明,以四乙基氢氧化铵为胶化剂合成的边长为8～13nm的正方形二氧化钛纳米晶构成的光阳极光电性能优于以四丁基氢氧化铵为胶化剂合成的边长为7～10nm的正方形二氧化钛纳米晶以及长18～35nm,宽10～18nm的长方形二氧化钛纳米晶构成的光阳极.用较高浓度的四甲基氢氧化铵胶化剂能合成球形或椭球形亚微米级二氧化钛颗粒,以其为散射中心在光阳极中构建散射层,染料敏化太阳能电池的光电转换效率能由6.77%提高到8.18%.