Laser-sintered mesoporous TiO2 electrodes for dye-sensitized solar cells

Low-temperature laser sintering has been successfully demonstrated to improve the overall conversion efficiency of dye-sensitized solar cells. Mesoporous TiO₂ electrodes were prepared from a colloidal solution of TiO₂ nanopowders by a laser direct-write technique and then sintered by a quasi-continuous-wave UV laser (λ=355 nm) for the fabrication of dye-sensitized solar cells. The overall conversion efficiency of the cells based on the laser-sintered TiO₂ electrodes was double that of the devices with non-laser-treated TiO₂ electrodes. This enhancement is attributed to both the removal of organic additives and the improved inter-nanoparticle electrical contacts induced by the laser-sintering process, which led to an increase in porosity and dye-absorption sites in the TiO₂ electrodes. PACS 61.80.Ba; 61.46.+w; 73.22.-f; 84.60.Jt     

ZnO-treated TiO2 inverse opal electrodes for dye-sensitized solar cells

We report that the photovoltaic properties of inverse opal TiO₂ (io-TiO₂) electrodes in dye-sensitized solar cells can be enhanced by ZnO treatment of the inverse opal structures. ZnO was coated on the surface of io-TiO₂ via the sol–gel reaction of ZnO precursors. Energy dispersive X-ray spectroscopy (EDX) measurements showed that the amount of ZnO on the io-TiO₂ surface was measured to be 0.12–0.50 wt% of zinc, depending on the number of coatings. Compared to bare inverse opal electrodes, the energy conversion efficiency of cells increased for the 0.35 wt% ZnO-coated electrodes, and then decreased for the 0.50 wt% ZnO-coated electrodes. The maximum efficiency of 5.3% was achieved, corresponding to a 23% increase in efficiency compared with bare io-TiO₂ electrodes. The enhanced efficiency was mainly attributed to the improvement of the open-circuit voltage (V_OC). EIS and dark current measurements confirmed that this enhancement in V_OC was due to the movement of the conduction band edge in a negative direction after ZnO treatment, rather than the formation of a barrier layer for electron recombination.     

Electrochemical properties of TiO2 nanoparticle/nanorod composite photoanode for dye-sensitized solar cells

A unique composite of TiO₂ nanoparticles (NPs) and nanorods (NRs) has been used to fabricate a photoelectrode for developing dye-sensitized solar cells (DSSCs) with higher sensitivity. The TiO₂ nanorods were synthesized using a mechanical process, in which electrospun TiO₂ nanofibers was grinded in a controlled way to obtain uniform size distribution. The characteristics of electron transport, recombination lifetime and charge collection were investigated by intensity-modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS). Photoelectrodes prepared with the composites of NRs and NPs showed significant improvements in electron transportation compared to only NP photoelectrodes, which would enhance the photovoltaic performance of DSSCs. IMPS and IMVS measurements show that fast electron transport and slightly decreased recombination lifetime resulted in the improvement of efficiency. The highest energy conversion efficiency obtained from the photoelectrodes fabricated with the as-prepared rutile TiO₂ nanofibers at 5 wt% NR content was up to 6.1% under AM1.5G solar illumination. The results demonstrate that the composite nanostructure can take advantage of both the fast electron transport of the nanorods and the high surface area of the nanoparticles.     

Electron transport in dye-sensitized solar cells based on TiO2 nanowires

Anatase titanium dioxide nanowire arrays were prepared by hydrothermally oxidizing titanium foils in aqueous alkali and transferred onto fluorinated tin oxide(FTO)glass for use as the photoanodes of front side illuminated dye-sensitized solar cells(DSCs).Electrochemical impedance spectroscopy(EIS)measurement was applied to compare the electron transport and recombination properties of DSCs using TiO2nanowire films and TiO2nanoparticle films as photoanodes.It was found that the nanowire array films possess smaller electron transport resistance(Rt)and larger electron diffusion length(Le)in the photoanodes,suggesting that the nanowire arrays can enhance the electron transport rate and have a potential to improve the charge collection efficiency of DSCs.     

锐钛矿相TiO2纳米管的制备及其染科敏化太阳电池

以商用金红石相TiO2粉末为原料,通过在碱性溶液中150℃水热48h的方法合TiO2纳米管.采用SEM,TEN,XRD分析手段对TiO2纳米管的形貌和结构演变进行了表征.制成的TiO2纳米管与TritonX-100,乙酰丙酮混合后,通过丝网印刷的方法涂敷到ITO导电玻璃衬底上,并且在450℃下烧结30min后得到可应用于染料敏化太阳电池的多孔光阳极.将此光阳极浸泡于N719染料敏化后,与镀铂对电极组装电池,两者之间灌入液态电解质,电池的有效面积为0.28 cm2.在标准氙灯模拟器下(AM 1.5,100 roW/cm2)测试r电池的J-V特性,得到2.17%的光电转换效率.     

TiO2颗粒尺寸对染料敏化太阳电池内电子输运特性影响研究

采用强度调制光电流谱(IMPS)和强度调制光电压谱(IMVS)研究了染料敏化太阳电池(DSC)内部电子传输和背反应动力学特性.在纳米TiO2薄膜厚度相同的情况下,借助于IMPS/IMVS测量了由3种不同TiO2颗粒尺寸大小薄膜制备出DSC的电荷传输特征参数值.IMPS/IMVS理论模型拟合实验测量数据的结果表明:在不同入射光强下,随着颗粒尺寸的增大,电子扩散系数(Dn)增大,而电子寿命(τn)减小,电子传输时间(τd)也减小.Dn随颗粒尺寸增大而增加归因于薄膜表面积的减小,而τn减小可以通过缺陷之间的跃迁频率来解释,τd减小是由于TiO2薄膜内缺陷浓度减小而导致的.     

Viologen impregnated PVDF with TiO2 nanofiller as a solid polymer electrolyte for dye-sensitized solar cells

Dye-sensitized solar cells were fabricated using viologen impregnated PVDF with TiO₂ nanofiller as a solid polymer electrolyte sandwiched in between N3 (cis-di(thiocyanato)N,N′-bis(2,2′-bipyridyl-4,4′-dicarboxylic acid)-ruthenium(II)) dye adsorbed over TiO₂ nanocrystalline film as anode and conducting carbon cement coated over conducting glass as cathode to mainly impede the back-electron transfer processes. The prepared polymer electrolytes were well characterized before using them in solar cells. The functioning of the solar cells fabricated was monitored and the current–voltage characteristics were measured.     

Synthesis of nanobranched TiO2 nanotubes and their application to dye-sensitized solar cells

Nanobranched TiO₂ nanotubes (TONTs) were synthesized by a sol–gel dipping method for the formation of seed layer, followed by a solution-phase deposition process. The different concentrations of seed solution influence the density of nanobranches on the top surface of TONT, achieving complete surface coverage of nanobranches in 10 mM TiCl₄ seed solution relative to 5 mM TiCl₄ seed solution. With a control sample of bare TONT, the nanobranched TONTs were explored as a photoanode for dye-sensitized solar cells (DSSCs). In the 5 mM TiCl₄ seed solution, the nanotree-shaped branches were sporadically formed on the top surface of TONT, with little effect on the photocurrent-voltage (J–V) properties, while in the 10 mM TiCl₄ seed solution, J_sc and fill factor increased, which may have been on account of the increased surface area and light scattering effect from rutile nanobranches, whereas the fill factor may be also increased by the electron transport property, leading to the degraded charge recombination. Accordingly, the nanobranched TONT showed 33% improved efficiency compared to bare TONT.     

PEO electrolytes containing dioctyl phthalate (DOP) for dye-sensitized nanocrystalline TiO2 solar cells

In this paper, we aim to prepare polymer electrolytes consisting of NaI and I₂ dissolved in poly(ethylene oxide) (PEO) and dioctyl phthalate (DOP) as an additive and apply the electrolytes to dye-sensitized solar cells (DSSC). Upon the incorporation of salt, the phthalic-stretching C=O bands of DOP in Fourier transform infrared spectra shifted to a lower wave number (Δf = 93 cm⁻¹), confirming the unusual strong complex formation between sodium ions and phthalic oxygen. Coordinative interactions and structural changes of PEO/NaI/I₂/DOP electrolytes have also been characterized by wide angle X-ray scattering, presenting an almost amorphous structure of the polymer electrolytes. The ionic conductivity of the polymer electrolytes reached ∼10^–4 S/cm at room temperature at the mole ratio of [EO]:[Na]:[DOP] = 10:1:0.5, as determined by the four-probe method. DSSC using the polymer electrolytes and conductive indium tin oxide glasses exhibited 2.9% of overall energy conversion efficiency (=P _max/P _in × 100) at one sun condition (100 mW/cm²). The good interfacial contact between the electrolytes and the dye-attached nanocrystalline TiO₂ layers were verified by field-emission scanning electron microscopy.     

Comparison of the performances of dye-sensitized solar cells based on different TiO2 electrode nanostructures

This article reports on the performances of dye-sensitized solar cells based on three different working electrode structures, i.e., (i) sintered TiO₂ nanoparticles (20–40 nm diameters), (ii) ordered arrays of TiO₂ nanotubules (150 nm external diameters and 80 nm internal diameters), and (iii) ordered arrays of TiO₂ nanorods (150 nm diameters). Even though the highest short-circuit current density was achieved with systems based on TiO₂ nanotubules, the most efficient cells were those based on ordered arrays of TiO₂ nanorods. This is probably due to higher open-circuit photovoltage values attained with TiO₂ nanorods than with TiO₂ nanotubules. The nanorods are thicker than the nanotubules and therefore the injected electrons, stored in the trap states of the inner TiO₂ molecules, are shielded from recombination with holes in the redox electrolyte at open circuit. The high short-circuit photocurrent densities seen in the ordered TiO₂ systems can be explained by the fact that, as opposed to the sintered nanoparticles, the parallel and vertical orientation of the ordered nanostructures provide well-defined electrons percolation paths thus significantly reduce the diffusion distance and time constant.     

纳米TiO2多孔膜的微结构对染料敏化纳米薄膜太阳电池性能的影响

采用溶胶-凝胶方法，在不同的实验条件下获得平均粒径从15到25nm左右的纳米TiO２2颗粒.利用这些颗粒制备出的纳米多孔薄膜，应用于染料敏化纳米薄膜太阳电池. 通过x射线 衍射仪分析，得到TiO２₂颗粒的晶相以及晶粒度大小，用透射电子显微镜观察 了纳米TiO２₂颗粒的形貌和尺寸.应用于太阳电池的纳米TiO２₂多 孔膜，经基于布朗诺尔-埃米特-泰 勒（BET）的多层吸附理论的比表面积测试和孔径分布测试，获得了多孔膜的微 关键词： 溶胶-凝胶法 2')" href="#">纳米TiO２₂ 染料敏化 太阳电池     

Improved short-circuit photocurrent densities in dye-sensitized solar cells based on ordered arrays of titania nanotubule electrodes

We report on the synthesis of highly ordered arrays of titania nanotubules and their applications in enhanced photoelectrochemical cells. Ordered arrays of titania nanotubules of ∼120 nm external diameter, ∼100 nm internal diameter, and ∼5 μm length were fabricated on transparent conductive oxide (TCO) glass substrates by sol–gel processes using in-house prepared anodic alumina templates. After thermal bonding and template removal, the resultant nanotubule structures were applied in dye-sensitized solar cells (DSCs). Overall photoconversion efficiency of nearly 4.8% was achieved with Ru-bipyridine dye, N719, and iodolyte liquid electrolyte. This remarkable performance, for electrodes only ∼5 μm thick, is attributed to an unexpectedly high short-circuit photocurrent density of 16 mA/cm² for masked cells and up to 17 mA/cm² for unmasked cells. The enhanced short-circuit photocurrent (J_sc) is attributed to the high surface area (roughness factor ca. 1207) of the nanotubules and thus improved dye adsorption to the electrodes. The improved J_sc is also attributed to the parallel and vertical orientation of the nanostructures and thus to a well-defined electron diffusion path.     

Thickness effect of the TiO2 nanofiber scattering layer on the performance of the TiO2 nanoparticle/TiO2 nanofiber-structured dye-sensitized solar cells

TiO₂ nanofibers (NFs) were fabricated by an electrospinning process and were used as scattering layers in dye-sensitized solar cells (DSSCs). The NF-coated photoanodes of the DSSCs were prepared with a variety of scattering layer thicknesses. The thickness effect of the scattering layer on the double-layered TiO₂ nanoparticle (NP)/TiO₂ NF structure was investigated through structural, morphological, and optical measurements. In the double-layered photoanode, the TiO₂ NP layer plays a major role in dye adsorption and light transmission, and the TiO₂ NF scattering layer improves the absorption of visible light due to the light scattering effects. The scattering effect of TiO₂ NFs layer was examined by the incident monochromatic photon-to-electron conversion efficiency (IPCE) and UV–Vis spectrometry. The conversion efficiency for the 12 μm-thick photoanode composed of a 2 μm-thick TiO₂ NF layer and 10 μm-thick TiO₂ NP layer was higher than that of DSSCs with only TiO₂ NPs photoanode by approximately 33%.     

Oriented ZnO nanotubes arrays decorated with TiO2 nanoparticles for dye-sensitized solar cell applications

Dye-sensitized solar cells (DSSCs) based on a novel composite photoanode of TiO₂ nanoparticles coating on electrodeposited ZnO nanotube arrays are fabricated and characterized. An efficiency of 3.94 % is achieved for the composite cell, increasing 86.7 % than 2.11 % of the ZnO nanotubes cell. The short-circuit current (J _sc) and open-circuit voltage (V _oc) are also enhancing 52.9 % and 25.3 %, respectively. The improvements are because of the high surface area of TiO₂ nanoparticles, as well as fast electron transport and light scattering effect of ZnO nanotubes.     

染料敏化太阳电池中TiO2膜内电子传输和背反应特性研究

采用强度调制光电流谱(IMPS)和强度调制光电压谱(IMVS)研究电池内部电子传输机理和电子背反应动力学特性.利用理论表达式对不同TiO2多孔膜厚度(d)的电池实验数据进行了拟合,得到了电池的吸收系数(a)、电子扩散系数(Dn)、电子寿命(τn)、电子传输时间(τd)和入射单色光光电转化效率(IPCE)等微观参数的数值.研究表明:膜薄有利于加快电子传输,膜厚有利于提高光生电子浓度,进而从微观层面上研究了薄膜厚度对于电池内部电子产生、传输和复合过程的影响.     

Effect of hydroxyl on dye-sensitized solar cells assembled with TiO_2 nanorods

TiO_2 nanorods have been prepared on ITO substrates by dc reactive magnetron sputtering technique. The hydroxyl groups have been introduced on the nanorods surface. The structure and the optical properties of these nanorods have been studied. The dye-sensitized solar cells(DSSCs) have been assembled using these TiO_2 nanorods as photoelectrode. And the effect of the hydroxyl groups on the properties of the photoelectric conversion of the DSSCs has been studied.