碳纳米复合对电极染料敏化太阳能电池的电化学性能

在染料敏化太阳能电池(DSCs)碳对电极中添加多壁碳纳米管,制作碳纳米复合对电极。通过循环伏安法研究复合电极中碳纳米管对I3?/I?氧化还原行为的影响。采用电化学阻抗谱表征,比较纳米炭黑、石墨鳞片、碳纳米管、纳米炭黑-纳米碳管复合材料对碳电极/电解质界面的影响。结果表明:添加纳米碳管后,电极的催化还原电位降低,电流密度增大;碳纳米管的加入使电极表面催化活性点增多,碳电极与电解液的界面电势差减少。光伏性能测试表明,添加10%(质量分数)的碳纳米管的DSCs的开路电压提高了17.9%,短路电流提高了24.1%,填充因子提高了14.4%。     

CNT/PEDOT core/shell nanostructures as a counter electrode for dye-sensitized solar cells

CNT/PEDOT nanostructures composed of carbon nanotube (CNT) cores and poly(3,4-ethylenedioxythiophene) (PEDOT) shells were synthesized by chemical oxidative polymerization of 3,4-ethylenedioxythiophene (EDOT) using FeCl₃ and dodecylbenzene sulfonic acid (DBSA) as the oxidant and surfactant, respectively. The resulting CNT/PEDOT nanostructures had a PEDOT layer thickness of 2–5 nm that exhibited not only higher polymerization yield but also enhanced thermal stability and electrical conductivity relative to pure PEDOT. N-Methyl-2-pyrrolidone (NMP)-based CNT/PEDOT paste containing polyvinylidene fluoride (PVDF) as a binder was painted directly onto fluorine-doped tin oxide (FTO) glass for use as a counter electrode (CE) material in dye-sensitized solar cells (DSSCs). While DSSCs made of pure CNT and PEDOT CE exhibited power conversion efficiencies of ～3.88% and 4.32% under standard AM 1.5 sunlight illumination, respectively, the cell efficiency was enhanced to ～4.62% with the CNT/PEDOT CE. This enhancement was due to the improved fill factor of the CNT/PEDOT-based DSSC realized by the increased electrical conductivity of the CNT/PEDOT composite.     

Enhancement of the photocurrent generation in dye-sensitized solar cell based on electrospun TiO2 electrode by surface treatment

We investigated the dye-sensitized solar cell (DSSC) using TiO₂ electrode electrospun directly onto the substrate from a mixture of titanium propoxide and poly(vinyl acetate) in dimethyl formamide (DMF). The electrospun electrode could be penetrated efficiently by a viscous polymer gel electrolyte because of porous structure. The energy conversion efficiency obtained from the DSSC with poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) gel electrolyte was over 90% of that obtained from liquid electrolyte. In order to improve the short-circuit photocurrent, we treated the electrospun TiO₂ electrode with TiCl₄ aqueous solution. The rutile crystal was grown epitaxially on anatase TiO₂ fibers. An additional TiO₂ layer increased the volume fraction of active materials resulting in an increase of sensitizer adsorption. The incident photon-to-current conversion efficiency (IPCE) of TiCl₄-treated electrode was higher than the untreated. In particular, the contribution from TiO₂ increases after the surface treatment due to an increase in packing density. The photocurrent of the DSSC with electrospun TiO₂ electrode was enhanced more than 30% after TiCl₄ treatment.     

Influences of magnesium particles incorporated on electrophoretically multiwall carbon nanotube film on dye-sensitized solar cell performance

Multiwall carbon nanotube (MWCNT) films are prepared on a conductive substrate by electrophoretic deposition. The thickness of MWCNT films is found to increase with the carbon nanotube concentration and the deposition duration. Scanning electron microscopy and energy dispersive X-ray measurements detect magnesium particles incorporated on the MWCNT films. The performance of dye-sensitized solar cell using the electrophoretically MWCNT films as a counter electrode shows a relationship dependent on the film thickness and the amount of magnesium loading. The increase in the magnesium loading on carbon films diminishes the solar cell efficiency. This is because magnesium particles cover the carbon nanotube surface reducing the nanotube catalytic sites and blocking electron transfer to tri-iodide (I₃⁻) ions.     

Mesoporous nanocrystalline TiO2 electrode with ionic liquid-based solid polymer electrolyte for dye-sensitized solar cell application

Thick mesoporous TiO₂ films with excellent properties have been prepared for dye-sensitized solar cell application using doctor-blade method. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) show the highly crystalline mesoporous anatase TiO₂ framework. On the other hand new solid electrolytes based on ionic liquid (IL) 1-methyl 3-propyl imidazolium iodide (PMII) and poly(ethylene oxide) (PEO) were prepared in film form and placed on porous-sensitized TiO₂ electrode following two-step casting technique. The doping of IL further provided large numbers of ions, resulting in the enhancement in conductivity and good solar cell performance.     

Influence of TiCl4 treatment on performance of dye-sensitized solar cell assembled with nano-TiO2 coating deposited by vacuum cold spraying

Titanium tetrachloride (TiCl4) treatment was employed to TiO2 coating deposited on fluoride-doped tin oxide (FTO) conducting glass and indium oxide doped tin oxide (ITO) conducting glass, respectively. The nano-crystalline TiO2coating was deposited using a composite powder composed of polyethylene glycol (PEG) and 25 nm TiO2 particles by vacuum cold spraying (VCS) process. A commercial N-719 dye was used to adsorb on the surface of TiO2 coating to prepare TiO2 electrode, which was applied to assemble dye-sensitized solar cell (DSC).The cell performance was measured under simulated solar light at an intensity of 100 mW·cm-2.Results show that with an FTO substrate the DSC composed of a VCS TiO2 electrode untreated by TiCl4 gives a short-circuit current density of 13.1 mA·cm-2 and an open circuit voltage of 0.60 V corresponding to an overall conversion efficiency of 4.4%. It is found that after TiCl4 treatment to the VCSTiO2 electrode with an FTO substrate, the short circuit current density of the cell increases by 31%, the open-circuit voltage increases by 60 mV and a higher conversion yield of 6.5% was obtained. However, when an ITOsubstrate is used to deposit TiO2 coating by VCS, after TiCl4 treatment, the conversion efficiency of the assembled cell reduces slightly due to corrosionof the conducting layer on the ITO glass by TiCl4.     

Development of large size dye-sensitized solar cell modules with high temperature durability

The DSSC sub-module of 120 mm² which has high temperature durability was fabricated. The durability was tested under 85 °C for 1000 h; at the end of the test the conversion efficiency was retained over 95% of the initial one. The high temperature durability was realized using the improved sealant, protective material of collecting grids and the new ruthenium-complex dye J2 which was developed by SIIT. By the same way the larger size module was developed.     

Improved photovoltaic performance of dye-sensitized solar cells by carbon-ion implantation of tri-layer titania film electrodes

TiO2tri-layer structure films were modified by C-ions implantation for improving the photovoltaic performance of dye-sensitized solar cells(DSSCs), in which the structure of TiO2 changes from rutile to anatase and the sizes of TiO2 particles increase. The optimal concentration of ions implantation for C-implanted cells is 19 1015 atom cm-2,and the maximum conversion efficiency of 5.32 % is achieved(luminous intensity of 1 sun, light irradiance of AM1.5G),which is 25.2 % higher than that of unimplanted cell. The significant improvement in conversion efficiency by carbonion implantation is contributed to reducing charge recombination and enhancing the light-harvesting ability, as indicated from incident photon-to-collected electron conversion efficiency(IPCE) and ultraviolet-visible(UV-Vis) measurements. Furthermore, the charge carrier's lifetime in the trilayer titania films is prolonged after carbon-ion implantations.     

Effect of polyethyleneimine on the growth of ZnO nanorod arrays and their application in dye-sensitized solar cells

A series of oriented hexagonal wurtzite ZnO nanorod-array films were grown on fluorine-doped tin oxide (FTO) coated glass substrates by chemical process. The effect of polyethyleneimine (PEI) on the structure and micro-morphology of ZnO nanorod array films, as well as the photoelectric conversion properties in dye-sensitized solar cells (DSSCs) was analyzed. It was found that with the addition of PEI in growth solution, the ZnO nanorods became smaller in diameter and longer in length and hence the dye absorption and the photovoltaic performance of DSSCs were improved. A power conversion efficiency of 2.30% had been achieved on a DSSC based on a 7.9 μm-long nanorod array film prepared by a growth solution containing the PEI.     

Synthesis and photovoltaic performance of new diketopyrrolopyrrole (DPP) dyes for dye-sensitized solar cells

Two new metal-free organic dyes (DPP-I and DPP-II) with diketopyrrolopyrrole (DPP) core were designed and synthesized, in which triphenylamine or N,N-bis(4-methoxyphenyl)benzenamine moieties was used as the electron donor, DPP units as the π-conjugated bridge, and carboxylic acid group as the electron acceptor. Photophysical and electrochemical properties of two dyes were investigated by UV–vis spectrometry and cyclic voltammetry. Electrochemical measurement data indicate that the tuning of the HOMO and LUMO energy levels can be conveniently accomplished by alternating the donor moiety. The DSSC based on dye DPP-I showed better photovoltaic performance: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 80.6% corresponding to an overall conversion efficiency of 2.68%. Although the power conversion efficiencies are not so high, this work explores new donor–π-accepter–π-donor models and the effects of molecular design on optical properties.     

Dye sensitized solar cells (DSSCs) based on modified iron phthalocyanine nanostructured TiO2 electrode and PEDOT:PSS counter electrode

An iron phthalocyanine with tetra-sulphonated substituents (FeTsPc) was used as photosentizer for the development of dye sensitized nanostructured TiO₂ solar cells. The influence of surface modification (TiO₂ film treated with HCl and HNO₃) and thermal annealing of TiO₂ photo-electrode on the performance of dye sensitized solar cell (DSSC) having structure FTO/TiO₂–FeTsPc/electrolyte/PEDOT:PSS (carbon added)/FTO was investigated through the analysis of current–voltage characteristics under illumination and electrochemical impedance spectra (EIS). The improvement in crystallinity of TiO₂, decrease in the internal surface area and adsorbed amount of dye and increase in the lifetime of injected electrons upon thermal annealing of TiO₂ photo-electrode affects the photovoltaic properties of DSSC. The increase in power conversion efficiency of DSSC based on nitric acid treatment for the photo-electrode is mainly attributed to the increase in photocurrent. A comparative photovoltaic investigation of DSSCs using HCl-treated TiO₂ photo-electrode, indicates that the HNO₃-treated photo-electrode retards back electron transfer at the interface with electrolyte and increases the amount of dye.     

Novel dye-sensitized solar cell architecture using TiO_2-coated Ag nanowires array as photoanode

With the aim of reducing series resistance and increasing dye loading, novel dye-sensitized solar cell architecture was designed with TiO_2 nanoparticle-coated Ag nanowires array as the photoanode. Ag nanowire array was prepared by anodic aluminum oxide(AAO) templateassisted electrochemical deposition route. Then, Ag nanowires were coated by TiO_2 nanoparticles in hydrothermal process. The structures of the photoanode were characterized by field emission scanning electron microscopy(FESEM). Ag nanowires are covered by a layer of very fine nanoparticles with a diameter of less than 5 nm. X-ray diffraction(XRD) and selected-area electron diffraction(SAED) show that Ag nanowires have a strong preferred orientation in(220) direction and the TiO_2 coating layer is a polycrystalline structure. With this photoanode, 3.2%conversion efficiency is achieved for the cell sensitized with N3 dye.     

Effect of H treatment on performance of HIT solar cells

Hydrogen is a ubiquitous element in semiconductor processing and particularly inamorphous and microcrystalline silicon where it plays a crucial role in the growth processes as well as in the material properties. Because of its low mass it can easily diffuse through the silicon network and leads to the passivation of dangling bonds but it may also play a role in the stabilization of metastable defects. Thus a lot of work has been devoted to the study of hydrogen diffusion, bonding and structure in disordered semiconductors. The sequence, deposition-exposure to H plasma-deposition was used to fabricate the microcrystalline emitter.A proper atomic H pretreatment of c-Si surface before depositions i layer was expected to clean the surface and passivatates the surface states, as a result improing the device parameters. In this study, H2 pretreatment of c-si surface was used at different time, power and temperature. It is found that a properH pretreatment improves passivation of c-si surface and improves the device parameters by AFM and testing I-V .     

Effects of surface-modified photoelectrode on the power conversion efficiency of dye-sensitized solar cells

The effects of Na₂SO₄ as a surface modification material on the performance of dye-sensitized solar cells (DSSCs) were studied. The surfaces of TiO₂ films were firstly modified with aqueous Na₂SO₄ solution by a dip coating process, and then the resulting electrode was applied to the photoelectrode of a DSSC. The DSSC with the Na₂SO₄-modified photoelectrode had a power conversion efficiency of 9.01% compared with that (7.97%) of the reference cell, which corresponds to an increase of about 13.0% in the efficiency due to an enhancement in short-circuit current (J _sc ) and open-circuit voltage (V _oc ). A series of measurements such as UV-visible absorption, electrochemical impedance, incident photon to current conversion (IPCE) efficiency and dark current revealed that incorporation of Na₂SO₄ onto the TiO₂ film led to an increase of dye adsorption and a longer lifetime of electrons injected from dyes to the TiO₂ electrodes, resulting in the improvement in both J _sc and V _oc , compared to those of a reference device without surface modification.     

Effects of annealing conditions on the properties of TiO2/ITO-based photoanode and the photovoltaic performance of dye-sensitized solar cells

Photovoltaic performance of dye-sensitized solar cell (DSSC) is enhanced by a two-step annealing process of the photoanode. The 1st-step of annealing is performed in oxygen at 450 °C for 30 min which effectively removes the residual organics originated from the TiO₂ precursor pastes. This enhances the dye adsorption on the TiO₂ nanoparticles and raises the short-circuit current density (J_SC). The 2nd-step of annealing is performed in nitrogen at 450 °C for 10 min which removes extra oxygen atoms resulted from the incorporation of oxygen atoms into the tin-doped indium oxide (ITO) film during the 1st-step of annealing. This reduces the sheet resistance of ITO and thereby enhances the fill factor (FF). With the enhanced J_SC of 15.9mAcm⁻² and FF of 0.65, the AM1.5 solar to electric conversion efficiency (η) of DSSC reaches 6.7% which is better than that based on the conventional one-step air annealing (η = 5.53%, J_SC = 14.08 mA cm⁻², FF = 0.6).     

Effect of surface free energy of acetylene black powder on air electrode performance

The effects of acetylene black powder surface free energy on air electrode electrochemical performance and lifetime were studied. The acetylene black was immersed in 30% H2O2 at room temperature and the changes of functional groups and surface free energy were investigated by X-ray Photoelectron Spectroscopy (XPS) and powder contact angle (CA). The air electrode performance was characterized by the potential polarization curves and the lifetime was measured by constant-current discharge. It shows that, its surface free energy is the lowest when the acetylene black is immersed in H2O2 for 240 h. The polarization potential of the air electrode prepared by the pretreated acetylene black is 0.25 V(vs. Hg/HgO), 0.21 V lower than the air electrode with untreated acetylene black when the working current density is 100 mA·cm-1 . And its lifetime is over 800 h at 80 mA·cm-1 . The pretreatment of acetylene black for proper time by H2O2 is favorable for the stability of the tri-phase reaction interface of air electrode and improvement of its performance.     

Ionic liquid doped poly(N-methyl 4-vinylpyridine iodide) solid polymer electrolyte for dye-sensitized solar cell

Ion conducting polymer electrolyte, poly(N-methyl 4-vinylpyridine iodide) (PVPI) is synthesized for dye-sensitized solar cell (DSSC) application. A new solid polymer electrolyte composite containing low viscosity ionic liquid (IL) 1-ethyl 3-methylimidazolium dicyanamide (EMImDCN) doped PVPI is developed and its structural, electrical and photoelectrochemical studies are presented in detail. Fourier transform infrared (FTIR) spectroscopy, proton NMR and atomic force microscopy (AFM) affirms the modified polymer and its composite nature with porous surface morphology. The developed solid polymer electrolyte shows enhancement in ionic conductivity (σ) due to IL doping. The maximum σ value of 9.12 × 10^?6 S cm^?1 was obtained at 40 wt% IL concentration. The redox behavior of the electrolyte has been verified by the cyclic voltammetry studies. For device application, we have fabricated a DSSC using this solid polymer–IL electrolyte system which shows energy conversion efficiency of the solid-state cell as 0.65% under irradiation of simulated sunlight (AM 1.5, 100 mW cm^?2).