染料敏化太阳能电池的非金属有机敏化剂

染料敏化太阳能电池(DSSC)是一种新型的太阳能电池,综述了DSSC的非金属有机染料敏化剂的研究现状,分析了各类敏化剂的结构与电池的能量转换效率的关系,并提出非金属有机染料结构的设计思路。     

Large efficiency improvement in nanoporous dye-sensitized solar cells via vacuum assistant dye adsorption

The positive effects of the vacuum assistant dye adsorption (VADA) process on the performances of the dye-sensitized solar cells (DSSCs) were investigated experimentally. Using commonly used materials and processes as a demonstration, nanoporous films and the resulted solar cells with different dye adsorption processes were fabricated and characterized for comparison. The amounts of dyes adsorbed by the TiO₂ nanoporous films were found to be enhanced greatly compared with dyes adsorbed in ambient condition. In accordance, a relative increase of about 29% for the short-circuit currents (I_sc) and 32% for the efficiencies (η) were observed for the resulted DSSCs. Photocurrent-voltage measurement indicated that the lifetime of the photogenerated charge carriers changed little. Hence, such improvements were originated from the application of VADA process, which realized full contact between the dye solution and TiO₂ nanoparticles by driving away the air bubbles concealed in the nanoporous film. The VADA process may be also applied in other kinds of solar cells, such as solid state DSSCs and organic or flexible solar cells to enhance the dye adsorption and further increase their efficiencies.     

Surface-oxidized tungsten for energy-storable dye-sensitized solar cells

Tungsten oxide electrodes were investigated as charge-storage materials for energy-storable dye-sensitized solar cells (ES-DSSCs). The electrochemical and structural properties of the surface-oxidized tungsten (so-WO_3 − x) and monoclinic nanocrystalline WO₃ (nc-WO₃) were studied on the difference of the charge-discharge properties. Although, the electromotive force (EMF) curve of the so-WO_3 − x was associated with structural change, the so-WO_3 − x did not show the significant structural change indicated by X-ray diffraction (XRD) patterns. On the other hand, the nc-WO₃ showed crystal transformation from monoclinic phase to tetragonal phase. The Li⁺ diffusion coefficients of the so-WO_3 − x with different Li⁺ content ratios obtained by the galvanostatic intermittent titration technique (GITT) did not fall down up to 0.3 of Li/W ratio, whereas the diffusion coefficients of nc-WO₃ decreased about two orders of magnitude in the vicinity of phase transitions. The different electrochemical properties could be explained by the less structural change of so-WO_3 − x compared with the nc-WO₃. The large-sized ES-DSSCs with the so-WO_3 − x were fabricated for the first time, and their photocharge-discharge performances were studied.     

Callindra haematocephata and Peltophorum pterocarpum flowers as natural sensitizers for TiO2 thin film based dye-sensitized solar cells

We have studied the performance of dye-sensitized solar cells employing natural dye extracted from the flowers Callindra haematocephata and Peltophorum pterocarpum as sensitizers for TiO₂ photoanode. The extracts have shown appreciable absorption in the visible region. FTIR studies indicated the presence of anthocyanins and β-carotene in the flowers of C. haematocephata and P. pterocarpum respectively. The extracts were anchored on TiO₂ film deposited on transparent conductive glass (FTO) which were used as photoanode. The dye coated TiO₂ film electrode, Pt counter electrode and electrolyte (I⁻₃) assembled into a cell module was illuminated by a light source with intensity 100 mW/cm² to measure the photoelectric conversion efficiency of the DSSCs. From the J-V characteristic curves of cells, the parameters related to the solar cell performance were determined. The conversion efficiency of the DSSC employing natural dye extract from the flower C. haematocephata and P. pterocarpumwere was found as 0.06% and 0.04%, with open-circuit voltage (V_OC) of 370 mV & 400 mV, short-circuit current density (J_SC) of 0.25 mA/cm² & 0.15 mA/cm², fill factor (FF) of 0.70 & 0.71 and P_max of 65 & 45 μW cm⁻² respectively. The extract of the flower C. haematocephata exhibited better photosensitization action compared to the flower of P. pterocarpum.     

New trends for solar cell development and recent progress of dye sensitized solar cells

This article reviews the new concepts and new trends of solar cell development. To increase the photoelectric conversion efficiency, reduce the cost, and for application in a much broader field, thin film solar cell, flexible solar cell, and tandem solar cell have become important subjects to be studied. As the representative of the solar cells of the third generation, the progress and challenges of dye sensitized solar cell was also reviewed.     

不同染料吸附状态下染料敏化太阳能电池电化学阻抗谱研究

研究了TiO2表面染料的吸附状态不同时,染料敏化太阳能电池(DSC)的光电转换性能,并采用电化学交流阻抗技术(EIS)考察了不同染料吸附状态下DSC中的电子界面复合效应。结果表明,在非饱和吸附染料状态下,通过调整TiO2薄膜表面染料分子吸附量,可以降低界面电荷复合效应,使电子在TiO2薄膜的传输过程中寿命增加,从而提高DSC的填充因子。     

Tunable synthesis of mesoporous titania with different morphologies for dye-sensitized solar cells

Different TiO₂ mesoporous structures, including core-shell spheres (CCSs) and micro-tubes (MTs), are synthesized through adjusting the pH of the solution using TiOSO₄ as titanium source in a hydrothermal route. TiO₂ CSSs with an average diameter of 1.3–3.5 μm exhibit excellent light scattering property and high specific surface area (177.63 m² g^?1). TiO₂ MTs show ultrahigh specific surface area of 276.03 m² g^?1. Dye-sensitized solar cell is fabricated using TiO₂ CSSs as the light scattering layer and TiO₂ nanoparticles (NPs) layer as the bottom layer. The efficiency of Cell-NPs + CSSs is up to 9.24% due to the good light scattering effect and excellent dye loading capacity. Furthermore, TiO₂ MTs are introduced to form the NPs/MTs bottom layer. The Cell-NPs/MTs + CSSs achieves an outstanding efficiency of 9.60% due to the further optimized electron transport path.     

Enhanced performances of dye-sensitized solar cells based on graphite-TiO2 composites

The graphite-incorporated TiO₂ composites for the photoanodes of the Dye-sensitized solar cells were prepared by ultrasound-assisted mixing method. The performances of these solar cells with different graphite additions were investigated by the photocurrent-voltage characteristics, open-circuit voltage decay measurement and electrochemical impedance spectroscopy. The results showed that the addition of graphite had a significant impact on the electron transport and recombination. The photocurrent-voltage results indicated that short-circuit current density (J_sc) and open-circuit voltage (V_oc) enhanced by 40% and 2%, respectively. A 30% improvement in conversion efficiency of dye-sensitized solar cell from 4.44% to 5.76% was achieved using 0.01 wt% graphite-TiO₂ composite electrodes compared to the pure TiO₂ electrode.     

Modification of ZnO nanorods through Au nanoparticles surface coating for dye-sensitized solar cells applications

Dye-sensitized solar cells (DSSC) based on ZnO nanorods were fabricated and modified through the addition of Au nanoparticles. The as-synthesized ZnO nanorods were well-dispersed and of high crystallinity quality leading to a high cell efficiency of 5.2%. On the other hand, thick layer of Au nanoparticles aggregation may have led to distortion of plasmonic effect. Also, the addition of Au nanoparticles have effectively decreased the surface area of ZnO nanorods with direct contact to the dye molecules, resulting in a lower amount of adhered dye molecules to convert sunlight. The electrons generated by the photo-absorption through thick aggregated Au nanoparticles layer may have a lower injection rate to ZnO nanorods as compared to those absorbed by the dye.     

Quasi-gel-state ionic liquid electrolyte with alkyl-pyrazolium iodide for dye-sensitized solar cells

A series of non-volatile viscous ionic liquid, 1-alkyl-2-methylpyrazolium iodides (RPyI: R = C₃-C₇), were synthesized for the electrolyte of dye-sensitized solar cells (DSSC). Most of RPyI revealed extremely viscous quasi-gel-state electrolytes potentially preventing leakage and evaporation of electrolytes of the solar cells. A DSSC using the electrolyte composed of 1-hexyl-2-methylpyrazolium iodide (C₆PyI) with iodine exhibiting higher conversion efficiency of 3.8% (under 1 Sun) for 10% larger short-circuit photocurrent, J_SC, than that with a conventional ionic liquid, 1-hexyl-3-methyllimidazolium iodide (C₆ImI) with iodine, in spite of less favorable viscosity (2013 mPa s (C₆PyI/I₂) vs. 1439 mPa s (C₆ImI/I₂)) for the physical diffusion of charge carriers in the electrolyte. Furthermore, the quasi-gel-state electrolytes composed of a series of RPyI ionic liquids surprisingly exhibiting comparable J_SC to that with much less viscous C₆ImI/I₂. We discuss the results of quasi-gel-state RPyI ionic liquid electrolyte for DSSC based on the Grotthus-like electron exchange mechanism of iodide redox species in the highly viscous RPyI ionic liquid evaluated qualitatively by Raman spectroscopic observation of poly-iodide species.     

用背反射提高染料敏化太阳能电池光电转换效率的研究

当光射入染料敏化太阳能电池(DSCs)时,有部分光不能被染料、电解液、导电玻璃等吸收,这部分光将透过电池而未被利用,本研究利用普通镀铝玻璃镜做为背底,将这部分透射光通过背反射重新射入电池来提高DSCs的光电转换效率.研究结果表明,背反射能大幅度提高DSCs的短路电流,短路电流的增加率随着测试遮光罩开孔尺寸的增加而增加,并且随纳米TiO2薄膜厚度的增加而降低.     

Non-aqueous preparation of anatase TiO2 hollow microspheres for efficient dye-sensitized solar cells

TiO₂ hollow spheres are fabricated by a facile and template-free approach, which is efficient, cost-saving and favorable for large scale production. The as-prepared TiO₂ hollow spheres with diameters ranging from 1 to 1.5 μm and a shell thickness of 150 nm are formed by the self-assembly of nanoparticles with a size of about 12 nm. The mesoporous TiO₂ hollow spheres possess a high specific surface area up to 166.2 m² g⁻¹. TiO₂ hollow spheres show superior light trapping characteristics and significantly improve the light scattering ability. The formation of hollow structure is interpreted by the Ostwald ripening mechanism. By employing a double-layered photoanode made of the as-prepared TiO₂ hollow spheres as the overlayer and P25 as the bottom layer, the dye-sensitized solar cell achieved a power conversion efficiency of 7.90%, which is ascribed to the enhanced dye loading and light scattering ability of TiO₂ hollow spheres.     

Ionic liquid-based electrolyte solidified with SiO2 nanoparticles for dye-sensitized solar cells

The performance of dye-sensitized solar cells (DSSC) based on the propyl-methyl-imidazolium iodide (PMII) ionic liquid (IL) with and without the addition of SiO₂ nanoparticles is studied. Results confirm that the presence of SiO₂ nanoparticles in PMII electrolyte improves the charge transport of iodide/tri-iodide redox couple in the electrolyte and consequently increases the efficiency of DSSC up to 20%, relatively. Short circuit current density (J_SC) of the DSSC under illumination may be limited by the charge transport of the redox couple in the IL-based electrolytes and a theoretical maximum of J_SC can be evaluated from the cyclic voltammetry measurements of simple symmetric cells (TCO-PtelectrolytePt-TCO). The results show a strong temperature dependence of the DSSC performance if the PMII/I₂-based electrolytes are used.     

Template- and surfactant-free synthesis of mesoporous TiO2 spheres with hollow core-shell structure for dye-sensitized solar cells

We have demonstrated a simple and effective hydrothermal route to synthesize titania mesoporous spheres with hollow core-shell structure. The synthesis is free of any surfactants or templates. The formation mechanism is investigated on the basis of the results of time-dependent experiments. The as-obtained mesoporous titania spheres with a specific surface area of 21.5?m²?g^?1 and diameters of 1.2–2.3?μm are composed of anatase titania nanocrystals. The excellent light scattering property of mesoporous titania spheres with hollow core-shell structure is proved. A higher cell efficiency of 8.27% is achieved with mesoporous titania spheres with hollow core-shell structure as a light scattering layer, compared with a cell efficiency of 6.63% for the P25 film electrode with the similar thickness. The higher cell efficiency is attributed to the hollow core-shell structure scattering layer, resulting in excellent pore fitting for electrolyte diffusion, enhanced light scattering ability, and reduced charge recombination.     

Optimization of titanium dioxide film prepared by electrophoretic deposition for dye-sensitized solar cell application

Nanocrystalline TiO₂ films were deposited on a conducting glass substrate by the electrophoretic deposition technique. It was found that the thickness of TiO₂ film increased proportionally with an increase in deposition time and deposition voltage. However, as the deposition duration or deposition voltage increased, the film surface was more discontinuous, and microcracks became more evident. The characteristic of the dye-sensitized solar cell using TiO₂ film as a working electrode was analyzed. The results of the energy conversion efficiency and the photocurrent density exhibited a relationship dependent on the TiO₂ thickness. Curve fitting of energy conversion efficiency vs. TiO₂ thickness revealed the optimum solar cell efficiency ~ 2.8% at the film thickness of ~ 14 μm.     

Probing mechanism of dye double layer formation from dye-cocktail solution for dye-sensitized solar cells

Absorption of photon in wide wavelength region is an important requirement for the enhancement of photoconversion efficiency of dye-sensitized solar cells (DSSC). Lack of photon absorption from visible to NIR wavelength region by a single dye requires the use of plural dyes for the panchromatic sensitization of nanoporous TiO₂. To our incredible surprise, when a dye cocktail of organic dye NK3705 and inorganic ruthenium based dye Z907 was implied for the dye adsorption, it led to the formation of dye double layer in spite of random arrangement of two dyes as evidenced from confocal laser microscopic investigations. Investigation pertaining to the evaluation of rate of dye adsorption and dye desorption for different organic and inorganic sensitizing dyes suggests that a combination of one dye with faster diffusion along with weak binding on TiO₂ surface and another dye with slow diffusion along with strong binding leads to the formation of dye double layer from a dye mixture by a simple dipping process.     

Novel tandem cell structure of dye-sensitized solar cell for improvement in photocurrent

A novel tandem cell structure is proposed to improve photocurrent of dye-sensitized solar cells (DSCs). Front and back parallel photoelectrodes are placed face-to-face; a common Pt-mesh counter electrode with transmittance is inserted between the electrodes. The short-circuit current density (J_sc) for the tandem cell is equivalent to the sum of the J_sc for the front and back photoelectrodes. A model using light energy absorbed by the photoelectrode is used to evaluate appropriate TiO₂ film thickness of the front photoelectrode. The J_sc for the tandem cell was improved to 13.3 mA/cm² for a cell with a 7.8-μm-thick front photoelectrode. The novel tandem cell has a great potential to improve DSC photocurrent and performance.     

All-solid,flexible solar textiles based on dye-sensitized solar cells with ZnO nanorod arrays on stainless steel wires

An all-solid, flexible solar textile fabricated with dye-sensitized solar cells (DSSCs) woven into a satin structure and transparent poly(ethylene terephthalate) (PET) film was demonstrated. A ZnO nanorod (NR) vertically grown from fiber-type conductive stainless steel (SS) wire was utilized as a photoelectrode, and a Pt-coated SS wire was used as a counter electrode. A graft copolymer, i.e. poly(vinyl chloride)-graft-poly(oxyethylene methacrylate) (PVC-g-POEM) was synthesized via atom transfer radical polymerization (ATRP) and used as a solid electrolyte. The conditions for the growth of ZnO NR and sufficient dye loading were investigated to improve cell performance. The adhesion of PET films to DSSCs resulted in physical stability improvements without cell performance loss. The solar textile with 10 × 10 wires exhibited an energy conversion efficiency of 2.57% with a short circuit current density of 20.2 mA/cm² at 100 mW/cm² illumination, which is the greatest account of an all-solid, ZnO-based flexible solar textile. DSSC textiles with woven structures are applicable to large-area, roll-to-roll processes.     

Performance improvement of dye-sensitized solar cells by surface patterning of fluorine-doped tin oxide transparent electrodes

The surface modification of fluorine-doped tin oxide (FTO) transparent electrodes was carried out by lithography and inductively coupled plasma etching to improve the conversion efficiency of dye-sensitized solar cells (DSSCs). The concentration of Cl₂ gas and dc-bias voltage to the substrate were varied as the main etch parameters. The transmittance and sheet resistance of the FTO electrodes were compared before and after etching. The DSSCs fabricated on the patterned FTO electrodes showed higher conversion efficiency than those fabricated on the ordinary FTO electrodes without patterns. Scanning electron microscopy showed that more TiO₂ particles could be involved in the DSSCs with patterned FTO electrodes, and that the contact between the TiO₂ layer and electrode were improved by patterning the FTO electrode. The current-voltage curves and incident photon to current efficiency spectra showed that a significantly higher photocurrent was produced in the DSSCs fabricated on the patterned FTO.     

Self-templated synthesis of large-scale hierarchical anatase titania nanotube arrays on transparent conductive substrate for dye-sensitized solar cells

The large-scale hierarchical anatase titania nanotube arrays on transparent conductive substrate are fabricated via in situ conversion from anatase titania nanowire arrays. The first-step hydrothermal reaction is the growth of ultra-long anatase titania nanowire arrays, and the second-step hydrothermal reaction is the conversion of titania nanowire arrays to titania nanotube arrays modified with a large number of nanosheets. The resultant hierarchical titania nanotube array film provides a large surface area and superior light scattering ability. Dye-sensitized solar cell based on the hierarchical titania nanotube array photoanode obtains a power conversion efficiency as high as 5.96% and shows a prominent increase compared to the pristine titania nanowire array photoanode (2.12%). In addition, the most interesting result is that an optimized efficiency of 7.54% is achieved for the cell based on the hierarchical titania nanotube array photoanode with titania sol modification.