Band gap engineering and modifying surface of TiO2 nanostructures by Fe2O3 for enhanced-performance of dye sensitized solar cell

Well-crystallized Fe₂O₃-modified TiO₂ nanoparticles are prepared by a hydrothermal method and were successfully used as the photoanode of dye-sensitized solar cell (DSSC). Structural, optical and thermal characterizations were carried out by SEM, XRD, AFM, EDAX, DTG, TG and UV–vis spectroscopy. We show that the solar conversion efficiency, incident photocurrent efficiency (IPCE) and fill factor (FF) of Fe₂O₃-modified TiO₂ are significantly increased, about 40%, compared those of to bare TiO₂. DSSC shows power conversion efficiency of 7.27% based on Fe₂O₃-modified TiO₂ while TiO₂ anatase shows 5.10% solar conversion efficiency. The high improvement in cell performance is attributed to the enhanced light harvesting and high specific surface area for adsorbing more dye molecules in Fe₂O₃-modified TiO₂ nanostructures.     

Synthesis of novel ruthenium II phenanthroline complex and its application to TiO2 and ZnO nanoparticles on the electrode of dye sensitized solar cells

Novel ruthenium (II) phenanthroline complex, Ru^II(4,4′,4″-tri-tert-butyl-2,2′:6′,2″-terpyridine)-(4,7-diphenyl-1,10-phenanthroline-disulfonic acid disodium salt)(thiocyanate), [Ru(L1)(L2)(NCS)], [K328] was designed and synthesized as a photosensitizer for the dye sensitized solar cells (DSSCs) using TiO₂ and ZnO electrodes. The density functional theory (DFT) calculation was used to estimate the photovoltaic properties of the complex in the design stage. In this paper, our aim was to investigate the interaction between semiconductor and anchoring groups like sulfonate group that binds onto TiO₂ and ZnO surface. The influence of the semiconductor type on the performance of TiO₂ and ZnO based photovoltaics has been tested. The solar cell performance of TiO₂ based solar cell shows better efficiencies compared to ZnO based solar cell. Although sulfonate group did offer stronger binding onto the semiconductor surface, this does not help to improve cell performance for ZnO based solar cells.     

Binder-free MWCNT/TiO2 multilayer nanocomposite as an efficient thin interfacial layer for photoanode of dye sensitized solar cell

Multiwalled carbon nanotube/TiO₂ multilayer nanocomposite was successfully deposited on the fluorine-doped tin oxide (FTO) glass via layer-by-layer assembly technique to modify interfacial contact between the FTO surface and nanocrystalline TiO₂ layer as well as carbon nanotube/TiO₂ contacts in photoanode of dye sensitized solar cell. Using this approach, binder-free interfacial thin film was developed with nonagglomerated, well-dispersed MWCNTs on FTO and into TiO₂ matrix and with maximum covering of TiO₂ nanoparticles on MWCNTs. Introduction of MWCNTs/TiO₂ interfacial layer into the TiO₂ photoanode increased short circuit current density (J_sc) from 11.90 to 17.25 mA/cm² and open circuit voltage (V_oc) from 730 mV to 755 mV, whereas there was no notable change in the fill factor (FF). Consequently, power conversion efficiency (η) was enhanced from 5.32% to 7.53%, yielding a 41.5% enhancement. The results suggest that our simple strategy can integrate reduction of back electron reaction at FTO/TiO₂ interface with the effective charge transport ability of carbon nanotubes and possessing high surface area for efficient dye loading.     

Coumarin based sensitizers with ortho-halides substituted phenylene spacer for dye sensitized solar cells

The performance of DSSCs (dye sensitized solar cells) with a new series of dyes having different halide groups (i.e. F, Cl and Br) on o-position substituted phenyl spacers with same coumarin donor moieties have been reported. Optical, electrochemical, molecular orbital and photovoltaic properties were studied by varying the halide groups using these dyes. The replacement of halide atoms in same coumarin based dye had a significant effect on the short circuit current density (J_sc), open circuit voltage (V_oc), and photo conversion efficiency (PCE). The J_sc and PCE of dye CD-1 (fluorine substituted) are 10.3 mA/cm² and 5.2% respectively, which is higher than CD-2 (chlorine substituted) and CD-3 (bromine substituted) dyes (having PCE 4.1% and 3.5% respectively) devices. The optimized geometry calculation of o-halide phenyl π-spacer dyes were ascertained by density functional theory (DFT) using the B3LYP/6-31G(d,p) basis set. Moreover, we have checked the effect of various substituents in the same dye structure by DFT analysis.     

Effects of carboxylic acid and phosphonic acid anchoring groups on the efficiency of dye sensitized solar cells: A computational study

In axially coordinated DSSCs the dye is attached to the surface via linker and the linker play a role of a conductor of electron and a bridge to the surface which has a very important effect on the efficiency of the cell. It has been shown that using one particular dye with different linkers could result in different efficiencies. In this paper, using density functional theory, different carboxylic acid (CA) linkers, and different phosphonic acid (PA) linkers are studied and their effects on the electronic structure of the surface and changes in the HOMO and LUMO of the linkers due to adsorption on the surface are investigated. For each family of linkers, based on calculations, the best one to be used in axially coordinated DSSCs is suggested. Comparing these two families, carboxylic acid linkers show superior properties in terms of cell efficiencies. phosphonic acid linkers, however, are shown to strongly bond to surface while resulting in lower conversion efficiencies compared to the carboxylic acid linkers the reason of which is still a question. Based on calculation of the changes in properties of the surface and properties of phosphonic acid linkers some reasons behind their low performances are suggested.     

Influence of Ti dopant on the properties and dye sensitized solar cell performance of ZnO chunk-shaped nanostructures

This paper presents the results of photoanode constructed with undoped and Ti-doped ZnO chunk shaped nanostructures for dye sensitized solar cells (DSSC). Nanostructures are prepared by simple chemical method and moreover the structural, morphological, optical and photovoltaic performances are investigated by XRD, SEM, UV–Vis, PL, and I–V measurements, respectively. The experimental observations demonstrate that the Ti is effectively doped into Zn site, which increases free electron concentration, hereby expected an enhancement in the DSSC performance. Fabricated DSSCs are tested and the results reveal that undoped ZnO shows conversion efficiency of 0.42% with better photocurrent density and photovoltage but the fill factor gets enhance up to 0.447 with 3 mole% (dilute) of Ti doping. Comparably, PEO/KI/LiI/I₂ electrolyte matches well for Ti doped ZnO DSSC due to the easier diffusion path offered by KI salt rather than TiO₂ and PEG additives.     

A new type of counter electrode for dye sensitized solar cells based on solution processed SnO2 and activated carbon

A new type of nano-composite material is investigated for use as the counter electrode of a dye sensitized solar cell. The proposed material consists of SnO₂ and activated carbon, which can be deposited using a cost-effective sol–gel technique. The effects of the activated carbon concentration on the structural and optoelectronic properties were investigated using scanning electron microscopy, X-ray diffraction, UV–vis spectroscopy and four probe measurements. It was found that the addition of activated carbon reduces resistivity and optical transmittance, and suppresses fluorine doped tin oxide (FTO) growth. The nanocomposite material was integrated into a dye sensitized solar cell and evaluated using cyclic voltammetry and J–V characteristics under solar light illumination, and demonstrated power conversion efficiency ~2.35%.     

A polyfluoroalkyl imidazolium ionic liquid as iodide ion source in dye sensitized solar cells

We report on the use of a fluorinated imidazolium ionic liquid as a source of iodide ions in solvent-based electrolytes for DSSCs. Efficient dye regeneration and fast charge transport in the fluorinated electrolyte result in an overall improvement of the device performances compared to conventional hydrogenated ionic liquids.     

Enhancement of dye sensitized solar cell efficiency via incorporation of upconverting phosphor nanoparticles as spectral converters

Upconverting NaYF₄:Yb³⁺,Er³⁺/NaYF₄ core‐shell (CS) nanoparticles (NPs) were synthesized by thermal decomposition of lanthanide trifluoroacetate precursors and mixed with TiO₂ NPs to fabricate dye‐sensitized solar cells (DSSCs). The CS geometry effectively prevents the capture of electrons because of the surface states and improves photo‐emission. The as‐synthesized CS NPs show upconversion (UC) luminescence, converting near infrared (NIR) light into visible light (450–700 nm), making the photon absorption by the ruthenium‐based dyes (which have little or no absorption in the NIR region) possible. The champion DSSCs fabricated using CS UC NPs (average size = 25 nm) show enhancements of ~12.5% (sensitized with black/N749 dye) and of ~5.5% (sensitized with N719 dye) in overall power conversion efficiency under AM 1.5G illumination. This variation in the enhancement of the DSSC efficiencies for black and N719 dyes is attributed to the difference in the extinction coefficient and the absorption wavelength range of dyes. Incident photon‐to‐current conversion efficiency measurements also evidently showed the photocurrent enhancement in the NIR region of the spectrum because of the UC effect. The results prove that the augmentation in efficiency is primarily due to NIR to visible spectrum modification by the fluorescent UC NPs. Copyright © 2015 John Wiley & Sons, Ltd.     

Performance analysis of dye solar cell with additional TiO2 layer under different light Intensities

Deployment of dye solar cells (DSCs) for building integration application would require a highly efficient solar cell that work well in diffused light. In order to improve the efficiency of dye solar cell, an additional layer of ultrathin anatase titanium dioxide (TiO₂) has been deposited for strengthening the adhesion of the porous TiO₂-based photo electrode to the conductive transparent substrate, which can lead to an enhancement in electron transportation. Fabricated cells of 1 cm² area were tested under different light intensities (100, 33 and 10 mW cm⁻²) and characterized by scanning electron microscopy (SEM), Raman spectroscopy and electrochemical impedance spectroscopy (EIS). Analysis showed an increment in overall quantum conversion efficiency (η), as high as 35% compared to the standard cell without the additional layer of TiO₂. EIS analysis has proven that the additional ultrathin anatase layer has improved the collection efficiency (Φ_COLL) as the result of the enhancement in both electron transport and lifetime within the porous TiO₂ film which translated into better conversion efficiency of DSCs.     

Enhanced photovoltaic performance of cross‐linked ruthenium dye with functional cross‐linkers for dye‐sensitized solar cell

Photovoltaic performance of cross‐linkable Ru(2,2′‐bipyridine‐4,4′‐bicarboxylic acid)(4,4′‐bis((4‐vinyl benzyloxy)methyl)‐2,2′‐bipyridine)(NCS)₂ (denoted as RuS dye) adsorbing on TiO₂ mesoporous film was enhanced by polymerizing with either ionic liquid monomer, 1‐(2‐acryloyloxy‐ethyl)‐3‐methyl‐imidazol‐1‐ium iodide (AMImI), to form RuS‐cross‐AMImI or di‐functional acrylic monomer with ether linkage, triethyleneglycodimethacrylate (TGDMA), to form RuS‐cross‐TGDMA. Their cross‐linking properties were investigated by UV–vis spectroscopy by rinsing with 0.1 N NaOH aqueous solution. The power conversion efficiencies (PCEs) of dye‐sensitized solar cells (DSSCs) with RuS‐cross‐AMImI and RuS‐cross‐TGDMA both reached over 8% under standard global air mass 1.5 full sunlight. The increased PCE for DSSCs with RuS‐cross‐AMImI comparing with cross‐linked RuS was attributed to the I⁻ counterion of AMImI increasing the charge regeneration rate of RuS dye, whereas that with RuS‐cross‐TGDMA was attributed to the Li⁺ coordination property of TGDMA. The photovoltaic performance of RuS‐cross‐TGDMA was also slightly better than that of RuS‐cross‐AMImI because of higher open‐circuit photovoltage (V_oc) and short‐circuit photocurrent (J_sc). Its higher V_oc was supported by the Bode plot of impedance under illumination and Nyquist plots at dark, whereas higher J_sc was supported by the incident monochromatic photon‐to‐current conversion efficiency spectra and charge extraction experiments. Copyright © 2013 John Wiley & Sons, Ltd.     

Zirconium oxide post treated tin doped TiO2 for dye sensitized solar cells

Sn doped TiO₂ nanorods with 0.1, 0.25%, 0.5% and 1% dopant compositions were grown by sol-gel and hydrothermal method. Synthesized Sn doped TiO₂ nanorods were post treated with Zr and HNO₃ and used as photo anode in DSSC with Ru dye and dye extracted from leaves of Camellia sinensis. The PCE of 1% Sn doped TiO₂ photo anode sensitized with Ru dye comparatively showed a better conversion efficiency of 4.96%. 1% Sn doped TiO₂ nanorods post treated and acid treated with Zr and HNO₃ sensitized with leaves of Camellia sinensis showed better PCE than untreated Sn doped TiO₂ photo anode. Increasing the oxygen vacancy by raising the dopant composition with low difference between successive levels improves the photocatalytic performance of the cell. The post treatment of zirconia and HNO₃ treatment enhances the photovoltaic parameters toward better performance of the cell. The synergistic effect of introduction of surface defects due to doping, surface modification by post treatment, retarding electron–hole recombination and protonation of the surface with acid treatment enhanced the efficiency of 1% Sn doped TiO₂ nanorods and it can be considered as a potential photo anode for DSSC.     

29种天然染料敏化的太阳电池的性能研究

采用超声波萃取法从29种天然植物中提取染料, 测试天然染料的紫外-可见光(UV-vis)吸收光谱,探讨天然染料所 含的色素种类。采用水热法制备了TiO₂薄膜电极,用所提取的29种天然染料敏化TiO₂光 电极并将其组装成染料敏化太阳电池(DSSCs)。测试天然染料敏化的DSSCs 的光电性能结果显示,天然染料敏化的DSSCs的开路 电压Voc为0.46~0.64 V,短路电流I_sc为0.07~3.61mA· cm－2,其中山竹皮敏 化的DSSCs光电性能最佳,对应的I_sc和光电转换 效率η分 别为3.61mA·cm－2和2.13%。从天然 染料中挑选出7种不同吸收波段色素的染料进行协同敏化,UV-vis吸收光谱测试结 果显示混合染料的吸收峰一般有微小偏移。光电性能测试结果表明,协同敏化后的DSSCs的 性能一般都介于天然染料单独敏 化的两个DSSCs的性能之间,其中山竹皮和芥蓝协同敏化的DSSCs的η最高,为1.70%。对实验结果进行深入分析,探讨提高天然染料 敏化的DSSCs光电性能的途径。     

An efficient titanium‐based photoanode for dye‐sensitized solar cell under back‐side illumination

Pretreatment of H₂O₂ is performed on titanium (Ti) foil as an efficient photoanode substrate for dye‐sensitized solar cell (DSSC). The H₂O₂‐treated Ti shows high surface area because of the formation of networked TiO₂ nanosheets, which enhances electrical contact between screen‐printed TiO₂ nanoparticles and Ti foil. Electron transfer on the photoanode is improved, as identified by reduced charge transfer resistance and improved electron transport properties. Compared with DSSC based on non‐treated Ti photoanode, DSSC with this H₂O₂‐treated Ti photoanode exhibits remarkable increases in short‐circuit current density (from 8.55 to 14.38 mA/cm²) and energy conversion efficiency (from 4.68 to 7.10%) under AM1.5 back‐side illumination. Copyright © 2011 John Wiley & Sons, Ltd.     

Enhanced photovoltaic performance of dye sensitized solar cell using TiO2 and ZnO nanoparticles on top of free standing TiO2 nanotube arrays

Photovoltaic performance of dye sensitized solar cell (DSSC) with absorber layer of TiO₂ nanotube (NT)/TiO₂ nanoparticles (NPs)/ZnO NPs was investigated. Fabricated DSSC exhibits enhanced open circuit voltage, current density and power conversion efficiency compared with DSSC having absorber layer of TiO₂ NT/ TiO₂ NPs and TiO₂ NT/ZnO NPs. To further explore the dynamics of charge transport and recombination processes, electrochemical impedance analysis, intensity modulated photovoltage spectroscopy and photocurrent spectroscopy were carried out on the fabricated DSSCs. It was found that an optimal combination of TiO₂/ZnO NPs on top of TiO₂ NTs reduces the electron recombination and improves transport pathways, resulting in an efficient charge collection of 99%.     

Stepwise co-sensitization as a useful tool for enhancement of power conversion efficiency of dye-sensitized solar cells: The case of an unsymmetrical porphyrin dyad and a metal-free organic dye

A tertiary arylamine compound (DC), which contains a terminal cyano-acetic group in one of its aryl groups, and an unsymmetrical porphyrin dyad of the type Zn[Porph]-L-H₂[Porph] (ZnP-H₂P), where Zn[Porph] and H₂[Porph] are metallated and free-base porphyrin units, respectively, and L is a bridging triazine group functionalized with a glycine moiety, and were synthesized and used for the fabrication of co-sensitized dye-sensitized solar cells (DSSCs). The photophysical and electronic properties of the two compounds revealed spectral absorption features and frontier orbital energy levels that are appropriate for use in DSSCs. Following a stepwise co-sensitization procedure, by immersing the TiO₂ electrode in separate solutions of the dyes in different sequence, two co-sensitized solar cells were obtained: devices C (ZnP-H₂P/DC) and D (DC/ZnP-H₂P).The two solar cells were found to exhibit power conversion efficiencies (PCEs) of 6.16% and 4.80%, respectively. The higher PCE value of device C, which is also higher than that of the individually sensitized devices based on the ZnP-H₂P and DC dyes, is attributed to enhanced photovoltaic parameters, i.e. short circuit current (J_sc = 11.72 mA/cm²), open circuit voltage (V_oc = 0.72 V), fill factor (FF = 0.73), as it is revealed by photovoltaic measurements (J–V curves) and by incident photon to current conversion efficiency (IPCE) spectra of the devices, and to a higher total dye loading. The overall performance of device C was further improved up to 7.68% (with J_sc = 13.45 mA/cm², V_oc = 0.76 V, and FF = 0.75), when a formic acid treated TiO₂ ZnP-H₂P co-sensitized photoanode was employed (device E). The increased PCE value of device E has been attributed to an enhanced J_sc value (=13.45 mA/cm²), which resulted from an increased dye loading, and an enhanced V_oc value (=0.76 V), attributed to an upward shift and increased of electron density in the TiO₂ CB. Furthermore, dark current and electrochemical impedance spectra (EIS) of device E revealed an enhanced electron transport rate in the formic acid treated TiO₂ photoanode, suppressed electron recombination at the photoanode/dye/electrolyte interface, as well as shorter electron transport time (τ_d), and longer electron lifetime (τ_e).     

SILAR次数对In掺杂CdS量子点敏化太阳电池的影响

以In掺杂CdS量子点太阳能电池为例,讨论了SILAR次数对In掺杂CdS量子点敏化太阳能电池性能的影响。通过SEM、EDS、IPCE、紫外吸收光谱、J-V曲线、EIS等实验测试结果表明,当In掺杂CdS的摩尔比固定在1:5时,随着SILAR次数的增加,电池的短路电流密度、开路电压和光电转换效率都随着增加,当SILAR次数为6次时,In掺杂CdS的QDSCs光电转化效率达到了最大值(η=0.76%)。随着SILAR次数的继续增加,其光电转换效率将会下降。     

Estimating the Maximum Attainable Efficiency in Dye‐Sensitized Solar Cells

For an ideal solar cell, a maximum solar‐to‐electrical power conversion efficiency of just over 30% is achievable by harvesting UV to near IR photons up to 1.1 eV. Dye‐sensitized solar cells (DSCs) are, however, not ideal. Here, the electrical and optical losses in the dye‐sensitized system are reviewed, and the main losses in potential from the conversion of an absorbed photon at the optical bandgap of the sensitizer to the open‐circuit voltage generated by the solar cell are specifically highlighted. In the first instance, the maximum power conversion efficiency attainable as a function of optical bandgap of the sensitizer and the “loss‐in‐potential” from the optical bandgap to the open‐circuit voltage is estimated. For the best performing DSCs with current technology, the loss‐in‐potential is ～0.75 eV, which leads to a maximum power‐conversion efficiency of 13.4% with an optical bandgap of 1.48 eV (840 nm absorption onset). Means by which the loss‐in‐potential could be reduced to 0.4 eV are discussed; a maximum efficiency of 20.25% with an optical bandgap of 1.31 eV (940 nm) is possible if this is achieved.     

Silicon coating of ceramic substrates for low cost solar cell applications

Mullite ceramic substrates were coated with silicon using a unique method of growth designed to produce low-cost material suitable for terrestial based solar cell applications. Pieces of mullite were carbon coated on one side and then dipped into molten silicon. The silicon wet the mullite only where the carbon was applied. Directional solidification occurs upon withdrawal. The film thicknesses were reasonably uniform over the area and could be controlled by varying the melt temperature and withdrawal rate, with higher temperatures and faster pull rates giving thinner films. Typical thicknesses of dip coated layers ranged between 20 and 150ym. The layers consist of large elongated grains aligned in the direction of withdrawal. The mullite substrates are slowly dissolved by the molten silicon resulting in some contamination of the silicon layers upon solidification. Glassy carboncoatings were found to be essentially impervious to the molten silicon and prevented dissolution of the substrate even after one hour of immersion. Cells of 1 cm² active area having J_SC This paper presents results of research performed for the Low-Cost Solar Array Project, Jet Propulsion Laboratory, California Institute of Technology, sponsored by the Department of Energy through an interagency agreement with the National Aeronautics and Space Administration. as high as 26.8 mA/cm² at 100 mW/cm² illumination with efficiencies of 9.6% were made from these layers. Solar cell properties have shown steady improvement as growth conditions and cell fabrication procedures have improved, so that siliconon-ceramic appears quite promising as a cost-effective solar cell material.