Efficient co-sensitization of dye-sensitized solar cells by novel porphyrin/triazine dye and tertiary aryl-amine organic dye

A novel porphyrin dye ZnP-triazine-(gly)₂, consisting of a zinc-metallated porphyrin unit covalently linked through its peripheral aryl-amino group with a 1,3,5-triazine group which is functionalized by two carboxylic acid groups of glycine moieties, has been synthesized. Photophysical and electrochemical measurements, as well as theoretical DFT calculations, suggest that the compound exhibits appropriate light absorption characteristics and frontier molecular orbital levels for use as sensitizer in dye-sensitized solar cells (DSSCs). The ZnP-triazine-(gly)₂ based solar cell was found to exhibit a power conversion efficiency (PCE) value of 4.72%. A significant improvement of the overall photovoltaic efficiency of the solar cell was achieved up to 7.34% upon co-sensitization with a tertiary aryl-amine D with two ethynyl-pyridine substituents and cyano-acetic acid anchoring group, which exhibits complementary light absorption characteristics with the porphyrin dye. The higher PCE value of the co-sensitized solar cell is attributed to its enhanced short circuit current (J_sc), which is due to improved light harvesting efficiency, reduced porphyrin aggregation, and faster electron injection and charge collection, as well as its enhanced open circuit voltage (V_oc), which is due to increased electron density in the TiO₂ conduction band of the photoanode. These results are in accordance with electrochemical impedance spectra (EIS) of the solar cells, which revealed higher charge recombination resistance (R_rec), longer electron lifetime (τ_e), and shorter electron transport time (τ_d) for the co-sensitized solar cell.     

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.     

Efficient dye regeneration in solid-state dye-sensitized solar cells fabricated with melt processed hole conductors

A new method for melting hole transporting materials (HTM) into mesoporous TiO₂ electrodes to obtain solid-state dye-sensitized solar cells (DSSC) is reported. Internal coverage is determined from the efficiency of hole conductor oxidation by photo-oxidized dyes (dye regeneration), measured using transient absorption spectroscopy. High efficiency regeneration indicates complete coverage of the electrode internal surface. A high work function hole conductor (>5.2 eV) was found to give shorter regeneration lifetimes (<1 μs) and better regeneration efficiencies (>90%) than expected. Cell photocurrents were low, but improved after iodine vapor doping of the hole conductor. Counter intuitively, doping also reduced the recombination rate constant 7-fold. A solid state solar cell with power conversion efficiency of 0.075% at 1 sun is reported.     

Preparation of dye sensitized titanium oxide nanoparticles for solar cell applications

A new method for synthesis of titanium dioxide (TiO₂)-dye nanoparticles is reported. TiO₂ nanocrystals were obtained at 150 and 200 °C by using chemically bonded TiO₂-sensitizer dye as a precursor. Titanium tetraisopropoxide was first modified with a dye molecule and then precipitated by dropping into acidic water. A strongly colored precipitate was obtained. Hydrothermal growth of a colloidal solution was carried out in a Teflon-lined stainless steel autoclave. Dye sensitized solar cell efficiencies obtained were comparable and fill factor values were close to the analogous cells prepared by the use of conventional TiO₂ paste techniques. This method allows the use of different substrates together with nanocrystalline TiO₂ for many technological applications.     

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.     

Enhanced electron injection/transportation by surface states increment in mesoporous TiO2 dye-sensitized solar cells

A strategy of surface modification to the mesoporous TiO2 photoanode with hydrochloric acid treatment was used in this study, and it was found that short circuit current and photovoltaic efficiency of dyesensitized solar cells (DSSCs) were increased by 5.5% and 8.9% respectively. The improvement was attributed to the reduced impedances in the TiO2 film and at the TiO2/dye/electrolyte interface. It was showed that the increased surface electronic states could remarkably prolong electron lifetime, which was responsible for the reduction of impedances. Under these quasi-continuous states in mesoporous structure, the electron injection/transportation can be notably facilitated, which will be beneficial for the DSSC performance.     

An oligothiophene dye with triphenylamine as side chains for efficient dye-sensitized solar cells

A novel oligothiophene-cyanoacrylic acid photosensitizer with two triphenylamine side chains (7T-2TPA) is designed and synthesized for dye-sensitized solar cells. 7T-2TPA exhibits broad (250-600 nm) and strong absorption (ε = 5.0 × 10⁴ L mol⁻¹ cm⁻¹ at 496 nm). The optical band gap (E_g) is estimated from the onset absorption edge to be 2.07 eV. The oxidation potential E_ox and reduction potential E_red vs NHE of the dye is 0.93 and −1.14 V, respectively. Dye-sensitized solar cell (DSSC) based on 7T-2TPA exhibits an open-circuit voltage (V_oc) of 724 mV, a short-circuit current density (J_sc) of 16.28 mA cm⁻², a fill factor (FF) of 0.684 and a power conversion efficiency of 8.06%. The efficiency of 8.06% is similar to that for widely used N719-based cell fabricated and measured under the same conditions.     

Novel organic dye employing dithiafulvenyl-substituted arylamine hybrid donor unit for dye-sensitized solar cells

In order to increase electron-donating ability of the donor part of the organic dye, two dithiafulvenyl (DTF) units were introduced into a triphenylamine unit to form dithiafulvenyl-substituted triphenylamine hybrid donor for dye-sensitized solar cells (DSSCs) for the first time. Novel donor–acceptor organic dye WD-10 containing this hybrid donor and 2-cyanoacetic acid acceptor has been designed, synthesized and applied in DSSCs. The influence of the substituent unit DTF in the dye on the device performance has been investigated. It was found that the dye with dithiafulvenyl-substituted triphenylamine hybrid donor gave higher photocurrent, open-circuit voltage, and efficiency value. The DSSC based on organic dye WD-10 displayed a short-circuit current (J_sc) of 9.58 mA cm^?2, an open-circuit voltage (V_oc) of 648 mV, and a fill factor (ff) of 0.71, corresponding to an overall conversion efficiency of 4.41%. An increase in η of about 79% was obtained from simple triphenylamine dye L0 to WD-10. The different photovoltaic behaviors of the solar cells based on the organic dyes were further elucidated by the electrochemical impedance spectroscopy. This work identifies that the introduction of DTF unit into the simple triphenylamine dye could significant improve the photovoltaic performance.     

Controllable synthesis of quasi-spherelike ZnO hierarchical nanostructures and performance of their dye-sensitized solar cells

Hierarchical zinc oxide (ZnO) quasi-spheres consisting of nanoparticles with diameter of about 20 nm were synthesized via a one-pot reaction. The size of ZnO quasi-spheres is easily tunable from 80 nm to 3 μm by varying the type of zinc source and its concentration. The three samples 1-3 with the diameter of 80-180 nm, 300-600 nm and 1.2-2.9 μm were selected for fabricating dyesensitized solar cells (DSSCs) and their photovoltaic properties were measured. The results demonstrate that DSSCs fabricated by sample 2 with the diameter within the wavelength of visible light obtain the highest short-circuit current density and over light conversion efficiency, due to resonant scattering increasing the photon absorption.     

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.     

Efficient dye-sensitized solar cells based on CNTs and Zr-doped TiO2 nanoparticles

The light scattering, harvesting and adsorption effects in dye-sensitized solar cells (DSSCs) are studied by preparation of coated carbon nanotubes (CNTs) with TiO₂ and Zr-doped TiO₂ nanoparticles in the forms of mono- and double-layer cells. X-ray diffraction (XRD) analysis reveals that the phase composition of Zr-doped TiO₂ electrode is a mixture of anatase and rutile phases with major rutile content, whereas it is the same mixture with major anatase content for coated CNTs with TiO₂. Furthermore, the average crystallite size of Zr-doped TiO₂ electrode is slightly decreased with Zr introduction. Field emission scanning electron microscope (FE-SEM) images show that the porosity of Zr-doped TiO₂ electrodes is higher than that of undoped electrode, enhancing dye adsorption. UV–visible spectroscopy analysis reveals that the absorption onset of Zr-doped TiO₂ electrodes is slightly shifted to longer wavelength (the red-shift) in comparison with that of undoped TiO₂ electrode. Moreover, the band gap energy of TiO₂ nanoparticles is decreased by Zr introduction, enhancing light absorption. It is found that electron injection of monolayer TiO₂ electrode is improved by introduction of 0.025 mol% Zr, resulted in enhancement of its power conversion efficiency (PCE) up to 6.81% compared with 6.17% for pure TiO₂ electrode. Moreover, electron transport and light scattering are enhanced by incorporation of 0.025 wt% coated CNTs with TiO₂ in the over-layer of double layer electrode. Therefore, double layer solar cell composed of 0.025 mol% Zr-doped TiO₂ nanoparticles as the under-layer and mixtures of these nanoparticles and 0.025 wt% coated CNTs with TiO₂ as the over-layer shows the highest PCE of 8.19%.     

Efficient flexible dye-sensitized solar cells from rear illumination based on different morphologies of titanium dioxide photoanode

The TiO₂ with nanoparticles(NPs),nanowires(NWs),nanorods(NRs) and nanotubes(NTs) structures were prepared by using a in-situ hydrothermal technique,and then proposed as a photoanode for flexible dye-sensitized solar cell(FDSSC).The influences of the morphology of TiO₂ on the photovoltaic performances of FDSSCs were investigated.Under rear illumination of 100 mW·cm^-2,the power conversion efficiencies of FDSSCs achieved 6.96%,7.36%,7.65%,and 7.83% with the TiO_...     

Investigations on the influence of surfactant in morphology and optical properties of zinc oxide nanopowders for dye-sensitized solar cells applications

We studied the influence of the synthesis route on the morphology and optical properties of zinc oxide (ZnO), with applications in dye-sensitized solar cells (DSSCs). For this purpose, we obtained surfactant capped ZnO nanopowders, in the presence of non-ionic surfactants with different structures, and demonstrated their behavior as semiconductors in DSSCs. The ZnO nanopowders and films (obtained from nanopowders using the doctor blading method) were analyzed by transmission electron microscopy (TEM), high resolution TEM (HRTEM), and selected area electron diffraction (SAED). The optical properties were examined by UV, visible spectroscopy, and the band gap energies were calculated using the Tauc equation. The values obtained for DSSCs efficiencies were in good agreement with the characteristics of ZnO, both powders and films, and can be correlated with the synthesis route. The highest efficiency (1.19%) was achieved using ZnO nanopowder capped with Triton X-100, having a mean diameter of ～19 nm. We find that the use of capped ZnO nanoparticles is favorable for DSSCs, possibly because of the good porosity of the film and better dye adsorption. Moreover, the efficiency of the cells is influenced by the surfactant structure, due to the particle morphology.     

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.     

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.     

Synthesis and photovoltaic property of pyrrole-based conjugated oligomer as organic dye for dye-sensitized solar cells

A new pyrrole-based conjugated oligomer (P1) was obtained with phenyl-linked triphenylamine moieties as an isolation group. Little aggregations were observed whether oligomer P1 was absorbed on titanium dioxide (TiO2) surface or in solid state. Since the pyrrole-based moieties in donor-π-acceptor type was the core component ofoligomer P1 for light absorption, the corresponding dyesensitized solar cell (DSSC) demonstrated the efficiency of light-to-electrical conversion by 0.48%. Higher conversion efficiency could be achieved by tuning the size of the isolation groups and the structure of the donor-π-acceptor type dyes.     

钛硅氧化物修饰对染料敏化太阳能电池性能影响研究

用溶胶-凝胶法配制了Ti-Si溶胶,并利用浸泡和煅烧法对染料敏化太阳能电池TiO2多孔光阳极进行了修饰处理,研究了Ti-Si氧化物修饰中Si含量对光阳极染料吸附量、TiO2/染料/电解质界面电荷传输电阻、电子寿命和光电转化性能的影响。发现Ti-Si氧化物修饰钝化了光阳极的表面态,改善了电极的电子寿命,促进了电荷的有效传输,提高了光生电子向TiO2中的注入效率;当Si含量为摩尔分数10%时,电池获得最高的光电转化效率7.11%。     

Fabrication of a counter electrode using glucose as carbon material for dye sensitized solar cells

Carbon material was produced from the graphitization of glucose at high temperature in flowing argon. The produced carbon material was characterized using Scanning electron microscopy, Transmission electron microscopy, Raman spectroscopy and XRD. Carbon slurry of the produced carbon was made in ethanol by using polyvinylpyrrolidone (PVP) as surfactant. Carbon slurry was coated homogeneously on fluorine doped tin oxide (FTO) glass by a doctor blade technique and applied as counter electrode for dye synthesized solar cell. The current density (J) and open circuit voltage (V_OC) of fabricated cell was 8.30 mA cm⁻² and 0.77 V respectively. The efficiency of the cell was 3.63%, which is comparable to 5.82% of cell with platinum counter electrode under the same experimental conditions.     

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。     

Effects of different electron donating groups on dye regeneration and aggregation in phenothiazine-based dye-sensitized solar cells

A series of phenothiazine-based dyes containing different auxiliary chromophores (TP, TTP, EP, and EEP) bring about unusual power conversion efficiency (PCE) for the corresponding dye-sensitized solar cells (DSSCs): EEP with the best electron-donating capability provides the lowest PCE of 2.24%, while TP with the weakest electron-donating capability leads to the highest PCE of 8.07%. The underlying influencing factors have been investigated by considering the electronic structures and aggregation properties based on density functional theory and Marcus theory. We found that the energy-mismatch between electron-donating units and the PTZ moiety results in poor EEP dye regeneration. Additionally, molecular dynamics simulations illustrate that the increased intermolecular interaction energy induced by preferable electron-donating groups aggravates the intermolecular aggregation. Especially, the calculated average values of the time-dependent intermolecular lateral charge transfer rate k for (EEP)₂ are nearly one order of magnitude higher than those of (TP)₂, revealing a more robust π-π stacking interaction induced by the donor unit of EEP. Importantly, the dye-TiO₂ interactions have been taken into account, which are absent in many previous theoretical work but crucial for accurate describing the aggregations. These deeper insights into the regeneration process and the aggregation mechanism induced by different donor units encourage researchers to balance various properties in designing novel components for photovoltaic devices.