WO3 passivation layer-coated nanostructured TiO2: An efficient defect engineered photoelectrode for dye sensitized solar cell

Major loss factors for photo-generated electrons due to the presence of surface defects in titanium dioxide (TiO2) were controlled by RF-sputtered tungsten trioxide (WO3) passivation.X-ray photoelectron spectroscopy assured the coating of WO3 on the TiO2 nanoparticle layer by showing Ti 2p,W 4f and O 1 s characteristic peaks and were further confirmed by X-ray diffraction studies.The coating of WO3 on the TiO2 nanoparticle layer did not affect dye adsorption significantly.Dye sensitized solar cells (DSSCs) fabricated using WO3-coated TiO2 showed an enhancement of ～10％ compared to DSSCs fabricated using pristine TiO2-based photo-electrodes.It is attributed to the WO3 passivation on TiO2 that creates an energy barrier which favored photo-electron injection by tunneling but blocked reverse electron recombination pathways towards holes available in highest occupied molecular orbital of the dye molecules.It was further evidenced that there is an optimum thickness (duration of coating) of WO3 to improve the DSSC performance and longer duration of WO3 suppressed photo-electron injection from dye to TiO2 as inferred from the detrimental effect in short circuit current density values.RF-sputtering yields pinhole-free,highly uniform and conformal coating of WO3 onto any area of interest,which can be considered for an effective surface passivation for nanostructured photovoltaic devices.     

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.     

A Near‐Infrared cis‐Configured Squaraine Co‐Sensitizer for High‐Efficiency Dye‐Sensitized Solar Cells

A cis‐configured squaraine dye (HSQ1), synthesized by incorporation of a strongly electron‐withdrawing dicyanovinyl group into the central squaric acid moiety, is employed in dye‐sensitized solar cells (DSCs). In solution, HSQ1 displays an intense absorption in the near‐infrared region with a maximum at 686 nm and when the dye is adsorbed on a TiO₂ surface, the absorption spectrum broadens in both the blue and the near‐infrared regions, which is favorable for efficient light harvesting over a broad wavelength range. A solar cell sensitized with HSQ1 shows a broader incident photon‐to‐current conversion efficiency (IPCE) spectrum (from 400 to 800 nm) and a higher IPCE in the long‐wavelength region (71% at 700 nm) than a cell sensitized with squaraine dye SQ1. Furthermore, a solar cell co‐sensitized with HSQ1 and N3 dye shows remarkably improved short‐circuit current density and open‐circuit voltage compared to those of a DSC based on N3 alone and fabricated under the same conditions. The energy‐conversion efficiency of the co‐sensitized DSC is 8.14%, which is the highest reported efficiency for a squaraine dye–based co‐sensitized DSC without using Al₂O₃ layer.     

Evolution of ZnO architecture on a nanoporous TiO2 film by a hydrothermal method and the photoelectrochemical performance

The synthesis of ZnO architecture on a fluorine-doped SnO2 (FTO) conducting glass pre-coated with nanoporous TiO2 film has been achieved by a one-step hydrothermal method at a temperature of 70 ℃.The effect of the reaction time on the morphology of the ZnO architecture has been investigated,and a possible growth mechanism for the formation of the ZnO architecture is discussed in detail.The morphology and phase structures of the as-obtained composite films have been investigated by field-emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD).The results show that the growth time greatly affects the morphology of the obtained ZnO architecture.The photoelectrochemical performances of as-prepared composite films are measured by assembling them into dye sensitized solar cells (DSSCs).The DSSC based on the as-prepared composite film (2 h) has obtained the best power conversion efficiency of 1.845％.     

Effects of the Morphology of a ZnO Buffer Layer on the Photovoltaic Performance of Inverted Polymer Solar Cells

The influences of morphology and thickness of zinc oxide (ZnO) buffer layers on the performance of inverted polymer solar cells are investigated. ZnO buffer layers with different morphology and thickness varying from several nanometers to ≈55 nm are fabricated by adjusting the concentration of the precursor sol. The ZnO buffer layers with nearly same surface quality but with thickness varying from ≈7 to ≈65 nm are also fabricated by spinning coating for comparison. The photovoltaic performance is found to be strongly dependent on ZnO surface quality and less dependent on the thickness. The use of dense and homogenous ZnO buffer layers enhances the fill factor and short‐circuit current of inverted solar cell without sacrificing the open‐circuit voltage of device due to an improvement in the contact between the ZnO buffer layer and the photoactive layer. Inverted devices with a dense and homogenous ZnO buffer layer derived from 0.1 M sol exhibit an overall conversion efficiency of 3.3% which is a 32% increase compared to devices with a rough ZnO buffer layer made from 1 M sol, which exhibited a power conversion efficiency of 2.5%. The results indicate that the efficiency of inverted polymer solar cells can be significantly influenced by the morphology of the buffer layer.     

Development of Nano‐TiO2 dye sensitised solar cells on high mobility transparent conducting oxide thin films

The optical transmission of dye‐sensitised solar cells (DSCs) can be tuned by altering the dye and/or particle size of the mesoporous TiO₂ layers, to allow their application as the top device in tandem solar cells. To benefit from this semi‐transparency, parasitic optical losses by the transparent electrodes must be minimised. This work investigates the influence of using two different transparent conductors, namely, the high mobility material titanium doped indium oxide (ITiO) and fluorine doped tin oxide (FTO) as electrodes for semi‐transparent DSCs. The overall NIR transparency through the DSCs increased significantly as each FTO electrode was replaced by an ITiO electrode. This increase was from 20–45% in the 1300–700 nm wavelength range for fully FTO‐based cells, to about 60% for fully ITiO‐based cells, across the same spectrum. DSCs prepared on these electrodes exhibited short circuit currents ranging from 14·0–14·9 mA/cm². The conversion efficiency of the cell with ITiO as both the front and rear electrodes was 5·8%, which though significant, was lower than the 8·2% attained by the cell using FTO electrodes, as a result of a lower fill factor. Improvements in the ITiO thermal stability and in the processing of the TiO₂ interfacial layer are expected to improve the cell efficiency of such single DSC devices. The high current density and optical transparency of ITiO‐based DSCs make them an interesting option for tandem solar cells. Copyright © 2008 John Wiley & Sons, Ltd.     

Polydisperse Spindle‐Shaped ZnO Particles with Their Packing Micropores in the Photoanode for Highly Efficient Quasi‐Solid Dye‐Sensitized Solar Cells

In this paper, a novel hierarchically structured ZnO photoanode for use in quasi‐solid state dye‐sensitized solar cells (DSCs) is presented. The film is composed of polydisperse spindle‐shaped ZnO particles that are prepared through direct precipitation of zinc acetate in aqueous solution. Without additional pore‐forming agents, the microporous structure is well constructed through the packing of polydisperse ZnO particles. In the film, small ZnO particles are able to improve interparticle connectivity and offer a large internal surface area for sufficient dye‐adsorption; on the other hand, particles of larger size can enhance the occurrence of light‐scattering and introduce micropores for the permeation of quasi‐solid state electrolytes. Meanwhile, morphologies, particle size, and specific areas of the products are controlled by altering the reactant concentration and synthetic temperature. Combined with a highly viscous polymer gel electrolyte, a device based on this ZnO photoanode shows high conversion efficiencies, 4.0% and 7.0%, under 100 and 30 mW cm^?2 illumination, respectively. Finally, the unsealed device is demonstrated to remain above 90% of its initial conversion efficiency after 7 days, showing excellent stability.     

Indoline‐Based Molecular Engineering for Optimizing the Performance of Photoactive Thin Films

New indoline dyes ( RK‐1 – 4 ) were designed with a planar geometry and high molar extinction coefficient, which provided surprising power conversion efficiency (PCE) with a thin titanium dioxide film in dye‐sensitized solar cells (DSCs). They had a difference in only alkyl chain length. Despite the same molecular structure, the performance of the respective DSCs varied significantly. Investigating the dye adsorption processes and charge transfer kinetics, the alkyl chain length was determined to affect the dye surface coverage as well as the recombination between the injected photoelectrons and the oxidized redox mediators. When applied to the DSCs as a light harvester, RK‐3 with the dodecyl group exhibited the best photocurrent density, consequently achieving the best PCE of 9.1% with a 1.8 μm active and 2.5 μm scattering layer because of the most favorable charge injection. However, when increasing the active layer thickness, overall device performance deteriorated and the charge collection and regeneration played major roles for determining the PCE. Therefore, RK‐2 featuring the highest surface coverage and moderate alkyl chain length obtained the highest PCEs of 8.8% and 7.9% with 3.5 and 5.1 μm active layers, respectively. These results present a promising perspective of organic dye design for thin film DSCs.     

ZnO纳米棒光阳极的制备及其天然染料敏化研究

采用溶胶-凝胶法和旋转涂覆法在FTO导电玻璃上制备ZnO种子层,以Zn(NO3)2和六亚甲基四胺(HMT)的混合溶液为生长液在ZnO种子层上制备出ZnO纳米棒薄膜,利用X射线衍射(XRD)、扫描电镜(SEM)对ZnO种子层及纳米棒薄膜的晶相及表面微观形貌进行了表征;研究了生长液浓度、生长时间对ZnO纳米棒薄膜生长的影响。实验表明,制备排列整齐的ZnO纳米棒阵列薄膜最佳条件为90℃环境下,基底竖直放置在0.025mol/L的生长液中,生长4h,纳米棒平均直径80nm左右。从新鲜草莓、桑葚中提取天然色素,对ZnO纳米棒电极进行敏化,组装成光电池;测试敏化电极的吸收光谱及光电池的伏安特性曲线。结果表明,桑葚色素在可见光区有更强的吸收特性,由桑葚色素敏化的电极组装的光电池,在模拟太阳光下,得到开路电压为228.75mV,短路电流为189μA,填充因子为0.37,光电转换效率为5.5×10-4。     

低压TiO_2系压敏陶瓷的伏安特性实验分析

采用耗尽层近似理论,分析了低压TiO2系压敏陶瓷在直流偏压下的伏安特性,并对ZnO、TiO2和SrTiO3系三种压敏陶瓷的伏安特性进行了测试、分析和比较。结果表明,在晶界势垒不太高(一般为零点几电子伏)及晶界电场强度不太大(约106V/m量级)的情况下,TiO2系压敏陶瓷晶界的电子传输机制不同于ZnO系压敏陶瓷,而与SrTiO3系压敏陶瓷的导电机制相似,属于肖特基热电子发射机制。     

Optoelectronic devices informatics: optimizing DSSC performance using random-forest machine learning algorithm

This paper provides an attempt to utilize machine learning algorithm, explicitly random-forest algorithm, to optimize the performance of dye sensitized solar cells (DSSCs) in terms of conversion efficiency. The optimization is implemented with respect to both the mesoporous TiO2 active layer thickness and porosity. Herein, the porosity impact is reflected to the model as a variation in the effective refractive index and dye absorption. Database set has been established using our data in the literature as well as numerical data extracted from our numerical model. The random-forest model is used for model regression, prediction, and optimization, reaching 99.87% accuracy. Perfect agreement with experimental data was observed, with 4.17% conversion efficiency.     

Electrochemical synthesis of a double‐layer film of ZnO nanosheets/nanoparticles and its application for dye‐sensitized solar cells

A double‐layer film, consisting of an upper layer of ZnO nanosheets and a lower layer of ZnO nanoparticles (designated as ZnONS/NP), was synthesized for the photoanode of a dye‐sensitized solar cell (DSSC) by a one‐step potentiostatic electrodeposition on a conducting fluorine‐doped tin oxide substrate at 70 °C in a solution containing zinc nitrate and sodium acetate, followed by the pyrolysis of the film at 300 °C. The growth mechanism of the double‐layer nanostructure was studied by monitoring the morphological changes at various periods of electrodeposition. The effects of the concentration of acetate anion on the morphology of the double‐layer structure were also studied. The double‐layer film of ZnONS/NP showed a better self‐established light scattering property, compared with that of a thin film of ZnO nanoparticles, prepared without acetate anion. The concentration of an acetate anion in the electrolyte for the electrodeposition of the double‐layer film, the electrodeposition period, and the period for dye adsorption were optimized for obtaining the best performance for a DSSC with a photoanode consisting of the double layer. A metal‐free dye, coded as D149, was used in this research. A conversion efficiency of 4.65% was achieved for a DSSC (0.2376 cm²) with the photoanode, consisting of the double‐layer film, under 100 mW/cm² illumination in the wavelength range of 400–800 nm. X‐ray diffraction patterns, thermo gravimetric curves, elemental analysis, scanning electron microscopic images, transmission electron microscopic image, transmission spectra, and electrochemical impedance spectra were used to explain observations. Copyright © 2012 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%.     

ZnO nano-ridge structure and its application in inverted polymer solar cell

We report a unique nano-ridge structure of zinc oxide (ZnO) and its application in high performance inverted polymer solar cells. The ZnO nano-ridge structure was formed by a sol–gel process using a ramp annealing method. As the solvent slowly evaporated due to the low heating rate, there was sufficient time for the gel particles to structurally relax and pile up, resulting in a dense and undulated film. Nano-ridges with peak as high as 120 nm and valley to valley distance of about 500 nm were formed. This film provided an effective hole blocking layer and also an increased interfacial area for electron collection. An inverted bulk heterojunction polymer solar cell was fabricated using the ZnO nano-ridge film as the electron collecting layer. The device showed a high power conversion efficiency of 4.00%, an improvement of about 25% over similar solar cells made with a planar film of ZnO nanoparticles.     

酞菁染料ZnPc和Q-PbS复合敏化纳米晶ZnO薄膜电极的研究

利用溶胶-凝胶旋涂镀膜法结合热处理工艺在FTO玻璃上制备了ZnO薄膜,并通过X射线衍射(XRD)、扫描电子镜(SEM)对其晶相及表面形貌进行了表征;以酞菁染料ZnPc和窄禁带半导体PbS量子点(Q-PbS)为敏化剂,分别制备了FTO/ZnO/ZnPc电极、FTO/ZnO/Q-PbS电极和FTOZnO/Q-PbS/ZnPc电极,结果表明,ZnPc和Q-PbS对ZnO纳米颗粒膜产生了良好的敏化作用,且两者的复合敏化效果最好;制备了FTO/ZnO/Q-PbS/ZnPc为光阳极的染料敏化太阳能电池(DSSC),在模拟太阳光下,电池的开路电压为304mV,短路电流为1.42mA,光电转换效率为0.696%,填充因子为0.348。     

一种柔性染料敏化太阳能电池的初步研究

染料敏化太阳能电池(DSSC)与商用硅电池相比,由于具有转化效率较高、制作成本低等一系列优点,近年来已受到人们的广泛关注.简要介绍了DSSC太阳能电池的结构和基本原理,重点分析了DSSC太阳能电池的关键组成和影响光电转化效率的因素.采用胶带涂覆法在柔性ITO衬底上制备了多孔纳米TiO2薄膜,通过给其配置相应的染料和电解...     

Design of conduction band structure of TiO2 electrode using Nb doping for highly efficient dye‐sensitized solar cells

A barrier layer of undoped TiO₂ was deposited on the Nb‐doped TiO₂ electrode to suppress the recombination at the Nb‐doped TiO₂/dye–electrolyte interface for highly efficient dye‐sensitized solar cells (DSCs). The Nb content in TiO₂ was varied in a range of 0.7–3.5 mol% to modify the TiO₂ energy‐band structure. Nb‐doped TiO₂/dye interfaces were characterized by a combination of ultraviolet photoemission spectroscopy and optical absorption spectroscopy measurements, allowing the determination of the conduction band minimum (CBM) of the TiO₂ electrode and the lowest unoccupied molecular orbital of the N719 dye. The lowering of TiO₂ CBM by Nb doping induced the increase in short‐circuit current of DSCs. However, open‐circuit voltage and fill factor are decreased, and this result was ascribed to the enhanced recombination at the Nb‐doped TiO₂/dye–electrolyte interface. The effect of doping on charge transport in DSCs was analyzed using electrochemical impedance spectroscopy. We have shown that by introducing of TiO₂ barrier layer, the Nb doping content, which results in DSC highest efficiency, can be increased because of the suppression of the dopant‐induced recombination. The energy conversion efficiency of the solar cells increased from 7.8% to 9.0% when undoped TiO₂ electrode is replaced with electrode doped with 2.7 mol% of Nb because of the improvement of the electron injection and collection efficiencies. The correlation between the electronic structure of the TiO₂ electrode, charge transfer characteristics, and photovoltaic parameters of DSCs is discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

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.     

TiO2/SnOxCly double layer for highly efficient planar perovskite solar cells

Recently, perovskite solar cells have attracted tremendous research interest due to their amazing light to electric power conversion efficiency (PCE). However, most high performance devices usually use mesoporous TiO₂ as the electron transport layer (ETL), which increases cost for practical application. Here, TiO₂/SnO_xCl_y double layer was employed as the ETL for planar perovskite solar cells. Compared with bare TiO₂, perovskite solar cell based on TiO₂/SnO_xCl_y shows drastically improved power conversion efficiency and reduced hysteresis. These improvements are attributed to TiO₂/SnO_xCl_y which could enhance electron extraction and reduce surface trap-state.     

Manipulation of light harvesting for efficient dye‐sensitized solar cell by doping an ultraviolet light‐capturing fluorophore

An organic fluorophore is doped into a mesoporous TiO₂ photoelectrode to absorb ultraviolet light and convert it to green light for more efficient light harvesting of N719 dye. This fluorescence conversion enables the absorption of additional green light by dye molecules by means of Förster resonance energy transfer between fluorescent compound donor and N719 dye acceptor. Owing to close fit between the emission peak of fluorophore and the absorption peak of N719 dye, the Förster resonance energy transfer effect enhances the incident photon to current conversion efficiency of the dye‐sensitized solar cells based on fluorophore‐doped TiO₂ photoelectrodes. Improved power conversion efficiency (8.03–8.13%) is also achieved for the fluorophore‐doped (10⁻⁴ M) dye‐sensitized solar cells compared with a cell without the doping of fluorophore (7.63%). Copyright © 2013 John Wiley & Sons, Ltd.