Controlled synthesis of TiO2-B nanowires and nanoparticles for dye-sensitized solar cells

Controllable synthesis of the TiO₂-B nanowires (NWs) and nanoparticles (NPs) had been achieved via a facile hydrothermal route, respectively, only by tuning the solution volume. The dye-sensitized solar cells prototypes had been fabricated using TiO₂-B NW and NP electrodes, respectively. The TiO₂-B NP cells had higher photocurrent and photoelectrical conversion efficiency than the TiO₂-B NW cells though the latter exhibited larger photovoltage compared to the former. The key factors such as the photogenerated electron injection drive force, surface defects and the interfacial charge transfer, which determined the photoelectrical properties, had been systematically researched with the surface photovoltage spectra (SPS) and the electrochemical impedance spectra (EIS). The SPS proved that there was larger photoelectron injection drive force in TiO₂-B NP photoelectrode than that in NW photoelectrode. And the electrochemical impedance spectra (EIS) revealed that TiO₂-B NP cells had faster interface charge transfer compared to TiO₂-B NW cells. Both proved that NP cells had the higher photocurrents.     

ZnO/TiO2 core–shell nanowire arrays for enhanced dye-sensitized solar cell efficiency

We present a new method of synthesizing ZnO/TiO₂ core–shell nanowire (NW) arrays for the fabrication of dye-sensitized solar cells (DSSCs). Vertically aligned ZnO NW arrays were obtained on Si substrates, and modified by a TiO₂ shell in order to solve the recombination problems via a cost-effective spin-coating method. The structure of the ZnO/TiO₂ composite NW arrays was characterized. The experimental results indicate that the TiO₂ shell enhances the performance of the DSSCs, through improving the stability of the ZnO NWs and decreasing the recombination of photogenerated electrons on the NW surface. The highest overall conversion efficiency of the cell reaches about 3.0 %.     

Symbiotic organism search algorithm for simulation of <Emphasis Type="Italic">J</Emphasis>-<Emphasis Type="Italic">V</Emphasis> characteristics and optimizing internal parameters of DSSC developed using electrospun TiO<Subscript>2</Subscript> nanofibers

In the present investigation, the recently developed, simple, robust, and powerful metaheuristic symbiotic organism search (SOS) algorithm was used for simulation of J-V characteristics and optimizing the internal parameters of the dye-sensitized solar cells (DSSCs) fabricated using electrospun 1-D mesoporous TiO₂ nanofibers as photoanode. The efficiency (η =?5.80%) of the DSSC made up of TiO₂ nanofibers as photoanode is found to be ～ 21.59% higher compared to the efficiency (η =?4.77%) of the DSSC made up of TiO₂ nanoparticles as photoanode. The observed high efficiency can be attributed to high dye loading as well as high electron transport in the mesoporous 1-D TiO₂ nanofibers. Further, the validity and advantage of SOS algorithm are verified by simulating J-V characteristics of DSSC with Lambert-W function.     

Synthesis of cauliflower-like ZnO-TiO2 composite porous film and photoelectrical properties

A series of cauliflower-like TiO₂-ZnO composite porous films with various molar ratios of Zn/Ti were prepared by the screen printing technique on the fluorine-doped SnO₂ (FTO) conducting glasses. The composite films were characterized by field-emission scanning electron microscopy (FE-SEM), X-ray energy-dispersive spectrometry (EDS) and UV-vis transmittance spectrum. The results showed composite film electrode had a novel cauliflower-like morphology, which could effectively increase the dye absorption. The corresponding dye-sensitized solar cells (DSCs) were made by the composite film, and effects of ZnO incorporation on the photovoltaic performances of the DSCs were studied. With the Zn/Ti molar ratio not more than 3% in ZnO-TiO₂ composite film of about 5 μm-thickness, the photocurrent density (J_sc) and the solar-to-electricity conversion efficiency (η) were greatly improved compared with those of the DSC based on bare TiO₂ film of same thickness. This increases in efficiency and J_sc were attributed to high electron conductivity of ZnO, the improved dye adsorption and large light transmittance of composite film.     

Natural dye-based photoelectrode for improvement of solar cell performance

In the present paper, photovoltaic studies of dye-sensitized solar cells (DSSCs) based on betacyanin/TiO₂ and betacyanin/WO₃–TiO₂ have been done. The cell performances were compared through I–V curves and wavelength dependant photocurrent measurements for the two new types of DSSCs. The TiO₂-coated DSSC showed the photovoltage and photocurrent of 300 mV and 4.96 mA/cm², whereas the cell employing WO₃–TiO₂ photoelectrode showed the values 435 mV and 9.86 mA/cm², respectively. The conversion efficiency of TiO₂ based dye-sensitized solar cell was found to be 0.69 %, while WO₃–TiO₂-based cell exhibited a higher conversion efficiency of 2.2 %. The better performance of the WO₃–TiO₂ dye-sensitized solar cell photoelectrode is thought to be due to an inherent energy barrier at the electrode/electrolyte interface leading to the reduced recombination of photoinduced electrons.     

Improvement of ZnO nanorod-based dye-sensitized solar cell efficiency by Al-doping

The current study investigates the performance of dye-sensitized solar cells (DSSCs) based on Al-doped and undoped ZnO nanorod arrays synthesized by a simple hydrothermal method. Current density-voltage (J-V) characterizations indicate that Al-doping in ZnO crystal structure can significantly improve current densities and the energy conversion efficiency (η) of ZnO nanorod-based DSSCs. The maximum η, 1.34%, was achieved in DSSC when Al-doped ZnO nanorod arrays were grown in 0.04 M zinc acetate dihydrate solution with 5 mM aluminum nitrate nonahydrate. This result represents a large increase of η in Al-doped ZnO nanorod-based DSSCs as compared to undoped (0.05%). The improved DSSC photovoltaic performance can be attributed to two main factors: (1) increased light harvesting efficiency due to a large amount of N719 adsorbed on the large surface area of Al-doped ZnO nanorod arrays, and (2) increased electrical conductivity due to A1³⁺ ion doped into the ZnO lattice at the divalent Zn²⁺ site, allowing electrons to move easily into the Al-doped ZnO conduction band.     

TiO2表面质子化对染料敏化太阳能电池性能及吸附染料稳定性的影响

采用致密平整TiO₂薄膜作为染料敏化太阳能电池光电极,并研究了HCl处理表面质子化对电池性能的影响. 结果表明,HCl处理后电池的短路电流显著提升,电池的开路电压则有轻微的下降,电池电流提升了31%,而能量转化效率则提升了25%. 这是因为TiO₂的表面质子化增强了吸附染料与TiO₂间的电学耦合,提高了染料中激发电子向TiO₂导带的注入速率. 而电压的下降,一方面是由于质子化会引起TiO₂导带能级     

Electrochemical properties of TiO2 nanoparticle/nanorod composite photoanode for dye-sensitized solar cells

A unique composite of TiO₂ nanoparticles (NPs) and nanorods (NRs) has been used to fabricate a photoelectrode for developing dye-sensitized solar cells (DSSCs) with higher sensitivity. The TiO₂ nanorods were synthesized using a mechanical process, in which electrospun TiO₂ nanofibers was grinded in a controlled way to obtain uniform size distribution. The characteristics of electron transport, recombination lifetime and charge collection were investigated by intensity-modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS). Photoelectrodes prepared with the composites of NRs and NPs showed significant improvements in electron transportation compared to only NP photoelectrodes, which would enhance the photovoltaic performance of DSSCs. IMPS and IMVS measurements show that fast electron transport and slightly decreased recombination lifetime resulted in the improvement of efficiency. The highest energy conversion efficiency obtained from the photoelectrodes fabricated with the as-prepared rutile TiO₂ nanofibers at 5 wt% NR content was up to 6.1% under AM1.5G solar illumination. The results demonstrate that the composite nanostructure can take advantage of both the fast electron transport of the nanorods and the high surface area of the nanoparticles.     

Chemical reactions in TiO2/SnO2/TiCl4 hybrid electrodes and their impacts to power conversion efficiency of dye-sensitized solar cells

This study examined the applicability of TiO₂/SnO₂/TiCl₄ hybrid electrodes in dye-sensitized solar cells (DSSCs) by combining chemical modeling with experimentation. The interfacial chemical reactions in a TiO₂/SnO₂/TiCl₄ system were simulated using a thermochemistry software package, which led to the design and testing of hybrid working electrodes. Chemical thermodynamic modeling proved that TiCl₄ is an effective agent in removing Tiⁿ⁺ (n<4) and Sn^m+ (m<4) ion impurities from dry-mixed TiO₂/SnO₂ composite particles. Our results demonstrate that the power conversion efficiency of DSSC with a TiO₂/SnO₂/TiCl₄ hybrid electrode exceeds that of the conventional DSSC with a TiO₂ electrode due to the effects of light-scattering and the formation of additional absorbance (SnCl₂), which is an unexpected side effect of TiCl₄ treatment enabling the absorption of visible light. The proposed approach is ideally suited to establishing relationships between chemistry theory and the structure and performance of advanced DSSCs as well as photo-electro-chemical systems.     

A novel TiO2 nanoparticles/nanowires composite core with ZrO2 nanoparticles shell coating photoanode for high-performance dye-sensitized solar cell based on different electrolytes

The novel TiO₂ nanopartilces/nanowires (TNPWs) composite with ZrO₂ nanoparticles (ZNPs) shell-coated photoanodes were prepared to fabricate high-performance dye-sensitized solar cell (DSSC) based on different types of electrolytes. Hafnium oxide (HfO₂) is a new and efficient blocking layer material applied over the TNPWs-ZNPs core-shell photoanode film. TiO₂ nanoparticles (TNPs) and TiO₂ nanowires (TNWs) were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). DSSCs were fabricated using the novel photoanodes with an organic sensitizer D149 dye and different types of electrolytes namely liquid electrolyte, ionic liquid electrolyte, solid-state electrolyte, and quasi-solid-state electrolyte. The DSSC-4 made through the novel core-shell photoanode using quasi-solid-state electrolyte showed better photocurrent efficiency (PCE) as compared to the other DSSCs. It has such photocurrent-voltage characteristics: short circuit photocurrent (Jsc)?=?19 mA/cm², the open circuit voltage (Voc)?=?650 mV, fill factor (FF)?=?65 %, and PCE (η)?=?8.03 %. The improved performance of DSSC-4 is ascribed to the core-shell with blocking layer photoanode could increased electron transport and suppressed recombination of charge carriers at the TNPWs-ZNPs/dye/electrolyte interface.     

Analysis of adsorption properties of N719 dye molecules on nanoporous TiO2 surface for dye-sensitized solar cell

Ordered nanoporous TiO₂ materials (MK-TiO₂, MS-TiO₂, and MU-TiO₂) were synthesized for the dye-sensitized solar cell (DSSC) by using different silica templates such as KIT-6, SBA-15, and MSU-H. To prepare a photoelectrode in DSSC, cis-bis(isothiocyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylato)-ruthenium(II)bis-tetrabutylammonium dye (N719) was adsorbed onto the synthesized nanoporous TiO₂ materials. The samples were characterized by XRD, TEM, FE-SEM, AFM, and N₂ adsorption analyses. The photovoltaic performance of DSSC was evaluated from the overall conversion efficiency, fill factor, open-circuit voltage, and short-circuit current from the I-V curves measured. It was found that the photoelectric performance is highly dependent on the adsorption properties of N719 dye molecules on the nanoporous TiO₂ replicas (MK-TiO₂, MS-TiO₂, and MU-TiO₂) synthesized from different silica templates.     

Thickness effect of the TiO2 nanofiber scattering layer on the performance of the TiO2 nanoparticle/TiO2 nanofiber-structured dye-sensitized solar cells

TiO₂ nanofibers (NFs) were fabricated by an electrospinning process and were used as scattering layers in dye-sensitized solar cells (DSSCs). The NF-coated photoanodes of the DSSCs were prepared with a variety of scattering layer thicknesses. The thickness effect of the scattering layer on the double-layered TiO₂ nanoparticle (NP)/TiO₂ NF structure was investigated through structural, morphological, and optical measurements. In the double-layered photoanode, the TiO₂ NP layer plays a major role in dye adsorption and light transmission, and the TiO₂ NF scattering layer improves the absorption of visible light due to the light scattering effects. The scattering effect of TiO₂ NFs layer was examined by the incident monochromatic photon-to-electron conversion efficiency (IPCE) and UV–Vis spectrometry. The conversion efficiency for the 12 μm-thick photoanode composed of a 2 μm-thick TiO₂ NF layer and 10 μm-thick TiO₂ NP layer was higher than that of DSSCs with only TiO₂ NPs photoanode by approximately 33%.     

Influence of TiO2 nanotube morphology and TiCl4 treatment on the charge transfer in dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) were fabricated using TiO₂ nanoparticles (NPs), TiO₂ nanotube arrays (NTAs), and surface-modified NTAs with a TiCl₄ treatment. The photovoltaic efficiencies of the DSSCs using TiO₂ NP, NTA, and TiCl₄-treated NTA electrodes are 4.25, 4.74, and 7.47 %, respectively. The highest performance was observed with a TiCl₄-treated TiO₂ NTA photoanode, although in the case of the latter two electrodes, the amounts of N719 dye adsorbed were similar and 68 % of that of the NP electrode. Electrochemical impedance measurements show that the overall resistance, including the charge–transfer resistance, was smaller with NTA morphologies than with NP morphologies. We suggest that a different electron transfer mechanism along the one-dimensional nanostructure of the TiO₂ NTAs contributes to the smaller charge–transfer resistance, resulting in a higher short circuit current (J _sc), even at lower dye adsorption. Furthermore, the TiCl₄-treated NTAs showed even smaller charge–transfer resistance, resulting in the highest J _sc value, because the downward shift in the conduction band edge improves the electron injection efficiency from the excited dye into the TiCl₄-treated TiO₂ electrodes.     

Investigation of the fill factor of dye-sensitized solar cell based on ZnO nanowire arrays

The fill factor of dye-sensitized solar cells based on the ZnO nanowire array is very low, which is usually ascribed to a rapid charge recombination. In this article, the influence on the fill factor of ZnO nanowire array cell is investigated and discussed by comparing dark current and decay rate of open circuit potential of the ZnO nanowire array cell with those of the ZnO nanoparticle cell, TiO₂ nanoparticle cell and TiO₂-coated ZnO nanowire array cell. The results demonstrate that the low fill factor of the ZnO nanowire array cell is largely caused by a rapid decrease of electron injection efficiency rather than a rapid charge recombination, which is decided by the absorption nature of Ru-complexed dye molecules on ZnO surface and repellency of radial electric field. The fill factor of the ZnO nanowire array cell can be improved by coating ZnO nanowires with a wide band gap semiconductor material or metal oxide insulator.     

Oriented ZnO nanotubes arrays decorated with TiO2 nanoparticles for dye-sensitized solar cell applications

Dye-sensitized solar cells (DSSCs) based on a novel composite photoanode of TiO₂ nanoparticles coating on electrodeposited ZnO nanotube arrays are fabricated and characterized. An efficiency of 3.94 % is achieved for the composite cell, increasing 86.7 % than 2.11 % of the ZnO nanotubes cell. The short-circuit current (J _sc) and open-circuit voltage (V _oc) are also enhancing 52.9 % and 25.3 %, respectively. The improvements are because of the high surface area of TiO₂ nanoparticles, as well as fast electron transport and light scattering effect of ZnO nanotubes.     

Zinc oxide nanostructures for applications as ethanol sensors and dye-sensitized solar cells

ZnO nanostructures were prepared by thermal oxidation technique for applying as ethanol sensors and dye-sensitized solar cells. To improve sensitivity of the sensor based on ZnO nanostructures, gold doping was performed in ZnO nanostructures. Gold-doped with 0%, 5%, and 10% by weight were investigated. The improvement of sensor sensitivity toward ethanol due to gold doping was observed at entire operating temperature and ethanol concentration. The sensitivity up to 145 was obtained for 10% Au-doped ZnO sensor. This can be explained by an increase of the quantity of oxygen ion due to catalytic effect of gold. Also, it was found that oxygen ion species at the surface of the Au-doped ZnO sensor remained O²⁻ as pure ZnO sensor. For dye-sensitized solar cell application, the dye-sensitized solar cell structure based on ZnO as a photoelectrode was FTO/ZnO/Eosin-Y/electrolyte/Pt counter electrode. ZnO with different morphologies of nanobelt, nano-tetrapod, and powder were investigated. It was found that DSSCs with ZnO powder showed higher photocurrent, photovoltage and overall energy conversion efficiencies than that of ZnO nanobelt and ZnO nano-tetrapod. The best results of DSSCs were the short circuit current (J_sc) of 1.25 mA/cm², the open circuit voltage (V_oc) of 0.45 V, the fill factor (FF) of 0.65 and the overall energy conversion efficiency (η) of 0.68%.     

Effect of Sn doping on the structural,optical and electrical properties of TiO2 films prepared by spray pyrolysis

In this work, highly oriented pure and Tin-doped Titanium dioxide (Sn-doped TiO₂) with porous nature photoelectrodes were deposited on ITO glass plates using spray pyrolysis technique. The XRD pattern revealed the formation of anatase TiO₂ with the maximum intensity of (101) plane while doping 6 at% of Sn. The morphological studies depicted the porous nature with the uniform arrangement of small-sized grains. The presence of tin confirmed with the EDX spectra. The size of particles of 13 nm was observed from High Resolution Transmission Electron Microscopy (HR-TEM) analysis. The average transmittance was about 85% for the doped photoelectrode and was observed for the photoelectrode deposited with 6 at% of tin, with decreased energy band gap. The PL study showed the emission peak at 391 nm. The maximum carrier concentration and Hall mobility was observed for the photoelectrode deposited with 6 at% of tin. With these studies, the DSSCs were prepared separately with the dye extracted from Hibiscus Rosasinesis and Hibiscus Surttasinesis and their efficiency was maximum for the DSSC prepared with 6 at% of tin.     

ZnO/TiO2 core–shell heterojunction for CdS and PbS quantum dot-cosensitized solar cells

ZnO nanorods (NRs) with regular morphology were prepared through hydrothermal method, and the TiO₂ shell was assembled onto the surface of ZnO NRs by spin coating to the ZnO/TiO₂ core–shell heterojunction. CdS and PbS quantum dots (QDs) were used to cosensitize the ZnO/TiO₂ nanostructure by direct adsorption (DA) and successive ionic layer adsorption and reaction, respectively. SEM, TEM, and HRTEM images show that the samples possessed a rough surface and four lattice fringes indicating the successful synthesis of the ZnO/TiO₂/CdS/PbS composite structure. The ZnO/TiO₂(10T)/CdS/PbS sample showed a high absorption intensity at a broad range of wavelength to visible light region. The ZnO/TiO₂(10T)/CdS/PbS photoelectrode with QDSSCs showed the highest IPCE of 36.04% and photoelectric efficiency (η) of 1.59%; these values increased by approximately 550% and 150% compared with those of unsensitized ZnO (0.29%) and ZnO/TiO₂(10T) (1.04%) and about 146% and 120% compared with those of ZnO/TiO₂(10T)/CdS and ZnO/TiO₂(10T)/PbS, respectively. The fill factor was 0.36, and the photocurrent density (J_sc) and open circuit voltage (V_oc) reached the maximum values of 9.73 mA cm⁻² and 0.46 V, respectively.     

Photovoltaic properties of ZnO photoanode incorporating with CNTs for dye-sensitized solar cell application

Zinc oxide carbon nanotube (ZnO-CNTs) thin films were prepared by a chemical bath deposition (CBD) method and immersed in N719 dye for 24 h. The structure and surface morphology of the samples was captured by X-ray diffraction (XRD) and field effect scanning electron microscopy (FESEM) unit, respectively. The photovoltaic properties of ZnO- and ZnO-CNT-based dye-sensitized solar cells (DSSCs) were measured by considering the power conversion efficiency (η), photocurrent density (J _sc), open-circuit voltage (V _oc), and fill factor (FF). The cell's efficiency doped with single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) reached 0.65 and 0.28 %, respectively. ZnO-based DSSC generated only η?=?0.003 %. The electrochemical impedance spectroscopy (EIS) unit was employed to investigate the electron transport properties such as effective electron lifetime (τ _eff), effective electron chemical diffusion coefficient (D _eff), and effective electron diffusion length (L _n ). The addition of CNTs has enhanced the photovoltaic properties of the DSSCs and reduced the recombination effect inside the solar cell.     

TiO2 treatment using ultrasonication for bubble cavitation generation and efficiency assessment of a dye-sensitized solar cell

In this study, the impacts of different ultrasonic treatments on TiO₂ particles were determined and they were used to manufacture the photoelectrodes of a dye-sensitized solar cell (DSSC). Two methods were used to prepare TiO₂ particles directly sonicated by an ultrasonic horn, and TiO₂ treated indirectly by an ultrasonic cleaner. TEM, XPS analysis was confirmed that cavitation bubbles generated during ultrasonication resulted in defects on the surface of TiO₂ particles, and the defect induced surface activation. To understand the effect of TiO₂ surface activation on energy conversion efficiency of DSSC, ultrasonic horn DSSC and ultrasonic cleaner DSSC were prepared. The UV–vis analysis exhibited that the ultrasonic horn DSSC possessed higher dye adsorption when compared to the ultrasonic cleaner DSSC, and the EIS analysis confirmed that the electron mobility was greatly increased in the ultrasonic horn DSSC. The energy conversion efficiency of the ultrasonic horn DSSC was measured to be 3.35%, which is about 45% increase in comparison to that of the non-ultrasonic treated DSSC (2.35%). In addition to this regard, recombination resistance of ultrasonic horn DSSC was calculated to be 450 Ω·cm², increasing more than two times compared to the non-ultrasonic treated DSSC (200 Ω·cm²). Taken together, these ultrasonic treatments significantly improved the energy conversion efficiency of DSSC, which was not tried in DSSC-related research, and might lead us to develop more efficient practical route in the manufacturing of DSSC.