TiCl4 Treatment Research Articles

Improved light harvest in diffraction grating-embedded TiO2 nanoparticle film

We show that a high-efficiency diffraction grating can be embedded into nanoparticulate TiO2 film via imprinting combined with TiCl4 treatment. The grating-embedded film consists of two layers in intimate contact. A thin TiO2 layer was first patterned on a glass substrate by imprinting. The patterned layer was TiCl4-treated with a higher concentration than the over-coated thicker layer, so that it diffracts incident light as a refractive-index grating. Gratings with a period scaled down to 1 µm could be embedded into the film. Diffraction efficiency increased with an increasing grating height and an efficiency over 80% was achieved in the near-ultraviolet and visible range. Dye-sensitized solar cells fabricated using a grating-embedded TiO2 photoanode exhibited much better photovoltaic performance than those without a grating. It was also found that the incorporation of a diffraction grating greatly enhances the photocatalytic activity of nanoparticulate TiO2 film. All these are attributed to improved light harvest.

Low-temperature photochemical activation of sol-gel titanium dioxide films for efficient planar heterojunction perovskite solar cells

To realize high-performance perovskite solar cells (PSCs) ensuring low-cost flexible application with low energy consumption, efficient electron transport layers (ETL) that can be processed at low temperatures are desired. In this contribution, low temperature (about 70 °C) UV/ozone irradiation was applied to synthesis crystallized TiO2 films as ETL. The UV exposure induces photo-catalytic removal of the organic ligands and spontaneous coalescence of the TiO2 framework, resulting in excellent TiO2 films with considerable crystallinity. UV irradiation induces both complete removal of organic media and more efficient charge collection. Accordingly, planar heterojunction (PH) PSCs with such ETL exhibited outstanding photovoltaic performance up to 17.03%, which is even higher than the value (12.98%) of counterpart device with high temperature thermal sintered TiO2 ETL (without TiCl4 treatment). These low temperature solution-processed TiO2 films by facile UV irradiation are suitable for the low-cost, large yield solution process on a flexible substrate for photoelectric devices.

Adjustment of Conduction Band Edge of Compact TiO2 Layer in Perovskite Solar Cells Through TiCl4 Treatment.

Perovskite solar cells (PSCs) without a mesoporous TiO2 layer, that is, planar-type PSCs exhibit poorer cell performance as compared to PSCs with a porous TiO2 layer, owing to inefficient electron transfer from the perovskite layer to the compact TiO2 layer in the former case. The matching of the conduction band levels of perovskite and the compact TiO2 layer is thus essential for enhancing PSC performance. In this study, we demonstrate the shifting of the conduction band edge (CBE) of the compact TiO2 layer through a TiCl4 treatment, with the aim of improving PSC performance. The CBE of the compact TiO2 layer was shifted to a higher level through the TiCl4 treatment and then shifted in the opposite direction, that is, to a lower level, through a subsequent heat treatment. These shifts in the CBE were reflected in the PSC performance. The TiCl4-treated PSC showed an increase in the open-circuit voltage of more than 150 mV, as well as a decrease of 100 mV after being heated at 450 °C. On the other hand, the short-circuit current decreased after the treatment but increased after heating at temperatures higher than 300 °C. The treated PSC subjected to subsequent heating at 300 °C exhibited the best performance, with the power conversion efficiency of the PSC being 17% under optimized conditions.

Improving Carbon‐Coated TiO2 Films with a TiCl4 Treatment for Photocatalytic Water Purification

AbstractBy using a simple thermal decomposition route, carbon‐TiO2 hybrid films have been synthesized from a catechol‐TiO2 surface complex. The coated films display enhanced visible region absorption, owing to the thin (≈2 nm) layer of carbon encapsulating the TiO2. Although photocatalytically active under visible light alone, it is demonstrated that the activity of the carbon‐coated films can be improved further by a hydrolytic treatment with TiCl4, leading to the introduction of small TiO2 particles (5–10 nm) and doping of chlorine into the structure. The combination of the carbon layer and TiCl4 treatment gives increased photocatalytic performance for the photodegradation of dyes, phenolic pollutants and the reduction of toxic CrVI to relatively benign CrIII. In addition, the carbon‐coated films show improved bactericidal activity under UV irradiation, and hence have been successfully tested against the most common types of pollutant present in potential drinking waters.

Highly efficient photoelectrochemical and photocatalytic anodic TiO2 nanotube layers with additional TiO2 coating

In this work, strong beneficial effects of thin and uniform TiO2 coatings within TiO2 nanotube layers for photocurrent generation and photocatalytical degradation of methylene blue are demonstrated for the first time. TiO2 nanotube layers were coated by TiO2 of various thicknesses (from 2.8nm to 22nm) using atomic layer deposition (ALD) and compared with TiO2 nanotube layers decorated by TiO2 nanoparticles (using established TiCl4 treatment) and with blank (uncoated) layers. By means of photocurrent measurements and cyclic voltammetry, it is demonstrated that the most efficient charge carrier separation can be achieved for TiO2 nanotube layers with an optimal ALD TiO2 coating thickness ≈11nm. Significant differences in flatband potentials and carrier density among all nanotube layers were revealed by Mott-Schottky measurements. Photocatalytic decomposition rates for methylene blue solutions were significantly enhanced for ALD TiO2 coated TiO2 nanotube layers compared to their uncoated or TiO2 nanoparticles - decorated counterparts. A perfect agreement in trends was obtained for photocurrent and photocatalytic results.

Effect of TiO2 modification on urchin-like orthorhombic Nb2O5 nanospheres as photoelectrodes in dye-sensitized solar cells

TiO2 modification via TiCl4 treatment has been widely used to improve the power conversion efficiency (PCE) of dye-sensitized solar cells (DSSCs), in which the effects usually attribute to the inhibition of charge recombination by barrier effect. Niobium pentoxide (Nb2O5) is considered a promising photoelectrode material for DSSCs. Here we prepared urchin-like orthorhombic Nb2O5 nanospheres consisting of ultrathin nanorods by a hydrothermal method, which were further developed as photoelectrodes for DSSCs. The TiO2 modification on the urchin-like orthorhombic Nb2O5 nanospheres increases the photocurrent and PCE of the DSSCs. However, the impedance spectroscopy showed that charge recombination was not reduced by the TiO2 modification. The improvement in the photocurrent and PCE has been attributed to the enhanced absorption of dye molecules (N719). The results indicate that the enhancement of dye absorption for orthorhombic Nb2O5 photoelectrodes is the desirable approach to improve the performance of orthorhombic Nb2O5-based DSSCs.

Improved performance of anodic titanium oxide nanotube arrays synthesized by sonoelectrochemical anodization method for dye-sensitized solar cells

With rising demand for using solar cell systems for energy and environmental applications, considerable interest in anode materials of these cells has dramatically emerged. In this work, TiO2 nanotubular electrodes of varying thicknesses as anode were fabricated using effective process in a short time by sonoelectrochemical anodizing of Ti using an organic electrolyte, containing Na2[H2EDTA]. Long TiO2 nanotubes about 30–40 μm thick containing ordered hexagonal TiO2 were achieved through manipulating anodization parameters. Dye-sensitized solar cells (DSSCs) with different TiO2 electrode morphologies of varying thicknesses were compared to DSSCs based on TiO2 Nanoparticle electrodes. The effect of controlling parameters of the sonoelectrochemical process including surface preparation and anodizing time was investigated. This report brings to attention the desirable properties of the structurally oriented TiO2 for dye-sensitized solar cell applications. It found that the best cell performance was achieved about 3.14% in the case of using TiO2 NT layers that were treated by TiCl4 treatment.

Enhanced Efficiency of Dye-Sensitized Solar Cells with Mesoporous–Macroporous TiO2 Photoanode Obtained Using ZnO Template

Improved light harvesting efficiency can be achieved by enhancing the optical properties of the titanium dioxide (TiO2) photoanode in dye-sensitized solar cells (DSSCs), leading to higher power conversion efficiency. By incorporating submicrometer cavities in TiO2 mesoporous film, using zinc oxide (ZnO) particles as a template, a bimodal pore size structure has been created, called a mesoporous–macroporous nanostructure. This photoanode structure consists of 20-nm TiO2 nanoparticles with two kinds of pores with size of 20 nm (mesopores) and 500 nm (macropores). Energy-dispersive x-ray spectroscopy and x-ray diffraction studies showed no trace of ZnO in the TiO2 after removal by TiCl4 treatment. Higher diffuse transmittance of this film compared with the standard transparent photoanode provides evidence of improved light scattering. When employed in a device, the incident-photon-to-current efficiency of ZnO-assisted devices showed enhancement at longer wavelengths, corresponding to the Mie light scattering effect with the macropores as scattering centers. This resulted in overall higher power conversion efficiency of the DSSC. In this work, a nonvolatile gel ionic liquid was used as the electrolyte to also demonstrate the benefit of this structure in combination with a viscous electrolyte and its promising application to prolong the stability of DSSCs.

Efficient photoelectrodes from anatase TiO2 nanotube arrays decorated with particles/rods/3D microflower rutile crystals for photoelectrochemical water splitting

Efficient photoanodes are designed of vertically aligned anatase TiO2 nanotube arrays (anatase TNTAs) decorated with different shaped rutile TiO2 structures (particles, 1D nanorods, 3D microflowers) to improve the photoelectrochemical water oxidation performance of pristine TNTAs. Anatase TNTAs were prepared by anodic oxidation of Ti substrate in NH4F electrolyte, and the rutile percent and shape are controlled by tuning the TiCl4 treatment time (20–120 min). The effects of treatment time on the morphology, crystal structure, band gap, photocurrent, and photoconversion efficiency are characterized by FESEM, HRTEM, XRD, UV–Vis diffuse reflectance spectroscopy, and photoelectrochemical measurements. XRD data confirmed that TiCl4 treatment induced the formation of the rutile phase of TiO2 over anatase TNTAs and the rutile amount in the TNTAs was increased upon increasing the treatment time. Additionally, the band gap of TNTAs was gradually decreased by increasing the rutile percent. The optimum treatment time is 80 min, which produces TiO2 photoanode array that possess the following characteristics: rutile/anatase mixed phase, nanorode/nanotube mixed morphology, 3.09 eV band gap, two times increase in photocurrent, and almost more than twofold enhancement in the photoconversion efficiency relative to pure TNTA.

Surface States in Ternary CdSSe Quantum Dot Solar Cells.

Ternary CdSSe quantum dot-sensitized solar cells (QDSCs) have demonstrated advantages such as wide absorption ranges and tunable band structures. However, the oxygen additives absorbed on such multicomponent quantum dot (QD) surfaces induce band bending at the TiO₂/CdSSe interface and prevent charge transport in QDSCs, as determined via X-ray photoelectron spectroscopy (XPS) and synchrotron-based X-ray Absorption Near-Edge Structure (XANES) analysis. Annealing of TiO₂/CdSSe QDs photoanodes was conducted at different temperatures under Ar atmospheres to eliminate oxygen additives and interfacial band bending. The short-circuit current (J(sc))of the annealed ternary CdSSe QDSCs is obviously improved, whereas the TiCl4 treatment and MgO coating of the TiO₂ nanocrystals are assisted by the annealing to compensate for the loss of opencircuit voltage (V(oc)) and fill factor (FF). Ternary CdSSe QDSCs with efficiencies of 4.72% have been achieved using the optimized annealing conditions.

Fabrication, Optimization and Characterization of Natural Dye Sensitized Solar Cell

The dyes extracted from pomegranate and berry fruits were successfully used in the fabrication of natural dye sensitized solar cells (NDSSC). The morphology, porosity, surface roughness, thickness, absorption and emission characteristics of the pomegranate dye sensitized photo-anode were studied using various analytical techniques including FESEM, EDS, TEM, AFM, FTIR, Raman, Fluorescence and Absorption Spectroscopy. Pomegranate dye extract has been shown to contain anthocyanin which is an excellent light harvesting pigment needed for the generation of charge carriers for the production of electricity. The solar cell’s photovoltic performance in terms of efficiency, voltage, and current was tested with a standard illumination of air-mass 1.5 global (AM 1.5 G) having an irradiance of 100 mW/cm2. After optimization of the photo-anode and counter electrode, a photoelectric conversion efficiency (η) of 2%, an open-circuit voltage (Voc) of 0.39 mV, and a short-circuit current density (Isc) of 12.2 mA/cm2 were obtained. Impedance determination showed a relatively low charge-transfer resistance (17.44 Ω) and a long lifetime, signifying a reduction in recombination losses. The relatively enhanced efficiency is attributable in part to the use of a highly concentrated pomegranate dye, graphite counter electrode and TiCl4 treatment of the photo-anode.

TiCl4 surface-treated SnO2 photoanodes for self-powered UV photodetectors and dye-sensitized solar cells

TiCl4 surface-treated SnO2 nanocrystal films were applied as photoanodes for photoelectrochemical self-powered UV photodetectors (UVPDs) and dye-sensitized solar cells (DCSs). It is found that the TiCl4-treated SnO2-based UVPD shows a higher photocurrent density (J) and open-circuit voltage (Voc) compared to the pure SnO2-based UVPD. The TiCl4-treated SnO2-based UVPD has a high on/off ratio of 6475, rapid response (0·009 s for rise time and 0·006 s for decay time), excellent spectral selectivity and linear optical signal response under UV light irradiance. In addition, the TiCl4-treated SnO2-based DSC with the ruthenium-based C106 dye also exhibits a higher power conversion efficiency (PCE) than that of the SnO2-based DSC. The effect of TiCl4 treatment on the performance of UVPDs and DSCs was investigated in detail by the incident photon-to-current conversion efficiency (IPCE), UV–vis absorption, electrochemical impedance, flat-band potential (VFB) and transient photoelectric decay measurements.

Tuning of perovskite solar cell performance via low-temperature brookite scaffolds surface modifications

The nature of metal oxide scaffold played a pivotal role for the growth of high quality perovskites and subsequently facilitates efficient photovoltaics devices. We demonstrate an effective way to fabricate a low-temperature TiO2 brookite scaffold layer with a uniform and pinhole-free layer for enhancing photovoltaic properties of perovskite solar cells. Various concentrations of TiCl4 were used to modify brookite TiO2 for efficient charge generation and fast charge extraction. We observed that the brookite layer with an appropriate TiCl4 treatment possesses a smooth surface with full coverage of the substrates, whereas TiCl4 treatment further improves the contact of the TiO2/perovskite interface which facilitates charge extraction and drastically influenced charge recombination. The surface treated brookite scaffolds perovskite devices showed an improved performance with an average power conversion efficiency more than 17%. The time resolved photoluminescence showed that the treated samples have obvious effect on the charge carrier dynamics. The striking observation of this study was very low appearance of hysteresis and high reproducibility in the treated samples, which opens up the possibilities for the fabrication of high efficient devices at relatively low temperatures with negligible hysteresis via facile surface modifications.

Fabrication and Characterization of Front-Illuminated Dye-Sensitized Solar Cells with Anodic Titanium Oxide Nanotubes

We have fabricated front-side illuminated dye-sensitized solar cells (DSSCs) with a thin film of vertically oriented TiO2 nanotubes used as the negative electrode. The TiO2 nanotube film was formed by anodizing a metallic titanium thin film that was deposited on a transparent conductive oxide (TCO) layer with an intermediate, protective TiO2 layer. We characterized the structural and electronic properties of the formed TiO2 nanotube films. Titanium tetrachloride (TiCl4) treatment was applied on the TiO2 nanotube film to improve the performance of the DSSCs. We have investigated effects of TiCl4 treatment on the solar cell parameters of the DSSCs: short-circuit current density (ISC), open-circuit voltage (Voc), ideal factor (n), series resistance (Rs) and shunt resistance (Rsh). The parameters have been derived by analyzing measured I-V characteristic of the DSSCs on the basis of the method we have previously proposed. We demonstrate that the performance of the DSSCs is improved by TiCl4 treatment. We discuss the effects of TiCl4 treatment on the performance on the basis of the derived cell parameters.

Efficiency enhancement in dye-sensitized solar cells using silver nanoparticles and TiCl4

ABSTRACTThis paper reports the efficiency enhancement in dye-sensitized solar cells (DSSCs) by incorporation of silver nanoparticles (AgNPs) in Titanium dioxide (TiO2) and using it as anode. Further enhancement in DSSC parameters was observed after TiCl4 treatment on TiO2Ag anode. It was observed that the short circuit current density Jsc was increased from 6.95 to 12.58 mA/cm2 by TiCl4 treatment with no change in Voc and fill factor increasing the efficiency from 3.29 to 5.61%. The fabricated DSSCs using TiO2AgNPs anode with both pre and post TiCl4 treatment appear to have the maximum efficiency as compared to other cells. Due to effective electron transport and enhanced absorption of dye on TiO2AgNPs anode surface, the maximum conversion efficiency of 7.3% was achieved.

Impact of a Mesoporous Titania-Perovskite Interface on the Performance of Hybrid Organic-Inorganic Perovskite Solar Cells.

We report on the optimization of the interfacial properties of titania in mesoscopic CH3NH3PbI3 solar cells. Modification of the mesoporous TiO2 film by TiCl4 treatment substantially reduced the surface traps, as is evident from the sharpness of the absorption edge with a significant reduction in Urbach energy (from 320 to 140 meV) determined from photothermal deflection spectroscopy, and led to an order of magnitude enhancement in the bulk electron mobility and corresponding decrease in the transport activation energy (from 170 to 90 meV) within a device. After optimization of the photoanode-perovskite interface using various sizes of TiO2 nanoparticles, the best photovoltaic efficiency of 16.3% was achieved with the mesoporous TiO2 composed of 36 nm sized nanoparticles. The improvement in device performance can be attributed to the enhanced charge collection efficiency that is driven by improved charge transport in the mesoporous TiO2 layer. Also, the decreased recombination at the TiO2-perovskite interface and better perovskite coverage play important roles.

Improved performance of dye-sensitized solar cell based on TiO2 photoanode with FTO glass and film both treated by TiCl4

The dye-sensitized solar cell (DSSC) based on TiO2 photoanode with FTO glass and TiO2 film co-treated by TiCl4 were fabricated. The effects of TiCl4 treatment on the photovoltaic performance of the DSSCs were investigated. TiCl4 treatment of the FTO glass resulted in the formation of a compact TiO2 thin layer on its surface, which could increase the electron collection efficiency. Meanwhile, TiCl4 treatment of the TiO2 film could fill gaps between nanoparticles in the TiO2 film, leading to better electron transfer. These advantages make the DSSC exhibit a highest conversion efficiency of 3.34% under a simulated solar irradiation with an intensity of 100mW/cm2 (1sun), increased by 38% compared with that of the untreated DSSC.

Low-Temperature TiOx Compact Layer for Planar Heterojunction Perovskite Solar Cells.

Here, we demonstrate an effective low-temperature approach to fabricate a uniform and pinhole-free compact TiO2 layer for enhancing photovoltaic performance of perovskite solar cells. TiCl4 was used to modify TiO2 for efficient charge generation and significantly reduced recombination loss. We found that a TiO2 layer with an appropriate TiCl4 treatment possesses a smooth surface with full coverage of the conductive electrode. Further studies on charge carrier dynamics confirmed that the TiCl4 treatment improves the contact of the TiO2/perovskite interface, facilitating charge extraction and suppressing charge recombination. On the basis of the treatment, we improved the open circuit voltage from 1.01 V of the reference cell to 1.08 V, and achieved a power conversion efficiency of 16.4%.

SnO2–TiO2 hybrid nanofibers for efficient dye-sensitized solar cells

Pristine SnO2 nanostructures typically result in low open circuit voltage (VOC) <500mV due to the lower Fermi energy (EF) when employed as a photoanode materials in dye sensitized solar cells (DSSCs). On the other hand, the most successful photoanode material, i.e., TiO2 nanoparticle although provides a high VOC⩾800mV result in poor charge collection owing to their inferior electron mobility (μn). Herein, we employ nanofiber–nanoparticle composite of SnO2–TiO2 which showed similar VOC and short circuit current density (JSC) to a reference TiO2 based DSSCs. The nanocomposite developed here involves multi-porous SnO2 nanofibers characterized by a lower EF; however, with higher μn and TiO2 nanoparticles of higher EF and lower μn. The TiO2 particles in the pores of SnO2 nanofibers were developed by TiCl4 treatment, whose concentration is optimized for the saturated JSC and VOC. The best performing DSSCs fabricated using the composite electrodes deliver power conversion efficiency (PCE) of ≈7.9% (VOC≈717mV; JSC≈21mAcm−2), which is significantly higher than pure SnO2 photoanode with PCE≈3.0% (JSC≈14.0mAcm−2 and VOC≈481mV) at similar experimental conditions.

Enhanced photovoltaic properties in dye sensitized solar cells by surface treatment of SnO2 photoanodes.

We report the fabrication and testing of dye sensitized solar cells (DSSC) based on tin oxide (SnO2) particles of average size ~20 nm. Fluorine-doped tin oxide (FTO) conducting glass substrates were treated with TiOx or TiCl4 precursor solutions to create a blocking layer before tape casting the SnO2 mesoporous anode. In addition, SnO2 photoelectrodes were treated with the same precursor solutions to deposit a TiO2 passivating layer covering the SnO2 particles. We found that the modification enhances the short circuit current, open-circuit voltage and fill factor, leading to nearly 2-fold increase in power conversion efficiency, from 1.48% without any treatment, to 2.85% achieved with TiCl4 treatment. The superior photovoltaic performance of the DSSCs assembled with modified photoanode is attributed to enhanced electron lifetime and suppression of electron recombination to the electrolyte, as confirmed by electrochemical impedance spectroscopy (EIS) carried out under dark condition. These results indicate that modification of the FTO and SnO2 anode by titania can play a major role in maximizing the photo conversion efficiency.