Compact TiO2 Research Articles

Dual‐Design of Nanoporous to Compact Interface via Atomic/Molecular Layer Deposition Enabling a Long‐Life Silicon Anode

AbstractThe rapid and reversible lithiation/delithiation of silicon materials remains a challenging yet marvelous goal. Herein, harnessing the “nanoporous to compact” gradient design, a dual‐film consisting of flexible porous zincone and rigid compact TiO2 (zincone/TiO2) is controllably deposited onto a silicon electrode using molecular layer deposition and atomic layer deposition techniques. This dual‐film can tailor the stress and ionic diffusion kinetics for silicon anodes. That is, the elastic zincone acts as a buffer layer to dissipate inner stress through the deformation of pores, while the rigid TiO2 (≈5 nm) provides silicon particles a satisfying mechanical strength and protects the silicon from engulfing by the solid electrolyte interphase. The density functional theory and galvanostatic intermittent titration technique results indicate the fast Li+ diffusion kinetics in Si@zincone/TiO2 electrode, resulting in a high initial Coulombic efficiency of 81.9% and an advantageous rate capability of 1224 mAh g−1 at 4 A g−1. More importantly, a low capacity‐fading rate of only 0.051% per cycle can be achieved (discharge capacity of 753 mAh g−1 after 1000 cycles). Additionally, fractal theory verifies the Si@zincone/TiO2 undergoes gentle reversible evolutions during cycling with a box fractal dimension (DB) of 1.73.

TiO2 thin films derived by facile sol-gel method: Influence of spin rate and Al-doping on the optical and electronic properties

Titanium dioxide (TiO2) thin films with enhanced properties have been synthesized by sol-gel method and they can be used for various applications as in field-effect transistors (FETs), sensors, photovoltaics etc. The properties of TiO2 thin films were optimized by changing spin speed (1000 and 3000 rpm) and doping Al in the TiO2 lattice. The influence of spin speed and Al doping on the grain orientation and surface morphology of titania were studied using x-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), and transmission electron microscopy (TEM). Uniform, smooth and compact TiO2 thin films having tetragonal anatase phase and a band gap of 3.54 eV along with an optimum thickness and high dielectric constant of ~28 were obtained at a spin speed of 3000 rpm. These films have been previously reported as a gate dielectric layer in the fabrication of flexible ZnO:Al thin film transistor with a mobility of 4.96 cm2/Vs, therefore, the samples prepared at different spin speed could be useful for the fabrication of organic and inorganic FETs. Detailed study was performed on Al-doped TiO2 thin films. XRD and various vibrational modes noticed in the Raman spectra confirmed the formation of crystalline TiO2 films with a pure anatase tetragonal phase. A systematic shift in (101) plane in XRD and E1 g mode in Raman spectra confirms the substitutional doping of Al in the TiO2 matrix. A red shift in the band gap energy with increased transmittance in visible region was observed for the Al-doped TiO2 samples. The higher value of Urbach energy for the Al-doped samples reveals the presence of defects related to oxygen which were further studied by the photoluminescence spectra (PL). AFM images revealed compact, void free and uniform deposition of both TiO2 and TiO2: Al films. The particle size was found to be in the range of 30–40 nm and 40–100 nm for TiO2 and TiO2: Al, respectively. Enhanced electrical conductivity was observed for the Al-doped TiO2 thin films. The current Al-doped TiO2 system with enhanced optical, morphological and electrical properties could be a potential candidate in optoelectronic, sensing and photovoltaics applications.

Near-Surface Composition, Structure, and Energetics of TiO2 Thin Films: Characterization of Stress-Induced Defect States in Oxides Prepared via Chemical Vapor Deposition versus Solution Deposition from Sol–Gel Precursors

We present here a comprehensive comparison of near-surface composition, structure, and energetics of compact ultrathin TiO2 thin films deposited by two approaches: (i) chemical vapor deposition (CV...

Zr-Doped TiO2 Electron Transport Layer for Reduced Hysteresis and Highly Efficient Perovskite Solar Cells

Zr-doped TiO2 electron transport layer for reduced hysteresis and highly efficient perovskite solar cells Chirag Saharan, Pawan S Rana* Department of Physics, Deenbandhu Chhotu Ram University of Science and Technology, Murthal, Sonepat, India, 131039 drpawansrana.phy@dcrustm.orgLarge number of defects in compact TiO2 (c-TiO2) layer hinders the power conversion efficiency (PCE) of hybrid perovskite solar cells (PSCs). Metal doping in c-TiO2 layer has been recognized as a successful approach for boosting the PCE of PSCs. In this work, different amount of Zr is added in c-TiO2 layer and its impact on the photovoltaic properties of methylammonium lead iodide (MAPbI3)-based PSCs is studied. Incorporation of Zr enhanced the charge carrier collection at TiO2/perovskite interface as well as conductivity of TiO2 layer. It is observed that Zr-doping has reduced the dark current significantly by suppressing the leakage path. Consequently, the PSCs with optimal Zr-doping (10 vol%) displays open-circuit voltage (V OC) of 1.076 V, short-circuit current density (J SC) of 23.57 mA cm-2, and PCE of 18.16% under one-sun illumination. From our fundamental study, we confirm that Zr doping in TiO2 is highly beneficial to reduce the hysteresis index (HI) as low as 6.8% in comparison to pristine TiO2 with large HI of 17.9% and it reduces the trap-state density as well as non-geminated recombination losses. Together, our findings will pave the way for engineering the energy level of electron transport layer and fabrication of highly efficient PSCs. Key Words: Hybrid perovskite solar cells; Zr-doping; band alignment, trap-state density, non-geminated recombination losses

Controlled Growth of Porous InBr3: PbBr2 Film for Preparation of CsPbBr3 in Carbon-Based Planar Perovskite Solar Cells.

Due to the low solubility of CsBr in organic solvents, the CsPbBr3 film prepared by the multi-step method has holes and insufficient thickness, and the light absorption capacity and current density of the perovskite film hinder the further improvement in the power conversion efficiency (PCE) of CsPbBr3 solar cells. In this study, we introduced InBr3 into the PbBr2 precursor solution and adjusted the concentration of PbBr2, successfully prepared PbBr2 with a porous structure on the compact TiO2 (c-TiO2) substrate to ensure that it fully reacted with CsBr, and obtained the planar carbon-based CsPbBr3 solar cells with high-quality perovskite film. The results reveal that the porous PbBr2 structure and the increasing PbBr2 concentration are beneficial to increase the thickness of the CsPbBr3 films, optimize the surface morphology, and significantly enhance the light absorption capacity. Finally, the PCE of the CsPbBr3 solar cells obtained after conditions optimization was 5.76%.

Modification of compact TiO2 layer by TiCl4-TiCl3 mixture treatment and construction of high-efficiency carbon-based CsPbI2Br perovskite solar cells

In the construction of high performance planar perovskite solar cells (PSCs), the modification of compact TiO2 layer and engineering of perovskite/TiO2 interfaces are essential for efficient electron transfer and retarded charge recombination loss. In this work, a facile and effective strategy is developed to modify the surface of compact TiO2 layer by TiCl4-TiCl3 mixture treatment. Compared with conventional sole TiCl4, the TiCl4-TiCl3 treatment takes the advantage of accelerated and controlled hydrolysis of TiCl3, therefore TiO2 with dominating anatase phase and moderate roughness is obtained to facilitate the growth of CsPbI2Br perovskite layer with high quality. Furthermore, the oxidation-driven hydrolysis of TiCl3 component results in surface Cl doping that facilitates interfacial electron transfer with retarded recombination loss. The average power conversion efficiency (PCE) of carbon-based CsPbI2Br planar PSCs based on TiCl4-TiCl3 treatment increases to 14.18% from the intial 13.04% based on conventional sole TiCl4 treatment. The champion PSC exhibits a PCE of 14.46% (Voc = 1.28 V, Jsc = 14.21 mA/cm2, and FF = 0.794), which is one of the highest PCEs for carbon-based CsPbI2Br PSCs.

In situ growth of TiO2 nanoparticles onto PBO fibers via a mussel‐inspired strategy for enhancing interfacial properties and ultraviolet resistance

AbstractIn this work, to overcome the poor interfacial adhesion and ultraviolet (UV) resistance of poly(p‐phenylene benzobisoxazole) (PBO) fiber simultaneously, a new hierarchical reinforcement was fabricated by in situ growing titanium dioxide (TiO2) nanoparticles on the surface of the fiber using mussel‐inspired polydopamine (PDA) as a robust reaction platform. The surface morphologies and chemical compositions of the modified fiber were measured to prove the TiO2 binding. The interfacial shear strength of PBO fiber‐reinforced epoxy resin composite had a 57.2% enhancement after TiO2 modification, which was caused by increased surface roughness (Ra) and wettability. In addition, the thermal stability of the fiber and hygrothermal aging resistance of the composite were improved remarkably. Moreover, the compact TiO2 coating on the surface of PBO/PDA/Ti led to excellent UV resistance.

UV-Shielding TiO2 thin film deposition on flexible and heat-labile substrate using an open-air hybrid CVD/Plasma method

In this work, compact scratch resistant transparent amorphous TiO2 thin films are deposited at low temperature, i.e. as low as 50 °C, by a scalable hybrid method combining atmospheric pressure chemical vapor deposition and plasma treatment in open air. Thin film morphology, chemical composition and scratch resistance properties are investigated. The role of the plasma in the process is investigated through comparison with coatings deposited without plasma ignition. The versatile method enables film deposition on polymer film and shows good UV protection. This method, operating in open air shows promising results for the simple, large scale deposition of low carbon containing transparent TiO2 coatings at low temperature.

Robust Protection of III-V Nanowires in Water Splitting by a Thin Compact TiO2 Layer.

Narrow-band-gap III–V semiconductor nanowires (NWs) with a suitable band structure and strong light-trapping ability are ideal for high-efficiency low-cost solar water-splitting systems. However, due to their nanoscale dimension, they suffer more severe corrosion by the electrolyte solution than the thin-film counterparts. Thus, short-term durability is the major obstacle for using these NWs for practical water-splitting applications. Here, we demonstrated for the first time that a thin layer (∼7 nm thick) of compact TiO2 deposited by atomic layer deposition can provide robust protection to III–V NWs. The protected GaAs NWs maintain 91.4% of its photoluminescence intensity after 14 months of storage in ambient atmosphere, which suggests the TiO2 layer is pinhole-free. Working as a photocathode for water splitting, they exhibited a 45% larger photocurrent density compared with unprotected counterparts and a high Faraday efficiency of 91% and can also maintain a record-long highly stable performance among narrow-band-gap III–V NW photoelectrodes; after 67 h photoelectrochemical stability test reaction in a strong acid electrolyte solution (pH = 1), they show no apparent indication of corrosion, which is in stark contrast to the unprotected NWs that fully failed after 35 h. These findings provide an effective way to enhance both stability and performance of III–V NW-based photoelectrodes, which are highly important for practical applications in solar-energy-based water-splitting systems.

The Influence of the Thickness of Compact TiO2 Electron Transport Layer on the Performance of Planar CH3NH3PbI3 Perovskite Solar Cells.

In recent years, lead halide perovskites have attracted considerable attention from the scientific community due to their exceptional properties and fast-growing enhancement for solar energy harvesting efficiency. One of the fundamental aspects of the architecture of perovskite-based solar cells (PSCs) is the electron transport layer (ETL), which also acts as a barrier for holes. In this work, the influence of compact TiO2 ETL on the performance of planar heterojunction solar cells based on CH3NH3PbI3 perovskite was investigated. ETLs were deposited on fluorine-doped tin oxide (FTO) substrates from a titanium diisopropoxide bis(acetylacetonate) precursor solution using the spin-coating method with changing precursor concentration and centrifugation speed. It was found that the thickness and continuity of ETLs, investigated between 0 and 124 nm, strongly affect the photovoltaic performance of PSCs, in particular short-circuit current density (JSC). Optical and topographic properties of the compact TiO2 layers were investigated as well.

Low cost copper zinc tin sulphide (CZTS) solar cells fabricated by sulphurizing sol-gel deposited precursor using 1,2-ethanedithiol (EDT)

In this paper, we report the preparation of crystalline CZTS thin films by sol–gel method followed by sulphurization using 1,2- Ethanedithiol (EDT) at 400 °C in a three zone horizontal tubular reactor equipped with computer controlled vacuum system. These films were characterized by XRD, Raman, Hall measurements and UV–Vis-NIR spectroscopy. XRD and Raman studies confirmed highly crystalline and single phase CZTS. Hall study revealed p-type semiconducting CZTS film having charge carriers density of 1.70 × 1018 cm−3 and the resistivity (ρ) of the order of 5.00 × 10−1Ω-cm. It was found that the direct band gap of 1.44 eV for CZTS film was seen from optical study. Further, double metal oxide layers having slightly different band gap were used to form a p-n junction with CZTS film. Cadmium-free solar cells with structure ITO/ZnO/CZTS/Ag (cell-1) and ITO/ZnO/com-TiO2/CZTS/Ag (cell-2) were fabricated. Electrochemical Impedance Spectroscopy (EIS) measurements were performed in the low frequency range with applied bias of 0.1 Volt for the devices. The EIS studies showed that the solar cell with ultrathin compact TiO2 layer provide a favorable path for the efficient charge transport process at the interface. The external quantum efficiency measured at 520 nm was found to be 62.5%. Cell-2 exhibited improved photovoltaic parameters with short circuit current density (Jsc) of 4.721 mA/cm2, fill factor of 0.46 and open circuit voltage (Voc) of 400 mV. The short circuit current density and fill factor of double metal oxide layers (cell-2) were increased by 78% and 46%, respectively, as compared to single metal oxide layer (cell-1).

Modeling and performance analysis of dye-sensitized solar cell based on ZnO compact layer and TiO2 photoanode

Renewable energy, especially solar energy is a vital alternative solution to power challenge in these present times. More recently, dye-sensitized solar cells (DSSC) play an important role in solar power generation. The performance of DSSC can be increased by adding more cells to a cell stack in a Tandem cell with a separate band gap. A double-layer structured DSSC was analyzed in this study in which ZnO and TiO2 composite photo-anodes were prepared on Fluorine-doped tin oxide. Photovoltaic properties such as current–voltage (I-V) and photocurrent density–voltage curves were investigated for different thickness, absorption coefficients, and wavelengths. DSSC solar cell characterization technique such as I-V measurement was analyzed to evaluate the cells performance. The experimental results show an approximate increase in current of 0.02 A causing the I-V characteristics to change significantly when ZnO and TiO2 are combined. In addition, it was observed that as the J-V characteristics of TiO2 varies with electrode thickness, the current densityJscincreases simultaneously and reaches its peak point at 10 μm.

Mesoporous TiO2 electron transport layer engineering for efficient inorganic-organic hybrid perovskite solar cells using hydrochloric acid treatment

We demonstrated effects of wet chemical processes using hydrochloric on crystallite structures, optical and electronic properties, and surface morphology of TiO2 thin films and enhancement in photovoltaic performance of perovskite solar cell using HCl-treated mesoporous TiO2 electron transport layers (ETLs). By treating mesoporous TiO2 thin films with HCl, hydroxyl groups on the surface were chemically neutralized and the film porosity was enhanced. Furthermore, the crystallite structure analyses indicated that CH3NH3PbI3 perovskite thin films deposited on the HCl-treated compact and mesoporous TiO2 ETLs possessed the relatively high crystallization along with avoiding formation of unexpected PbI2 crystals. As a result, the best power conversion efficiencies of devices using the HCl-treated mesoporous TiO2 ETLs were improved to 18.4% under forward bias scans.

Constructing CdS-Based Electron Transporting Layers With Efficient Electron Extraction for Perovskite Solar Cells

The electron transporting layer (ETL) is a critical component in perovskite solar cells (PSCs) and plays an important role in extracting and transporting electrons. However, the commonly used wide-bandgap metal oxides (TiO2, ZnO, SnO2, etc.) often involve undesirable photocatalytic activity towards perovskite materials under UV light, which would undermine the long-term stability of PSCs. In this article, nonoxide CdS ultra-thin films were deposited onto conducting substrates through chemical bath deposition to serve as ETLs. It is revealed that the subsequent CdCl2 treatment followed by annealing is not essential to CdS ETLs for PSCs; this fact is quite different from the scenario demonstrated for conventional thin-film solar cells. Moreover, a compact TiO2 (c-TiO2) blocking layer was introduced between the conducting substrate and the CdS layer to further enhance the electron extraction capability of ETLs and boost the photovoltaic performance of PSCs. Through careful morphology, optical and electrical characterizations, it is found that the presence of the c-TiO2 underlayer avoids the partially exposure of substrate bumps, enlarges the subsequently deposited perovskite crystals, forms cascade energy level alignments, and accelerates the electron extraction from perovskite to ETLs. Therefore, the shunt current leakage and the charge recombination at the ETL/perovskite interface are significantly suppressed. Eventually, the CH3NH3PbI3 PSC based on the bilayer c-TiO2/CdS ETL yields a promising power conversion efficiency of 15.11%, which is much higher than that of the single-layer CdS-based device. This work delivers one of the few CdS ETL-based PSCs that exhibit efficiencies over 15%.

Synergistic Effect of RbBr Interface Modification on Highly Efficient and Stable Perovskite Solar Cells.

Compact TiO2 films are one of the most widely used electron transport layers (ETLs) in planar perovskite solar cells (PSCs). However, the performance of the PSC device is controlled by the comprehensive qualities of the functional layers and their bilateral surfaces. In this work, the alkali metal halide of RbBr as the interfacial modifier is introduced into the interface of the TiO2 ETL and perovskite absorber. By spin-coating the proper content of RbBr, the surface of the TiO2 film consisting of smooth morphology and low density of oxygen-deficiency defect is readily obtained. The perovskite layer successively fabricated on the RbBr-modified TiO2 film demonstrates large grain size, low surface roughness, and low bulk defect density, which enhances the electron extraction and decreases nonradiation recombination. By virtue of the modulation of the perovskite crystal quality and the passivation of the interfacial defects, the light-harvesting efficiency of the corresponding device is increased to 21.15 from 19.21% for the PSC without a RbBr insertion layer. More importantly, the passivation strategy enables impressive device stability by retaining 90% of its initial efficiency in an ambient environment for 500 h. This study provides a promising and feasible strategy to regulate surface passivation engineering and simultaneously facilitate the perovskite crystal growth for the achievement of efficient and stable perovskite photovoltaics.

Influence of Nb addition on the oxidation behavior of novel Ni-base superalloy

Influence of Nb on oxidation behavior of novel Ni-base superalloy was investigated in detail at 1000 °C. Although alloy with 2 wt%Nb (2Nb) exhibits significantly higher weight gain than alloy without Nb (0Nb), oxide scale of 2Nb was more continuous and compact. In contrast, 0Nb underwent severe vaporization and spallation in oxide scale. Nb was found to accelerate the formation of compact TiO2 on Cr2O3 layer, leading to inhibited vaporization and spallation in oxide scale. Nb also accelerated the formation of continuous CrTaO4 layer beneath the Cr2O3, enhancing the oxidation resistance via inhibiting the interdiffusion of oxygen, nitrogen and metallic elements.

Preparation of compact TiO2 thin film by artist spray gun-assisted pyrolysis method for lead-free perovskite solar cell

In the present investigation, compact TiO2 thin film was prepared by using an artist spray gun (ASG)-assisted pyrolysis method to use as an electron transport layer (ETL) for perovskite solar cell (PSC). The influence of the distance between the spray gun nozzle and the substrate was studied to get quality TiO2 thin film onto FTO substrate among three different distantly deposited TiO2 thin films. The formation of anatase TiO2 thin film was confirmed by XRD and Raman spectroscopy studies. The bandgap of this thin film was measured by UV–Vis analysis and it was found to be 3.19 eV. The emission spectrum and charge separation of TiO2 thin film were analysed by photoluminescence studies. The emission spectrum of TiO2 thin film exhibited at 380 nm confirmed the indirect transition from the conduction band to the valence band. The FE-SEM image confirmed that the prepared TiO2 thin film was uniformly deposited over the substrate without any pinhole, which shows a good agreement with the Raman mapping analysis. A power conversion efficiency (PCE) of 2.69% has been achieved with Pb-free PSC fabricated from uniformly deposited TiO2 ETL.

Aluminium-doped TiO2 nanotubes with enhanced light-harvesting properties

Titanium dioxide (TiO2) application in light-harvesting processes is hindered by its wide band gap. Strategies such as morphology shifts from nanoparticles to nanotubes and doping of fabricated nanostructures are widely used to address this issue. Combining both approaches, this work successfully synthesizes, for the first time, aluminium-doped TiO2 nanotubes via a single-step anodization method at three distinct potentials (20, 40 and 60 V). SEM images revealed the successful formation of remarkably thin layers of TiO2 nanotubes produced at 40 and 60 V. X-ray diffractograms and Raman spectra suggest the successful insertion of aluminium into the anatase lattice. Diffuse reflectance confirmed the doping process through a marked effect on the absorbance of visible light for the higher voltages, as well as through a reduction in the optical band gap. For utilization purposes, the photoelectrochemical performance of 40 V Al–TiO2 was able to deliver a comparable response to that of a compact TiO2 layer of the same thickness. The current density developed by the 60 V sample was increased by 120% in comparison to the undoped material, despite having an absorbance much lower than that of the latter. Overall, synthesizing an Al-doped TiO2 nanotubular structure has proven to be a great strategy in the development of materials for application in advanced light-harvesting electrodes.

Pulsed laser deposition of thin films of TiO2 for Li-ion batteries

Microbatteries produced by physical deposition methods are expected to play a pivotal role in many different micro-electronic applications such as stand-alone sensors, implantable or wearable medical devices, radio frequency identification-based systems and smart-cards. In this study pulsed laser deposition (PLD) using a femtosecond-pulsed laser has been applied to TiO2 target materials to produce thin films of anatase-based nanoparticles on aluminum substrates suitable for application as negative electrode in Li-ion MBs. Different post-deposition treatments have been evaluated: films morphology and composition have been investigated with a multi-technique approach and the corresponding performance and electrochemical properties in Li-ion MBs have been analyzed by cyclic voltammetry and galvanostatic techniques. Compact and dense TiO2 films composed by nanoparticles were obtained by PLD with co-crystallization of both anatase and rutile phases. Post-deposition annealing at temperature of 500 °C promote the rutile to anatase phase transition. As deposited TiO2 films are electrochemically almost inactive in lithium half cells, whereas post deposition annealing (either in Ar or Air) boosts the electrochemical activity: air annealing outperforms Ar annealing. The additional deposition of a outer carbon layer by PLD on the TiO2 films further improves the Li+ transport properties, the reversibility of the electrochemical intercalation/de-intercalation reaction as well as the battery performance in terms of capacity retention upon cycling and rate response.

Tin Oxide Electron-Selective Layers for Efficient, Stable, and Scalable Perovskite Solar Cells.

Perovskite solar cells (PSCs) have become a promising photovoltaic (PV) technology, where the evolution of the electron-selective layers (ESLs), an integral part of any PV device, has played a distinctive role to their progress. To date, the mesoporous titanium dioxide (TiO2 )/compact TiO2 stack has been among the most used ESLs in state-of-the-art PSCs. However, this material requires high-temperature sintering and may induce hysteresis under operational conditions, raising concerns about its use toward commercialization. Recently, tin oxide (SnO2 ) has emerged as an attractive alternative ESL, thanks to its wide bandgap, high optical transmission, high carrier mobility, suitable band alignment with perovskites, and decent chemical stability. Additionally, its low-temperature processability enables compatibility with temperature-sensitive substrates, and thus flexible devices and tandem solar cells. Here, the notable developments of SnO2 as a perovskite-relevant ESL are reviewed with emphasis placed on the various fabrication methods and interfacial passivation routes toward champion solar cells with high stability. Further, a techno-economic analysis of SnO2 materials for large-scale deployment, together with a processing-toxicology assessment, is presented. Finally, a perspective on how SnO2 materials can be instrumental in successful large-scale module and perovskite-based tandem solar cell manufacturing is provided.