Band Structure Of TiO2 Research Articles

Biotemplated Fe/La-co-doped TiO2 for photocatalytic depth treatment of compressed leachate from refuse transfer station.

Compressed leachate is a contaminated liquid containing various organic and inorganic pollutants produced in municipal refuse transfer stations, which pollute soil and groundwater, posing serious risks to the environment and human health. The Environmental Technology Co., Ltd. (Shenzhen, Guangdong Province, South China) treated compressed leachate obtained from a refuse transfer station. The chemical oxygen demand (COD) (641.2mg/L) of treated compressed leachate did not meet the wastewater quality standards in China for discharge into municipal sewers (COD ≤ 500mg/L) and the company's design discharge requirements (COD ≤ 400mg/L). Therefore, their further in-depth treatment is necessary. To this end, waste tobacco leaves were used as the biotemplate herein, and Fe/La-co-doped TiO2 (xFe,yLa)-TTiO2(g) was synthesized using a solvothermal-assisted biotemplating method. The photocatalytic depth treatment of compressed leachate was performed under simulated solar light using the prepared catalysts. After (3Fe,3La)-TTiO2(g) treatment, the COD of the leachate decreased from 641.2 to 280.1mg/L, and the COD removal rate was 1.2, 1.1, and 1.6 times higher than that of pure Fe-doped, La-doped and non-biological template TiO2, respectively. Characterization confirmed that the biological template endowed the catalyst with a unique morphology and high specific surface area. Its rich activity sites are conducive to enhancing the adsorption capacity of pollutants and providing an ideal place for photocatalytic reactions. Co-doping with iron and lanthanum ions altered the band structure of TiO2 and promoted the interconversion of Fe3+/Fe2+ and La3+/La2+ during photocatalysis. First-principles density functional theory simulations demonstrated that co-doping Fe and La in TiO2 created impurity levels that facilitated the transfer of photogenerated electrons. This study provides a new purification pathway for the depth treatment of compressed leachate.

Highly Stable and Reversible Coloration of Oxide Nanoparticles Film by Ultrafast‐CW Laser Induced Band Engineering

AbstractColoration in oxides meets the challenge in achieving high stability and repeatability simultaneously. In this work, reversible coloration of TiO2 nanoparticles (NPs) film is demonstrated by alternate ultrafast (UF) laser and continuous wave (CW) laser irradiation. Under UF laser irradiation, oxygen vacancies are introduced in the TiO2 lattice, which lead to the bandgap reduction (2.73 to 1.50 eV) and surface blackening. The blackened area can achieve high resolution with size down to ≈1.1 µm. This coloration in TiO2 also shows excellent thermal stability that color fading is negligible even after thermal annealing at 700 K for 2 h in air. The generated high temperature by CW irradiation is known to be beneficial for the O2 dissociation on defected TiO2, thus promoting the internal oxygen diffusion to eliminate the vacancies. The energy band structure of TiO2 can be recovered accordingly, and decoloration is achieved. TiO2‐NPs film shows stable microstructures with barely changed optical properties after 12 cycles of coloration–decoloration process. This band engineering‐induced reversible coloration can also be applicable for broad oxides, e.g., ZnO, HfO2, and Ga2O3. Such highly stable and reversible coloration is promising in high‐performance micro/nano‐devices development for color display and optical encryption.

Investigation on the stability, mechanism and electronic properties of rutile TiO2 via first-principle calculations

Through first-principles calculations, the structural stability, electrical properties, and mechanical characteristics of TiO2 in the P42/mcm space group under varying external pressures were explored. The dynamical and elastic stability of TiO2 with P42/mcm space group are evaluated based on calculated results of phonon dispersion curves and elastic constants. Furthermore, the evaluation of the theoretical elastic modulus, derived through the stress-strain method, reveals a notable anisotropic characteristic in the TiO2 structure. In light of the ideal strength values ascertained through a range of strain conditions, coupled with the two-dimensional electron localization function maps pertinent to various pivotal structural models, the fundamental mechanism that dictates the mechanical properties of the TiO2 structure has been pinpointed. Meanwhile, the contributions of oxygen (O) and titanium (Ti) atoms to the conduction and valence bands in the band structure of TiO2 have been systematically analyzed. The results of the research will aid in exploring the inherent mechanical and electrical properties of TiO2 compounds.

Defect engineered N-S codoped TiO2 nanoparticles for photocatalytic and optical limiting applications: Experimental and DFT insights

N-S codoped TiO2 nanoparticles (NPs) were synthesized using a sol–gel cum hydrothermal approach, with ammonium sulfate as the nitrogen and sulfur source compound. The calcination temperature was varied from 500 to 700 °C. The pristine samples exhibited a mixed phase of anatase and brookite, while the doped samples exhibited only the anatase phase, as confirmed by X-ray diffraction (XRD) analysis. Fourier-transform infrared spectroscopy (FTIR) confirmed the presence of N-H vibrations and S-O bidentate complexation with Ti4+ ions. Electron paramagnetic resonance (EPR) revealed the presence of Ti3+ signals, confirming the creation of oxygen defects in the doped samples. The absorption and emission properties of the samples were investigated using ultraviolet–visible (UV–Vis) and photoluminescence (PL) spectroscopy. Vibrating sample magnetometry (VSM) analysis confirms the room-temperature ferromagnetic behavior of the N-S doped TiO2, which was attributed to the presence of oxygen vacancies, as evidenced by the EPR and PL results. The N-S doped TiO2 samples demonstrated superior photocatalytic degradation of Rhodamine B (RhB), Methylene Blue (MB), and Congo Red (CR) dyes under visible light illumination compared to the pristine TiO2. This enhanced performance was attributed to the presence of N and S dopants in TiO2, which create new energy levels within the band structure of TiO2, allowing for efficient absorption of visible light and subsequent generation of reactive species for dye degradation. N-S doping modifies the electronic structure of TiO2, enhancing two-photon absorption (TPA). This increased TPA efficiency suggests promising applications in optical devices, such as laser protection systems and optical limiters. Density Functional Theory (DFT) investigation also confirms that the presence of oxygen vacancies generates energy states below the conduction band. This, in turn, benefits the absorption of more visible light during photocatalytic activities and leads to a notable nonlinear absorption in optical limiting. Overall, the N-S doping strategy significantly improves the photocatalytic and optical limiting performance of TiO2 NPs, making them promising candidates for a wide range of applications.

Deciphering the role of (Er3+/Nd3+) co-doping effect on TiO2 as an improved electron transport layer in perovskite solar cells

Charge injection and transport at the interface of the electron transport layer (ETL) and perovskite interface are crucial for the perovskite solar cell (PSC) device performance. Titanium dioxide (TiO2) is well established as a photoanode in numerous solar energy conversion and storage. The bandgap engineering of TiO2 by Rare-Earth (RE)-doping has become a significant way to improve the optoelectronic device performance. This study demonstrates the improved performance of Rare-Earth doped TiO2 (RETO) photoanode based solar cells under the doping of Er3+, Nd3+ and following codoping of the (Er3+/Nd3+) effect. It is note that the Er, and Nd dopants are responsible for producing Ti3+ states and the oxygen vacancies near the surface, which drives the charge transportation much more effectively. With the (Er/Nd) codoping into TiO2, the band structure of TiO2 is modified better to make a quasi-Ohmic contact with the perovskites, by fermi level shifting as well changes in the conduction band minima (ECBM) energy states. This results evidence the preliminary conformation for the improvement of Jsc and Voc. Furthermore, the photoluminescence (PL) emission quenching effects of perovskite-deposited RETO attributes the suppression in the charge recombination. By insight into all these favourable results in the(Er3+/Nd3+) codoped TiO2, the RETO photoanode-based perovskite solar cell (PSC) devices were constructed and exhibited improved photovoltaic properties. The composition of (Er0.002Nd0.002Ti0.996O2) ETL employed PSC reported with a better photoconversion efficiency (PCE %) among all the compositions.

Bio-inspired V-TiO2 architectures with regulable surface ultrastructure for visible-light photocatalytic selective oxidation of cyclohexane

Photocatalytic selective oxidation of cyclohexane is more energy saving and sustainable when compared with traditional thermal catalysis, but highly effective visible-light photocatalyst for this reaction remains challenging. Herein, vanadium-doped TiO2 was prepared by using a solvent-thermal-assisted biotemplating method, while glycerol was used to regulate the surface ultrastructure of the catalyst. It is found that the use of the biotemplate, regulation of the surface ultrastructure of the catalyst by glycerol, as well as vanadium doping are all beneficial to improve the performance of the photocatalyst. Resultantly, the biotemplated TiO2 doped with 2 % vanadium, which has a needle-like surface ultrastructure (2 %V-CTiO2(g)) achieves the best performance for cyclohexane conversion (0.98 %), which is 7.0, 8.9 and 49 times higher than TiO2 sample without vanadium doping, surface ultrastructure adjustment and biotemplating, respectively. Characterizations and DFT calculations confirm that biotemplating and the use of glycerol endow the sample with unique morphology, oxygen vacancies and high surface area. Doping of vanadium not only changes the band structure of TiO2 but also introduces the interconversion of V4+ and V5+ into the photocatalytic process. This work offers a new approach to the green conversion of cyclohexane.

Enhanced photocatalytic detoxication properties of OVs-rich Pd/N–TiO2 heterojunctions: excellent charge separation and mechanism insight

Improving the separation efficiency of photoinduced carriers and light absorption range is a crucial target to improve the photocatalytic properties of wide-band semiconductor photocatalysts. In this work, OVs-rich Pd/N–TiO2 was prepared by a sol-gel method. The results display that N doping and construction of OVs can meliorate the energy band structure of TiO2 based on the various characterizations. The surface plasmon resonance (SPR) effect of Pd0 particles, N doping and introduction of abundant OVs play a synergistic role, which elevates the separation efficiency of photoinduced charge pairs effectually and further enhances the photocatalytic properties of the catalysts. The Density Functional Theory (DFT) calculations solidly support that the construction of Schottky heterojunctions and the transfer of electrons from N–TiO2 to Pd0 particles, enabling efficient separation of photoinduced e−/h+ pairs. The strengthened photocatalytic performance of the optimized TiO2 can be contributed to the enhanced visible light absorption and the effective separation and migration of photogenerated carriers of catalysts. The results of photocatalytic degradation of two typical contaminants (phenol and RhB) reveal that OVs-rich Pd/N–TiO2 samples show superior activity than the reference N–TiO2. This work highlights a simple and effective method that can be used to prepare TiO2 composites with excellent photocatalytic properties.

Band Structure Engineering of Single Pt Atoms on Fe-TiO2 for Enhanced Photocatalytic Performance.

Single atomic site catalysts display the maximal atom-utilization efficiency, unique structural properties, and remarkable enhancements on catalytic activity. Herein, single Pt atoms loaded Fe-TiO2 catalysts were prepared. Fe3+ doping leads to the formation of oxygen vacancies and improve the interaction between TiO2 and Pt. Single Pt atoms are thus anchored and effectively modify the local energy band structure of TiO2 . The optimized local band structures improve the intrinsic photoexcitation of Pt/Fe-TiO2 , promote the separation of photogenerated carriers, and extend the lifetime of photogenerated carriers. Meanwhile, the electrons transfer from the excited dyes to the conduction band edge of Pt/Fe-TiO2 is also facilitated due to the shift-down of the conduction band edge. Therefore, with the increase of the Pt content (till up to 0.6 wt%), the photocatalytic performance of Pt/ Fe-TiO2 with the confined single Pt atoms is significantly boosted in either the intrinsic or the sensitized photocatalytic process.

Colloidal Cu-doped TiO2 nanocrystals containing oxygen vacancies for highly-efficient photocatalytic degradation of benzene and antibacterial

Development of suitable colloidal photocatalysts with excellent photocatalytic performance under visible light is essential for indoor environmental remediation. In this study, colloidal Cu-doped TiO2 (Cu-TiO2) nanocrystals containing oxygen vacancies (OVs) were synthesized by a facile sol-hydrothermal method and their photocatalytic performances for benzene degradation and antibacterial were investigated. Characterization results revealed that the doping of Cu induced grain size reduction and bandgap narrowing of TiO2 nanocrystals, as well as the formation of abundant OVs in the TiO2 crystal structure, resulting in enhanced light absorption capacity and charge carrier separation efficiency. The optimized colloidal Cu-TiO2 nanocrystals could achieve a maximum degradation rate constant of 0.364 h−1 for the photocatalytic degradation of benzene and a high antibacterial rate of more than 99.99% against both Escherichia coli and Staphylococcus aureus, which were far superior to those of the pristine TiO2. The effects of Cu dopants and OVs on the band structure of TiO2 were revealed by density functional theory (DFT) calculations combined with experimental characterizations, and a possible mechanism for the enhancement of Cu-TiO2 photocatalytic performance was proposed. This work offers a promising method for the synthesis of colloidal TiO2-based nanocrystals with excellent photocatalytic performances for the practical application in indoor environmental remediation.

24.20%-Efficiency MA-Free Perovskite Solar Cells Enabled by Siloxane Derivative Interface Engineering.

Suppressing defects at the interface between the TiO2 electron transport layer (ETL) and perovskite film is critical for high efficiency and stable perovskite solar cells (PSCs). Herein, a siloxane derivative diethylphosphatoethylsilicic acid (PSiOH) is developed to modify the interface of TiO2 ETL/FA0.83 Cs0.17 PbI3 perovskite. Comprehensive characteristics reveal that silicon hydroxyl (SiOH) in PSiOH can reduce surface defects, improve the electrical propertiesand optimize the energy band structure of TiO2 by forming a SiOTi bond, while the phosphate bond (PO) in PSiOH can passivate Pb-related defects on the perovskite bottom surface. Consequently, PSiOH-modified PSCs yield a remarkable power conversation efficiency of 24.20% and improved air, thermal, or illumination stabilities. This study provides insight into passivation defects at the buried interface for efficient and stable PSCs.

Boosting the Photocatalytic Ability of TiO2 Nanosheet Arrays for MicroRNA-155 Photoelectrochemical Biosensing by Titanium Carbide MXene Quantum Dots

The electrodes of two-dimensional (2D) titanium dioxide (TiO2) nanosheet arrays were successfully fabricated for microRNA-155 detection. The (001) highly active crystal face was exposed to catalyze signaling molecules ascorbic acid (AA). Zero-dimensional (0D) titanium carbide quantum dots (Ti3C2Tx QDs) were modified to the electrode as co-catalysts and reduced the recombination rate of the charge carriers. Spectroscopic methods were used to determine the band structure of TiO2 and Ti3C2Tx QDs, showing that a type Ⅱ heterojunction was built between TiO2 and Ti3C2Tx QDs. Benefiting the advantages of materials, the sensing platform achieved excellent detection performance with a wide liner range, from 0.1 pM to 10 nM, and a low limit of detection of 25 fM (S/N = 3).

A facile method for Tauc exponent and corresponding electronic transitions determination in semiconductors directly from UV–Vis spectroscopy data

In this work, a facile method allowing for estimation of the exponent in the Tauc equation directly from the UV–vis spectra is presented. It is based on the Taylor expansion of the logarithmic version of the Tauc equation. The Tauc exponent is calculated from the tangent slope of the absorption data. Knowledge of this coefficient provides information about the optical transition types and is used as an input for the calculations of the band gap. As an exemplar material, TiO2 in form of thin film and nanotubes as well as their nanocomposites with other metal oxides are chosen. For the transparent thin 15 nm film of TiO2, two linear ranges with n = 2.0 and 1.2 are found. The first is assigned to the well-established indirect (allowed) transition. In the case of the second one, the n does not correspond to typically used values. Therefore, it is speculated that more than one transition is probable. This consideration is supported with ab-initio DFT calculations of the band structure of TiO2 with Hubbard U correction. Similar results are found for TiO2 nanotubes using diffuse reflectance spectroscopy indicating that the presented method applies both to transmission and reflection.

Synthesis and Characterization of Manganese-Modified Black TiO2 Nanoparticles and Their Performance Evaluation for the Photodegradation of Phenolic Compounds from Wastewater.

The release of phenolic-contaminated treated palm oil mill effluent (TPOME) poses a severe threat to human and environmental health. In this work, manganese-modified black TiO2 (Mn-B-TiO2) was produced for the photodegradation of high concentrations of total phenolic compounds from TPOME. A modified glycerol-assisted technique was used to synthesize visible-light-sensitive black TiO2 nanoparticles (NPs), which were then calcined at 300 °C for 60 min for conversion to anatase crystalline phase. The black TiO2 was further modified with manganese by utilizing a wet impregnation technique. Visible light absorption, charge carrier separation, and electron–hole pair recombination suppression were all improved when the band structure of TiO2 was tuned by producing Ti3+ defect states. As a result of the enhanced optical and electrical characteristics of black TiO2 NPs, phenolic compounds were removed from TPOME at a rate of 48.17%, which is 2.6 times higher than P25 (18%). When Mn was added to black TiO2 NPs, the Ti ion in the TiO2 lattice was replaced by Mn, causing a large redshift of the optical absorption edges and enhanced photodegradation of phenolic compounds from TPOME. The photodegradation efficiency of phenolic compounds by Mn-B-TiO2 improved to 60.12% from 48.17% at 0.3 wt% Mn doping concentration. The removal efficiency of phenolic compounds from TPOME diminished when Mn doping exceeded the optimum threshold (0.3 wt%). According to the findings, Mn-modified black TiO2 NPs are the most effective, as they combine the advantages of both black TiO2 and Mn doping.

Rare-Earth-Modified Titania Nanoparticles: Molecular Insight into Synthesis and Photochemical Properties.

A molecular precursor approach to titania (anatase) nanopowders modified with different amounts of rare-earth elements (REEs: Eu, Sm, and Y) was developed using the interaction of REE nitrates with titanium alkoxides by a two-step solvothermal–combustion method. The nature of an emerging intermetallic intermediate was revealed unexpectedly for the applied conditions via a single-crystal study of the isolated bimetallic isopropoxide nitrate complex [Ti2Y(iPrO)9(NO3)2], a nonoxo-substituted compound. Powders of the final reaction products were characterized by powder X-ray diffraction, scanning electron microscopy–energy-dispersive spectroscopy, Fourier transform infrared, X-ray photoelectron spectroscopy, Raman spectroscopy, and photoluminescence (PL). The addition of REEs stabilized the anatase phase up to ca. 700 °C before phase transformation into rutile became evident. The photocatalytic activity of titania modified with Eu3+ and Sm3+ was compared with that of Degussa P25 titania as the control. PL studies indicated the incorporation of Eu and Sm cations into titania (anatase) at lower annealing temperatures (500 °C), but an exclusion to the surface occurred when the annealing temperature was increased to 700 °C. The efficiency of the modified titania was inferior to the control titania while illuminated within narrow wavelength intervals (445–465 and 510–530 nm), but when subjected to a wide range of visible radiation, the Eu3+- and Sm3+-modified titania outperformed the control, which was attributed both to doping of the band structure of TiO2 with additional energy levels and to the surface chemistry of the REE-modified titania.

In-situ formation of carboxylate species on TiO2 nanosheets for enhanced visible-light photocatalytic performance

It still remains challenge for expanding the photo-response range of TiO2 with dominant {0 0 1} facets due to the hardly achieving modification of the electronic structure without destroying the formation of TiO2 high energy facets. Herein, we report the construction of carboxylate species modified TiO2 nanosheets with dominant {0 0 1} facets by employing ethanol as a carbon source through a low-temperature (300 °C) carbonization method. The as-obtained samples were investigated in detail by using various characterization techniques. The results indicate that the carboxylate species derived from the oxidation and carbonization of ethanol are coordinated to the {0 0 1} facets in a bidentate bridging mode. The electron-withdrawing carboxylate species induce TiO2 to form a lower valence band edge and a narrower bandgap, which enhances the oxidation ability of photogenerated holes and expands the photo-response range. The partially carbonized carboxylate species can also act as a photosensitizer to induce visible-light photocatalytic activity of TiO2 nanosheets. In addition, the carboxylate species can further promote the separation of photogenerated charge carriers. The findings of this work may provide a new perspective for tuning the band structure of TiO2 with dominant {0 0 1} facets and improving its photocatalytic performance.

Nitrogen doping of TiO2 and annealing treatment of photoanode for enhanced solar cell performance

Mild doping of nitrogen (N) in TiO2 followed by an optimized aerial annealing treatment of CdS quantum dot (QD) sensitized photoanode resulted in efficient electron transfer and low recombination rates for the corresponding quantum dot solar cell (QDSC). Nitrogen doping passivates the surface defects in TiO2, reduces the density of recombination centers, and promotes electron injection into the current collector. N-doping also modifies the electronic band structure of TiO2 and reduces the band gap from 3.17 to 2.91 eV. Therefore in the QDSC with the N-TiO2/CdS photoanode, both N-TiO2 and CdS, undergo charge separation upon illumination thereby producing a higher photocurrent compared to the undoped-TiO2/CdS based QDSC. N-doping also increased the redox activity of TiO2, allowing facile ion and electron transport across its cross-section which is advantageous for solar cell performance. Optimal annealing temperature of 150 °C for the N-TiO2/CdS or TiO2/CdS photoanode restricted the back electron movement effectively, and imparted a significantly enhanced power conversion efficiency (PCE) to the N-TiO2/[email protected] °C/polysulfide gel/C-fabric- solar cell, greater by 55% compared to its unannealed counterpart. Lowered average excited electron lifetime, increased-incident photon-to-current conversion efficiency, recombination resistance and photovoltage decay response time, confirm the ability of the annealed photoanodes to undergo enhanced charge separation contrasting with the unannealed photoanode. This first time study relies on two simple approaches of nitrogen doping and annealing treatment to achieve considerably improved photovoltaic parameters, and opens up realistic possibilities for commercialization of QDSCs.

Step-wise transitions of electrons between valence and conduction bands: a tri-doped TiO2 approach

The unwanted structural changes and isolated unoccupied states in the band structure of TiO2 due to doping could be minimized by proper selection of dopants. A good combination of dopants would improve the optical response in visible regime and remove the isolated states from the band gap while keeping minimum structural distortion. Enhanced visible light absorption and effective utilization of photo-generated carriers would improve the photoactivity of TiO2 under solar irradiations. Mono-doped, co-doped and tri-doped models of molybdenum (Mo), carbon (c), and nitrogen (N) are developed in the structure of anatase TiO2 and the corresponding change in the geometrical structure, band structure, and optical response is noted. The Mo and C co-doping produced least structure modification when compared to a reference TiO2 system. The Mo 3d states are mixed with Ti 3d states reducing the band gap of Mo-doped TiO2. While shifting the Fermi level to the middle of the band gap, the C 2p states are introduced around the middle of the gap of C doped TiO2. The impurity states are occupied and maximum reduction in the band gap is found in Mo, C codoped TiO2. The addition of N in the Mo, C codoped TiO2 modified the band structure by creating isolated states in the band gap. The photo-response of Mo, C, N tri-doped TiO2 is prominent among the simulated models attributed to the step wise transition of electrons by the C 2p and N 2p states. The improved optical response allows more visible photons for absorptions but the isolated states may annihilate it. The Mo, C codoped system provided minimum structure changes with clear band structure and reasonable visible light absorption.

Modulating the photo-active anatase TiO2 by cationic co-dopants: A case of iron and lanthanum

The electronic band structure of TiO2 could be modulated by dopants to harvest the major part of the solar spectrum. A cationic pair of dopant comprising of iron and lanthanum is studied in the lattice of anatase TiO2 and modifications in the geometrical structure, band structure and optical response are observed. Ferrum and lanthanum doping reduced the band gap of TiO2 along with inducing visible light absorption. Isolated states due to Fe are created above top of the valence band in Fe@TiO2. In case of La@TiO2, the La states successfully mixed with the valence and conduction band reducing the band gap. Substitutional La at Ti site in Fe@TiO2 changed the nature of Fe 3d in the band structure and strongly contributed to the narrowing of band gap. The Fe and La co-doped TiO2 possess reduced band gap with superior optical response in the visible regime. The Fe and La as cationic pair of dopant synergistically stabilize the system with the improved optical response explaining the experimental observation of enhanced photoactivity.

Fabrication of biomaterial/TiO2 composite photocatalysts for the selective removal of trace environmental pollutants

Abstract Trace environmental pollutants have become a serious problem with special attention on the hazardous heavy metals, refractory organics, and pathogenic microorganisms. With coupling biosorption and photocatalysis to develop biomaterial/TiO2 composite photocatalysts is a promising method to remove these trace pollutants because of the synergistic effect. Biomaterials provide multiple function groups which can selectively and efficiently enrich trace pollutants onto the surface of the photocatalysts, thus facilitating the following transformation mediated by TiO2 photocatalysis. Biomaterials can also help the dispersion and recovery of TiO2, or even modify the band structure of TiO2. The fabrication of chitosan/TiO2, cellulose/TiO2, as well as other biomaterial/TiO2 composite photocatalysts is discussed in detail in this review. The application significance of these composite photocatalysts for the selective removal of trace pollutants is also addressed. Several problems should be solved before the realistic applications can be achieved as discussed in the final section.

Resolving Hysteresis in Perovskite Solar Cells with Rapid Flame‐Processed Cobalt‐Doped TiO2

AbstractTo further increase the open‐circuit voltage (V oc) of perovskite solar cells (PSCs), many efforts have been devoted to doping the TiO2 electron transport/selective layers by using metal dopants with higher electronegativity than Ti. However, those dopants can introduce undesired charge traps that hinder charge transport through TiO2, so the improvement in the V oc is often accompanied by an undesired photocurrent density–voltage (J–V) hysteresis problem. Herein, it is demonstrated that the use of a rapid flame doping process (40 s) to introduce cobalt dopant into TiO2 not only solves the J–V hysteresis problem but also increases the V oc and power conversion efficiency of both mesoscopic and planar PSCs. The reasons for the simultaneous improvements are two fold. First, the flame‐doped Co‐TiO2 film forms Co‐Ov (cobalt dopant‐oxygen vacancy) pairs and hence reduces the number density of Ti3+ trap states. Second, Co doping upshifts the band structure of TiO2, facilitating efficient charge extraction. As a result, for planar PSCs, the flame doping of Co increases the efficiency from 17.1% to 18.0% while reducing the hysteresis from 16.0% to 1.7%. Similarly, for mesoscopic PSCs, the flame doping of Co increases the efficiency from 18.5% to 20.0% while reducing the hysteresis from 7.0% to 0.1%.