p-i-n heterojunctions with BiFeO3 perovskite nanoparticles and p- and n-type oxides: photovoltaic properties

A MXene-BiFeO3-ZnO nanocomposite photocatalyst served as a high-performance supercapacitor electrode

MXenes have attracted considerable attention in the field of energy storage and conversion due to their high surface area, excellent electrical conductivity, and ability to intercalate various ions. However, simultaneously achieving high capacitance, rate capability, cycling stability, and mechanical flexibility is a significant challenge for designing MXene-based supercapacitors. In this article, we explored MXene-BiFeO3-ZnO nanocomposites for both photocatalytic and electric double-layer supercapacitor applications. While the BiFeO3-ZnO nanohybrid heterostructure improves the charge separation properties in nanocomposite photocatalysts, it was applied as an interlayer spacer between the MXene layers to prevent the stacking effect of electrodes in the supercapacitor. Furthermore, the optimization of MXene content in the nanocomposite was established by photocatalytic studies on methylene blue dye, which revealed a maximum of 98.72% degradation under direct sunlight with superior stability. The electrochemical studies on the best composition material reveal a maximum areal capacitance (Ccv) of 142.8 mF cm-2, an energy density (E) of 1.65 μW h cm-2, and a capacitive retention of 99.98% after 8000 cycles at 7 μA cm-2. Additionally, the flexible solid-state supercapacitor fabricated with the same material demonstrates an areal capacitance of 47.6 mF cm-2 and a capacitive retention of 66% after 8000 cycles at 7 μA cm-2, with potential for high-performance flexible supercapacitors.

Photocatalytic oxidation of Mn(II) on the surface of Bi2.15WO6via the ligand-to-metal charge transfer (LMCT) pathway

Biotic and abiotic oxidation of Mn(II) in aqueous environments is an important process for the cycling of many elements. However, the mechanism involved in photocatalytic oxidation of Mn(II) has not been clearly elucidated yet. In this study, the photocatalytic oxidation of Mn(II) on the surface of self-doped Bi_2+xWO₆ (Bi_2.15WO₆) under visible light was conducted. Kinetics results show that visible light apparently accelerates the oxidation of Mn(II) to Mn(III, IV) oxides on Bi_2.15WO₆. The average oxidation states (AOS) of manganese reach 2.18 after 80 min of reaction under visible light at pH 8.50. Characterizations indicate the formation of Bi(III)-O-Mn(II) surface complexes between Mn(II) and surface Bi(III) on Bi_2.15WO₆, which then decreases the bandgap of [Bi_2.15WO₆ + Mn(II)]_light (2.53 eV) compared with those of [Bi_2.15WO₆ + Mn(II)]_dark (2.72 eV) and pure Bi_2.15WO₆ (2.86 eV), suggesting the contribution of the ligand-to-metal charge transfer (LMCT) pathway to the photocatalytic oxidation of Mn(II). Moreover, the addition of inorganic oxidants with strong oxidizing capacities (such as Cr₂O₇^2-, NO₃^- or NO₂^-) significantly increases the oxidation rate of Mn(II), further verifying the contribution of the LMCT pathway to Mn(II) oxidation. We therefore suggest that the LMCT pathway is one of the important oxidation routes for Mn(II) oxidation on Bi_2.15WO₆ under visible light.

Impact of Molybdenum Dichalcogenides on the Active and Hole-Transport Layers for Perovskite Solar Cells, X-Ray Detectors, and Photodetectors

The interface architectures of inorganic-organic halide perovskite-based devices play key roles in achieving high performances with these devices. Indeed, the perovskite layer is essential for synergistic interactions with the other practical modules of these devices, such as the hole-/electron-transfer layers. In this work, a heterostructure geometry comprising transition-metal dichalcogenides (TMDs) of molybdenum dichalcogenides (MoX₂  = MoS₂ , MoSe₂ , and MoTe₂ ) and perovskite- or hole-transfer layers is prepared to achieve improved device characteristics of perovskite solar cells (PSCs), X-ray detectors, and photodetectors. A superior efficiency of 11.36% is realized for the active layer with MoTe₂ in the PSC device. Moreover, X-ray detectors using modulated MoTe₂ nanostructures in the active layers achieve 296 nA cm^-2 , 3.12 mA (Gy cm² )^-1 and 3.32 × 10^-4 cm² V^-1 s^-1 of collected current density, sensitivity, and mobility, respectively. The fabricated photodetector produces a high photoresponsivity of 956 mA W^-1 for a visible light source, with an excellent external quantum efficiency of 160% for the perovskite layer containing MoSe₂ nanostructures. Density functional theory calculations are made for pure and MoX₂ doped perovskites' geometrical, density of states and optical properties variations evidently. Thus, the present study paves the way for using perovskite-based devices modified by TMDs to develop highly efficient semiconductor devices.

Fabrication Strategies and Optoelectronic Applications of Perovskite Heterostructures

Metal halide perovskites (MHPs) are emerging low‐cost and multifunctional semiconductor materials. They have been widely used in optoelectronic devices such as perovskite solar cells, light‐emitting diodes, photodetectors, memristors, and lasers. Developing new MHPs, defects passivation, optimizing device structures, and packaging techniques are all effective methods to improve photoelectric performance and stability of perovskite devices. Particularly, the fabrication of perovskite/perovskite heterostructures (PPHSs) is a novel and arresting method to obtain stable and high‐performing optoelectronic perovskite devices since it can passivate defects, regulate energy gaps, and provide new carrier transmission modes of MHPs for multiple semiconductor applications. In this paper, representative fabrication strategies of PPHSs including films and single‐crystal heterostructures are reviewed, and their applications in optoelectronic devices are summarized. Furthermore, the challenges and prospects of PPHSs are discussed based on the current status.

All-Inorganic p-n Heterojunction Solar Cells by Solution Combustion Synthesis Using N-type FeMnO3 Perovskite Photoactive Layer

This study outlines the synthesis and physicochemical characteristics of a solution-processable iron manganite (FeMnO₃) nanoparticles via a chemical combustion method using tartaric acid as a fuel whilst demonstrating the performance of this material as a n-type photoactive layer in all-oxide solar cells. It is shown that the solution combustion synthesis (SCS) method enables the formation of pure crystal phase FeMnO₃ with controllable particle size. XRD pattern and morphology images from TEM confirm the purity of FeMnO₃ phase and the relatively small crystallite size (∼13 nm), firstly reported in the literature. Moreover, to assemble a network of connected FeMnO₃ nanoparticles, β-alanine was used as a capping agent and dimethylformamide (DMF) as a polar aprotic solvent for the colloidal dispersion of FeMnO₃ NPs. This procedure yields a ∼500 nm thick FeMnO₃ n-type photoactive layer. The proposed method is crucial to obtain functional solution processed NiO/FeMnO₃ heterojunction inorganic photovoltaics. Photovoltaic performance and solar cell device limitations of the NiO/FeMnO₃-based heterojunction solar cells are presented.

An Interface Heterostructure of NiO and CeO2 for Using Electrolytes of Low-Temperature Solid Oxide Fuel Cells

Interface engineering can be used to tune the properties of heterostructure materials at an atomic level, yielding exceptional final physical properties. In this work, we synthesized a heterostructure of a p-type semiconductor (NiO) and an n-type semiconductor (CeO2) for solid oxide fuel cell electrolytes. The CeO2-NiO heterostructure exhibited high ionic conductivity of 0.2 S cm-1 at 530 °C, which was further improved to 0.29 S cm-1 by the introduction of Na+ ions. When it was applied in the fuel cell, an excellent power density of 571 mW cm-1 was obtained, indicating that the CeO2-NiO heterostructure can provide favorable electrolyte functionality. The prepared CeO2-NiO heterostructures possessed both proton and oxygen ionic conductivities, with oxygen ionic conductivity dominating the fuel cell reaction. Further investigations in terms of electrical conductivity and electrode polarization, a proton and oxygen ionic co-conducting mechanism, and a mechanism for blocking electron transport showed that the reconstruction of the energy band at the interfaces was responsible for the enhanced ionic conductivity and cell power output. This work presents a new methodology and scientific understanding of semiconductor-based heterostructures for advanced ceramic fuel cells.

Regulation of Ferroelectric Polarization to Achieve Efficient Charge Separation and Transfer in Particulate RuO2 /BiFeO3 for High Photocatalytic Water Oxidation Activity

Exploiting spontaneous polarization of ferroelectric materials to achieve high charge separation efficiency is an intriguing but challenging research topic in solar energy conversion. This work shows that loading high work function RuO₂ cocatalyst on BiFeO₃ (BFO) nanoparticles enhances the intrinsic ferroelectric polarization by efficient screening of charges to RuO₂ via RuO₂ /BFO heterojunction. This leads to enhancement of the surface photovoltage of RuO₂ /BFO single nanoparticles nearly 3 times, the driving force for charge separation and transfer in photocatalytic reactions. Consequently, efficient photocatalytic water oxidation is achieved with quantum efficiency as high as 5.36 % at 560 nm, the highest activity reported so far for ferroelectric materials. This work demonstrates that, unlike low photocurrent density in film-based ferroelectric devices, high photocatalytic activity could be achieved by regulating the ferroelectric spontaneous polarization using appropriate cocatalyst to enhance driving force for efficient separation and transfer of photogenerated charges in particulate ferroelectric semiconductor materials.

Ag-doped BiVO4/BiFeO3 photoanode for highly efficient and stable photocatalytic and photoelectrochemical water splitting

In a conventional photoelectrochemical (PEC) water splitting system using BiVO₄ (BVO), most of the charge carriers have very sluggish photocatalysis reaction kinetics because they are easily recombined from the defects developed from the bulk or the surface of the photoanodes before reaching the fluorine-doped tin dioxide (FTO). Herein, we present a facile design and fabrication technique for a Ag-BVO/BiFeO₃ (BFO) heterostructure photoanode by Ag doping and surface passivation with BFO on the as-preparedBVO photoanode. Its photocatalytic properties for PEC water splitting and tetracycline (TC) degradation are compared to those of BVO/BFO, BVO, and Ag-BVO photocatalyst nanoparticle (NP) films. The effect of Ag-doping/BFO surface passivation on the morphological, structural, and optical properties and surface electronic structure of the as-obtainedBVO electrodes was investigated. The photocatalytic degradation of TC in aqueous solution by Ag-BVO/BFO was greatly increased (>1.5-fold) compared to that of BVO. The TC was completely photodegraded in 50 min of visible-light irradiation. The as-preparedAg-BVO/BFO heterojunction photoanode not only exhibited 4-fold higher PEC performance (0.72 mA cm^-2 vs. RHE) and stability than those of the pure BVO components, but also the onset potential in the Ag-BVO/BFO photoanode was cathodically shifted by 600 mV compared to that of the bare BVO. The Ag-BVO/BFO photoelectrode with the highest donor density and the lowest charge transfer resistance exhibited a 4.46-fold higher carrier density than that of the pure BVO photoelectrode. More specifically, the Mott-Schottky (MS) and electrochemical impedance spectroscopy (EIS) results demonstrated that the Ag-doping not only effectively increased the carrier charge density of BVO, thus increasing the consumption rate of charge carriers, but also increased the charge transfer and transport efficiencies of the BVO photoanodes.

Recent progress in hybrid perovskite solar cells through scanning tunneling microscopy and spectroscopy

Currently, sustainable renewable energy sources are urgently required to fulfill the cumulative energy needs of the world's 7.8 billion population, since the conventional coal and fossil fuels will be exhausted soon. Photovoltaic devices are a direct and efficient means to produce a huge amount of energy to meet these energy targets. In particular, hybrid-perovskite-based photovoltaic devices merit special attention not only due to their exceptional efficiency for generating appreciable energy but also their tunable band gaps and the ease of device fabrication. However, the commercialization of such devices suffers from the instability of the compositional materials. The cause of instability is the perovskite's structure and its morphology at the sub-molecular level; thereby revealing and eliminating these instabilities are a striking challenge. To address this issue, scanning tunneling microscopy/spectroscopy (STM/STS) presents a comprehensive method to allow the visualization of the morphology and electronic structure of materials at atomic-level resolution. Here, we review the recent developments of perovskite-based solar cells (PSCs), the STM/STS analysis of photoactive halide/hybrid and oxide materials, and the real-time STM/STS investigation of electronic structures with defects and traps that are believed to mainly affect device performances. The detailed STM/STS analysis can facilitate a better understanding of the properties of materials at the nanoscale. This informative study may hold great promise to advance the development of stable PSCs under atmospheric conditions.

Integration-Friendly, Chemically Stoichiometric BiFeO3 Films with a Piezoelectric Performance Challenging that of PZT

As a prototype single-phase multiferroic, BiFeO₃ exhibits excellent electrical, magnetic, and magnetoelectric properties, appealing to many modern technological applications. One of its overlooked merits is a high piezoelectric performance originating from its large remnant polarization (P_r) and low dielectric constant (ε_r). Furthermore, its high Curie temperature and large coercive field ensure good stabilities in device applications. However, to achieve close-to-intrinsic properties, a high processing temperature is usually used for the preparation of highly crystalline (epitaxial or highly oriented) BiFeO₃ films. Proliferation of defects due to loss of volatile Bi₂O₃ in the high-temperature process and its incompatibility with CMOS-Si technologies have hindered the development of BiFeO₃ film-based piezoelectric micro-electro-mechanical systems (piezo-MEMS) devices. In this work, we successfully sputter-deposited highly (100) oriented BiFeO₃ thick films (∼1 μm) on Si at 350 °C through the use of a conductive perovskite buffer layer of LaNiO₃. Formation of bulk and interfacial defects is suppressed by the combination of a low deposition temperature and an oxygen-rich processing atmosphere, resulting in chemically stoichiometric BiFeO₃ films. These films displayed a high P_r (∼60 μC·cm^-2), a low ε_r (∼200), and a small dielectric loss (<0.02), as well as large coercive and self-bias voltages in their as-grown and aged states. Together with a large transverse piezoelectric coefficient (e_31,f ∼ -2.8 C·m^-2), excellent electromechanical performances with outstanding fatigue and aging resistances are demonstrated in patterned BiFeO₃-Si cantilever devices. These integration-friendly BiFeO₃ films are ideal replacements of PZT films in piezo-MEMS applications.

Recent advances in amphiphilic block copolymer templated mesoporous metal-based materials: assembly engineering and applications

Mesoporous metal-based materials (MMBMs) have received unprecedented attention in catalysis, sensing, and energy storage and conversion owing to their unique electronic structures, uniform mesopore size and high specific surface area. In the last decade, great progress has been made in the design and application of MMBMs; in particular, many novel assembly engineering methods and strategies based on amphiphilic block copolymers as structure-directing agents have also been developed for the "bottom-up" construction of a variety of MMBMs. Development of MMBMs is therefore of significant importance from both academic and practical points of view. In this review, we provide a systematic elaboration of the molecular assembly methods and strategies for MMBMs, such as tuning the driving force between amphiphilic block copolymers and various precursors (i.e., metal salts, nanoparticles/clusters and polyoxometalates) for pore characteristics and physicochemical properties. The structure-performance relationship of MMBMs (e.g., pore size, surface area, crystallinity and crystal structure) based on various spectroscopy analysis techniques and density functional theory (DFT) calculation is discussed and the influence of the surface/interfacial properties of MMBMs (e.g., active surfaces, heterojunctions, binding sites and acid-base properties) in various applications is also included. The prospect of accurately designing functional mesoporous materials and future research directions in the field of MMBMs is pointed out in this review, and it will open a new avenue for the inorganic-organic assembly in various fields.

Enhanced photovoltaic response of lead-free ferroelectric solar cells based on (K,Bi)(Nb,Yb)O3 films

Herein, we firstly present the (K,Bi)(Nb,Yb)O₃ inorganic ferroelectric photovoltaic (FPV) film, in which a nearly ideal bandgap of ∼1.45 eV in the center of the solar spectrum and the co-existence of oxygen vacancies as well as ferroelectric polarization were confirmed. Furthermore, a novel cell structure is successfully fabricated by combining charge-transporting TiO₂ nanoparticles, the perovskite sensitizer and a light-absorbing oxide hole p-type NiO conductor to realize a 1 V open circuit voltage, which can be increased to 1.56 V by adjusting the test bias near the coercive voltage. Additionally, under simulated standard AM 1.5G illumination, a fill factor of 86% and a power conversion efficiency of 0.85% are achieved via oxygen vacancy electromigration and polarization switching modulation. It is shown that the obtained power conversion efficiency is one to three orders of magnitude higher than those of pure BiFeO₃ and Pb(Zr,Ti)O₃. The enhanced PV effects are well elucidated using the transformation from a Schottky-like barrier to Ohmic contacts caused by polarization switching and oxygen vacancies. Building upon the above studies, deep insights into the bandgap tunability and PV effects in ferroelectric films with high oxygen vacancy concentration are provided and will facilitate a new versatile route for exploring high PV performance based on inorganic ferroelectric films.

Progress in BiFeO3-based heterostructures: materials, properties and applications

BiFeO3-based heterostructures have attracted much attention for potential applications due to their room-temperature multiferroic properties, proper band gaps and ultrahigh ferroelectric polarization of BiFeO3, such as data storage, optical utilization in visible light regions and synapse-like function. Here, this work aims to offer a systematic review on the progress of BiFeO3-based heterostructures. In the first part, the optical, electric, magnetic, and valley properties and their interactions in BiFeO3-based heterostructures are briefly reviewed. In the second part, the morphologies of BiFeO3 and medium materials in the heterostructures are discussed. Particularly, in the third part, the physical properties and underlying mechanism in BiFeO3-based heterostructures are discussed thoroughly, such as the photovoltaic effect, electric field control of magnetism, resistance switching, and two-dimensional electron gas and valley characteristics. The fourth part illustrates the applications of BiFeO3-based heterostructures based on the materials and physical properties discussed in the second and third parts. This review also includes a future prospect, which can provide guidance for exploring novel physical properties and designing multifunctional devices.

Tuning the Energy Band Structure at Interfaces of the SrFe0.75Ti0.25O3-δ-Sm0.25Ce0.75O2-δ Heterostructure for Fast Ionic Transport

Interface engineering holds huge potential for enabling exceptional physical properties in heterostructure materials via tuning properties at the atomic level. In this study, a heterostructure built by a new redox stable semiconductor SrFe_0.75Ti_0.25O_3-δ (SFT) and an ionic conductor Sm_0.25Ce_0.75O₂ (SDC) is reported. The SFT-SDC heterostructure exhibits a high ionic conductivity >0.1 S/cm at 520 °C, which is 1 order of magnitude higher than that of bulk SDC. When it was applied into the fuel cell, the SFT-SDC can realize favorable electrolyte functionality and result in an excellent power density of 920 mW cm^-2 at 520 °C. The prepared SFT-SDC heterostructure materials possess both electronic and ionic conduction, where electron states modulate local electrical field to facilitate ion transport. Further investigations to calculate the structure and electronic structure/state of SFT and SDC are done using density functional theory (DFT). It is found that the reconstruction of the energy band at interfaces is responsible for such enhanced ionic conductivity and cell power output. The current study about the perovskite-based heterostructure presents a novel strategy for developing advanced ceramic fuel cells.

Manipulation of Oxygen Vacancy for High Photovoltaic Output in Bismuth Ferrite Films

Very recently, the ferroelectric photovoltaic property of bismuth ferrite (BiFeO₃, BFO) has attracted much attention. However, the physical mechanisms for its anomalous photovoltaic effect and switchable photovoltaic effect are still largely unclear. Herein, a novel design was proposed to realize a high photovoltaic output in BiFeO₃ films by manipulating its oxygen vacancy concentration through the alteration of the Bi content. Subsequent results and analysis manifested that the highest photovoltaic output was achieved in Bi_1.05FeO₃ films, differing 1000 times from that of Bi_0.95FeO₃ films. Simultaneously, the origin of photovoltaic effect in all BiFeO₃ films was suggested as the bulk photovoltaic mechanism instead of the Schottky effect. Moreover, oxygen vacancy migration should be the dominant factor determining the switchable photovoltaic effect rather than the ferroelectric polarization. A switchable Schottky-to-Ohmic interfacial contact model was proposed to illustrate the observed switchable photovoltaic or diodelike effect. Therefore, the present work may open a new way to realize the high power output and controllable photovoltaic switching behavior for the photovoltaic applications of BiFeO₃ compounds.

Electron-hole separation in ferroelectric oxides for efficient photovoltaic responses

Photovoltaics (PVs) benefitting from ferroelectric polarizations can overcome critical limitations of conventional type PVs. In this class, Bi₂FeCrO₆ is known to be the best-performing material; however, a fundamental understanding of the origin is lacking, which has limited further performance improvements. Here, we carried out a theoretical investigation of the electronic structure of this material. As a result, electron−hole (e-h) pairs are observed to separate upon photoexcitation, which can be a dominant underlying mechanism for the exceptional PV responses. Based on this understanding, we further suggest five novel materials that can offer a combination of strong e-h separations and visible-light absorptions. We expect the community of ferroelectric PVs to immediately benefit from the features of the new suggested materials.

Despite their potential to exceed the theoretical Shockley−Queisser limit, ferroelectric photovoltaics (FPVs) have performed inefficiently due to their extremely low photocurrents. Incorporating Bi₂FeCrO₆ (BFCO) as the light absorber in FPVs has recently led to impressively high and record photocurrents [Nechache R, et al. (2015) Nat Photonics 9:61–67], which has revived the FPV field. However, our understanding of this remarkable phenomenon is far from satisfactory. Here, we use first-principles calculations to determine that such excellent performance mainly lies in the efficient separation of electron−hole (e-h) pairs. We show that photoexcited electrons and holes in BFCO are spatially separated on the Fe and Cr sites, respectively. This separation is much more pronounced in disordered BFCO phases, which adequately explains the observed exceptional PV responses. We further establish a design strategy to discover next-generation FPV materials. By exploring 44 additional Bi-based double-perovskite oxides, we suggest five active-layer materials that offer a combination of strong e-h separations and visible-light absorptions for FPV applications. Our work indicates that charge separation is the most important issue to be addressed for FPVs to compete with conventional devices.

Highly Sensitive Switchable Heterojunction Photodiode Based on Epitaxial Bi2FeCrO6 Multiferroic Thin Films

Perovskite multiferroic oxides are promising materials for the realization of sensitive and switchable photodiodes because of their favorable band gap (<3.0 eV), high absorption coefficient, and tunable internal ferroelectric (FE) polarization. A high-speed switchable photodiode based on multiferroic Bi₂FeCrO₆ (BFCO)/SrRuO₃ (SRO)-layered heterojunction was fabricated by pulsed laser deposition. The heterojunction photodiode exhibits a large ideality factor ( n = ∼5.0) and a response time as fast as 68 ms, thanks to the effective charge carrier transport and collection at the BFCO/SRO interface. The diode can switch direction when the electric polarization is reversed by an external voltage pulse. The time-resolved photoluminescence decay of the device measured at ∼500 nm demonstrates an ultrafast charge transfer (lifetime = ∼6.4 ns) in BFCO/SRO heteroepitaxial structures. The estimated responsivity value at 500 nm and zero bias is 0.38 mA W^-1, which is so far the highest reported for any FE thin film photodiode. Our work highlights the huge potential for using multiferroic oxides to fabricate highly sensitive and switchable photodiodes.

Enhanced Switchable Ferroelectric Photovoltaic Effects in Hexagonal Ferrite Thin Films via Strain Engineering

Ferroelectric photovoltaics (FPVs) are being extensively investigated by virtue of switchable photovoltaic responses and anomalously high photovoltages of ∼10⁴ V. However, FPVs suffer from extremely low photocurrents due to their wide band gaps (E_g). Here, we present a promising FPV based on hexagonal YbFeO₃ (h-YbFO) thin-film heterostructure by exploiting its narrow E_g. More importantly, we demonstrate enhanced FPV effects by suitably exploiting the substrate-induced film strain in these h-YbFO-based photovoltaics. A compressive-strained h-YbFO/Pt/MgO heterojunction device shows ∼3 times enhanced photovoltaic efficiency than that of a tensile-strained h-YbFO/Pt/Al₂O₃ device. We have shown that the enhanced photovoltaic efficiency mainly stems from the enhanced photon absorption over a wide range of the photon energy, coupled with the enhanced polarization under a compressive strain. Density functional theory studies indicate that the compressive strain reduces E_g substantially and enhances the strength of d-d transitions. This study will set a new standard for determining substrates toward thin-film photovoltaics and optoelectronic devices.

Determining the Conduction Band-Edge Potential of Solar-Cell-Relevant Nb2O5 Fabricated by Atomic Layer Deposition

Often key to boosting photovoltages in photoelectrochemical and related solar-energy-conversion devices is the preferential slowing of rates of charge recombination-especially recombination at semiconductor/solution, semiconductor/polymer, or semiconductor/perovskite interfaces. In devices featuring TiO₂ as the semiconducting component, a common approach to slowing recombination is to install an ultrathin metal oxide barrier layer or trap-passivating layer atop the semiconductor, with the needed layer often being formed via atomic layer deposition (ALD). A particularly promising barrier layer material is Nb₂O₅. Its conduction-band-edge potential E_CB is low enough that charge injection from an adsorbed molecular, polymeric, or solid-state light absorber and into the semiconductor can still occur, but high enough that charge recombination is inhibited. While a few measurements of E_CB have been reported for conventionally synthesized, bulk Nb₂O₅, none have been described for ALD-fabricated versions. Here, we specifically determine the conduction-band-edge energy of ALD-fabricated Nb₂O₅ relative to that of TiO₂. We find that, while the value for ALD-Nb₂O₅ is indeed higher than that for TiO₂, the difference is less than anticipated based on measurements of conventionally synthesized Nb₂O₅ and is dependent on the thermal history of the material. The implications of the findings for optimization of competing interfacial rate processes, and therefore photovoltages, are briefly discussed.

Hydrogen-treated BiFeO3 nanoparticles with enhanced photoelectrochemical performance

Compared with pristine BiFeO₃, hydrogen-treated BiFeO₃ nanoparticles exhibit higher photoelectrochemical performance.

Template synthesis of NiO ultrathin nanosheets using polystyrene nanospheres and their electrochromic properties

NiO ultrathin nanosheets synthesized by a template method exhibit fast coloration/bleaching responses.