Band Energy Levels Research Articles

Thermally stable Al4B2O9:Ce3+ nanofibers with intense blue emission and Al4B2O9:Ce3+/Dy3+ nanofibers with color-tunable luminescence and white-light emission via energy transfer

Dy3+ can achieve white-light emission at the appropriate intensity ratio of yellow to blue light in specific hosts due to its wide yellow and blue emitting bands. However, luminescence intensity of singly doped Dy3+ in the matrix is low, which limits its application in PC-WLEDs. Al4B2O9 has become a promising rare earth ion-doped matrix owing to its ease of doping, low price, excellent chemical and thermal stability. In this work, to improve the Dy3+ emission intensity and to achieve color-tunable luminescence and white-light emission, with the help of energy level matching engineering, Ce3+ ions with a strong and broad absorption band and suitable energy levels matching with Dy3+ are selected as high-efficient sensitizers. Ce3+ doped and Ce3+/Dy3+ co-doped one-dimensional (1D) Al4B2O9 nanofibers are designed and successfully synthesized using a simple electrospinning coupled with an oxidative calcination. Under the excitation of 286-nm UV light, Al4B2O9:Ce3+ nanofibers emit intense blue light and can be used as blue-emitting phosphor, and the emission peak of Al4B2O9:Ce3+/Dy3+ nanofibers at 374 nm is attributed to the 5d→2F5/2 energy level transition of Ce3+, and emission peaks at 483 and 575 nm are ascribed to the 4F9/2→6H15/2, 13/2 energy level transitions of Dy3+, respectively. By modulating the doping concentration of Dy3+ and Ce3+→Dy3+ energy transfer (ET) process, color-tunable luminescence and white-light emission are resoundingly realized to address the weak luminescence intensity of Dy3+. In addition, Al4B2O9:Ce3+/Dy3+ nanofibers have excellent thermal stability. The formation mechanism and luminescence mechanism of Al4B2O9:Ce3+/Dy3+ nanofibers are presented, and the Ce3+→Dy3+ ET mechanism in Al4B2O9:Ce3+/Dy3+ nanofibers is elucidated. The designing concept and the technology in this work are instructive for preparing new phosphors with 1D morphology and super fluorescence.

Slowing down the hot electron cooling to activate near-infrared photocatalytic activity in potassium/carbon co-doped polymeric carbon nitride

The research on hot electron cooling in photocatalysis has been neglected. Here, taking polymeric carbon nitride as an example, a potassium/carbon (K/C) co-doping strategy is proposed to slow down hot electron cooling. The K/C co-doping reduces the specific arrangement and overlap of electronic band structures, and decreases the degeneracy of conduction band energy levels, thus exciting phonon bottleneck effect to effectively suppress the relaxation of hot electrons by reducing the interaction between hot electrons and phonons. Our work benefits to improve the efficiency of photocatalytic energy conversion.

Recent advances in cadmium sulfide (CdS)-based photocatalysts

Organic compounds from different industries produce a range of problematic pollutants in wastewater. Cadmium sulfide (CdS) based photocatalyst as a typical photocatalytic material, due to its high efficiency and stability, shows great potential in the field of environmental restoration, which has strong visible light absorption, suitable band energy level and excellent electron charge transport performance. Research on degradation of organic pollutants using cadmium sulfide (CdS) based photocatalyst has made significant progress. In order to improve the rate and ability of cadmium sulfide (CdS) based photocatalyst to degrade pollutants, this paper introduces various strategies to modify the shape and structure of photocatalyst to improve its performance. In addition, the reaction conditions were optimized, and the mechanism of photocatalytic degradation was discussed. In conclusion, the research of cadmium sulfide based photocatalysts provides valuable insights for the degradation of organic pollutants and offers hope for future application in ecological environmental protection.

Mesoporous Vinylene-Linked Covalent Organic Frameworks with Heteroatom-Tuned Crystallinity and Photocatalytic Behaviors.

Owing to its prominent π-delocalization and stability, vinylene linkage holds great merits in the construction of covalent organic frameworks (COFs) with promising semiconducting properties. However, carbon-carbon double bond formation reaction always exhibits relatively low reversibility, unfavorable for the formation of high crystalline frameworks through self-error correction and assembling processes. In this work, we report a heteroatom-tuned strategy to build up a series of two-dimensional (2D) vinylene-linked COFs by Knoevenagel condensation of an electron-deficient methylthiazolyl-based monomer with different triformyl substituted (hetero-)aromatic derivatives. The resulting COFs show high-quality periodic mesoporous structures with high surface areas. Embedding heteroatoms into the backbones enables significantly improving their crystallinity, and finely tailoring their semiconducting structures. Upon visible light stimulation, one of the as-prepared COFs with donor-π-acceptor structure could deliver a nearly seven-fold increase in the catalytic activity of hydrogen generation as compared with the other two. Meanwhile, in combination with high crystallinity and the matched conduction band energy level, such kind of COFs can be able to selectively generate singlet oxygen and superoxide radicals in a high ratio of up to 30:1, allowing for catalyzing aerobic thioanisole oxidation in distinctly tunable activities through the substituent electronic effect of the substrates.

Mesoporous Vinylene‐Linked Covalent Organic Frameworks with Heteroatom‐Tuned Crystallinity and Photocatalytic Behaviors

AbstractOwing to its prominent π‐delocalization and stability, vinylene linkage holds great merits in the construction of covalent organic frameworks (COFs) with promising semiconducting properties. However, carbon‐carbon double bond formation reaction always exhibits relatively low reversibility, unfavorable for the formation of high crystalline frameworks through self‐error correction and assembling processes. In this work, we report a heteroatom‐tuned strategy to build up a series of two‐dimensional (2D) vinylene‐linked COFs by Knoevenagel condensation of an electron‐deficient methylthiazolyl‐based monomer with different triformyl substituted (hetero−)aromatic derivatives. The resulting COFs show high‐quality periodic mesoporous structures with high surface areas. Embedding heteroatoms into the backbones enables significantly improving their crystallinity, and finely tailoring their semiconducting structures. Upon visible light stimulation, one of the as‐prepared COFs with donor‐π‐acceptor structure could deliver a nearly seven‐fold increase in the catalytic activity of hydrogen generation as compared with the other two. Meanwhile, in combination with high crystallinity and the matched conduction band energy level, such kind of COFs can be able to selectively generate singlet oxygen and superoxide radicals in a high ratio of up to 30 : 1, allowing for catalyzing aerobic thioanisole oxidation in distinctly tunable activities through the substituent electronic effect of the substrates.

Impact of Different π-Bridges on the Photovoltaic Performance of A-D-D'-D-A Small Molecule-Based Donors.

Three small donor molecule materials (S1, S2, S3) based on dithiophene [2,3-d:2',3'-d']dithiophene [1,2-b:4,5-b']dithiophene (DTBDT) utilized in this study were synthesized using the Vilsmeier-Haack reaction, traditional Stille coupling, and Knoevenagel condensation. Then, a variety of characterization methods were applied to study the differences in optical properties and photovoltaic devices among the three. By synthesizing S2 using a thiophene π-bridge based on S1, the blue shift in ultraviolet absorption can be enhanced, the band gap and energy level can be reduced, the open circuit voltage (VOC) can be increased to 0.75 V using the S2:Y6 device, and a power conversion efficiency (PCE) of 3% can be achieved. Also, after developing the device using Y6, S3 introduced the alkyl chain of thiophene π-bridge to S2, which improved the solubility of tiny donor molecules, achieved the maximum short-circuit current (JSC = 10.59 mA/cm2), filling factor (FF = 49.72%), and PCE (4.25%). Thus, a viable option for future design and synthesis of small donor molecule materials is to incorporate thiophene π-bridges into these materials, along with alkyl chains, in order to enhance the device's morphology and charge transfer behavior.

Nanoscale Graded Nitrogen-Doping of TiO2 via Pulsed Laser Deposition for Enhancing Charge Transfer in Perovskite Solar Cells.

An electron transport layer (ETL) for highly efficient perovskite solar cells (PSCs) should exhibit superior electrical transport properties and have its band levels aligned with interfacing layers to ensure efficient extraction of photo-generated carriers. Nitrogen-doped TiO2 (TiO2:N) is considered a promising ETL because it offers higher electrical conductivity compared to conventional ETLs made from spray-pyrolyzed TiO2. However, the application of highly doped TiO2:N in PSCs is often limited by the misalignment of energy band levels with adjacent layers and reduced optical transparency. In this study, a novel approach is introduced to enhance the charge transport characteristics and accurately align the electronic band alignment of TiO2:N layer through nanoscale doping level grading, achieved through the pulsed laser deposition (PLD) technique. The TiO2:N ETL with a graded doping profile can combine characteristics of both highly doped and lightly doped phases on each side. Furthermore, a nanoscale doping gradation, employing an ultrathin sub-layer structure with graded doping levels, creates a smoothly cascading band-level alignment that bridges the adjacent layers, enhancing the transport of photo-generated carriers. Consequently, this method leads to a substantial increase in the power conversion efficiency (PCE), exceeding 22%, which represents a relative improvement of 11% compared to traditional spray-pyrolyzed TiO2-based PSCs.

Enhanced Photodetection and Air Stability of Lead‐Free Tin Perovskite Photodiodes via Germanium Incorporation and Organic Cation‐Mediated Dimensionality Control

AbstractThis work presents the advancement of lead‐free tin perovskite photodiodes in terms of their photodetection and air stability by incorporating germanium (Ge) and ethylenediamine (EDA) to formamidinium tin iodide (FASnI3). EDA0.01FA0.98SnI3:Ge‐based photodiodes demonstrate a significantly improved specific detectivity (1.6 × 1012 Jones at −0.1 V), cut‐off frequency (6.6 × 105 Hz), response speed (0.53 µs), and signal‐to‐noise ratio (45 dB) compared with control devices. The superior performance is attributed to the stronger Ge─I bond, the passivation of Sn2+ and I– vacancies by smaller Ge2+ ions, the promotion of a fully 3D perovskite structure, the elevation of the conduction band energy level, and the formation of a protective GeO layer. Various film analyses, including X‐ray photoelectron spectroscopy, UV photoelectron spectroscopy, density functional theory, as well as device testing using time‐of‐flight secondary ion mass spectrometry and voltage‐dependent admittance, support and explain the mechanisms behind the enhancements. Ge‐ and EDA‐incorporated photodiodes exhibit excellent air stability, as evidenced by the time‐dependent ultraviolet visible spectra and the considerably high certified power conversion efficiency without encapsulation in air, demonstrating their potential for practical applications. The obtained photodetection performance is highest among the published lead‐free tin‐based perovskite photodetectors, presenting a monumental progress from the previous report of the same group.

Inorganic salts released from polypyrrole nanocapsules on compact TiO2 layer for highly efficient inorganic CsPbI3-type perovskite solar cells

The compact TiO2 serves as a crucial electron transport layer (ETL) for fabricating high-efficiency CsPbI3 solar cells. Modifying TiO2 with inorganic ions is regarded as a simple and effective method to optimize the band energy level, eliminate interface defects, and enhance the crystallinity of the CsPbI3 film. However, inorganic ions risk being washed away by perovskite solvents such as DMF and DMSO. In this work, core–shell inorganic salt (LiCl, NaCl, ZnCl2)@polypyrrole nanocapsules (PPy NCPs) were fabricated as a buffer layer at the interface of TiO2/CsPbI3 layer. The inorganic salts are released from PPy NCPs during the annealing process of the CsPbI3 precursor film, thereby preventing them from being washed away by the DMF/DMSO solvents. Compared to NaCl@PPy NCPs-TiO2, ZnCl2@PPy NCPs-TiO2, and pristine TiO2 films, the LiCl@PPy NCPs-TiO2 exhibited the best electron conductivity and highest Fermi level. The released LiCl not only passivates point defects in TiO2 by forming Li-O-Ti bonds, optimizing the energy level at the TiO2/perovskite interface, but also incorporates into the CsPbI3 lattice, improving its crystallinity. As a result, solar cells based on LiCl@PPy NCPs-TiO2 layer demonstrated a higher PCE of 19.78 %, along with increased open-circuit voltage (VOC) and fill factor (FF) values of 1.161 V and 83.1 %, respectively. Furthermore, the LiCl@PPy NCPs-TiO2 layer also enhanced the stability of CsPbI3 solar cells under humidity conditions.

Photo-Modulation of Atomically Thin Molybdenum Diselenides Functionalized with Photochromic Molecules

Two-dimensional (2D) transition metal dichalcogenide semiconductors have garnered significant attention due to their extraordinary electrical and optical properties. It has been increasingly important to develop strategies for modulating their properties. A number of methods have been introduced, including doping, electric and magnetic fields, mechanical strain, etc. Herein, we report a novel approach of using photochromic molecules to modulate optoelectronic properties of monolayer MoSe2 with light. We have synthesized photochromic diarylethene (DAE) molecules that can switch between two isomeric forms, referred to as open and closed, under UV and visible light, respectively. The DAE molecules formed a uniform layer with a thickness of approximately 2 nm on monolayer MoSe2. Our density functional theory (DFT) calculations suggest that the TMD and DAE will align their band energy levels such that UV irradiation moves the lowest unoccupied molecular orbital (LUMO) energy of DAE in between the conduction band minimum (CBM) and valence band minimum (VBM) of MoSe2. This will facilitate photoexcited electron transfer from MoSe2 to DAE LUMO. Experimentally, we have confirmed our predictions by observing a strong quenching of photoluminescence (PL) and an increase of electrical conductivity in MoSe2. In contrast, visible light induced isomerization to the open form of DAE and expanded its energy levels, moving the LUMO level above the MoSe2 CBM. Therefore, the PL was retained and there was no significant change in electrical conductivity. We showed that this photoswitching can dynamically modulate the optoelectronic properties by demonstrating multiple cycles of PL emission and quenching, by alternating UV and visible light repeatedly. Lastly, our Kelvin probe force microscopy (KPFM) revealed that the potential of MoSe2 monolayers can also be modulated with photochromic molecules and external light irradiation. Our work elucidates photo-processes and exciton mechanisms at the hybrid interfaces and lays the foundation for novel applications including new phototransistors and other 2D optoelectronic devices.

Intramolecular Quaternary Carbon Nitride Homojunction for Enhanced Visible Light Hydrogen Production.

In this work, an intramolecular carbon nitride (CN)-based quaternary homojunction functionalized with pyridine rings is prepared via an in situ alkali-assisted copolymerization strategy of bulk CN and 2-aminopyridine for efficient visible light hydrogen generation. In the obtained structure, triazine-based CN (TCN), heptazine-based CN (HCN), pyridine unit incorporated TCN, and pyridine ring inserted HCN constitute a special multicomponent system and form a built-in electric field between the crystalline semiconductors by the arrangement of energy band levels. The electron-withdrawing function of the conjugated heterocycle can trigger the skeleton delocalization and edge induction effect. Highly accelerated photoelectron-hole transfer rates via multi-stepwise charge migration pathways are achieved by the synergistic effect of the functional group modification and molecular quaternary homojunction. Under the addition of 5mg 2-aminopyridine, the resulting homojunction framework exhibits a significantly improved hydrogen evolution rate of 6.64mmol g-1 h-1 with an apparent quantum efficiency of 12.27% at 420nm. Further, the catalyst verifies its potential commercial value since it can produce hydrogen from various real water environments. This study provides a reliable way for the rational design and fabrication of intramolecular multi-homojunction to obtain high-efficient photocatalytic reactions.

Enhanced terahertz ISBT in GaAsBi/AlGaAs quantum well: impact of doping modulation

One of the pivotal characteristics of quantum wells (QW) designed for applications in filters or modulators is its absorption coefficient. This study investigates the combined influence of doping and active layer thickness on the absorption coefficient in GaAsBi/AlGaAs quantum wells. The self-consistent coupling between Schrödinger and Poisson equations was employed for this purpose. A comprehensive analysis of conduction band structure, energy levels, potentials, and densities is presented. This analysis discerns the effects of doping on intersubband transitions (ISBTs) in the terahertz (THz) frequency domain. An introduction of a donor impurity into the system greatly influenced the intersubband absorption coefficient, increasing its intensity and causing the optical response to shift toward the lowest frequency. The obtained resonant peak energies, situated within the terahertz spectrum, hint at promising applications for GaAsBi-based devices within this frequency band.

Extraordinary photoexcitation of semimetal 1T'-MoTe2 inducing ultrafast charge transfer in lateral 2D homojunction

Exploring novel and more efficient photoexcitation transition mechanisms in two-dimensional transition metal dichalcogenides (TMDCs) is crucial for the advancement of high-performance optoelectronic devices. In this study, an extraordinary photoluminescence (PL) phenomenon is discovered that originates from a vertical transition between specific bands in the X-point energy valley of K-space in multilayer Weyl semi-metal monoclinic (1T') MoTe2 without a gap structure. This effective transition is independent of the bandgap and is unaffected by the number of layers in 1T'-MoTe2, breaking the limitations of traditional TMDCs semiconductor materials and promoting the development of advanced two-dimensional (2D) semimetal-based optoelectronic devices. In a lateral multilayer 1T'-MoTe2-2H hetero-phase homojunction, a record ultrafast transfer of photogenerated charges up to 25 fs is achieved. The highly efficient interband transition, small conduction band energy level difference (less than 100 meV), and exceptionally strong e-p coupling synergistically promote the ultrafast transfer of photo-generated charges. Together with the merits of multilayer 1T'-MoTe2 such as higher carrier densities and lower resistance, these findings open the door to potentially ultra-high performance optoelectronic applications.

Improving the Water Resistance of Bi‐Based Perovskite‐Inspired Materials for Vapor‐Phase Photocatalytic Overall Water Splitting

Lead halide perovskites are well known for their exceptional photophysical and electronic properties, which have placed them at the forefront of challenging optoelectronic applications and solar‐to‐fuel conversion. However, their air/water instability, combined with their toxicity, is still a critical problem that has slowed down their commercialization. In this sense, bismuth‐based halide derivatives attract much interest as a potentially safer, air‐stable alternative. Herein, a novel Bi‐based perovskite‐inspired material, IEF‐19 (IEF stands for IMDEA Energy Framework), which contains a bulky aromatic cation (1,5‐diammonium naphthalene), is prepared. Additionally, an N‐alkylation strategy is successfully employed to achieve four water‐stable perovskite‐inspired materials, which contains diammonium naphthalene cations that are tetra‐alkylated by methyl, ethyl, propyl, and butyl groups. Moreover, computational studies are performed to gain a deeper understanding of the intrinsic structural stability and affinity of water molecules for Bi‐based perovskite‐inspired materials. Importantly, the air‐ and water‐stable IEF‐19‐Et (i.e., stable at least 12 months under ambient conditions and 3 weeks in contact with water) is found to be an active photocatalyst for vapor‐phase overall water splitting in the absence of any sacrificial agent under both ultraviolet–visible or simulated sunlight irradiation. This material exhibits an estimated apparent quantum yield of 0.08% at 400 nm, partially explained by its adequate energy band level diagram.

Enhancing efficiency in inverted perovskite solar cells: The role of dual-site binding ligands

Despite the rapid progress in efficiency, PSCs encounter substantial challenges regarding durability and scalability. Inverted p-i-n PSCs provide enhanced long-term operating stability over the conventional n-i-p structures but lag in PCE (Park and Zhu, 2020 [3]). This limitation is mainly due to the interface between the perovskite light-absorbing layer and charge transport materials, where energy band misalignment and energy level pinning hinder PCE. Furthermore, surface defects exacerbate these constraints. In the endeavor to improve performance of PSCs, surface passivation is crucial for reducing nonradiative recombination at the interface. A recent study by Chen et al., published in the journal Science, introduces an innovative interface passivation strategy for p-i-n PSCs that could set a new benchmark for efficiency and stability (Chen et al., 2024 [4]). This commentary assesses the potential impact of dual-site-binding ligands on PSCs and anticipates their transformative effect on the field.

Influence of Eu, Gd and Lu dopants on the properties of TiO2: A first-principles study

The present study investigates the electronic structure, magnetic properties, and optical performance of anatase TiO2 and pure TiO2 systems with the addition of rare earth elements RE (Eu/Gd/Lu). Using first-principles calculations based on density-functional theory, we explore the effects of RE doping on these systems. Our calculations reveal that the structural stability remains intact under the conditions of RE doping. The total magnetic moment is determined to be 2.987 μB, 6.052 μB, and 0 μB for Eu, Gd, and Lu-doped TiO2 respectively. Furthermore, the band gap of Eu/Gd/Lu-doped TiO2 decreases significantly to 1.91eV, 1.8eV, and 1.88eV, leading to a lower energy requirement for electron transition, as compared to the initial energy band gap of 2.31eV. The incorporation of rare earth elements also results in an increase in the number of valence and conduction band energy levels near the Fermi level, primarily influenced by orbital electrons in the 4f layer of the rare earth elements. Additionally, our findings demonstrate a remarkable shift towards the red region in the absorption spectrum of the Eu-TiO2 system, accompanied by a relatively long photocarrier lifetime. These characteristics suggest its potential as a photocatalyst with enhanced performance. Overall, this research provides valuable theoretical insights towards the development and synthesis of novel TiO2 photocatalysts.

Synergy of functionalized activated carbon and ZnO nanoparticles for enhancing photocatalytic degradation of methylene blue and carbaryl

This study proposes preparing ZnO and ZnO/activated carbon (AC) for photocatalytic applications. ZnO and AC were synthesized using precipitation and carbonization processes, respectively. Particle sizes of ZnO and ZnO/AC were estimated at 121–135 nm. The crystalline structure analysis confirmed the presence of hexagonal wurtzite structures in ZnO. Microcrystalline graphite and amorphous carbon structures were observed in AC. The combination of these characteristics was observed in ZnO/AC. ZnO/AC exhibited an increase in surface area from 25.36 to 29.86 m2/g and a decrease in pore diameter from 5.66 to 4.31 nm. The chemical states of ZnO and AC remained unchanged. Therefore, the nanocompound structure of ZnO/AC can be inferred. The ZnO/AC nanocompounds were then employed to degrade methylene blue (MB) dye and carbaryl (CBR) insecticide, demonstrating excellent photocatalytic performance compared to pure ZnO. The apparent degradation rate constant reached an average value of 3.49 × 10−3 and 16.25 × 10−3 min−1 for MB and CBR, respectively. AC functions as carrier collectors in the ZnO/AC nanocompound structures due to the suitable energy band level for facilitating electron and hole transfers. This results in recombination suppression and prolonged lifetime, thus enhancing photocatalytic activity. The finding suggests the potential use of ZnO/AC nanocompounds to degrade agricultural chemicals in contaminated natural water under sunlight.

Graphitic carbon nitride sheets sandwiched metal oxides: A novel platform for S-Scheme heterojunction generation for efficient photodegradation of volatile organics

This study reports the preparation of new kind of S-Scheme heterojunction (SSHJ) photocatalyst by distributing two semiconducting metal oxides (titanium dioxide and ZnO) onto the surface of graphitic carbon nitride (G-CN) two dimensional (2D) sheets. The composite photocatalysts, designated as T/Z@ GCN SSHJ, were prepared with different mass ratios of T,Z and G-CN.X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), field emission scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy were used to characterize the microstructure, morphology, chemical composition, electronic states, and optical properties of the T/Z@ GCN SSHJ composite. TEM image of the typical T/Z@ GCN SSHJ composite shows the presence of distribution of particles with sizes in the range 40–80 nm on the lamellar surface of G-CN inferring the formation of a heterostructure Z(0 D) /G-CN(2D)/T(0D) SSHJ composite. The comparison of the core level XPS spectrum of Ti 2p, Zn 2p, C1s, O1s and N1s of T/Z@ GCNSSHJ composite with the binary composites (T+G-CN and Z+G-CN) and pristine components clearly suggests that that Z, T and G-CN are kept together through van der Walls interactions. The T/Z@ GCN SSHJ composite photocatalyst with T: Z: G-CN mass ratio of 1.0: 0.80: 0.12 exhibited enhanced photocatalytic degradation (%) over binary and pristine single components for all the tested volatile organic compounds (VOCs), namely, acetaldehyde (ACD), ethyl acetate (EA), toluene (T) and benzaldehyde (BA). On comparing the % removal of VOCs after 20 minute of light irradiation, BA showed the highest removal % (94.3 %) and the others take the following order: ACD (70.9 %) >EA (56.45 %)> TL (40.12 %). The study explains the enhanced performance of T/Z@ G-CN HJ composite towards VOC photodegradation in terms of S-Scheme based charge transfer and internal electric field driven efficient charge separation. The charge transfer process of T/Z@ GCN HJ composite photocatalysts is discussed through S-Scheme HJ formation and supported with electronic states and band energy levels of the constituent components derived through the results of XPS and DRS analysis. This study gives insight into the design for regulating the hetero-interfaces for enhancing the photocatalysis and expected to further understand into charge transfer mechanism at multi-junction-based photocatalysts.

Ce-Doped SnO2 Electron Transport Layer for Minimizing Open Circuit Voltage Loss in Lead Perovskite Solar Cells.

In the planar heterostructure of perovskite-based solar cells (PSCs), tin oxide (SnO2) is a material that is often used as the electron transport layer (ETL). SnO2 ETL exhibits favorable optical and electrical properties in the PSC structures. Nevertheless, the open circuit voltage (VOC) depletion occurs in PSCs due to the defects arising from the high oxygen vacancy on the SnO2 surface and the deeper conduction band (CB) energy level of SnO2. In this research, a cerium (Ce) dopant was introduced in SnO2 (Ce-SnO2) to suppress the VOC loss of the PSCs. The CB minimum of SnO2 was shifted closer to that of the perovskite after the Ce doping. Besides, the Ce doping effectively passivated the surface defects on SnO2 as well as improved the electron transport velocity by the Ce-SnO2. These results enabled the power conversion efficiency (PCE) to increase from 21.1% (SnO2) to 23.0% (Ce-SnO2) of the PSCs (0.09 cm2 active area) with around 100 mV of improved VOC and reduced hysteresis. Also, the Ce-SnO2 ETL-based large area (1.0 cm2) PSCs delivered the highest PCE of 22.9%. Furthermore, a VOC of 1.19 V with a PCE of 23.3% was demonstrated by Ce-SnO2 ETL-based PSCs (0.09 cm2 active area) that were treated with 2-phenethylamine hydroiodide on the perovskite top surface. Notably, the unencapsulated Ce-SnO2 ETL-based PSC was able to maintain above 90% of its initial PCE for around 2000 h which was stored under room temperature condition (23-25 °C) with a relative humidity of 40-50%.

Large-area phosphorene for stable carbon-based perovskite solar cells

Carbon-based perovskite solar cells (c-PSCs) have attracted increasing attention due to their numerous advantages including ease of fabrication, the potential of assembling flexible devices, low manufacturing costs as well as large-scale production. However, c-PSCs suffer from the limited hole extraction and high charge carrier recombination due to the inadequate interface contact between the carbon electrode and perovskite film. Herein, we report the fabrication of planar c-PSCs with high efficiency and excellent stability by employing electrochemically produced large-area phosphorene flakes as a hole-transporting layer (HTL). Large-area phosphorene shows well-aligned band energy levels with the perovskite, and thus led to the efficient hole extraction and the reduced hysteresis behaviour. Consequently, while exhibiting excellent stability under various harsh testing conditions, the devices with phosphorene HTL delivered a power conversion efficiency of over 15% with an open-circuit voltage of 1.082 V, which is the highest reported value for c-PSCs without traditional hole transporting materials to date.