Energy Levels In Band Gap Research Articles

Effects of manganese-doping on the enhanced solar photocatalytic properties of AgBr catalyst: Mechanism and DFT modeling

Manganese ion doping engineering, is promising in the field of photocatalysis, but its effect on simple structure semiconductor is not clear. In this work, high-efficiency manganese doped AgBr photocatalysts were manufactured via an ice bath deposition process and were systematically characterized. Under simulated sunlight irradiation, Mn2+ doped AgBr possessed good degradation activity to rhodamine B (RhB) and Ciprofloxacin (CIP). Notably, the optimal sample AM-2 (the mole ratio of Mn element in the whole sample is 0.014 %) can degrade RhB at a reaction rate constant of 0.10334 min-1, which was 7.72 times that of pure AgBr. In light of density functional theory (DFT), the improvement of photocatalytic performance was due to the incorporation of Mn ions that induced lattice strain, affected the charge distribution, and generated an intermediate Mn 3d-Br 2p two-dimensional energy level in the AgBr band gap. Photoelectrochemical experiments verified that Mn2+ doping promoted the separation and transfer of photogenerated carriers and enhanced light absorption. In addition, the practical application ability of photocatalyst was investigated, and a reliable photocatalytic mechanism was proposed. This study may provide enlightening significance for the general application of doping engineering.

A Medium-Bandgap Nonfullerene Acceptor Enabling Organic Photovoltaic Cells with 30% Efficiency under Indoor Artificial Light.

The correlation between molecular structure and photovoltaic performance is lagging for constructing high-performance indoor organic photovoltaic (OPV) cells. Herein, this relationship is investigated in depth by employing two medium-bandgap nonfullerene acceptors (NFAs). The newly synthesized NFA of FTCCBr exhibits a similar bandgap and molecular energy level, but a much stronger dipole moment and larger average electrostatic potential (ESP) compared with ITCC. After blending with the polymer donor PB2, the PB2:ITCC and PB2:FTCCBr blends exhibit favorable bulk-heterojunction morphologies and the same driving force, but the PB2:FTCCBr blend exhibits a large ESP difference. In OPV cells, the PB2:ITCC-based device produces a power conversion efficiency (PCE) of 11.0%, whereas the PB2:FTCCBr-based device gives an excellent PCE of 14.8% with an open-circuit voltage (VOC ) of 1.05V, which is the highest value among OPV cells with VOC values above 1.0V. When both acceptor-based devices work under a 1000 lux of 3000 K light-emitting diode, the PB2:ITCC-based 1 cm2 device yields a good PCE of 25.4%; in contrast, the PB2:FTCCBr-based 1 cm2 device outputs a record PCE of 30.2%. These results suggest that a large ESP offset in photovoltaic materials is important for achieving high-performance OPV cells.

Effects of Co Doping on the Growth and Photocatalytic Properties of ZnO Particles.

The present work reports on the synthesis of ZnO photocatalysts with different Co-doping levels via a facile one-step solution route. The structural and optical properties were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and UV-Vis diffuse reflectance spectra. The morphology of Co-doped ZnO depends on the reaction temperature and the amount of Co and counter-ions in the solution. Changes with the c-axis lattice constant and room temperature redshift show the replacement of Zn with Co ions without changing the wurtzite structure. Photocatalytic activities of Co-doped ZnO on the evolution of H2 and the degradation of methylene blue (MB) reduce with the doping of Co ions. As the close ionic radii of Co and Zn, the reducing photocatalytic activity is not due to the physical defects but the formation of deep bandgap energy levels. Photocurrent response experiments further prove the formation of the recombination centers. Mechanistic insights into Co-ZnO formation and performance regulation are essential for their structural adaptation for application in catalysis, energy storage, etc.

Synthesis and characterization of hole transporting materials containing bis(carbazole) groups for solid-state dye-sensitized solar cells

In this study, bis(carbazole) derivatives, such as bis[N-(2-ethylhexyl)-carbazole-3-yl] (HTM_I) and bis[N-(2-ethylhexyloxylphenyl)-carbazole-3-yl] (HTM_II), were successfully synthesized for use as small-molecule organic hole-transporting materials (HTMs) in solid-state dye-sensitized solar cells (ssDSSCs) by coupling two respective carbazole moieties using FeCl3 catalyst. The structural integrity of two compounds was identified by 1H and 13 NMR. Maximum UV-vis absorption and photoluminescence peaks were observed at 306 nm and 425 nm for HTM_I, and at 306 nm and 425 nm for HTM_II, respectively. From the optical and electrochemical characterization, bandgap, HOMO, and LUMO energy levels were measured to be 3.26 eV, −5.52 eV, and −2.26 eV for HTM_I, and 3.37 eV, −5.61 eV, and −2.24 eV for HTM_II. The ssDSSC fabricated with HTM_II doped with TBP, MPII, and LiTFSI showed the highest PEC of 2.54%, with J sc = 6.55 mA/cm2, V oc = 0.55 V, and FF = 0.70.

Versatile Pendant Polymer for Selective Charge Carrier Transport via Controlling the Supramolecular Self-Assembly.

Polyvinyl carbazole (P0)-based pendant polymers were synthesized by modifying carbazole motifs with pyrene derivatives (P1 and P4) to manipulate the bandgap and frontier orbital energy levels. To establish the electronic properties of pendant polymers according to structural differences, the polymers were utilized as additional hole transport layers in planar-type perovskite solar cells and organic photovoltaic cells. When P4 with thiophene-pyrene pendant was used as hole transport layer, all device parameters, except open-circuit voltage, were significantly improved in comparison with P0 and P1 (conjugated with t-butyl pyrene derivatives). Since P4 had more electrically conductive thiophene units than benzene units with fewer alkyl groups, the supramolecular assembly of P4 was found to be more favorable in electronic devices. Furthermore, devices with P4 demonstrated lower dark current than others, which could potentially be useful for charge carrier transport and sensitive photo detecting devices.

Influence of the Location of Electron-Donating 3,4-Ethylenedioxythiophene (EDOT) Moiety in the A–π–D–π–A Type Conjugated Molecules on the Optoelectronic Properties and Photovoltaic Performances

A–π–D–π–A type conjugated small molecules play an indispensable role in organic photovoltaics. Understanding the relationship between the molecular structure and performance is a fundamental question for the further rational design of high-performance organic materials. To red-shift the absorption spectrum of benzo[1,2-b:4,5-b']dithiophene (BDT) based A–π–D–π–A type compounds, an electron-donating 3,4-ethylenedioxythiophene (EDOT) moiety was introduced into the π-conjugation bridge unit. Two new compounds with EDOT next to the central BDT core (COOP-2HT-EDOT-BDT) or next to the terminal electron acceptor unit (COOP-EDOT-2HT-BDT) were synthesized and characterized. The compound COOP-2HT-EDOT-BDT showed higher molar extinction coefficient (εabs max = 1.06 × 105 L mol−1 cm−1), lower optical band gap (E g = 1.56 eV) and high HOMO energy level (E HOMO = −5.08 eV) than COOP-EDOT-2HT-BDT (εabs max = 0.96 × 105 L mol−1 cm−1, E g = 1.71 eV, E HOMO = −5.26 eV), which is attributed to the intensive interaction between the EDOT unit and the HOMO orbital, as confirmed by the theoretical calculation results. However, the higher power conversion efficiency of 3.58% was achieved for the COOP-EDOT-2HT-BDT:PC61BM-based solar cells, demonstrating that the electron-donating EDOT unit adjacent to the electron-withdrawing end-capped group (COOP) is a better way to achieve high-performance photovoltaic materials.

Cu(I) complexes sensitized ZnO nanorods for photocatalytic water splitting

The earth-abundant Cu(I) is one of the promising dye-sensitized photoelectrochemical cells (DS-PECs) for sustainable energy production. We report that the heteroleptic Cu (I) complex's catalysis consisting of diphenylphosphinoaminoacetic acid and bipyridine derivatives have investigated with DS-PECs on water splitting application. HOMO-LUMO energy levels of 2,2′bipyridine Cu(I) diphenylphosphinoaminoacetic acid (Cu(L1)) 4,4′dimethyl-2,2′bipyridineCu(I)diphenyl phosphinoaminoacetic acid (Cu(L2)) are calculated with cyclic voltammetry and Uv-vis spectrometer. Both optic band gap and electrochemical band gap energy levels of Cu(I) complex indicates that Cu(L1) has a narrower band gap (2.74 eV and 2.75 eV) compared with Cu(L2) (2.86 eV and 2.79 eV). The photocatalytic hydrogen production of Cu(L1) and Cu(L2) complexes on ZnO nanorods are monitored with linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) in 0.5 M Na2SO4 under 100 mW cm−2 solar light irradiation. Cu(L1) modified ZnO nanorod photoelectrode indicates an utmost photocatalytic response (0.452 mA cm−2), the lowest charge transfers resistance (Rct) against to bare the ZnO and Cu(L2)/ZnO electrodes, and Cu(I) complex decreases injected electron lifetime leading to the enhanced photocatalytic response under solar light irradiation.

Facile construction of nickel-doped hierarchical BiOCl architectures for enhanced visible-light-driven photocatalytic activities

Doping modifications can endow BiOCl with dramatically improved photocatalytic performance via modifying the electronic structure. Here, the hierarchical Ni-doped BiOCl microflowers self-assembled by 2D nanosheets were synthesized through a one-step solvothermal method. Notably, the as-obtained Ni-doped BiOCl sample presented a remarkably enhanced photocatalytic degradation activity, totally decomposed Rhodamine B aqueous solution (15 mg/L) within 5 min under visible-light irradiation. Based on the experimental and calculated results, the introduction of Ni can narrow the band-gap and form defect energy levels simultaneously, resulted in a red shift in the absorption edge and much stronger absorption in the visible-light range. In addition, Ni-doped BiOCl exhibits an enhanced photocurrent density and a suppressed peak intensity of PL emission, indicating the efficient transportation and suppressed recombination of photoinduced charge carriers. This study sheds light on a possible application of Ni-doped BiOCl in photocatalytic degradation of organic pollutants under visible-light irradiation and provides a feasible strategy to synthesis of high active Ni-doped BiOX (X = Cl, Br and I) photocatalysts.

Ultrashallow defects in SiC MOS capacitors

Capacitance-voltage measurements performed at cryogenic temperatures (14 – 500 K) have been used to determine the ultrashallow interface states in SiC MOS capacitors. These states occupies energy levels in SiC band gap on different energy levels up to 27 meV below the conduction band. Moreover, the capacitance-voltage characteristics are moving to lower voltages with temperature increasing, indicating a reduction in flat band voltage from 14.65 (14 K) to 2.77 V (500 K). It was demonstrated that a complete ionization of the nitrogen donors from the epitaxial layer occurs at 420 K. From these analysis, an activation energy of around 26.79 meV was determined. In order to determine the energy levels distribution of the interface states in SiC band gap, the Fermi level variation with temperature was calculated, starting from a value of around 27.1 meV at 14 K and reaching a value of 321 meV at 500 K under SiC conduction band. Six peaks (D1 – D6) have been identified in interface states density distribution at different levels of energy in SiC band gap, which could correspond to different defects at the SiO2/SiC interface.

Theoretical analysis on O vacancy and cation inversion in NiCo2O4

We have implemented polarized density function theory (DFT) on the transition metal d orbitals to explore the effects of oxygen vacancy and cation inversion on properties of NiCo2O4. The results show that NiCo2O4 has ferrimagnetic half-metallic ground states. Oxygen vacancy introduces additional energy levels in the majority spin band gap, which increases the chance of electron transition. In addition, O vacancy only affects the magnetic moment of the neighbor Oct Ni and Oct Co atoms. Calculations on NiCo2O4 with cation inversion confirms that coordinated sites of metal ions affect their spin state and valence, which further influence the conductivity and ferrimagnetic properties. The valence information of metal ions in NiCo2O4 was given. And the increased electron states in top of valence band make great contributions to p-type conductivity of NiCo2O4.

14.55% efficiency PBDB-T ternary organic solar cells enabled by two alloy-forming acceptors featuring distinct structural orders

Ternary organic solar cells (OSCs) have demonstrated great potential in boosting the power conversion efficiencies (PCEs) of single-junction devices. Screening suitable third component is crucial but challenging for different host binary OSCs. We report herein an efficient ternary strategy in achieving highly efficient PBDB-T based devices by incorporating two alloy-forming fused-ring electron acceptors (FREAs) with distinct structural orders. INPIC-Si as the third component showcases a relatively narrower bandgap and higher energy levels than the host acceptor IDTO-T-4F. Featuring good compatibility and alloy-forming blends, two FREAs generate Förster resonance energy transfer from IDTO-T-4F to INPIC-Si, facilitating efficient exciton dissociation and charge carrier transport. Importantly, the low crystalline INPIC-Si decreases the strong aggregation of PBDB‐T:IDTO-T-4F blends for optimal phase-separation and structural order. Consequently, the best PBDB‐T:IDTO-T-4F:INPIC-Si ternary OSCs deliver a champion PCE of 14.55% with simultaneously improved device parameters over binary ones. To the best of our knowledge, this performance is among the highest for PBDB-T-based ternary OSCs in literature. Our work demonstrates the incorporation of a narrow bandgap FREA with low structural order into heavily aggregated binary blends can optimize the blend morphology for reduced energy loss and significantly improved photovoltaic performance in ternary OSCs.

Investigations of photoresponse characteristics of ultrasonic spray pyrolysis deposited zinc oxide-based phototransistors at different quiescent points

How quiescent-points affect the performance of the ultrasonic spray pyrolysis deposited zinc oxide-based phototransistor is investigated in this study. It is well known that gate bias and drain bias control quiescent-points. By changing gate bias, strong accumulation, weak accumulation, weak depletion, and strong depletion in the active layer of the phototransistor are obtained. Meanwhile, by changing drain bias, either triode or saturation operation regions of the phototransistor is obtained. Therefore, total 8 different quiescent-points are investigated in this study. The material characteristics such as crystal structure, oxygen deficiency, bandgap, and trap energy levels are characterized. Moreover, the performance of the phototransistor at different quiescent-points are investigated. The present phototransistor shows four operation modes, including high responsivity, high UV-to-visible rejection ratio, fast response speed, and high specific detectivity, and each mode corresponds to a specific quiescent point.

Sol–gel synthesized ZnO/Mn–TiO2 core–shell nanocomposite and its elevated activity for methyl orange degradation

Photocatalysis is a new advanced oxidation process based on the irradiation of semiconductors such as TiO2 and ZnO for photodegradation of contaminants. In this process, the semiconductor absorbs the photon energy of ultraviolet radiation, generating highly reactive species for the degradation of organic compounds. It has been reported that doping of transition metals (e.g., Cu, Ni, Co, and Mn) into the structure of oxide semiconductors can reduce the band gap and expand their adsorption properties to the visible solar spectrum. Accordingly, a new hybrid photocatalyst of Mn-doped TiO2 / ZnO with an Mn content of 1 to 5 wt. % was synthesized via the sol–gel process followed by thermal calcinations in air at 500°C. The prepared photocatalyst powder was characterized in terms of crystalline structure, thermal property, surface morphology, and band gap energy level. Its photocatalytic performance was then assessed based on photodegradation of methylene orange under visible light irradiation. Compared with the pure TiO2 / ZnO, the lattice of Mn-doped TiO2 / ZnO was found to be more thermally stable, and thus phase transformation of anatase to rutile was postponed to a higher calcination temperature. The photocatalysis evaluation showed an increased activity of Mn–ZnO / TiO2 compared with pure TiO2 and TiO2 / ZnO under visible light irradiation. Accordingly, the highest degradation of 98% was obtained by the Mn–ZnO / TiO2 with 3 wt. % Mn.

Improving the efficiency of CZTSSe solar cells by engineering the lattice defects in the absorber layer

One of the major challenges in increasing the efficiency of the CZTSSe solar cells is to control the lattice defects formation and secondary phases in the absorber layer of the cells. Moreover, by controlling and decreasing lattice defects and thus improving the efficiency, larger-scale applications would be financially acceptable. In this paper, several CZTSSe thin-film solar cells have been prepared and one device with champion efficiency of 10.33% has been chosen for the modeling. Afterward, numerical simulations based on the Finite Element Method (FEM) and Finite Difference (FD) were conducted on these cells. The effect of defects density and defect types, which are located at different energy levels in the absorber layer bandgap, was evaluated. The results indicated that by decreasing the defects which are located close to the electron Fermi level and the middle of the band gap (Eg/2), the maximum efficiency of 18.47% for these solar cells can be achieved.

Effect of the band gap and the defect states present within band gap on the non-linear optical absorption behaviour of yttrium aluminium iron garnets

Abstract The effect of variation of band gap and electronic defect energy levels within the band gap on non-linear optical absorption of 532 nm (green) laser light by coral-like yttrium aluminium-iron garnet (YAIG, Y3Al5-xFexO12) ceramics prepared by solution combustion route is investigated using Z-scan technique. Our yttrium aluminium garnet (YAG) sample with band gap of ≥ ~ 6.5 eV, is transparent to visible light. The band gap of YAG was tuned by substituting Fe at the aluminium site and consequently, the surface defects in YAG were also modified. The defects in the YAIG samples introduce electronic defect states within the band gap. We observed that the intensity of the non-linear absorption (NLA) signal increases with increase in the amount of iron content. We assigned this enhancement of NLA signal to: (1) the decrease in the band gap from ≥ ~ 6.5 eV for YAG to ~ 2.6 eV for yttrium iron garnet (YIG) facilitating two photon absorption (2 PA) process rather than three photon absorption (3 PA), and (2) the increase in excited state absorption (ESA) due to the spread of the defect energy states into the band gap region. As the band gap gets closer to the photon energy of the laser, the non-linear optical absorption is enhanced due to ESA, in combination with the occurrence of the relatively stronger 2 PA process rather than the very weak 3 PA process. Our results demonstrate a method to tune the NLA performance of YAG through iron substitution at the Al sites and provide a better understanding of the non-linear absorption behaviour of YAIG ceramics for their application in optical limiting devices such as laser shields.

Synthesis and Characterization of Yb−Ag@TiO2 Hollow Spheres for Enhancing Visible‐Light Photocatalytic Activity

AbstractUsing melamine‐formaldehyde microspheres as templates and n‐butyl titanate, silver nitrate and ytterbium nitrate hexahydrate as raw materials, the TiO2 hollow spheres (TiO2HS), which were doped with Yb and loaded with Ag, were successfully prepared by sol‐gel template method and high‐temperature calcinations and reduction. The combined action of Yb and Ag on the photocatalytic effect of methyl orange in visible light was studied. The results show that Yb3+ did not affect the reduction of Ag+ in the synthetic process, and Ag did not affect the substitution of Yb3+ for Ti4+ into the lattice of anatase phase TiO2. The introduction of Yb created impurity energy levels in the TiO2 band gap, which broadened the light absorption range and shortened the band gap width. At the same time, the Ag with strong electron conduction ability improved the carrier transfer speed. Benefitting from the combined action of Yb and Ag, the photo‐degradation efficiency of Yb−Ag@TiO2HS on methyl orange in visible light was significantly improved compared with that of undoped, Yb‐doped and Ag‐loaded TiO2HS. The degradation efficiency of Yb−Ag@TiO2HS on methyl orange was 7 times, 3 times and 4 times higher than that of TiO2HS, Yb@TiO2HS and Ag@TiO2HS, respectively.

Synthesis, Characterization and Evaluation of Antimicrobial, Antioxidant & Anticancer Activities of Copper Doped Zinc Oxide Nanoparticles

The present work reveals the influence of copper (Cu) doping in band gap energy level as well as selective cytotoxicity of ZnO nanoparticles against human breast cancer cells (MCF7), human cervical carcinoma (HeLa), and one normal (Vero) cell line. Cu-doped ZnO nanoparticles (Cu-ZnO NPs) were synthesized and validated by UV-Vis, FT-IR, XRD, SEM and EDX. Cu-doping diminished the band gap energy of ZnO NPs from 3.54 eV to 3.29 eV. Antimicrobial activity has been evaluated against three bacterial and fungal strains. Antioxidant activity was examined using a DPPH free radical, ABTS+ radicals, hydroxyl radicals and nitric oxide scavenging assay. Cu-ZnO NPs showed anticancer activity with IC50 value of 219.56 µg/mL against MCF7 and 137.27 µg/mL against HeLa cell lines. The doping of Cu with ZnO improved the selective cytotoxicity of ZnO NPs towards MCF7 and HeLa cells without affecting the normal cells.

Crucial Role of Fluorine in Fully Alkylated Ladder-Type Carbazole-Based Nonfullerene Organic Solar Cells.

Two fused ladder-type nonfullerene acceptors, DTCCIC and DTCCIC-4F, based on an electron-donating alkylated dithienocyclopentacarbazole core flanked by electron-withdrawing nonfluorinated or fluorinated 1,1-dicyanomethylene-3-indanone (IC or IC-4F), are prepared and utilized in organic solar cells (OSCs). The two new molecules reveal planar structures and strong aggregation behavior, and fluorination is shown to red-shift the optical band gap and downshift energy levels. OSCs based on DTCCIC-4F exhibit a power conversion efficiency of 12.6%, much higher than that of DTCCIC-based devices (6.2%). Microstructural studies reveal that while both acceptors are highly crystalline, bulk heterojunction blends based on the nonfluorinated DTCCIC result in overly coarse domains, while blends based on the fluorinated DTCCIC-4F exhibit a more optimal nanoscale morphology. These results highlight the importance of end group fluorination in controlling molecular aggregation and miscibility.

Effect of Interface Traps on the Device Performance of InGaAs-Based Gate-All-Around Tunneling Field-Effect Transistors.

The effect of interface traps on InGaAs-based vertical gate-all-around (GAA) tunneling field-effect transistors (TFETs) has been investigated using technology computer-aided design (TCAD) simulation. The interface traps distributed within different energy levels (Et) in the energy bandgap of a semiconductor material exhibit various influences on the device performances. In this work, InGaAs-based TFETs are simulated to analyze the effects on the on-state current (Ion), off-state current (Ioff), threshold voltage (Vth), subthreshold swing (SS), and the ambipolar characteristics according to Et and type of the interface traps. We have confirmed that Ioff and SS are degraded by the interface traps. Further, it can be shown that Ion is mainly affected by the acceptor-like traps and ambipolar behavior is affected by the donor-like traps. All the effects increase as Et becomes closer to the midgap. The effects of the interface traps with gate underlap and overlap at the source-channel region also have been investigated, considering the device fabrication. Additionally, the analysis of the effect of junction trap created at the source-channel junction has been performed.

Characterization of Lithium Tantalate (LiTaO3) Film on the Concentration Variations of Ruthenium Oxide (RuO2) Dope

One of the ferroelectric materials that has a large potential to be developed is LiTaO3 film. LiTaO3 film has been successfully produced by doping with RuO2 concentrations of 0%, 2%, 4%, and 6% using the CSD (Chemical Solution Deposition) method with a spin coating technique at 8000 rpm and an annealing temperature of 850° C. Samples were characterized using UV-Vis Spectrophotometry, SEM, XRD, and EDX. The film thicknesses at dope concentrations of 0%, 2%, 4%, and 6% 0.2681 µm, were 0.2234 µm, 0.2234 µm, and 0.5078 µm, respectively, with bandgap energy levels of 2.38 eV, 2.29 eV, 2.04 eV, and 2.47 eV. The lattice parameters obtained were a = 5.098961 Å and c = 14.316897 Å (0% RuO2), a = 5.065135 Å and c = 14.058488 Å (2% RuO2), a = 5.069937 Å and c = 114.275256 Å (4% RuO2), and a = 5.058727 Å and c = 14.253829 Å (6% RuO2) causing the crystal structure to be hexagonal (α = β = 90° and γ = 120°) with crystal sizes for each film 0.258 µm, 0.285 µm, 0.295 µm, and 0.36 µm.