Narrow Band Gap Research Articles

Effects of Ni Doping on Thermoelectric Properties of Chalcopyrite

Chalcopyrite (CuFeS2) has attracted interest as a thermoelectric material due to its narrow bandgap and its ability to tailor its carrier concentration through doping. In this study, we investigated the effects of Ni2+ substitution at Cu+ sites in chalcopyrite (Cu1−xNixFeS2) on its structural, microstructural, and thermoelectric properties. Samples were synthesized using mechanical alloying followed by hot pressing to ensure high-density compaction. X-ray diffraction analysis confirmed the formation of the tetragonal chalcopyrite phase without detectable secondary phases. The observed reduction in lattice parameters with increasing Ni content provided evidence of successful Ni incorporation at Cu sites within the chalcopyrite structure. Microstructural analysis and elemental mapping further supported the uniform distribution of Ni within the chalcopyrite matrix. Thermoelectric property measurements revealed that Ni-doped chalcopyrite exhibited n-type conduction. As the Ni concentration increased, the carrier concentration and electrical conductivity increased significantly, with Cu0.92Ni0.08FeS2 achieving the highest electrical conductivity of 2.5 × 104 Sm−1 at 723 K. However, the absolute value of the Seebeck coefficient decreased with increasing Ni doping, following the expected trade-off between electrical conductivity and thermopower. The optimized composition, Cu0.96Ni0.04FeS2, exhibited the highest thermoelectric performance, with a power factor of 0.50 mWm−1K−2 and a maximum dimensionless figure of merit (ZT) of 0.18 at 623 K. Compared to undoped chalcopyrite, these enhancements represent a 43% increase in power factor and a 50% improvement in ZT.

Preparation and Characterization of CS/GO/Bi2Ce2O5S2@Ag Composite Photocatalytic Membrane and Its Adsorption Catalytic Removal of Cr(VI)

ABSTRACTThe separation and purification of wastewater containing Cr(VI) remains a challenging subject. The preparation of composite membranes capable of adsorbing and photocatalytically reducing Cr(VI) is a promising method for treating wastewater containing Cr(VI). In this study, a novel photocatalyst CS/GO/Bi2Ce2O5S2 was prepared through the hydrothermal reaction of (NH4)2Ce(NO3)6 with Bi(NO3)3 and (NH2)2CS. Then the photocatalyst was dispersed in chitosan (CS)/graphene oxide (GO) solution to prepare the CS/GO/Bi2Ce2O5S2 membrane, which was then immersed in AgNO3 solution and in situ reduced to produce AgNPs, resulting in a novel photocatalytic membrane (CS/GO/Bi2Ce2O5S2/Ag). The results show that the membrane can reduce 99.75% of Cr(VI) in wastewater. The adsorption capacity of the photocatalytic membrane for Cr(VI) reached 235.34 mg/g, and the absorption processes conformed to the pseudo‐second‐order model and Langmuir model. This photocatalyst features a narrow band gap and a very high photogenerated carrier generation rate and photocatalytic efficiency. The electrochemical test shows that CS/GO/Bi2Ce2O5S2@Ag has the maximum photocurrent density and the minimum impedance, which can be more beneficial to the generation of photogenerated charge carriers. The results of this study realize the simultaneous adsorption, photocatalytic reduction, separation, and purification of wastewater containing Cr(VI), which has high efficiency, economic, and practical significance.

Precisely Tuning 3D/Quasi-2D Perovskite Heterojunctions in Wide-Bandgap Perovskites for High-Performance Tandem Solar Cells.

Wide-bandgap (WBG) perovskite sub-cells in all-perovskite tandem solar cells (AP-TSCs) suffer from severe open-circuit voltage loss and poor light stability. The formation of 3D/2D or 3D/quasi-2D perovskite heterojunctions can effectively passivate interface defects and optimize energy level alignments at the 3D perovskite/C60 interface, thereby enhancing both the efficiency and stability of perovskite solar cells. Herein, a combined evaporation/solution technique is employed to construct Dion-Jacobson (DJ) 2D or quasi-2D perovskites with uniform-phase distribution on wide-bandgap 3D perovskite substrates. By tuning the n values of the DJ phase perovskites, well-refined WBG 3D/2D or quasi-2D perovskite heterostructures are achieved, which exhibit tunable energy levels and mitigate the non-radiative recombination losses at the WBG 3D perovskite/C60 interface. The devices with the WBG (1.78eV) 3D/quasi-2D n = 3 perovskite heterostructures achieve the champion power conversion efficiency (PCE) of 20.71% (certified 20.53%). When combined with narrow-bandgap (NBG) perovskite sub-cells, the fabricated 2-terminal AP-TSCs achieve a PCE of 28.99% (certified 28.81%). The tandem device maintains 80% of its initial PCE after 501h of operation at maximum power point.

Photothermal-Enhanced Anti-SO2 Performance of a MoWOx/CeO2 Catalyst in Low-Temperature NH3-SCR.

Cerium-based catalysts for the selective catalytic reduction of NOx with ammonia (NH3-SCR) face significant challenges in practical applications, particularly their poor low-temperature activity and susceptibility to SO2 poisoning. In this study, photothermal catalysis was innovatively applied to the NH3-SCR reaction over MoWOx/CeO2 catalysts, achieving remarkable improvements in the low-temperature performance and SO2 resistance. Under photothermal conditions, the catalyst maintained NOx conversion above 90% at 200 °C, even in the presence of 250 ppm of SO2. Comprehensive characterization revealed that light irradiation significantly enhanced the formation of oxygen vacancies on the catalyst surface and weakened NO adsorption, indicating that the NH3-SCR reaction follows the Eley-Rideal mechanism, which contributes to its excellent low-temperature activity. Moreover, photothermal conditions reduced the chemical adsorption intensity of SO2, effectively inhibiting the formation of ammonium sulfate. Density functional theory calculations further demonstrated that the narrow band gap of MoWOx promotes electron transfer from the O 2p orbital to the Ce 4f orbital at the Ce-O-Mo(W) interface under light, leading to electron enrichment at active sites and suppression of SO2 oxidation. This work not only provides a novel strategy for enhancing the NH3-SCR performance but also represents a groundbreaking advancement in the design of highly efficient, SO2-resistant catalysts for low-temperature applications.

Fabrication of Microgel@TiO2/ZnO NPs for Efficient Degradation of Methylene Blue Under Solar Light

ABSTRACTDeveloping a narrow bandgap nanocomposite photocatalyst capable of degrading pollutants under visible light is a challenging task. This report presents the design of microgel‐based nanocomposites through free‐radical emulsion polymerization, achieved by adjusting the concentration of the N‐hydroxymethyl acrylamide (NHMA) monomer as a crosslinker. Distinct three grades of microgel (MNP) were prepared by altering the quantity of NHMA. Titanium/Zinc oxide nanoparticles (TiO2/ZnO NPs) were effectively integrated into the microgels of polymers using the hydrothermal method for application in catalytic degradation. The characterization of synthesized samples has been performed utilizing a range of methods, viz. dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FT‐IR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), powder X‐ray diffraction (Powder XRD), energy dispersive X‐ray spectroscopy (EDX) and transmission electron microscopy (TEM). The effective integration of microgel with TiO2/ZnO nanoparticles enhances the photocatalytic performance at different temperatures, as the microgel offers an extensive surface area for pollutant adsorption. The microgel‐nanocomposite (MNP@TiO2/ZnO NCs) has been successfully reused for the photodegradation of dyes, owing to the recyclability of microgels. This research provides valuable insights toward developing a noteworthy visible‐light‐driven photocatalyst aimed at environmental remediation.

Tellurium nanowire retinal nanoprosthesis improves vision in models of blindness.

Present vision restoration technologies have substantial constraints that limit their application in the clinical setting. In this work, we fabricated a subretinal nanoprosthesis using tellurium nanowire networks (TeNWNs) that converts light of both the visible and near-infrared-II spectra into electrical signals. The broad-spectrum coverage is made possible by a combination of narrow bandgaps, strong absorption, and engineered asymmetries. Implanted into blind mice, the TeNWNs restored pupillary reflexes and enabled visually cued learning under visible and near-infrared 1550-nanometer light. In nonhuman primates, TeNWNs elicited robust retina-derived neural responses, confirming biocompatibility and feasibility. By restoring lost photosensitivity and extending vision to near-infrared, this nanoprosthesis offers a promising approach for restoring vision.

Effect of Chalcogen Interaction on the Structure of Methine-Bridged Trichalcogenophenes.

Polythienylenemethylidenes (PTMs) are promising conjugated polymers for organic electronics owing to their narrow bandgaps and extended π-conjugation. However, their stereochemistry remains unexplored. In this study, methine-bridged trithiophene and trifuran analogs were synthesized to investigate stereochemistry and chalcogen bonding effects. The compounds were obtained as mixtures of ZZ, EZ(= ZE), and EE geometric isomers, established through detailed NMR analyses. At thermal equilibrium, the ZZ isomer predominated in trithiophene (ZZ:(EZ+ZE):EE=58:35:6), whereas trifuran showed a near-statistical distribution. X-ray crystallography revealed intramolecular S···S chalcogen bonding in trithiophene with S···S distances (≈3.04 Å) shorter than van der Waals radii and C-S···S angles of 171°. Comprehensive conformer searches and DFT calculations not only validated the higher stability of the ZZ isomer in trithiophene but also provided calculated isomer distributions that closely matched the experimental values. Multi-faceted computational analysis (electron localization function (ELF), noncovalent interaction (NCI), quantum theory of atoms in molecules (QTAIM), and natural bond orbital (NBO))confirmed the presence of these chalcogen-centered interactions and quantified their strength through lone pair (LP)(S)→σ*(S-C) donor-acceptor orbital interactions. Trithiophene exhibited a unique dual-chalcogen bonding mode in the ZZ configuration. These findings elucidate the role of chalcogen bonding in stabilizing ZZ-trithiophenes and contribute to designing PTMs with controlled stereochemistry for organic electronics applications.

Efficient CO2 Electroreduction to Methane on Covalent Organic Frameworks with CuN4 and CuN2Cl2 Dual Sites

Abstract Cu‐based covalent organic frameworks (COFs) are expected to promote methane (CH4) generation in CO2 electroreduction (CO2ER). However, traditional COF catalysts, which have relatively simple types and functions of active sites, face challenges in achieving high CH4 selectivity in CO2ER. Herein, a novel Cu‐based COF catalyst (CuPor‐DFBpy‐Cu) with CuN4 and CuN2Cl2 dual sites is developed by combining porphyrin and bipyridine moieties. Compared with Cu‐based COFs containing only CuN4 or CuN2Cl2 sites, CuPor‐DFBpy‐Cu significantly improved the efficiency of CO2ER to CH4. The maximum Faradaic efficiency of CH4 on CuPor‐DFBpy‐Cu reached 82.5% in the H‐type cell and increased to 84.9% in the flow cell, while the corresponding CH4 partial current density is as high as 365.1 mA cm−2. Theoretical calculations revealed that, compared to conventional Cu‐based COFs, the introduction of Cu dual sites endowed CuPor‐DFBpy‐Cu with a narrower band gap, optimized d‐band centers, and significant thermodynamic advantages in the CH4 generation pathway.

Mixed-Dimensional Nanowires/Nanosheet Heterojunction of GaSb/Bi2O2Se for Self-Powered Near-Infrared Photodetection and Photocommunication

With high surface-to-volume ratio, the abundant surface states and high carrier concentration are challenging the near-infrared photodetection behaviors of narrow band gap semiconductors nanowires. In this study, the narrow band gap semiconductor of Bi2O2Se nanosheets (NSs) is adopted to construct mixed-dimensional heterojunctions with GaSb nanowires (NWs) for demonstrating the impressive self-powered NIR photodetection. Benefiting from the built-in electric field of ~ 140meV, the as-constructed NW/NS mixed-dimensional heterojunction self-powered photodetector shows the low dark current of 0.07 pA, high Ilight/Idark ratio of 82 and fast response times of < 2/2ms at room temperature. The self-powered photodetector performance can be further enhanced by fabricating the NW array/NS mixed-dimensional heterojunction by using a contact printing technique. The excellent photodetection performance promises the as-constructed NW/NS mixed-dimensional heterojunction self-powered photodetector in imaging and photocommunication.

Understanding the Photocatalytic Water Reduction Capability of NaM(WO4)2 (M = Ga, Sc) by the Electronic Structure and Bond Characteristic Analysis.

m-WO3 has a narrow band gap, making it a promising photocatalyst. However, its antibonding W-O orbitals limit water reduction capability due to insufficient reduction potential. Incorporating a weakly bonded M-O in NaM(WO4)2 (M = Ga, Sc) enhances W-O covalency compared to that in m-WO3, resulting in a more negative conduction band minimum (CBM) potential, sufficient for photocatalytic water reduction. Here, NaM(WO4)2 (M = Ga, Sc) were synthesized via high-temperature solid-state reactions, and their precise structures were determined through Rietveld refinement of high-resolution XRD data. Density functional theory (DFT) calculations were performed to analyze the electronic structures, and bond characters were further examined using the crystal orbital Hamilton population (COHP), crystal orbital bond index (COBI), and electron localization function (ELF). Experimentally, NaGa(WO4)2 loaded with 0.63 wt % Pd and NaSc(WO4)2 loaded with 0.94 wt % Pd exhibited photocatalytic H2 generation rates of 2.45 and 6.30 μmol/h, respectively, under UV irradiation in a methanol aqueous solution. Apparent quantum yields at 295 nm are estimated to be 0.66 and 2.21%, respectively. Notably, NaSc(WO4)2 displayed a superior photocatalytic activity, which can be attributed to its more negative CBM potential, as discussed through a comparison of their electronic structures.

Crystal Facet Engineering of 2D SnSe2 Photocatalysts for Efficient Degradation of Malachite Green Organic Dyes

Wastewater containing triphenylmethane dyes such as malachite green (MG), discharged by textile and food industries, poses significant carcinogenic risks and ecological hazards. Conventional physical adsorption methods fail to degrade these pollutants effectively. To address this challenge, we focused on two-dimensional SnSe2 semiconductor materials. While their narrow bandgap and unique structure confer exceptional optoelectronic properties, prior research has predominantly emphasized heterojunction systems. We synthesized SnSe2 with well-defined hexagonal plate-like structures via a one-step hydrothermal method by precisely controlling precursor ratios (Sn:Se = 1:2) and reaction temperatures (120–240 °C). Systematic investigations revealed that hydrothermal temperature modulates the van der Waals forces between crystal planes, enabling selective exposure of (001) and (011) facets, as confirmed by XRD, SEM, and XPS analyses, thereby influencing the exposure of specific crystal facets. Experiments demonstrated that pure SnSe2 synthesized at 150 °C achieved complete degradation of MG (40 mg/L) within 60 min under visible light irradiation, exhibiting a reaction rate constant (k) of 0.099 min⁻¹. By regulating the exposure ratio of the active (001)/(011) facets, we demonstrate that crystal facet engineering directly optimizes carrier separation efficiency, thereby substantially enhancing the catalytic performance of standalone SnSe2. This work proposes a novel strategy for designing noble-metal-free, high-efficiency standalone photocatalysts, providing crystal facet-dependent mechanistic insights for the targeted degradation of industrial dyes.

High-valent nickel oxyhydroxides self-derived through a low-temperature thermochemical strategy for an efficient oxygen evolution reaction.

High-valent nickel oxyhydroxides self-derived through a low-temperature thermochemical strategy for an efficient oxygen evolution reaction.

Functionalized ZnOFe3O4 semiconductor oxides, grafted to the epoxy groups of graphene oxide with a narrow band gap and enhanced photocatalytic activities

Functionalized ZnOFe3O4 semiconductor oxides, grafted to the epoxy groups of graphene oxide with a narrow band gap and enhanced photocatalytic activities

Oxygen/sulfate radicals-generating CaS2O8 nanosonosensitizers induce PANoptosis and calcium overload for enhanced peritoneal metastasis immunotherapy.

Oxygen/sulfate radicals-generating CaS2O8 nanosonosensitizers induce PANoptosis and calcium overload for enhanced peritoneal metastasis immunotherapy.

Defect-engineered magnetic bismuth nanomedicine for dual-modal imaging and synergistic lung tumor therapy.

Defect-engineered magnetic bismuth nanomedicine for dual-modal imaging and synergistic lung tumor therapy.

Suppressing the Interface Photodegradation towards Efficient and Stable All Perovskite Tandem Solar Cells

Abstract All perovskite tandem solar cells (PTSCs) were expected to overcome the Shockley‐Queisser limit of single‐junction perovskite solar cells (PSCs). Nevertheless, wide bandgap (WBG) subcells suffer from large photovoltage loss and device instability due to extensive film defect, interfacial degradation and phase segregation. Herein, a polymeric multi‐dentate anchoring (PMDA) strategy by introducing poly(carbazole phosphonic acid) was employed to engineer the bottom interface and suppress phase segregation. The reinforced and homogeneous anchorage by multiple repeat phosphonic acid groups onto NiOx significantly optimised the bottom interface, suppressing unfavourable interfacial reactions and thus alleviating phase segregation of WBG perovskite. As a result, the PMDA‐modified WBG PSCs showed higher power conversion efficiency (PCE) than the control device (19.84% vs. 18.18%), along with better device photostability (T80 = 1200 vs. 500 h). Coupled with narrow bandgap (NBG) PSCs, the PMDA‐modified PTSCs reached a PCE of up to 28.51% with device operation photostability over 700 h (T80).

Suppressing the Interface Photodegradation towards Efficient and Stable All Perovskite Tandem Solar Cells.

All perovskite tandem solar cells (PTSCs) were expected to overcome the Shockley-Queisser limit of single-junction perovskite solar cells (PSCs). Nevertheless, wide bandgap (WBG) subcells suffer from large photovoltage loss and device instability due to extensive film defect, interfacial degradation and phase segregation. Herein, a polymeric multi-dentate anchoring (PMDA) strategy by introducing poly(carbazole phosphonic acid) was employed to engineer the bottom interface and suppress phase segregation. The reinforced and homogeneous anchorage by multiple repeat phosphonic acid groups onto NiOx significantly optimised the bottom interface, suppressing unfavourable interfacial reactions and thus alleviating phase segregation of WBG perovskite. As a result, the PMDA-modified WBG PSCs showed higher power conversion efficiency (PCE) than the control device (19.84% vs. 18.18%), along with better device photostability (T80=1200 vs. 500 h). Coupled with narrow bandgap (NBG) PSCs, the PMDA-modified PTSCs reached a PCE of up to 28.51% with device operation photostability over 700 h (T80).

High-Performance Phototransistor Based on a 2D Polybenzimidazole Polymer.

Photodetectors are fundamental components of modern optoelectronics, enabling the conversion of light into electrical signals. The development of high-performance phototransistors necessitates materials with both high charge carrier mobility and robust photoresponse. However, achieving both in a single material poses challenges due to inherent trade-offs. Herein, this study introduces a polybenzimidazole-(1,3-diazole)-based 2D polymer (2DPBI), synthesized as few-layer, crystalline films covering ≈28 cm2 on the water surface at room temperature, with large crystalline domain sizes ranging from 110 to 140 µm2. The 2DPBI incorporates a π-conjugated photoresponsive porphyrin motif through a 1,3-diazole linkage, exhibiting enhanced π-electron delocalization, a narrow direct band gap of ≈1.18eV, a small reduced electron-hole effective mass (m* = 0.171m0), and a very high resonant absorption coefficient of up to 106 cm-1. Terahertz spectroscopy reveals excellent short-range charge carrier mobility of ≈240 cm2 V-1 s-1. Temperature-dependent photoconductivity measurements and theoretical calculations confirm a band-like charge transport mechanism. Leveraging these features, 2DPBI-based phototransistors demonstrate an on/off ratio exceeding 108, photosensitivity of 1.08 × 107, response time of 1.1ms, and detectivity of 2.0 × 1013 Jones, surpassing previously reported standalone few-layer 2D materials and are on par with silicon photodetectors. The unique characteristics of 2DPBI make it a promising foundation for future optoelectronic devices.

Enhancement of bismuth tungstate perovskite photoelectrical performance using elemental co-doping and construction of ternary heterojunction for sensitive detection of Trenbolone.

Enhancement of bismuth tungstate perovskite photoelectrical performance using elemental co-doping and construction of ternary heterojunction for sensitive detection of Trenbolone.

Structural engineering of small molecule-based narrow bandgap dithieno-3,2-b:2′,3′-dlpyrrole-based non-fullerene electron acceptors for efficient organic solar cells

Structural engineering of small molecule-based narrow bandgap dithieno-3,2-b:2′,3′-dlpyrrole-based non-fullerene electron acceptors for efficient organic solar cells