Narrow Band Gap Research Articles

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.

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

Boosting solar-driven metal-free activation of sulfites by biochar-based photocatalyst for organic pollutants degradation: in-situ precise regulation and the enhancement mechanism

The photocatalytic activation of sulfites, a common by-product in industries, is a green and sustainable technology with great promise for the treatment of refractory pollutants in water. In this study, N vacancies and N doping were constructed at precise sites in graphitic carbon nitride (CN), following the combination with biochar (BC), synthesizing the BVCN with excellent photocatalytic activation of sulfites under solar light. When the BC was 5wt% (5BVCN), the reaction rate constant of reactive red 120 (RR120) in SO32−-containing solution reached 0.0247 min−1, which was 5.49 times of CN and 15.43 times of 5BVCN in SO32−-free solution. Characterizations and density functional theory (DFT) calculations revealed that N vacancies could trap electrons, while N doping regulated the electronic structure, forming mid-gap states to enhance the separation of carriers. In BVCN, BC rich in pyridinic N serves as both electron transfer channel and electron storage medium, having π-π interaction with structurally regulated CN (VCN). BVCN has narrower band gap and low recombination rate of photogenerated carriers, responds well to visible light, and is easy to firmly associated with SO32−, enhancing the electron transfer from SO32− to BVCN. In the SO32−-containing system, the primary active species were identified as SO3•−, •O2− and h+. Moreover, BVCN exhibited good stability and recyclability. The system shows potential for treating wastewater containing sulfites, realizing resource utilization.Graphical

Ultrabroadband photoresponse based on Te/SnS2 heterojunction with fast speed

Abstract Tellurium, a two-dimensional (2D) p-type semiconductor with a narrow bandgap and notable carrier mobility, has garnered significant research attention for polarization-sensitive infrared photodetectors. In this work, we present a wide-spectrum photodetector constructed from the 2D van der Waals p–n heterojunction Te/SnS2. This device demonstrates a broadband photodetection capability ranging from 275 nm (solar-blind ultraviolet, SBUV) to 10.6 μm (long-wave infrared, LWIR). Under SBUV illumination, it achieves a high responsivity (R) of 317.0 AW−1 and exhibits a minimal noise equivalent power (NEP) of 2.7 × 10−13 WHz−1/2. In the visible range, the device shows rapid photoresponse characteristics with a rise time (τ r) of 0.62 μs and a decay time (τ d) of 0.66 μs, along with polarization sensitivity characterized by a dichroic ratio of approximately 1.32. Remarkably, the device also demonstrates strong LWIR detection performance at room temperature, with a responsivity of 57.9 mAW−1 and a NEP of 8.9 × 10−11 WHz−1/2. These results suggest a novel approach to designing advanced polarization-resolving photodetectors using anisotropic 2D materials.

Prediction and Screening of Lead-Free Double Perovskite Photovoltaic Materials Based on Machine Learning

The search for stable, lead-free perovskite materials is critical for developing efficient and environmentally friendly energy solutions. In this study, machine learning methods were applied to predict the bandgap and formation energy of double perovskites, aiming to identify promising photovoltaic candidates. A dataset of 1053 double perovskites was extracted from the Materials Project database, with 50 feature descriptors generated. Feature selection was carried out using Pearson correlation and mRMR methods, and 23 key features for bandgap prediction and 18 key features for formation energy prediction were determined. Four algorithms, including gradient-boosting regression (GBR), random forest regression (RFR), LightGBM, and XGBoost, were evaluated, with XGBoost demonstrating the best performance (R2 = 0.934 for bandgap, R2 = 0.959 for formation energy; MAE = 0.211 eV and 0.013 eV/atom). The SHAP (Shapley Additive Explanations) analysis revealed that the X-site electron affinity positively influences the bandgap, while the B″-site first and third ionization energies exhibit strong negative effects. Formation energy is primarily governed by the X-site first ionization energy and the electronegativities of the B′ and B″ sites. To identify optimal photovoltaic materials, 4573 charge-neutral double perovskites were generated via elemental substitution, with 2054 structurally stable candidates selected using tolerance and octahedral factors. The XGBoost model predicted bandgaps, yielding 99 lead-free double perovskites with ideal bandgaps (1.3~1.4 eV). Among them, four candidates are known compounds according to the Materials Project database, namely Ca2NbFeO6, Ca2FeTaO6, La2CrFeO6, and Cs2YAgBr6, while the remaining 95 candidate perovskites are unknown compounds. Notably, X-site elements (Se, S, O, C) and B″-site elements (Pd, Ir, Fe, Ta, Pt, Cu) favor narrow bandgap formation. These findings provide valuable guidance for designing high-performance, non-toxic photovoltaic materials.

HgTe Nanocrystals Carrier Density and Its Tuning

HgTe nanocrystals (NCs) are now an established material for colloidal optoelectronics. In the mid‐ and far‐infrared range, there is to date no viable colloidal alternative material that can emit or detect light with such a high efficiency. Advancements have been rapid, primarily concentrating on the direct application of the narrow bandgap material spectrum in devices. However, certain material properties, such as carrier density, have been suboptimally addressed, despite their critical importance to device design. Therefore, this review aggregates most of the recent developments related to the determination and control of the carrier density with HgTe NCs. The manuscript is organized along three scales: the intrinsic properties that mostly relate to the inorganic core of the NCs, the nanoscale functionalization that relates to the surface modification of the NCs, and the device scale mostly driven by gating methods. The review provides a systematic discussion on strategies and technologies to control the carrier density and their use for optoelectronics. Finally, a discussion is done on the directions to be developed to push even further the efficiency of devices based on this material.

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 (ELF, NCI, QTAIM, and NBO) confirmed the presence of these chalcogen-centeredinteractions 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.

Tailoring β-Bi2O3 Nanoparticles via Mg Doping for Superior Photocatalytic Activity and Hydrogen Evolution

Bismuth oxide (β-Bi2O3) is a promising visible-light-driven photocatalyst due to its narrow direct bandgap, but its practical application is hindered by rapid electron–hole recombination and limited surface active sites. This study demonstrates a sol-gel synthesis approach to tailor β-Bi2O3 nanoparticles through magnesium (Mg) doping, achieving remarkable enhancements in the photocatalytic degradation of organic pollutants and hydrogen evolution. The structural analysis through XRD, SEM, and EDX confirmed Mg-doping concentrations of 0.025 to 0.1 M led to crystallite size reduction from 79 nm to 13 nm, while the UV–Vis bandgap measurement showed it decreased from 3.8 eV to 3.08–3.3 eV. The photodegradation efficiency increased through Mg doping at a 0.1 M concentration, with the highest rate constant value of 0.0217 min−1. The doping process led to VB potential reduction between 3.37 V (pristine) and 2.78–2.91 V across the doped samples when referenced to SCE. The photocatalytic performance of Mg0.075Bi1.925O3 improved with its 3.2 V VB potential because the photoelectric band arrangement enhanced both light absorption and charge separation. The combination of modifications through Mg doping yielded an enhanced photocatalytic performance, which proves that magnesium doping is a pivotal approach to modifying β-Bi2O3 suitable for environmentally and energy-related applications.

Preparation of Strontium Hydroxystannate by a Hydrothermal Method and Its Photocatalytic Performance

To address the challenge of abatement of volatile organic compounds (VOCs) in environmental catalysis, this study developed a temperature-gradient hydrothermal strategy to fabricate SrSn(OH)6 nanocatalysts and systematically investigatd their photocatalytic performance and mechanisms for gaseous toluene degradation. SrSn(OH)6 (SSH) was synthesized via a simple hydrothermal method with optimal preparation conditions identified as a reaction temperature of 140 °C and duration of 12 h. The crystallinity of SrSn(OH)6 was modulated by adjusting the pH of the precursor solution, yielding materials with distinct morphologies, specific surface areas, and band gaps. The narrowed band gap of SrSn(OH)6 nanocatalysts facilitated electron excitation to generate additional photogenerated electron-hole pairs. The SSH-10.5 sample with ordered planar and hole-like structures promoted carrier migration, effectively suppressed electron-hole recombination, and enhanced the conversion of abundant surface hydroxyl groups into hydroxyl radicals. Under UV irradiation, SSH-10.5 achieved a toluene degradation efficiency of 69.56% and showed excellent stability after five reuse cycles. Electron spin resonance analysis confirmed the presence of •OH and •O2− radicals in the reaction system, with •OH identified as the dominant active species. In situ FT-IR spectroscopy revealed that •OH and •O2− radicals attacked the methyl group of toluene, converting it into intermediates including benzyl alcohol, benzaldehyde, and benzoic acid. This work provides a novel design of high-efficiency VOC-photocatalytic materials and shows significant implications for advancing industrial exhaust gas purification technologies.

Tuning the Crystallization and Photothermal Aging Chemistry of CsPb0.4Sn0.6I3 for Inorganic Perovskite Tandem Photovoltaics.

The poor performance of inorganic narrow bandgap perovskite solar cells (PSCs) hinders the development of inorganic perovskite tandem solar cells (IPTSCs). We modulate the crystallization and photothermal aging chemistry for CsPb0.4Sn0.6I3 (1.31eV) with guanidinoacetic acid (GCA) to develop IPTSC. The CsPb0.4Sn0.6I3:GCA PSC reaches an efficiency of 16.93% and maintains an initial efficiency of ∼80% (T80) for 1300h under maximum power point tracking (MPPT) at 65°C. We identify that there are not only ionic migration species (I-, I3 -) but also molecular migration species (SnI4, I2) for CsPb0.4Sn0.6I3 correlated to the photothermal dynamics. For CsPb0.4Sn0.6I3 film, the intractable pinholes accelerate the iodine migration to the electrode and photothermal degradation. The photodegradation of PbI2 produces I2 and then promotes the Sn2+ oxidation to Sn4+, causing tin migration in the form of SnI4 to accumulate at the electron transport layer/perovskite interface, and in turn generating more pinholes and Sn-Pb segregation. In CsPb0.4Sn0.6I3:GCA film, due to the coordination bonds with Pb/Sn cations and hydrogen bonds with I- ions, GCA incorporation-induced pinhole-free morphology can significantly suppress ion/molecule migration. Combined with CsPbI2Br subcell, two-terminal IPTSC delivers an efficiency of 22.18%, accompanied by T80=850h under MPPT at 65°C.

Electrical Transport Interplay with Charge Density Waves, Magnetization, and Disorder Tuned by 2D van der Waals Interface Modification via Elemental Intercalation and Substitution in ZrTe3, 2H-TaS2, and Cr2Si2Te6 Crystals.

Electrical transport in 2D materials exhibits unique behaviors due to reduced dimensionality, broken symmetries, and quantum confinement. It serves as both a sensitive probe for the emergence of coherent electronic phases and a tool to actively manipulate many-body correlated states. Exploring their interplay and interdependence is crucial but remains underexplored. This review integratively cross-examines the atomic and electronic structures and transport properties of van der Waals-layered crystals ZrTe3, 2H-TaS2, and Cr2Si2Te6, providing a comprehensive understanding and uncovering new discoveries and insights. A common observation from these crystals is that modifying the atomic and electronic interface structures of 2D van der Waals interfaces using heteroatoms significantly influences the emergence and stability of coherent phases, as well as phase-sensitive transport responses. In ZrTe3, substitution and intercalation with Se, Hf, Cu, or Ni at the 2D vdW interface alter phonon-electron coupling, valence states, and the quasi-1D interface Fermi band, affecting the onset of CDW and SC, manifested as resistance upturns and zero-resistance states. We conclude here that these phenomena originate from dopant-induced variations in the lattice spacing of the quasi-1D Te chains of the 2D vdW interface, and propose an unconventional superconducting mechanism driven by valence fluctuations at the van Hove singularity, arising from quasi-1D lattice vibrations. Short-range in-plane electronic heterostructures at the vdW interface of Cr2Si2Te6 result in a narrowed band gap. The sharp increase in in-plane resistance is found to be linked to the emergence and development of out-of-plane ferromagnetism. The insertion of 2D magnetic layers such as Mn, Fe, and Co into the vdW gap of 2H-TaS2 induces anisotropic magnetism and associated transport responses to magnetic transitions. Overall, 2D vdW interface modification offers control over collective electronic behavior, transport properties, and their interplays, advancing fundamental science and nanoelectronic devices.

Silver Telluride Quantum Dots on Silicon Near-Infrared Photodetectors.

Ag2Te quantum dots (QDs) are narrow-bandgap, heavy metal-free QDs with significant potential for near-infrared detection. In this study, we fabricated a silicon-based Ag2Te QD near-infrared photodetector to assess its feasibility for large-scale silicon-based integration. The Ag2Te QDs synthesized by hot injection method, have an average size of 5 nm and a bandgap of 0.73 eV. These narrow bandgap Ag2Te QDs were successfully deposited onto silicon wafers following ligand exchange. At room temperature, the QD photodetector demonstrated a high responsivity of 150 A/W and a specific detectivity of 4.8 × 1012 Jones under 1050 nm illumination. Additionally, we investigated the effects of electrode positioning and QD film thickness on the device performances, establishing a foundation for the low-cost, large-scale integration of the narrow-bandgap QD materials with the silicon platform.

"Two-in-One" DPP Building Blocks for Ambipolar Conjugated Polymers in Flexible Transistors.

Advancements in conjugated donor-acceptor (D-A) polymers with superior semiconducting performance and reliability are pivotal to the evolution of flexible electronics. However, the development of electron-accepting building blocks has lagged far behind that of electron-donating ones, hindering the progression of ambipolar and n-type semiconductor polymers-especially ambipolar types-and thereby limiting the construction of logic circuits and p-n heterojunctions. In this study, we introduce a new electron-accepting building block, 2Ar'Ar2DPP, meticulously engineered for semiconducting polymers tailored to flexible electronics applications. Synthesized through the modification of conventional diketopyrrolopyrrole (DPP), 2Ar'Ar2DPP─including 2TPh2DPP and 3T2DPP─incorporates structural innovations, merging a single DPP unit with two aromatic groups into a configuration featuring two DPP units and three aromatic groups. This modification enhances the electron-accepting ability and modulates intra- and intermolecular D-A interactions. 2TPh2DPP and 3T2DPP were investigated to explore their structure-property relationships. Specifically, 3T2DPP demonstrates improved backbone planarity, extended π-conjugation, and more efficient intramolecular D-A interactions. These features result in significantly lower LUMO levels and narrower band gaps compared to those of conventionally utilized thiophene-flanked DPP and even its dimer. Moreover, the change in the molecular structural symmetry of 3T2DPP induces a relatively large dipole moment, thereby enhancing intermolecular interactions. Consequently, polymers derived from 2Ar'Ar2DPP exhibit ambipolar semiconducting performance in flexible organic field-effect transistors, achieving hole and electron mobilities of up to 6.0 and 2.1 cm2 V-1 s-1, respectively, with good bending resistance. These preliminary results indicate that 2Ar'Ar2DPP holds significant promise for the future design of conjugated materials for flexible electronics.

Heterovalent-Doped Sb2S3 Glass for Large-Area Sensitive X-ray Detection and Imaging.

Flat-panel X-ray detectors are indispensable in a variety of imaging applications ranging from medical radiography to industrial inspections. Current commercial detectors (α-Se/CdTe) suffer from unsatisfactory image contrast and high-dose X-ray exposure owing to the limited attenuation and charge collection. Here, we show that heterovalent-doped Sb2S3 glass (α-Sb2S3) can effectively convert X-ray photons to electrical current signals. SnI2 doping modifies the Sb-S network and stabilizes the noncrystalline structure, enabling bulk α-Sb2S3 with a narrow bandgap (1.66 eV), large mobility-lifetime product (5.6 × 10-5 cm2 V-1), and strong radiation attenuation capacity simultaneously. The α-Sb2S3-based detector exhibits a high sensitivity of 4397 μC Gy1- cm-2, a low detection limit of 66 nGy s-1, and excellent stability. Thermally evaporated α-Sb2S3 on a pixelated thin film transistor (TFT) backplane enables high-resolution X-ray imaging. This is the first demonstration of Sb2S3-based X-ray detection and imaging, creating new possibilities for the development of amorphous semiconducting materials and devices.

Microhole Structure in Flexible Semitransparent Perovskite Solar Cells Using Nickel Mesh as the Framework and Electrode.

Semitransparent perovskite solar cells can provide auxiliary power in applications such as power-generating windows and smart car windows. However, in conventional planar-structured devices, both the power conversion efficiency (PCE) and the average visible light transmittance (AVT) of the devices are restricted by the band gap or thickness of the perovskite absorption layer, which hinders the development and application of semitransparent perovskite solar cells. In this work, we construct a new type of semitransparent perovskite solar cell with a three-dimensional (3D) mesh structure using nickel mesh as a framework and bottom electrode. The AVT of the device is controlled by a nickel mesh. When narrow band gap perovskite materials were deposited, the PCE of the device was 4.48%, the average visible light transmittance was 16.5%, the color rendering index was 98.35, and the bifacial coefficient reached 79%. Additionally, due to the flexible nature of the nickel mesh, the device exhibited excellent mechanical stability, maintaining 90% of its initial PCE after 1000 bending cycles at R = 10 mm. This three-dimensional mesh structure provides a new idea for realizing the transmittance of semitransparent flexible perovskite solar cells with high efficiency and high transmittance. It is expected to promote their wide application in fields such as building-integrated photovoltaics.

Graphene as Infrared and Electron Transparent Electrode Applied to the Design of Narrow Bandgap Nanocrystal‐Based Photodiode

AbstractColloidal nanocrystals (NCs) are a promising platform for infrared optoelectronics. Current efforts focus on designing NCs that absorb in the short‐ and mid‐wave infrared and integrating them into diode stacks. A major challenge is to coupling these sensors to read‐out integrated circuits (ROICs) for infrared imaging, which requires infrared‐transparent top electrodes. Conventional materials like tin‐doped indium oxide lose transparency at longer wavelengths, limiting their effectiveness. Metallic grids have emerged as an alternative but struggle to maintain a uniform potential, as shown by nanobeam X‐ray photoemission microscopy. To address this, graphene is explored as a transparent electrode. A novel diode stack is proposed to maintain a backside mirror, accommodate HgTe NCs’ chemical constraints, and incorporate electrodes that efficiently extract both electrons and holes. Unlike conventional designs limited to near‐zero bias, this stack operates optimally under CMOS read‐out‐integrated‐circuit (ROIC) conditions. Additionally, its transparent electrode allows photoelectron emission from within the diode, enabling in situ electric field analysis. This capability enables to rationalize the optimization process of photodiode design.

Design of a novel visible light bandstop photonic crystal filter based on mesoporous SiO2 thin films

Abstract Currently, within the spectral ranges of visible light, ultraviolet radiation, and high-energy x-ray photons, the predominant filtering technology employed is the photonic crystal (PC) passband filter. Nevertheless, these filters exhibit notable limitations, such as a relatively restricted filtering frequency range and intricate fabrication processes. In response to the aforementioned challenges, this paper introduced for the first time the concept of a structurally simple and wideband-stopband filter based on mesoporous SiO2 thin films, thereby offering a novel solution for relevant domains. The transfer matrix method was used to analyze the impact of different filling ratios and lattice constants on the photonic band gap (PBG) properties of mesoporous SiO2 thin films. The results showed that, under the optimal filling ratio (r/a = 0.06), narrow PBGs and high transmission could be achieved in the violet (437.54 nm), green (510.46 nm), yellow (583.55 nm), and red (656.35 nm) light bands by adjusting the lattice constant. By extending the range of the horizontal axis for analysis, it was observed that the stopband range of the designed filter had substantially broadened, covering wavelengths above 227.9 nm, 264.8 nm, 303.4 nm, and 340.3 nm, respectively. Consequently, a novel filter with wide bandwidth, narrow bandgap, high reflectivity, and a simplified fabrication process was successfully developed. Additionally, in the X-Z and Y-Z planes, the position and properties of the PBG remained largely unchanged when the incident angle is less than 11.5°. This study not only expands the theoretical research scope of PC materials but also opens new possibilities for their practical applications.

All-Inorganic Tin-Containing Perovskite Solar Cells: An Emerging Eco-Friendly Photovoltaic Technology.

All-inorganic tin (Sn)-containing perovskites have emerged as highly promising photovoltaic materials for single-junction and tandem perovskite solar cells (PSCs), owing to their reduced toxicity, optimal narrow bandgap, and superior thermal stability. Since their initial exploration in 2012, significant advancements have been achieved, with the highest efficiencies of single-junction and tandem devices now surpassing 17% and 22%, respectively. Nevertheless, the intrinsic challenges associated with the oxidation susceptibility of Sn2+ and the uncontrolled crystallization dynamics impede their further development. Addressing these issues necessitates a comprehensive and systematic understanding of the degradation mechanisms inherent to all-inorganic Sn-containing perovskites, as well as the development of effective mitigation strategies. This review provides a detailed overview of the research progress in all-inorganic Sn-containing PSCs, with a particular focus on the basic properties and degradation pathways of both pristine Sn and mixed Sn-Pb perovskites. Furthermore, various strategies to improve the efficiency and stability of Sn-containing PSCs are thoroughly discussed. Finally, the existing challenges and perspectives are provided for further improving the photovoltaic performance of eco-friendly PSCs.

Component modulation engineering of NiOx hole transport layers in perovskite solar cells by magnetron sputtering

Abstract This study systematically investigates the component modulation of NiOx hole transport layers fabricated via reactive magnetron sputtering for high-performance perovskite solar cells. By precisely controlling O2 flow rates (4–8 sccm) during deposition, we elucidate the interplay between O stoichiometry, crystallographic ordering, defect dynamics, and optoelectronic properties of NiOx films. Structural characterization reveals a critical O2 flow (≥6 sccm) for cubic phase crystallization, with XRD demonstrating enhanced crystallinity and XPS showing increased Ni3+/Ni2+ ratios under O-rich conditions. Optical studies correlate elevated O2 flow with bandgap narrowing (3.62–3.45 eV) and transmittance degradation, attributed to Ni3+-mediated mid-gap states and free carrier absorption. Optimized NiOx HTLs deposited at 6 sccm O2 flow yield PSCs with peak power conversion efficiency of 17.29%, outperforming devices with 4 sccm (17.10%) and 8 sccm (16.64%) counterparts. Accelerated aging tests under thermal (85 °C) and light-soaking (AM1.5) stresses reveal superior stability for 6 sccm-optimized devices, retaining 94% and 97.3% of initial PCE after 400 h, respectively. These findings establish O2 flow as a critical lever for balancing defect engineering and interfacial energetics, providing a pathway for scalable fabrication of efficient and stable NiOx-based perovskite solar cells.