Narrow Band Gap Research Articles

Severe Plastic Deformation of Ceramics by High-Pressure Torsion: Review of Principles and Applications

Ceramics are typically brittle at ambient conditions due to their covalent or ionic bonding and limited dislocation activities. While plasticity, and occasionally superplasticity, can be achieved in ceramics at high temperatures through thermally activated phenomena, creep, and grain boundary sliding, their deformation at ambient temperature and pressure remains challenging. Processing under high pressure via the high-pressure torsion (HPT) method offers new pathways for severe plastic deformation (SPD) of ceramics. This article reviews recent advances in HPT processing of ceramics, focusing primarily on traditional ceramics (e.g., oxides, carbides, nitrides, oxynitrides) and to a lesser extent advanced ceramics (e.g., silicon, carbon, perovskites, clathrates). Key structural and microstructural features of SPD-processed ceramics are discussed, including phase transformations and the generation of nanograins and defects such as vacancies and dislocations. The properties and applications of these deformed ceramics are summarized, including powder consolidation, photoluminescence, bandgap narrowing, photovoltaics, photocatalysis (dye degradation, plastic waste degradation, antibiotic degradation, hydrogen production, CO2 conversion), electrocatalysis, thermoelectric performance, dielectric performance, and ion conductivity for Li-ion batteries. Additionally, the article highlights the role of HPT in synthesizing novel materials, such as high-entropy ceramics (particularly high-entropy oxides), black oxides, and high-pressure polymorphs, which hold promise for energy and environmental applications.

Facilitated electron-hole separation and enhanced uranium(VI) capture via La-doped WO3: Insights into oxygen vacancies and superior recyclability.

Facilitated electron-hole separation and enhanced uranium(VI) capture via La-doped WO3: Insights into oxygen vacancies and superior recyclability.

Two-dimensional superlattice nanocatalysts unlock multimodal energy transformation-driven catalytic therapy

While the development of nanochemistry has spurred the emergence of catalytic nanomedicine, nanocatalysts with multifaceted catalytic properties for therapeutic applications remain underexplored. Here, we present two-dimensional BiCuSeO nanosheets (BCSO NSs) as the superlattice nanocatalyst for multimodal energy transformation-driven nanocatalytic therapy. Benefiting from the intrinsic layered heterostructures and a narrow bandgap, BCSO NSs feature photothermoelectric and sono-piezoelectric catalytic effects, as well as enzyme-mimicking catalytic activities. Theoretical calculations reveal that the internal electric fields within superlattice nanostructures contribute to the rapid separation and suppressed recombination of charge carriers. Consequently, BCSO NSs enable controlled reactive oxygen species generation under the second near-infrared light or ultrasound irradiations. The enzymatic activity of BCSO NSs also facilitates the transformation of tumor-specific substrates, dysregulating the redox homeostasis. The photothermoelectric and sono-piezoelectric/enzymatic activities of BCSO NSs have been exemplified by antibacterial and anticancer applications, highlighting the potential of two-dimensional superlattice nanocatalysts to address diverse pathological abnormalities.

Narrowing of lithium niobate band gap by fabricating Ag/MWCNT/LiNbO3 nanocomposites for solar—Driven photocatalysis applications

Narrowing of lithium niobate band gap by fabricating Ag/MWCNT/LiNbO3 nanocomposites for solar—Driven photocatalysis applications

Novel ultrathin Bi@Fe-based metal-organic frameworks nanosheets for efficient solar-driven photocatalytic water purification: Synergistic effect of localized surface plasmon resonance and high-density exposed metal active centers.

Novel ultrathin Bi@Fe-based metal-organic frameworks nanosheets for efficient solar-driven photocatalytic water purification: Synergistic effect of localized surface plasmon resonance and high-density exposed metal active centers.

Effects of non-metal doping in graphene-like structure: Engineering narrow bandgaps and reserved carrier mobility

Effects of non-metal doping in graphene-like structure: Engineering narrow bandgaps and reserved carrier mobility

First principles investigation of zb-TiSn: A promising narrow bandgap semiconductor

First principles investigation of zb-TiSn: A promising narrow bandgap semiconductor

Enhancing detectivity in multi-barrier Ag2Se-PbS CQD photodetector through numerical optimization of design parameters

Colloidal quantum dots (CQDs) with variable narrow bandgaps have emerged as powerful competitors to epitaxially grown semiconductors in the domain of infrared light transitions. This class of materials holds great promise for the development of next-generation optoelectronic devices, especially photodetectors. In recent developments, the use of silver chalcogenide CQDs has extended into biomedical applications of quantum dots. This expansion is attributed to their advantageous properties, such as low toxicity and tunable intraband transitions reaching the mid-infrared window. In this research, we investigate a structure for mid-infrared photon detection in the form of an intraband Ag2Se-PbS colloidal quantum dot (CQD) photodetector. Detectivity, a crucial performance parameter, is enhanced through numerical optimization by manipulating key design parameters such as Ag2Se CQD diameter, Ag2Se film doping density, and the number of PbS CQD layers in the barrier layer of the device's active region. This optimization process is conducted at various temperatures and biases. The results reveal that, under conditions of a 1 V bias and 80 K, the designed Ag2Se-PbS CQD infrared photodetector achieves peak detectivities. Specifically, observed peak detectivities of 13.13×109 Jones for Ag2Se CQDs with a diameter of 3.7 nm, and 11.01×109 Jones for a film doping density of 6.7×1018 cm-3 of Ag2Se CQDs.

Disentangling degradation pathways of narrow bandgap lead-tin perovskite material and photovoltaic devices

Narrow bandgap lead-tin perovskites are essential components of next-generation all-perovskite multi-junction solar cells. However, their poor stability under operating conditions hinders successful implementation. In this work, we systematically investigate the underlying mechanisms of this instability under combined heat and light stress (ISOS L-2 conditions) by measuring changes in phase, conductivity, recombination and current-voltage characteristics. We find an increased impact of the redistribution of mobile ions during device operation to be the primary driver of performance loss during stressing, with further losses caused by a slower increase in non-radiative recombination and background hole density. Crucially, the dominant degradation mode changes with different hole transport materials, which we attribute to variations in iodine vacancy generation rates. By quantifying the impact of these mechanisms on device performance, we provide critical insights for improving the operational stability of lead-tin perovskite solar cells.

Steric Confinement and Dynamic Coordination Synergy for Crystallization Control in 27.9%‐Efficient All‐Perovskite Tandem Solar Cell

Abstract The inhomogeneous Pb/Sn distribution in Sn–Pb narrow‐bandgap (NBG) perovskites (PVK), arising from divergent crystallization dynamics and Sn2+ segregation, leads to deleterious bandgap fluctuations and interfacial recombination. Herein, a multifunctional cyclodextrin derivative (MCD) additive engineered with 6–8 thiol (‐SH) groups is reported that synchronously addresses these challenges through in situ crystallization modulation and ion‐homogenization, which concurrently suppress Sn2+ oxidation through their reductive capacity and modulate crystallization kinetics via dual chelation of Pb2+/Sn2+ ions through dynamic sulfur–metal coordination bonds. Theoretical and experimental analyses reveal that this dual‐function mechanism decelerates ion migration during nucleation, enabling the growth of high‐quality NBG PVK films with suppressed defect densities and homogenized Pb/Sn distribution. This homogenization stems from MCD's multidentate thiol coordination, which forms a dynamic chelation network with Pb2+/Sn2+, regulating ion release rates and suppressing localized supersaturation. The cyclic oligosaccharide backbone further imposes steric confinement, inhibiting ion clustering and disordered nucleation. Consequently, optimized NBG PVK solar cells achieve a 22.3% power conversion efficiency with suppressed non‐radiative losses, enabling 27.9%‐efficient all‐PVK tandem solar cell with extremely high long‐term stability for 1,320 h. This work establishes molecular crowding and dynamic coordination as dual levers to control crystallization thermodynamics in multinary perovskites.

Bilateral Anchoring for Enhanced Mechanical Stability and Efficiency in Flexible all-Perovskite Tandem Solar Cells.

Flexible all-perovskite tandem solar cells (TSCs) feature an outstanding power-to-weight ratio, rendering them perfect for building-integrated photovoltaic, wearable electronics, and aerospace applications, owing to their adaptability to flexible and lightweight substrates. However, the weak mechanical adhesion between the perovskite and adjacent functional layers, combined with tin (Sn) oxidation at the buried interface in tin-lead (Sn-Pb) narrow-bandgap (NBG) perovskites solar cells (PSCs), substantially hampers the durability and performance of device. Herein, a bilateral anchoring strategy is proposed by employing 2-bromoethylamine hydrobromide (2-BH) at the NBG perovskite/ hole transporting layer (PEDOT:PSS) interface. The incorporation of 2-BH establishes robust bonds with both PEDOT:PSS and the perovskite layer, thereby enhancing interfacial adhesion and charge transfer. Meanwhile, the morphology and crystallinity of the perovskite films are also improved due to the mitigated oxidation of Sn2+. Thus, this approach yields flexible single-junction NBG with a power conversion efficiency (PCE) of 18.5%, maintaining its 95% efficiency after 3000 bending cycles. When integrated into monolithic flexible all-perovskite TSCs, a certified PCE of 24.01% is achieved.

Solvent-free mechanochemical access to phase-pure Cs-Co-Cl halometalates with tuneable electronic properties for energy applications.

We report a solvent-free mechanochemical route for the selectively synthesis of three different caesium cobalt chlorides: CsCoCl3, Cs2CoCl4, and Cs3CoCl5, by simply tuning the CsCl : CoCl2 precursor ratio. This is the first comprehensive comparative study of these phases synthesized in pure form, enabling a clear correlation between composition, crystal structure, and optoelectronic properties. Each phase exhibits a unique Co2+ coordination geometry: octahedral in CsCoCl3 and tetrahedral in Cs2CoCl4 and Cs3CoCl5, as revealed by XRD, SEM-EDS, Raman, and XPS, with several features reported here for the first time. All phases display high thermal stability and narrow optical bandgaps (1.65-1.70 eV), supported by ligand field analysis and CIE colorimetry. Valence and conduction band energies determined by VB-XPS and cyclic voltammetry reveal a systematic, composition-driven tuning of energy levels across the series. Importantly, the band edge alignment are suitable for visible-light-driven hydrogen evolution and photovoltaic applications. SCAPS-1D simulations predict power conversion efficiencies up to 17.1%, positioning these halocobaltates as promising absorbers. Altogether, this work introduces a scalable synthesis route and demonstrates the potential of cobalt-based halide frameworks as modular systems for solar energy conversion and photocatalysis.

Acoustic shock wave driven dynamic recrystallization induced reversible rod-to-cube morphology transition in CdS: preserving structural integrity with optical modifications.

Cadmium sulfide (CdS) is a promising semiconductor with a narrower bandgap, making it highly suitable for optoelectronic and energy storage applications. However, its response to extreme conditions, such as acoustic shock waves, remains unexplored. In this study, CdS samples were subjected to varying shock pulses such as 100, 200, 300, and 400 at a transient pressure of 0.59 MPa and a temperature of 520 K, with a Mach number of 1.5, to investigate structural, optical, and morphological modifications. Analytical techniques, including X-ray diffraction (XRD), Raman spectroscopy, UV-Vis Diffuse Reflectance Spectroscopy (DRS), Photoluminescence (PL) spectroscopy, and Field-Emission Scanning Electron Microscopy (FE-SEM), were employed for comprehensive analysis. XRD and Raman results confirm that the structure remains stable up to 400 shock pulses, with only a minor peak shift observed at 300 shock pulses and, at 400 shock pulses which subsequently reverts to its original position. Optical studies reveal a reversible bandgap shift from 2.37 eV to 2.24 eV, while the PL emission peak shifts from 518 nm to 528 nm and reverts to its original position at 400 shock pulses. Most interestingly, FE-SEM analysis reveals a morphological transition, and the rod morphology evolves into a cube morphology at 300 shock pulses due to shock wave-induced dynamic recrystallization. Remarkably, at 400 shock pulses, the morphology reverts to its original rod morphology, highlighting the reversibility of morphology. These results highlight the critical role of dynamic recrystallization in enabling morphology modulation without structural phase alteration. This study establishes acoustic shock waves as a promising pathway to tune both optical properties and morphology of materials while preserving their structural integrity, offering new directions for functional material design and processing.

Nearly 50-50 Face-on to Edge-on Crystallites in Regioisomeric Polymers Based on n-Type Thienylvinyl-1,1-dicyanomethylene-3-indanone for High Electron Mobility.

To better understand how backbone regioregularity at the molecular level influences the bulk properties of conjugated polymers, we investigated the optical and electrochemical properties, energetics, microstructure, and charge transport characteristics of newly synthesized regioisomeric polymers. These include a regiorandom polymer (PTIC) and two regioregular analogs (PTIC-γ and PTIC-δ). All these polymers exhibit a broad infrared absorption band covering from 300 to 1000 nm, a narrow band gap of 1.25 eV, and a low-lying lowest unoccupied molecular orbital deeper than 3.88 eV. PTIC-γ features weaker chain-to-chain packing owing to its U-shape backbone, whereas PTIC and PTIC-δ present strong aggregation with their wave-like backbone shapes. Initially, all pristine polymer films reveal a bimodal texture dominated by a preferential face-on orientation. Following thermal annealing, the crystallites reorient further into a nearly exclusive face-on packing for PTIC-γ and PTIC-δ films, whereas PTIC films maintain a roughly 50-50 face-on to edge-on orientation ratio. As a result, the best electron mobility, reaching 1.43 × 10-1 cm2 V-1 s-1, is achieved from the annealed PTIC film owing to the construction of a continuous 3D charge-transport pathway.

Revealing the Effects of Inert Annealing on Low-Noise Near-Infrared Organic Photodetectors via Precise Trap and Noise Characterization.

The utilization of near-infrared (NIR) organic photodetectors (OPDs) holds considerable promise, primarily owing to their solution processability and flexibility characteristics. The recent reduction of dark current in the NIR-OPDs is critical for achieving high performance in OPDs using the narrow bandgap of the active layer. However, recent NIR-OPDs with excellent low-dark current exhibit measurement limitations, particularly regarding noise and trap measurements, which are crucial for evaluating specific detectivity and understanding the physics of the NIR-OPDs. This study comprehensively analyzes precise noise and trap measurements at varying inert annealing temperatures applied to the electron-transport layer. The optimized annealing process led to a high specific detectivity of 1.3 × 1013 cm Hz1/2 W-1 at 850 nm and a low trap density of 9.9 × 1013 cm-3 at a shallow-trap-energy level of 0.37 eV. The inert annealing process offers an example of typical issues, such as water-induced trap analysis. Our research explains some pitfalls of noise and trap measurements, addresses them adequately, and demonstrates their limitations. Noise-spectrum measurements should be conducted in a specific range limited by the shot-noise current and the gain bandwidth. In addition, the shallow and slight trap-density reduction can be captured by capacitance-voltage and capacitance-frequency measurements using a series resistance correction. The adequate measurement settings play a vital role in extracting the key physical characteristics of the recent high-performance OPD.

Recent Progress in the Utilization of Silver Nanoparticle and its Derivatives as Photocatalyst: a Mini Bibliometric Study

The narrow bandgaps of silver nanostructure and its derivatives make them photocatalytic-efficient. This bibliometric examines silver nanoparticle research in photocatalysis to identify its growth, research gap, and trends. The 1,941 Web of Science Core Collection publications from 2018 to 2023 were used as research data. The search used Publish or Perish, and the investigation was established on topic area with titles, abstracts, keywords, and terms co-occurrence in the study of silver-based photocatalyst. The visualisation was done with VOSviewer. The number of papers on silver nanoparticles and their derivatives as photocatalysts fluctuated, peaking in 2019. The publications focused on visible-light-irradiated photocatalysts. These findings also revealed a research gap that can be filled by studying silver derivatives including silver chloride, silver oxide, silver sulfide, and silver iodide. This bibliometric study should help researchers examine silver nanoparticles in photocatalysis.

Optimising photovoltaic modules for indoor energy-harvesting systems

Abstract By harvesting low-intensity ambient light, indoor photovoltaics (PVs) could soon power countless Internetof-Things (IoT) devices and sensors. However, indoor illumination conditions vary from room to room and even hour to hour, leading to inconsistent PV power generation. To overcome this, energy-harvesting circuitry can be used alongside indoor PV modules to recharge batteries or capacitors, forming energy-harvesting systems that enable consistent discharge into IoT devices. The optimisation of such systems is a topic of intense research. In this work, we use thermodynamic principles to model power generation in indoor PV modules based on inorganic, perovskite, and organic semiconductors, before evaluating the efficiency of the whole energy-harvesting system. In these investigations, we account for detailed device physics, including sub-gap absorption, band-filling effects, point defects, and parasitic resistances, while also considering performance under several different light sources. Ultimately, we find that the maximum power point voltage (Vmpp) is pivotal in determining the optimal number of cells for an indoor PV module. Despite some PV materials having a lower Vmpp due to narrower bandgaps or increased voltage losses, we find that this can be compensated for by increasing the number of cells; though too many cells can actually lead to inefficient energy harvesting. As a final case study, we evaluate the power generated and stored in a typical day (where an interplay between daylight and artificial light is present) to determine how stored energy translates to measurements made with an IoT device.

Broadband Photomultiplication-Type Organic Photodetectors by Employing an Interfacial Layer for Minimizing Dark Current.

Broadband photomultiplication-type organic photodetectors (PM-OPDs) were fabricated by employing a wide bandgap donor P3HT and narrow bandgap acceptor QxIC as the photoactive layers. The optimal weight ratio of P3HT to QxIC is adjusted as approximately 100:1 to achieve numerous isolated electron traps formed by P3HT/QxIC/P3HT and an efficient hole transport channel in the photoactive layers. The trapped photogenerated electrons in QxIC near the Al electrode will induce interfacial band bending for more efficient hole tunneling injection to obtain a large light current density (JL), resulting in the external quantum efficiency (EQE) over 100% of the PM-OPDs. The dark current density (JD) of broadband PM-OPDs can be further suppressed by employing MPA2FPh-BT-BA as an interfacial layer instead of a PEDOT:PSS layer on the ITO electrode. The optimal PM-OPDs display a rather low JD of 5.7 × 10-7 A cm-2 under a -8 V bias, which is lower than 5.3 × 10-6 A cm-2 for PM-OPDs with PEDOT:PSS as an interfacial layer under the same bias. Additionally, the JL of broadband PM-OPDs exhibits a slightly decreased trend by using the MPA2FPh-BT-BA interfacial layer. The signal-to-noise ratio (SNR) of broadband PM-OPDs can be increased from 667 to 3788 by replacing PEDOT:PSS with MPA2FPh-BT-BA as the interfacial layer, benefiting from the markedly decreased JD and relatively high JL. The optimal broadband PM-OPDs exhibit EQE values of 8010% at 355 nm and 2170% at 835 nm, as well as specific detectivity values of 9.1 × 1012 Jones at 355 nm and 5.8 × 1012 Jones at 835 nm under a -8 V bias.

High performance rigid and flexible tandem perovskite photovoltaics under mimic high-altitude platform satellite environments

Perovskite photovoltaics (PPV) have the potential to be used for aerospace applications due to, e.g., their high power-per-mass, high flexibility, and low-cost. Recent developments in narrow bandgap (NBG), wide bandgap (WBG), and tandem perovskite-based PPV devices have delivered excellent photovoltaic performance for outdoor applications. In this work, we have studied NBG, WBG, and tandem (on glass and flexible substrates) PPV devices under mimic high-altitude platform satellites (HAPS) operating environment, including light irradiation (AM0), temperature (+10 to −20 °C), and vacuum. Furthermore, the thermal cycling (TC) (+20 to −85 °C) stability is also conducted for NBG, WBG, and tandem PPV devices. Tandem devices on glass and flexible substrates delivered power conversion efficiency (maximum power) of 22.98% (31.39 mW/cm2) and 21.92% (29.91 mW/cm2), respectively, under AM0 irradiation and also showed promising TC stability in the HAPS environment. Interestingly, the tandem PPV (using the NBG and WBG perovskites) retains high performance under low temperatures compared to NBG and WBG devices. Therefore, it demonstrated the promising potential of Tandem PPV for HAPS application.

Enhancing the Removal Efficiency of Rhodamine B by Loading Pd onto In2O3/BiVO4 Under Visible Light Irradiation

A simple method for synthesizing novel Pd-In2O3/BiVO4 composites by using a hydrothermal technique is proposed. The synthesized samples showed a monoclinic phase and featured homogeneously dispersed Pd and BiVO4 dopants on In2O3, as confirmed by XRD, SEM, and XPS analyses. The Pd-In2O3/BiVO4 composite exhibited notable improvements, such as broadened visible-light absorption (up to 596.1 nm) and a narrowed band gap (2.08 eV vs. 2.82 eV for pure In2O3), a more compact and integrated morphology observed by SEM, which are expected to promote improved light harvesting and facilitate charge separation during photocatalysis. Under visible-light irradiation, the optimized 1 wt% Pd-In2O3/BiVO4 achieved 99% degradation of Rhodamine B (10 mg/L) within 40 min, while pure In2O3 showed less than 10% removal after 60 min—highlighting the strong synergistic effect of dual doping. Additionally, the composite demonstrated excellent stability and reusability over multiple cycles. A plausible photocatalytic mechanism for this process is proposed, providing insights into the design of efficient photocatalysts for wastewater treatment.