Enhanced Carrier Mobility Research Articles

Halogen‐free solvent processed organic solar sub‐modules (≈55 cm2) with 14.70% efficiency by controlling the morphology of alkyl chain engineered polymer donor

AbstractGoals of high efficiency, morphological analysis, and the ability to produce organic solar cell (OSC) sub‐modules using halogen‐free solvents are demanding. In this study, a robust conjugated polymer with thienothiophene π‐spacer with pendant alkyl side chain (NapBDT‐C12) was synthesized and used to fabricate sub‐modules. Excellent efficiencies were demonstrated by a NapBDT‐C12 integrated ternary blend, which was used to produce stable small‐area‐to‐sub‐module devices using O‐xylene. The efficiency of the NapBDT‐C12 added small‐area ternary devices (PM6:NapBDT‐C12:L8‐BO) was 18.71%. Owing to the controlled homogeneity of the blend with favorable nanoscale film morphology, enhanced carrier mobilities, and exciton dissociation/splitting properties, contributed to the efficiencies of small‐area‐to‐sub‐module OSCs. Moreover, a 55 cm2 sub‐module with an efficiency of 14.69% was accomplished by bar coating using O‐xylene under ambient conditions. This study displays the potential of a ternary blend based OSC device to produce high efficiency scalable sub‐modules at ambient conditions.image

Chemiresistive triethylamine detection based on the novel Ti3C2Tx/Co-BDC gas sensor

Triethylamine (TEA), a representative volatile organic environmental pollutant, poses significant environmental pollution risks and can adversely affect the liver and nervous system, potentially leading to fatal outcomes. However, existing gas sensors for TEA detection have pressing drawbacks, such as safety hazards associated with high-temperature operation and poor timeliness due to time-consuming testing. Herein, the Ti3C2Tx/Co-BDC sensor demonstrates ultra-sensitive detection of TEA at a low temperature of 100 °C. This temperature is below the threshold for explosion-proof operation, ensuring safe application in flammable and explosive environments. Meanwhile, the introduction of the metal-like MXene with ultra-high conductivity accelerates the response and recovery process (11 s/20 s), facilitating highly efficient TEA detection within a sub-minute timeframe. The Ti-O-Co interfacial bonds between Ti3C2Tx and Co-BDC, confirmed by both XPS analysis and theoretical calculations, enhance carrier mobility across the two materials, significantly boosting gas-sensing performance. The rapid detection of TEA at low temperatures makes the Ti3C2Tx/Co-BDC sensor more suitable for practical environmental monitoring in flammable and explosive areas, further contributing to human health and production safety.

Carrier Mobility Enhancement in Ultrathin-Body InGaAs-on-Insulator n-Channel Metal-Oxide-Semiconductor Field-Effect Transistors Based on Dual-Gate Modulation

As a promising candidate for More Moore technology, InGaAs-based n-channel metal-oxide-semiconductor field-effect transistors (nMOSFETs) have attracted growing research interest, especially with InGaAs-on-insulator (InGaAs-OI) configurations aimed at alleviating the short channel effects. Correspondingly, the fabrication of an ultrathin InGaAs body becomes necessary for the full depletion of the channel, while the deteriorated semiconductor–insulator interface-related scattering could severely limit carrier mobility. This work focuses on the exploration of carrier mobility enhancement strategies for 8 nm body-based InGaAs-OI nMOSFETs. With the introduction of a bottom gate bias on the substrate side, the conduction band structure in the channel was modified, relocating the carrier wave function from the InGaAs/Al2O3 interface into the body. Resultantly, the channel mobility with an inversion layer carrier concentration of 1 × 1013 cm−2 was increased by 62%, which benefits InGaAs-OI device application in monolithic 3D integration. The influence of the dual-gate bias from front gate and bottom gate on gate stability was also investigated, where it has been unveiled that the introduction of the positive bottom gate bias is also beneficial for gate stability with an alleviated orthogonal electric field.

Halogenated-edge polymeric semiconductor for efficient spin transport.

Organic semiconductors (OSCs) are featured by weak spin-orbit coupling due to their light chemical element composition, which enables them to maintain spin orientation for a long spin lifetime and show significant potential in room-temperature spin transport. Carrier mobility and spin lifetime are the two main factors of the spin transport performance of OSCs, however, their ambiguous mechanisms with molecular structure make the development of spintronic materials really stagnant. Herein, the effects of halogen substitution in bay-annulated indigo-based polymers on carrier mobility and spin relaxation have been systematically investigated. The enhanced carrier mobility with an undiminished spin lifetime contributes to a 3.7-fold increase in spin diffusion length and a record-high magnetoresistance of 8.7% at room temperature. By analyzing the spin-orbit coupling and hyperfine interaction, it was found that the distance of the substitution site from the conjugated center and the nitrogen atoms in the molecules play crucial roles in spin relaxation. Based on the above results, we proposed a molecular design strategy of halogen substitution far from conjugate center to enhance spin transport efficiency, presenting a promising avenue for advancing the field of organic spintronics.

Growth of anthracene microcrystals by the micro-space sublimation method and their photophysical properties

Anthracene and its derivatives are widely utilized in optoelectronic devices due to their unique properties. Generally, single-crystal structures can avoid non-radiative recombination, enhance carrier mobility, and ultimately improve device performance. In this work, anthracene microcrystals were prepared using the micro-space sublimation method. Through real-time in-situ observation, the crystallization dynamics of anthracene molecules were revealed. Unlike traditional vacuum evaporation deposition technique, the close proximity of the substrate to the source facilitates the self-assembly of anthracene molecules into an ordered crystal structure. Six peaks can be observed in the photoluminescence spectrum, corresponding to various lowest excited state decay processes. The fluorescence intensity at the peak of 423 nm decreases significantly with increasing temperature. The reason for this is the relatively high exciton binding energy, which makes excitons more stable and easier to form. The lattice vibrations induced by increased temperature were found to affect the transport and separation of excitons. Time-resolved fluorescence spectroscopy imaging revealed that a relatively uniform distribution of fluorescence lifetimes in the anthracene microcrystals, indicating high crystallization quality. This work provides valuable insights for controlling the morphology and investigating the photophysical properties of organic semiconductors.

A route to high thermoelectric performance of lead chalcogenides: enhancing carrier mobility

A route to high thermoelectric performance of lead chalcogenides: enhancing carrier mobility

Enhanced Piezocatalytic Water Splitting by Platinum‐Decorated Barium Titanate

AbstractPiezocatalysis has emerged as a promising field of research that uses mechanical energy to drive a chemical change. There is growing evidence that piezocatalysts can perform challenging chemical conversions from organic transformations to water splitting. A key challenge to piezocatlaysis is mitigating the inherent high relative permittivity of a ferroelectric material. This high permittivity restricts the transfer of carriers required for a chemical reaction to occur and reduces the reaction rate. Here the concept of producing a co‐catalyst system is taken to enhance carrier mobility increasing the observed reaction rate. The study highlights the importance of determining the sonochemical and piezocatalytic contributions to catalysis. The combination of a Pt metal co‐catalyst with BaTiO3 through a simple solid‐state method led to a four fold increase in the rate of H2 production compared to BaTiO3 and sonochemical reactions in the absence of a catalyst. BaTiO3/Pt is found to exhibit stable piezocatalytic performance over 12 h. Where there is a deviation from steady‐state water splitting, it is shown that this is due to mechanical removal of Pt rather than a phase change in the catalyst system. This work confirms the additive benefits of hybrid materials for improving piezocatalytic processes.

Cerium rare-earth ions reinforced built-in electric field to enable efficient carrier extraction for highly efficient and stable perovskite solar cells

Perovskite solar cells prepared by inorganic-organic three-dimensional hybrid have good power conversion efficiency, but their operational stability remains a major challenge for commercialization. The defect of perovskite is an important factor restricting its charge dynamics and stability. Here, the rare earth metal chloride CeCl3 is introduced into perovskite solution to passivate the defects, where the Pb2+ part of the B position is replaced by Ce3+. The prepared films have the characteristics of increasing grain size, enhancing carrier mobility and excellent crystallinity. Meanwhile, via passivating interface defects and improving carrier transport capacity, the generation of non-radiative recombination is reduced, the carrier migration length is extended, and the device performance is improved. The results show that the PCE of the standard device is only 65 % after 2880 h of N2 atmosphere at room temperature, while the efficiency of the device doped with CeCl3 can remain at 93 %. When the unencapsulated sample was placed in an air environment (40–60 % humidity), the control sample was reduced to 72 % at 1060 h, while the CeCl3 was maintained at 87 %. Additionally, the reduction of residual stress in the perovskite layer also provides good bending stability for the flexible target device. These results show that the incorporation of rare earth metal ions is an effective way to stabilize and improve the efficiency of the device.

Twist angle-driven photoreduction of carbon dioxide on bilayer black phosphorus – A first-principles study

Utilizing first principles calculations, the product selectivity in photocatalytic CO2 reduction was modulated by manipulating the twisted angle in bilayer black phosphorus. Four twisted angles, 0° (AA stacking), 15.40°, 19.00° and 24.66°, were constructed. Comprehensive investigations revealed enhanced carrier mobility and lifetime, especially at a 24.66° twist. Furthermore, an in-depth analysis of the CO2 reduction processes in these four systems was undertaken. Our simulations indicate that in the AA stacking, the photocatalytic CO2 reduction yields multiple products, including HCHO, CH3OH, and CH4, demonstrating limited product selectivity. However, when the surface is twisted at 15.40°, 19.00°, or 24.66°, the sole product is CH4. Remarkably, the 24.66° configuration exhibits the lowest energy barrier for the rate-determining step, measuring just 1.29 eV. These observations suggest that by carefully adjusting the twisted angle in bilayer black phosphorus, we can significantly improve both the activity and selectivity of CO2 photoreduction.

Tension Induced Photoluminescence Enhancement in an Organic Single Crystal.

Organic single crystals possess distinct advantages due to their highly ordered molecular structures, resulting in improved stability, enhanced carrier mobility, and superior optical characteristics. However, their mechanical rigidity and brittleness impede the applications in flexible and wearable optoelectronic devices. Here, photoluminescence (PL) emission from 2,6-diphenylanthracene (DPA) single crystals is studied under tensile strain, which shows PL enhancement by more than two times with a strain of ≈1.42%. Such a tension induced PL enhancement is reversible, exhibiting no clear optical degradations during 100 cycles of bending and recovery processes. Theoretical calculations reveal that the deformation of molecular structure under strain induces a decrease of the dihedral between anthracene and benzene moieties in DPA molecules. Further, the increased molecular conjugation enhances the molecular oscillator strength, leading to the brightened PL emission. Meanwhile, with the decreased dihedral, the molecular vibrations in DPA crystals are suppressed, which can reduce the non-radiative decay rate. In contrast, no tension induced PL enhancement is observed in polycrystalline DPA thin films as the strain can be released via the grain boundaries. This study highlights the superior optical performance of DPA single crystals under strain field, which will provide new possibilities for DPA-based flexible devices.

CuInS2/Red Phosphorus Nanosheet Interleaved Heterostructures with Improved Interfacial Charge Transfer for Photoelectrochemical Aptasensing.

Accelerating the migration of interfacial carriers in heterojunctions is crucial for achieving highly sensitive photoelectrochemical (PEC) sensing. In this study, we developed three-dimensional (3D)/two-dimensional (2D) CuInS2/red phosphorus nanosheet (CuInS2/RP NS) n-n heterojunction functional materials with enhanced interfacial charge transfer capabilities for PEC sensing. The 3D CuInS2 serves as a conductive layer, providing excellent electronic conductivity and superior electron absorption and transport properties. In contrast, the ultrathin RP NS acts as a transport layer that enhances carrier mobility. The 3D/2D heterojunction ensures a large interface contact surface, shortening the carrier transport distance. A well-aligned band position generates a substantial built-in electric field, providing a significant driving force for efficient carrier separation and migration, thereby improving response sensitivity. A PEC aptamer sensor was constructed based on the synthesized heterostructure for ciprofloxacin detection. The detection limit of the CuInS2/RP NS aptamer sensor for ciprofloxacin is 2.03 × 10-15 mg·mL-1, with a linear range from 1.0 × 10-14 to 1.0 × 10-5 mg·mL-1. This work presents a strategy for enhancing the photoelectric response by modulating the interface structure of heterojunctions, thereby opening new prospects for the application of highly sensitive PEC sensors in antibiotic detection.

Magnetic field expulsion in optically driven YBa2Cu3O6.48.

Coherent optical driving in quantum solids is emerging as a research frontier, with many reports of interesting non-equilibrium quantum phases1-4 and transient photo-induced functional phenomena such as ferroelectricity5,6, magnetism7-10 and superconductivity11-14. In high-temperature cupratesuperconductors, coherent driving of certain phonon modes has resulted in a transient state with superconducting-like optical properties, observed far above their transition temperatureTc and throughout the pseudogap phase15-18. However, questions remain on the microscopic nature of this transient state and how to distinguish it from a non-superconducting state with enhanced carrier mobility. For example, it is not known whether cuprates driven in this fashion exhibit Meissner diamagnetism. Here we examine the time-dependent magnetic field surrounding an optically driven YBa2Cu3O6.48 crystal by measuring Faraday rotation in a magneto-optic material placed in the vicinity of the sample. For a constant applied magnetic field and under the same driving conditions that result in superconducting-like optical properties15-18, a transient diamagnetic response was observed. This response is comparable in size with that expected in an equilibrium type II superconductor of similar shape and size with a volume susceptibility χv of order -0.3. This value is incompatible with a photo-induced increase in mobility without superconductivity. Rather, it underscores the notion of a pseudogap phase in which incipient superconducting correlations are enhanced or synchronized by the drive.

Improving Thermoelectric Performance of AgSbTe2 through Suppression of Ag2Te and Band Convergence via Mg and Ti Codoping.

In this study, the impact of codoping Mg and Ti on the thermoelectric performance of AgSbTe2 materials was investigated. Through a two-step synthesis process involving slow cooling and spark plasma sintering, AgSb0.98-xMg0.02TixTe2 samples were prepared. The introduction of Mg and Ti dopants effectively suppressed the formation of the undesirable Ag2Te phase. Density functional theory (DFT) calculations confirmed that Ti doping facilitated the band convergence, leading to a reduction in the effective mass of the carriers. This optimization enhanced carrier mobility and, consequently, electrical conductivity. Additionally, the codoping strategy resulted in the reinforcement of point defects, which contributed to a decrease in lattice thermal conductivity. The AgSb0.98-xMg0.02TixTe2 sample achieved a maximum figure of merit (ZT) value of 1.45 at 523 K, representing an 87% improvement over the undoped AgSbTe2 sample. The average ZT value over the temperature range of 323-573 K was 1.09, marking a significant enhancement in thermoelectric performance. This research demonstrates the potential of Mg and Ti codoping as a strategy to improve the thermoelectric properties of AgSbTe2-based materials.

Optimizing the thermoelectric properties of flexible Bi0.5Sb1.5Te3 thin films via modulating magnetron sputtering power

High-performance flexible Bi2Te3-based thin films carry significant promise for future portable and wearable thermoelectric devices. In this study, a series of Bi[Formula: see text]Sb[Formula: see text]Te3 thin films were deposited on polyimide substrates under different RF magnetron sputtering powers from 60 W to 140 W. The crystallinity, (00[Formula: see text]) preferential orientation and atomic composition can be effectively modulated by varying the sputtering power. Benefiting from the synchronous enhancements of the electrical conductivity (mostly due to the enhanced carrier mobility) and Seebeck coefficient, the film deposited under the sputtering power 100 W presents the best PF of 12.86 [Formula: see text]W cm[Formula: see text] K[Formula: see text] at 360 K and the highest average PF of 11.25 [Formula: see text]W cm[Formula: see text] K[Formula: see text] in the temperature range of 300–560 K, which are much better than those of the films deposited under other sputtering powers.

Enhancing n-type PbTe thermoelectric performance through Cd alloying and strategic defects management

The significant performance disparity between n-type and p-type PbTe hinders their commercial viability in thermoelectric (TE) applications. While conventional multi-element alloying has demonstrably improved n-type PbTe thermoelectrics, it introduces stability concerns and cost escalation. Here, we propose a simpler approach utilizing a single isovalent element alloying strategy with Cd and defect management to enhance the TE performance of n-type PbTe. Cd doping widens the bandgap, leading to an increased effective mass and Seebeck coefficient, particularly at higher temperatures due to improved Cd solubility. However, as documented in previous studies on the PbTe-Cd system, Cd introduction can potentially deteriorate TE performance by reducing carrier mobility. To address this, we implemented defect engineering to optimize carrier mobility. A small excess of Pb atoms was introduced to occupy intrinsic Pb vacancies, achieving a remarkable 65.5 % enhancement in carrier mobility. Consequently, the maximum power factor of Cd-alloyed Pb1.01Te samples reaches 31.5 μW cm−1 K−2, marking a significant 69.3 % improvement compared to pristine PbTe. Additionally, the Cd-induced bandgap widening effectively mitigates bipolar diffusion. This, combined with enhanced phonon scattering due to the secondary CdTe phase, results in a 34.3 % decrease in thermal conductivity. By leveraging the multifaceted effects of Cd alloying and defect management, the ZT value of Pb1.01Te-2 %Cd samples reaches 1.35 at 782 K. These findings offer a new perspective on the versatile use of single isovalent element alloying strategy and performance optimization in other TE materials.

Unraveling Dual Mechanisms in Quasi‐Layered Bi2O2Se via Defect Modulation for High‐Performance Aqueous Zn‐Ion Batteries

AbstractDeveloping cathode materials for aqueous zinc‐ion batteries (ZIBs) that offer high capacity, rapid charge–discharge rates, and prolonged cycle life remains a significant challenge. This study explores the use of zipper‐type Bi2O2Se nanoplates modified by selenium vacancy (Vse) modulation, which reduces electron scattering, enhances carrier mobility in [Bi2O2] conducting channels, and decreases coulombic interactions within electrostatic layers. The introduction of Se vacancies facilitates electron transfer from the host to [Bi2O2] channels and reduces scattering in the [Bi2O2] framework, thus improving carrier mobility. These Se‐poor Bi2O2Se nanoplates demonstrate a greater affinity for zinc ions, reduced diffusion barriers, and faster transport kinetics, which enable more efficient Zn‐ion insertion, tripling the electrochemical capacity, improving rate capabilities, and extending cycling life. Enhancements such as reinforced structural integrity and expanded interlayer spaces support a dual Zn‐ion‐driven mechanism involving both insertion and conversion reactions, essential for superior electrochemical storage performance. The results include an impressive discharge/charge capacity of 380.3 mA h g−1 at 0.1 A g−1, a cycle life of up to 10 000 cycles at 5 A g−1, and a current tolerance exceeding 10 A g−1. This research highlights how nano‐ and defect engineering of Bi2O2Se can significantly enhance ionic conductivity, expedite electron transfer, and improve Zn‐ion diffusion.

Enhanced Femtosecond Nonlinear Optical Susceptibility and Terahertz Conductivity in MoSe2‐Noble Metal Nanocomposites

AbstractCreating heterojunctions or composites by incorporating noble metals offers a remarkable means to modulate the electronic charge transfer and the nonlinear optical (NLO) properties in 2D transition metal dichalcogenides (TMDCs). The response of such 2D‐TMDC‐noble metal composites to femtosecond (fs) infrared (IR) and terahertz (THz) radiation, however, remains vastly unexplored. While the linear optical characteristics of a prototypical 2D‐TMDC, namely, MoSe2 nanosheets incorporated with noble metal (such as Au, Pt, and Ag) nanoparticles in the UV–Vis and the THz spectral range, the NLO characteristics are measured using a 70‐fs pulse at 800 nm excitation is investigated. The results demonstrate a clear reduction of band gap with the incorporation of noble metals in MoSe2, indicating an effective charge transfer mechanism at play. Notably, the MoSe2‐noble metal nanocomposites depicted a significant enhancement in the THz conductivities. In addition, a dramatic 4‐fold enhancement in the third‐order nonlinear coefficient and ≈2‐fold enhancement in the third‐order NLO susceptibility is achieved in MoSe2‐Ag nanocomposite. These results univocally suggest that the noble metal‐based composites with suitable charge transfer channels promote enhanced carrier mobilities and tunable electron transfer dynamics, making these hybrid materials promising candidates for optoelectronic applications both at IR and THz frequencies.

Optimizing the power conversion processes in diluted donor/acceptor heterojunctions towards 19.4% efficiency all-polymer solar cells

All polymer solar cells (all-PSCs) promise mechanically-flexible and morphologically-stable organic photovoltaics and have aroused increased interests very recently. However, due to their disorderly conformation structures within the photoactive film, inefficient charge generation and carrier transport are observed which lead to inferior photovoltaic performance compared to smaller molecular acceptor-based photovoltaics. Here, by diluting PM6 with a cutting-edge polymeric acceptor PY-IT and diluting PY-IT with PM6 or D18, donor-dominating or acceptor-dominating heterojunctions were prepared. Synchrotron X-ray and multiple spectrometer techniques reveal that the diluted heterojunctions receive increased structural order, translating to enhanced carrier mobility, improved exciton diffusion length, and suppressed non-radiative recombination loss during the power conversion. As the results, the corresponding PM6+1%PY-IT/PY-IT+1%D18 and PM6+1%PY-IT/PY-IT+1%PM6 devices fabricated by layer-by-layer deposition received superior power conversion efficiency (PCE) of 19.4% and 18.8% respectively, along with enhanced operational lifetimes in air, outperforming the PCE of 17.5% in the PM6/PY-IT reference device.

Enhanced carrier mobility and interface charge transfer in Bi–MoS2 heterojunctions induced by point defects

Semimetal Bi in contact with monolayer MoS2 (mMoS2) as a substrate reduced contact resistance. This phenomenon has attracted widespread attention. Presently, systematic research on defects in semimetal-TMDs heterojunctions remains limited. In this paper, nine types of vacancy defects (three S-vacancies at the heterojunction interface (VSI, II, III), three S-vacancies on the top layer (VSI, II, IIIt), one Mo vacancy (VMo), Mo–S double vacancies (VMo–S) and Mo–S triple vacancies (VMo–2S)) and defect-free structure (Perfect) are designed in mMoS2. Their impact on defect formation energy, Interface charge transfer, and carrier mobility in three-layer (3L)Bi(0001)-mMoS2 heterojunctions are studied by the First-Principles. The energy analysis indicates that in the 3LBi-mMoS2 contact, VS are more prone to formation than VMo, VSt, VMo–S and VMo–2S. At the same time VSⅡ has the lowest formation energy under Mo-rich environments. The analysis of electron and charge redistribution in the 3LBi-mMoS2 contact with defects indicates that defect generation introduces peaks at the Fermi level, enhancing the hybridization of Mo_4d and S_3p. The hybridization rate of electron orbitals in VMo surpasses that in VS and VSt, signifying that heterojunction structures with defects exhibit increased electron injection efficiency at the interface compared to Perfect. The charge carrier mobility of S and Mo defects in 3LBi-mMoS2 reveals a significant reduction in the effective mass of charge carriers due to vacancy defects. Due to the location of defects, heterojunctions exhibit anisotropy. Obtain Perfect > VMo > VSII (370.7 > 277>125.1 cm2V−1S−1) for the x-direction carrier mobility (μx), while VMo > Perfect > VSII (440.8 > 279.7>131.6 cm2V−1S−1) for the y-direction carrier mobility (μy). These findings offer practical insights for utilizing defects to modulate the electronic properties of Semimetal-MoS2 heterojunction interfaces.

Enhancing Carrier Mobility in Monolayer MoS2 Transistors with Process-Induced Strain.

Two-dimensional electronic materials are a promising candidate for beyond-silicon electronics due to their favorable size scaling of electronic performance. However, a major challenge is the heterogeneous integration of 2D materials with CMOS processes while maintaining their excellent properties. In particular, there is a knowledge gap in how thin film deposition and processes interact with 2D materials to alter their strain and doping, both of which have a drastic impact on device properties. In this study, we demonstrate how to utilize process-induced strain, a common technique extensively applied in the semiconductor industry, to enhance the carrier mobility in 2D material transistors. We systematically varied the tensile strain in monolayer MoS2 transistors by iteratively depositing thin layers of high-stress MgOx stressor. At each thickness, we combined Raman spectroscopy and transport measurements to unravel and correlate the changes in strain and doping within each transistor with their performance. The transistors displayed uniform strain distributions across their channels for tensile strains of up to 0.48 ± 0.05%, at 150 nm of stressor thickness. At higher thicknesses, mechanical instability occurred, leading to nonuniform strains. The transport characteristics systematically varied with strain, with enhancement in electron mobility at a rate of 130 ± 40% per % strain and enhancement of the channel saturation current density of 52 ± 20%. This work showcases how established CMOS technologies can be leveraged to tailor the transport in 2D transistors, accelerating the integration of 2D electronics into a future computing infrastructure.