Increase In Carrier Mobility Research Articles

Analyzing Carrier Density and Hall Mobility in Impurity‐Free Silicon Virtually Doped by External Defect Placement

AbstractImpurity doping at the nanoscale for silicon is becoming less efficient with conventional techniques. Here, an alternative virtual doping method is presented for silicon that can achieve an equivalent carrier density while addressing the primary limitations of traditional doping methods. The doping for silicon is carried out by placing aluminum‐induced acceptor states externally in a silicon dioxide dielectric shell. This technique can be referred to as direct modulation doping. The resistivity, carrier density, and mobility are investigated by Hall effect measurements to characterize the carrier transport using the new doping method. The results thereof are compared with carrier transport analysis of conventionally doped silicon at room‐temperature, demonstrating a 100% increase in carrier mobility at equal carrier density. The sheet density of hole carriers in silicon due to modulation doping remains nearly constant, ≈4.7 × 1012 cm−2 over a wide temperature range from 300 down to 2 K, proving that modulation‐doped devices do not undergo carrier freeze‐out at cryogenic temperatures. In addition, a mobility enhancement is demonstrated with an increase from 89 cm2 Vs−1 at 300 K to 227 cm2 Vs−1 at 10 K, highlighting the benefits of the new method for creating emerging nanoscale electronic devices or peripheral cryo‐electronics to quantum computing.

Standing 1D Chains Enable Efficient Wide-Bandgap Selenium Solar Cells.

The recent surge in tandem solar cells and indoor photovoltaics has renewed interest in selenium (Se), the world's first photovoltaic material, due to its intrinsic wide bandgap of ≈1.9eV, high stability, and non-toxicity in small quantities when applied in photovoltaics. However, with a 1D chained crystal structure, Se tends to grow crystalline films with a lying orientation-chains parallel to substrates arising from the low surface energy; this results in poor carrier transport across chains held together by weak van der Waals forces. Here a substrate-heating strategy that facilitates the interfacial bonding between Se and substrate is introduced, enabling the growth of Se films with a standing orientation-chains perpendicular to substrates. This achieves efficient carrier transport along covalently bonded chains. The resulting Se films thereby exhibit a fourfold increase in carrier mobility compared to lying-oriented Se films. Consequently, Se solar cells are achieved with the highest power conversion efficiency of 8.1% under AM1.5G 1-sun illumination. The unencapsulated devices exhibit negligible efficiency loss after 1000 h of storage under ambient conditions.

Effect of Temperature and Electric Field Strength on Carrier Mobility of Oil-Impregnated Pressboard Under DC Voltage

The influence of carrier mobility on the space charge transport behavior inside the oil-impregnated pressboard insulation of converter transformers cannot be neglected. However, at present, current knowledge is usually derived from empirical or theoretical values, lacks experimental studies, and often ignores the effects of temperature and field strength under actual operating conditions. In this paper, based on the variable-temperature surface potential decay (SPD) method, a carrier mobility measurement platform for oil-impregnated pressboard is established, and the carrier mobility values for different combinations of oil and oil-impregnated pressboard are obtained experimentally to analyze and reveal the influence mechanisms of temperature and field strength on the carrier mobility. The results indicate the following: (1) The positive and negative carrier mobilities of oil-impregnated pressboard are in the range of 10−12–10−13 m2·V−1·s−1, and the negative carrier mobility is always higher than the positive carrier mobility. (2) The carrier mobility is positively correlated with the changes of temperature and field strength, and when the temperature increases from 20 °C to 80 °C, the positive and negative carrier mobilities increase by 4.01 times and 4.72 times, respectively; when the field strength increases from 1 kV/mm to 7 kV/mm, the positive and negative carrier mobility increases by 2.53 and 2.72 times, respectively. (3) The carrier mobility of the pressboard with a higher oil absorption rate changes more significantly with temperature; when the field strength is 7 kV/mm and the temperature increases from 20 °C to 80 °C, the positive polarity carrier mobility increases from 3.96 × 10−13 m2·V−1·s−1 to 2.64 × 10−11 m2·V−1·s−1, an increase of 66.67 times, while the increase in the carrier mobility of the pressboard with a lower oil absorption rate is only 1.59 times. (4) The carrier mobility of the naphthenic transformer oil-impregnated pressboard is higher than that of the paraffin-based transformer oil-impregnated pressboard, and the carrier mobility of two kinds of naphthenic transformer oil-impregnated pressboard is 3.16 times and 2.47 times higher than that of the paraffin-based transformer oil-impregnated pressboard, respectively, under the conditions of 60 °C and 7 kV/mm. (5) Utilizing the Darcy model and microscopic scanning results of the pressboard morphology, it was revealed that permeability and fiber structure are key factors influencing the variation in carrier mobility. The research results of this paper can provide theoretical basis for the calibration and optimization of the oil-pressboard insulation structure of converter transformers.

Hybrid Density Functional Study on the p-Type Conductivity Mechanism in Intrinsic Point Defects and Group V Element-Doped 2D β-TeO2.

The newly discovered two-dimensional (2D) β-TeO2 possesses extraordinarily high p-type carrier mobility and demonstrates immense potential in the electronics field. However, current research on its p-type conductivity mechanisms and the modifications of element doping remains relatively insufficient. In this study, the intrinsic point defects and extrinsic element doping in monolayer β-TeO2 are comprehensively analyzed to probe the potential sources of the intrinsic p-type conductivity and the extrinsic p-type doping possibility in 2D β-TeO2 through hybrid density functional calculations. Our results reveal that the vacancy defects with low formation energies have deep transition levels and thus cannot be used as sources of unintentional p-type conductivity in 2D β-TeO2. The investigations and discussions via Group V element doping modifications in 2D β-TeO2 indicate that bismuth (Bi) doping can easily and significantly enhance the p-type conductivity of 2D β-TeO2 under the presence of O-rich, which can be achieved experimentally. Furthermore, Bi doping can significantly increase carrier mobility without seriously affecting the electronic structure. The finding shows that the Bi element is an ideal dopant candidate for a p-type modification in 2D β-TeO2. Our calculations pave an alternative strategy to achieve the realization of superior p-type conductivity in 2D β-TeO2.

Influence of morphology, crystal structures on the enhanced photoluminescence dynamics, zeta potential, and AC resistance of disc shaped cesium oxidex@cobalt oxide nanostructures

In the present study, cesium oxidex@cobalt oxide (Cs2Ox@Co3O4) (x = 5, 10 and 12 wt%) nanostructures (NS) were successfully synthesized by chemical precipitation method and characterized by XRD (X-ray diffraction), SEM (scanning electron microscope), EDX (energy dispersive X-ray), XPS (X-ray photoelectron spectroscopy), BET (Brunauer-Emmett-Teller), Raman, and UV–visible analytical techniques. XRD studies revealed the formation of the mixed phase of orthorhombic/monoclinic crystal structure. Disc shaped morphology of the cesium oxidex@cobalt oxide NS was noticed from SEM images. Redshift in optical absorbance and decrease in optical band gap (Eg) resulted in increase in Cs1+ concentration. Room temperature photoluminescence (RTPL) studies of cesium oxidex@cobalt oxide NS at various excitation wavelengths showed sharp and broad emission peaks located at 668.2 nm (red), 675.1 nm (red), 561.8 nm (yellow-green), 834.5 nm (near infrared region), 594 nm (yellow). Steady state photoluminescence (SSPL) studies revealed a sharp emission peak at ∼ 428.0 nm (violet) with large stoke’s shift (21.1 to 590.0 eV). The zeta potential studies showed a decrease in conductance from 62 to 57 μs with an increase in mobility of the charge carriers (0.4 to 1.08 μ/s V/cm) and an increase in zeta potential (31.90 to 82.92 mV). AC resistance studies at various temperatures showed inducting coupling phenomenon in cesium oxidex@cobalt oxide NS with DC resistance of cesium oxide5 wt.%@cobalt oxide was found to be 8.2 × 10–4 Sm–1. The relaxation frequency of cesium oxide12 wt.%@cobalt oxide NS was found be 1.2 × 105 Hz. The synthesized NS is a promising candidate for optoelectronics and photonic applications.

Graphene modulator and 2-bit encoder based on plasma induced transparency effect

Within this study, a periodic metasurface structure made up of two graphene strips, two fan-shaped graphene and a square ring graphene with notches is introduced to achieve plasma-induced transparency (PIT). The PIT effect is analyzed utilizing the Lorentz oscillatory coupling model, and it has been discovered that the theoretical values closely match the simulated values. The role of the Fermi level adjustments in graphene on the PIT effect was examined, and the PIT window was dynamically modified as the Fermi level changed, which was used to realize a 2-bit graphene encoder at 5.78 THz and 7.18 THz. The encoder boasts a greatest modulation depth of 80.9 % and exhibits a minimal insertion loss of 0.17 dB. By controlling the polarization direction of the incident photoelectric field, a high performance dual-channel switching modulator is successfully realized. Moreover, by increasing carrier mobility, the depth of modulation for the modulator at 11.22 THz is increased from 97.5 % to 99.5 %, and the insertion loss has dropped from 0.075 dB to 0.06 dB. In addition, the structure has superior sensing properties and slow light properties, featuring a sensitivity reaching up to 1.07 THz/RIU and a maximum group index of 293. The outcomes of our study contribute novel insights for the advancement of modulator, encoder, sensor technology and slow-light devices.

Ultrahigh Power Factor of Sputtered Nanocrystalline N-Type Bi2Te3 Thin Film via Vacancy Defect Modulation and Ti Additives.

Magnetron-sputtered thermoelectric thin films have the potential for reproducibility and scalability. However, lattice mismatch during sputtering can lead to increased defects in the epitaxial layer, which poses a significant challenge to improving their thermoelectric performance. In this work, nanocrystalline n-type Bi2Te3 thin films with an average grain size of ≈110nm are prepared using high-temperature sputtering and post-annealing. Herein, it is demonstrated that high-temperature treatment exacerbates Te evaporation, creating Te vacancies and electron-like effects. Annealing improves crystallinity, increases grain size, and reduces defects, which significantly increases carrier mobility. Furthermore, the pre-deposited Ti additives are ionized at high temperatures and partially diffused into Bi2Te3, resulting in a Ti doping effect that increases the carrier concentration. Overall, the 1µm thick n-type Bi2Te3 thin film exhibits a room temperature resistivity as low as 3.56 × 10-6 Ω∙m. Notably, a 5µm thick Bi2Te3 thin film achieves a record power factor of 6.66mWmK-2 at room temperature, which is the highest value reported to date for n-type Bi2Te3 thin films using magnetron sputtering. This work demonstrates the potential for large-scale of high-quality Bi2Te3-based thin films and devices for room-temperature TE applications.

Ce Doping Effects on the Hydrogen Sensing Properties of Graphene/SnO2-Based Sensors.

The development of a sensor capable of selectively detecting hydrogen levels in the environment holds immense importance for ensuring the safer utilization of hydrogen energy. In this study, a hydrogen sensor made of Ce-doped single-layer graphene (SLG)/SnO2 composite material was fabricated using a hydrothermal method. The study examined the impact of varying Ce doping concentrations on the hydrogen sensing capabilities of the SLG/SnO2 matrix. The results show that the SLG/SnO2 hydrogen sensor doped with 2 mol% Ce demonstrated optimal performance at a humidity of 20%. It operated most efficiently at 250 °C, with a response of 2.49, representing a 25.75% improvement over the undoped sample. The response/recovery times were 0.46/3.92 s, which are 54.9% shorter than those of the undoped sample. The enhancement in hydrogen sensitivity stems from the synergistic effect of Ce and SLG, which facilitates the coexistence of n-n and p-n heterojunctions, thereby increasing carrier mobility and refining grain structure. Analysis via X-ray photoelectron spectroscopy (XPS) reveals that Ce increases the material's oxygen vacancy concentration, enhancing its hydrogen sensitivity. Ce-doped SLG/SnO2, with its robust hydrogen sensitivity, represents one of the leading candidates for future hydrogen gas sensors.

Nonvolatile ferroelectric control of electronic properties of Bi2Te3

Abstract Nonvolatile electric-field control of the unique physical characteristics of topological insulators (TIs) is essential for fundamental research and development of practical electronic devices. Electrically tunable transport properties through electrostatic gates have been extensively investigated. However, the relatively weak and volatile tunability limits its practical applications in spintronics. Here, we demonstrate the nonvolatile electric-field control of Bi2Te3 transport properties via constructing ferroelectric Rashba architectures, i.e., 2D Bi2Te3/α-In2Se3 ferroelectric field effect transistors. Through switching the polarization states of the α-In2Se3, the Fermi level, resistance, Fermi wave vector, carrier mobility, carrier density, and magnetoresistance (MR) of the Bi2Te3 film can be effectively modulated. Importantly, a shift of Fermi level toward band gap with surface state occurs as switching to negative polarization state, the contribution of the surface state to the conductivity increases, thereby increasing carrier mobility and electron coherence length significantly, and resulting in enhanced WAL effect. These results provide a nonvolatile electric-field control method to tune the electronic properties of TI and can further extend to the quantum transport properties.

Probing the contribution of bismuth on electronic transport and phonon scattering properties of Mg3Sb2-xBix solid solutions

In this work, first-principles calculations have been used to investigate the electronic structure, phonon scattering, and Debye temperature of Mg3Sb2-xBix alloys. The electronic transport properties were predicted by solving the Boltzmann equations. Additionally, thermoelectric properties of alloys with corresponding compositions prepared using directional solidification were analyzed and compared with the predicted results. The research findings reveal that the increase in Bi content is accompanied by an increase in carrier concentration and mobility, and a decrease in carrier effective mass. The Mg3Sb1.5Bi0.5 alloy showed the highest power factor value of 0.49 mWm−1K−2 due to the synergistic effect between the electrical conductivity and the Seebeck coefficient. As the Bi atoms replace Sb sites, the scattering rates of low-frequency phonons become stronger, significantly reducing the lattice thermal conductivity. The Mg3Sb0.5Bi1.5 alloy reaches the lowest thermal conductivity, especially in the low and medium temperature range. Mg3Sb1.5Bi0.5 alloy provides the maximum ZT value of 0.29 at 630 K. This study systematically analyzes the impact of Bi on electronic transport and phonon scattering in Mg3Sb2-xBix alloys，and extensively discusses the dependence of thermoelectric performance parameters on Bi content. This work also provides a theoretical reference for the subsequent research on doping modification of Mg3Sb2-xBix alloys.

Ultrahigh-mobility microbial cytochrome nanowires generate power from humidity.

Mixed electronic-ionic conductors are crucial for various technologies, including harvesting power from humidity in a durable, self-sustainable, manner unrestricted by location or environment1,2. Biological proteins have been proposed as mixed conductors for 50 years3,4. Recently, Geobacter sulfurreducens pili filaments have been claimed to act as nanowires to generate power5,6. Here, we show that the power is generated by G. sulfurreducens-produced cytochrome OmcZ nanowires that show 20,000-fold higher electron conductivity than pili7. Remarkably, nanowires show ultrahigh electron and proton mobility (>0.25 cm2/Vs), owing to directional charge migration through seamlessly-stacked hemes and a charged, hydrogen-bonding surface, respectively. AC impedance spectroscopy and DC conductivity measurements using four-probe van der Pauw and back-gated field-effect-transistor devices reveal that humidity increases carrier mobility by 30,000-fold. Cooling halves the activation energy, thereby accelerating charge transport. Electrochemical measurements identify the voltage and mobilities required to switch pure electronic conduction to mixed conduction for power generation. The high aspect ratio (1:1000) and hydrophilic nanowire surface captures moisture efficiently to reduce oxygen reversibly, generating large potentials (>0.5 V) necessary to sustain high power. Our studies establish a new class of biologically-synthesized, low-cost and high-performance mixed-conductors and identify key design principles for improving power output using highly-tunable electronic and protein structures.

Improved thermoelectric properties of graphene reinforced multiphase cement composites: experiments and modeling

Nanoscale graphene has demonstrated effectiveness in self-sensing cement composites and energy harvesting in buildings. However, the widespread application of graphene reinforced cement composites (GRCCs) in energy conversion is hindered by their low thermoelectric conversion efficiency. To address this limitation, multiphase cement composites with high Seebeck coefficient and low thermal conductivity are designed by using Cu2Se and ZnO. The increase in carrier mobility and enhanced phonon scattering lead to an order of magnitude improvement in the figure of merit (ZT) compared to GRCCs without incorporating Cu2Se/ZnO. A hybrid micromechanical model (HMM) based on effective medium theory and the Mori–Tanaka method is developed for predicting the electrical and thermal conductivity of the multiphase cement composites, which can be used to evaluate the thermoelectric performances of the composites. The combined experiments and modeling aim to provide guidelines for developing high-performance GRCCs with improved thermoelectric properties, potentially expanding their application in energy conversion technologies.

Strain and orientation modulated optoelectronic properties of La-doped SrSnO3 epitaxial films

We have studied the structural, electrical, and optical properties of La0.05Sr0.95SnO3 thin films, which exhibited a strong dependence upon the substrate’s orientation and strain. X-ray diffraction results show that the LSSO films grow epitaxially on (001) and (011)-oriented LaAlO3 substrates, and the in-plane compressive strain decreases gradually upon increasing film thickness. Room-temperature resistivity varies from 4.23 (13.0) to 1.37 (4.76) mΩ cm as the film thickness increases for (001) orientation ((011) orientation). Temperature dependent resistivity curves of all the samples show a metal–semiconductor transition (MST), which can be explained by the electron–electron interactions below MST rather than weak localization. Both reducing the in-plane compressive strain and transferring the orientation from (011) to (001) can drive the MST point shifts toward lower temperature, indicative of the enhancement of the metallic transport in the films. The band gap increases upon increasing film thickness due to Burstein-Moss effect. The charge distributions of Sn and O from density functional theory (DFT) calculations illustrate that (001)-plane has a better conductivity. Furthermore, our DFT results also demonstrate that decreasing the in-plane strain will lead to a smaller electron effective mass, thus the increased carrier mobility can be obtained. These comprehensive investigations advance our knowledge of the optoelectronic characteristics and provide valuable insights for future research in related transparent materials.

Tailoring interfacial states for improved n-type bismuth telluride thermoelectrics

Efforts to enhance the thermoelectric (TE) efficiency of n-type bismuth telluride (BTS) have focused on leveraging 2D nanostructures, as they have been proven effective in inhibiting phonon transport and simultaneously improving electrical properties. Herein, we introduce g-C3N4 as a suitable candidate for disrupting phonon transport, with the potential to finely tune charge carrier mobility. Crucially, our investigation provides insights into the potential of externally introduced conducting states as a feasible strategy for facilitating carrier transport at heterogeneous interfaces. In contrast, the carrier scattering and localization events play an inverse role. By carefully modulating the competition, we effectively increase carrier mobility, boosting electrical conductivity and optimizing the power factor. This orchestrated strategy leads to a high figure of merit (ZT) of 1.29 at 400 K and an average ZT (ZTave) of 1.20 within 300–500 K. At temperature difference ∆T = 180 K, a maximum power output Pmax = 0.91 W and a 6.2 % conversion efficiency (η) can be achieved over the fabricated TE module. Our findings underscore the potential of 2D nanomaterials and interfacial engineering (IE) as a promising avenue for unlocking the full potential of n-type thermoelectric materials, advancing sustainable and efficient TE power generation.

Uniaxial‐Stress Driven Performance Enhancement of Multi‐Beam Spark Plasma Sintered BiSbTe/Epoxy Flexible Films

AbstractThe multi‐beam discharge plasma sintering (MB‐SPS) method is successfully applied to the preparation of Bi2Te3‐based thermoelectric (TE) films with insulating substrates. Herein, the impact of uniaxial stress on the microstructure evolution and TE performance are explored systematically. The results indicate that the increase of uniaxial stress promotes the preferential growth of Bi0.5Sb1.5Te3 (BST) grains along the (000l) crystal plane, leading to the remarkable increase in carrier mobility. The maximum (000l) preferential orientation factor reaches 80% for the BST/epoxy (EP) film sintered under 25 MPa, which is 3.08 times higher than that of BST/EP film sintered at 10 MPa. While the highest power factor reaches 2.36 mW m−1 K−2 at 300 K for the BST/EP film sintered under 20 MPa, increased by 97% as compared with that of the film sintered under 10 MPa. This work once again confirms that the MB‐SPS technology is an effective approach to prepare high‐performance Bi2Te3‐based films with insulating substrates and demonstrates that the (000l) preferential orientation and TE performance of the films can be further enhanced by an appropriate uniaxial stress.

Using Bulky Dodecaborane-Based Dopants to Produce Mobile Charge Carriers in Amorphous Semiconducting Polymers.

Conjugated polymers are a versatile class of electronic materials featured in a variety of next-generation electronic devices. The utility of such polymers is contingent in large part on their electrical conductivity, which depends both on the density of charge carriers (polarons) and on the carrier mobility. Carrier mobility, in turn, is largely controlled by the separation between the polarons and dopant counterions, as counterions can produce Coulombic traps. In previous work, we showed that large dopants based on dodecaborane (DDB) clusters were able to reduce Coulombic binding and thus increase carrier mobility in regioregular (RR) poly(3-hexylthiophene-2,5-diyl) (P3HT). Here, we use a DDB-based dopant to study the effects of polaron-counterion separation in chemically doped regiorandom (RRa) P3HT, which is highly amorphous. X-ray scattering shows that the DDB dopants, despite their large size, can partially order the RRa P3HT during doping and produce a doped polymer crystal structure similar to that of DDB-doped RR P3HT; Alternating Field (AC) Hall measurements also confirm a similar hole mobility. We also show that use of the large DDB dopants successfully reduces Coulombic binding of polarons and counterions in amorphous polymer regions, resulting in a 77% doping efficiency in RRa P3HT films. The DDB dopants are able to produce RRa P3HT films with a 4.92 S/cm conductivity, a value that is ∼200× higher than that achieved with 3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), the traditional dopant molecule. These results show that tailoring dopants to produce mobile carriers in both the amorphous and semicrystalline regions of conjugated polymers is an effective strategy for increasing achievable polymer conductivities, particularly in low-cost polymers with random regiochemistry. The results also emphasize the importance of dopant size and shape for producing Coulombically unbound, mobile polarons capable of electrical conduction in less-ordered materials.

Optimizing thermoelectric performance of BiSbPbTe thin films through controlled post-annealing: A comprehensive structural and electronic study

This study investigates the structural and electronic properties of BiSbPbTe thin films, focusing on the impact of post-annealing time and temperature. The X-ray diffraction (XRD) analysis reveals a stable rhombohedral phase formation in all samples, with no secondary phases detected within the detection limit. The high crystallinity of the films is confirmed, and post-annealing leads to an increase in peak intensity, indicating enhanced crystalline structure. Surface morphology analysis using scanning electron microscopy (SEM) demonstrates a transition from inhomogeneous features in as-grown films to homogeneous and dense formations in post-annealed films. The grain size increases with post-annealing time, attributed to diffusion, energy minimization, nucleation, growth, and thermal activation processes. The electronic transport properties, including carrier concentration and conductivity, are influenced by post-annealing temperature and duration. A stable carrier concentration is observed for films post-annealed for up to 2 h, while longer durations decrease due to reduced defect vacancies and grain boundaries. The increase in charge carrier mobility, confirmed by SEM results, contributes to enhanced electrical conductivity. The Seebeck coefficient shows an initial enhancement up to 2 h post-annealing, attributed to defect creation and increased grain boundaries. However, further increases in post-annealing duration result in a decrease in the Seebeck coefficient due to enhanced charge carrier mobility and reduced grain boundaries. The thermoelectric power factor (4.4 μW/cm1K2), determined by the square of the Seebeck coefficient and electrical conductivity, reaches its maximum value in the 2-h post-annealed sample, emphasizing the importance of optimizing post-annealing conditions for improved thermoelectric performance.

Stable and efficient perovskite solar cells based on tert-butyl peroxy-2-ethylhexanoate modified hole transport layer

Nowadays, perovskite solar cells (PSCs) have gained significant attention as one of the most promising new energy technologies. However, the application of spiro-OMeTAD, a highly efficient organic hole transport material (HTM) in PSCs, is limited due to its inherent weaknesses in conductivity and hole mobility. Here, a free radical initiator, tert-butyl peroxy-2-ethylhexanoate (TBPEH) is introduced to induce the rapid and controllable oxidation of Spiro. TBPEH-modified hole transport layer (HTL) produces more free radical cations, increasing carrier mobility and electrical conductivity. A smoother surface of the modified HTL improves the charge transport efficiency. Additionally, trap-state density and defect-induced nonradiative recombination of TBPEH-modified device are decreased. In addition, better energy level matching between the HTL and perovskite layer enables more efficient hole transport. Consequently, the PSC doped with TBPEH achieves a champion power conversion efficiency (PCE) of 24.33 %, surpassing the PCE of 21.72 % obtained from the pristine device. Furthermore, the TBPEH-modified devices show better stability. Storing in the atmosphere at 30 % relative humidity for 42 days, the TBPEH-modified device maintains 90.8 % of its highest efficiency, compared to the 73.8 % of the pristine one.

Atomic‐scale strain analysis for advanced Si/SiGe heterostructure by using transmission electron microscopy

AbstractThree‐dimensional stacked transistors based on Si/SiGe heterojunction are a potential candidate for future low‐power and high‐performance computing in integrated circuits. Observing and accurately measuring strain in Si/SiGe heterojunctions is critical to increasing carrier mobility and improving device performance. Transmission electron microscopy (TEM) with high spatial resolution and analytical capabilities provides technical support for atomic‐scale strain measurement and promotes significant progress in strain mapping technology. This paper reviews atomic‐scale strain analysis for advanced Si/SiGe heterostructure based on TEM techniques. Convergent‐beam electron diffraction, nano‐beam electron diffraction, dark‐field electron holography, and high‐resolution TEM with geometrical phase analysis, are comprehensively discussed in terms of spatial resolution, strain precision, field of view, reference position, and data processing. Also, the advantages and critical issues of these strain analysis methods based on the TEM technique are summarized, and the future direction of TEM techniques in the related areas is prospected.

Enhancing Electroluminescence of Medium‐Gap Organic Photovoltaic Cells Through the Incorporation of Pyrrole Rings in Acceptors

AbstractHigh electroluminescence of acceptors can effectively decrease nonradiative energy losses and improve the performance of organic photovoltaic (OPV) cells. Pyrrole ring is a promising building block to enhance the electroluminescence of acceptors, while pyrrole‐based acceptors with medium bandgap are rarely reported. Here, two medium‐gap acceptors named FICC‐EH and FICC‐BO are synthesized. Both acceptors exhibit strong electroluminescence properties, giving satisfying quantum efficiency (QE) of 0.1% in organic light‐emitting diodes (OLEDs). Moreover, PBQx‐TF:FICC‐BO presents a longer film formation process due to the longer alkyl chains. This contributes to more distinct fibril‐network morphology and ordered molecular stacking, thus increasing carrier mobility and suppressing charge recombination. Consequently, benefiting from decreased energy losses, PBQx‐TF:FICC‐BO‐based OPV cells reach a PCE of 12.0% with a VOC of 1.04 V under AM 1.5G and achieve a PCE of 25.4% under 1000 lux LED. This work demonstrates the potential of pyrrole for constructing medium‐gap acceptors with strong electroluminescence for photovoltaic applications.