Br Doping Research Articles

The Impact of Bromine Surface Doping on the Structural, Optical, and Morphological Properties of Bismuth‐Based Perovskite Film as a Light‐Absorber in Perovskite Solar Cells

Bismuth‐based perovskite materials have concerned significant attention due to their low‐toxic and stable properties. However, achieving smooth and dense thin films for the preferential growth of bismuth‐based perovskite along the c‐axis, which is conducive to the preparation of solar cells, is challenging. Therefore, using halogen atoms to partially replace iodine atoms and constrain anisotropic growth has been shown to be an effective method for obtaining high‐quality perovskite films. Herein, Br doping with varying concentrations is used to treat bismuth‐based perovskite films with larger and denser grains compared to those without doping. When a small amount of Br ions is doped, the surface of the perovskite layer becomes more uniform, significantly improving the compactness of the perovskite film. Additionally, proper Br doping can reduce internal defects in the films, effectively inhibiting nonradiative recombination, enhancing light absorption, and increasing carrier lifetime. The optimal power conversion efficiency of Br‐doped bismuth halide perovskite solar cells is found to be 0.136%, compared to 0.087% for pristine devices.

Novel Br-doped Bi2WO6 photocatalyst for high-efficiency removal of norfloxacin: mechanism and photocatalytic activity.

In this work, the bismuth tungstate (Bi2WO6) photocatalyst was successfully prepared, and the pure Bi2WO6 was modified with Br (Br-Bi2WO6). The effects of different experimental conditions on the degradation of norfloxacin (NOR) solution under visible light were investigated. The Br-Bi2WO6 photocatalyst was characterized by FTIR, XRD, SEM, BET, XPS, DRS, EIS, and EPR. The results show that the Br-modified Bi2WO6 photocatalyst can effectively improve the photocatalytic performance. The best photocatalytic performance of Br-Bi2WO6 was observed when the doping amount of Br was 3%. The degradation percentage of norfloxacin can reach 94.67%. The presence of anions and cations (Cl-, SO42-, Ag+, and Cu2+) in the solution significantly inhibited the photocatalytic activity of 3%Br-Bi2WO6. The photocatalytic degradation of norfloxacin by 3%Br-Bi2WO6 was not greatly affected in the presence of HCO3- and NO3-. The characterization analysis showed that Br was successfully doped on the Bi2WO6 photocatalyst, and the original structure of Bi2WO6 was not destroyed by the addition of Br. Br doping increased the specific surface area of Bi2WO6 and decreased the band gap of Bi2WO6 resulting in a broader visible light absorption range. In addition, Br doping promoted the migration rate of photogenerated electron-hole pairs. The ·O2- and h+ played a major role in the photodegradation of norfloxacin, and the mechanism of photocatalytic degradation of norfloxacin by Br-Bi2WO6 was proposed.

Effects of K, Rb, and Br doping on Cs3Bi2I9 perovskites: A design of experiments approach

This work presents the effect of doping with different species on the structural sites of lead-free halide perovskites, aiming to evaluate the potential of the produced materials as photoabsorbing layers in 3rd generation solar cells. Lead-free perovskite films of Cs3Sb2I9, CsCu2I3, Cs3Bi2I9, and CsPbI3 were synthesized via the spin-coating method and characterized using X-ray diffraction, scanning electron microscopy with chemical microanalysis (SEM-EDS), and Uv-Vis spectroscopy. Computational models based on Density Functional Theory (DFT) were used to simulate the structures and properties of some of the perovskites synthesized in this study, in order to validate the experimentally obtained data. The Cs3Bi2I6Br3 perovskite was subjected to modification through A-site doping with K and Rb and X-site doping with Br, with a comprehensive study on the effects of processing variables, anti-solvent quantity, and crystallization temperature using a 23 experimental design. The outcomes highlighted the critical role of the anti-solvent quantity in structure formation and electronic properties. Toluene, as an anti-solvent, produced unique morphologies not commonly reported. Computational studies were performed using Density Functional Theory (DFT) to complement the experimental findings. The optimization process revealed that Cs3Bi2I9 structures mainly constituted [CsI12] and [BrI6] clusters, with Cs–I and Bi–I average bond lengths consistent with experimental results. X-site Br doping induced slight distortion, while A-site Rb/K doping showed minimal lattice parameter changes. Notably, K-induced morphological alterations suggested potential electronic transformations. From an electronic structure perspective, Cs3Bi2I9 had a band gap of 2.07 eV, slightly increased to 2.10 eV with Br doping. Rb maintained Br-doped structure, while K significantly reduced the band gap to 1.96 eV. These computational results align well with our experimental data, showcasing the accuracy of our calculations in predicting material properties. The results confirmed that the perovskites selected through experimental design and validated by computational simulation are promising semiconductor materials for photovoltaic applications, as well as being a lead-free photoabsorbing material option.

Stability, electronic and magnetic properties of boronphosphide (BP) graphenylene induced by interstitial atomic doping

In the context of low-dimensional materials, incorporating foreign atoms through doping processes has the potential to modulate the properties of host materials, which is favorable for diverse functional applications. In this study, we introduce a series of six distinct B6P6X ternary graphenylene monolayers. The B6P6X is designed through interstitial X = Cl, Br, I, O, S, and Te atomic doping of pure BP graphenylene. Through spin-polarized density functional theory (DFT), we comprehensively investigate the stability, electronic, and magnetic properties of B6P6X monolayers. We demonstrate that B6P6X monolayers are mechanically, dynamically and thermally stable with ferromagnetic ground state properties. We show that the metallic features of B6P6X (X = Cl, Br, I, O, S) and half-metallic property of B6P6Te monolayers at the PBE level can be further modulated when subjected to the HSE06 level. It is revealed that the B6P6X (X = O, S) monolayers exhibit a sizeable magnetic moment and a large magnetic anisotropy energy (MAE) value with an easy out-of-plane magnetization axis. We also found an out-of-plane MAE magnetization axis for B6P6X (X = Br, I) monolayers and an in-plane easy magnetization axis for B6P6X (X = Cl, Te) monolayers. Further investigation show that the B6P6S monolayer exhibit above room-temperature TC up to 565 K. The estimated Berezinskii–Kosterlitz–Thouless transition (BKT) temperature value of B6P6Te monolayer is 254 K. Our findings show that the B6P6X monolayers, particularly doped with chalcogens are potential candidates for nanoscale electronics and spintronics applications.

Construction of Br-Cu2O@NiFe-LDHs Z-scheme heterojunction and photocatalytic degradation of catechol

Facet regulation and construction of heterojunctions are important means to enhance the photocatalytic performance of single-phase materials. In this paper, the facet index of Cu2O was changed through Br doping, and then a Br doped Cu2O@NiFe-LDHs Z-scheme heterojunction (BC@LDHs) was constructed for photocatalytic degradation of catechol. The optimal conditions for photocatalytic degradation reaction were explored; the kinetic and thermodynamic parameters of the reaction, as well as the stability and reusability of the material were studied. Under optimal reaction conditions, the photocatalytic degradation of catechol can reach up to 95.68 % by BC@LDHs, which is much higher than that of single-phase materials and Cu2O@LDHs. By combining experiments and theoretical calculations, the intrinsic reasons and mechanisms for Br doping to enhance the photocatalytic degradation performance of BC@LDHs Z-scheme heterojunctions were fully explored from the perspectives of band structure and oxygen adsorption, determination of built-in electric field in Z-scheme heterojunctions, calculation of built-in electric field strength and bulk charge separation efficiency. This work proposes the insights that using Br doping to alter exposed facets and regulate the strength of the built-in electric field in Br-Cu2O@NiFe-LDHs heterojunctions, thereby promoting its efficient photocatalytic degradation.

Enhanced Performance of P-Channel CuIBr Thin-Film Transistor by ITO Surface Charge-Transfer Doping.

The process development and optimization of p-type semiconductors and p-channel thin-film transistors (TFTs) are essential for the development of high-performance circuits. In this study, the Br-doped CuI (CuIBr) TFTs are proposed by the solution process to control copper vacancy generation and suppress excess holes formation in p-type CuI films and improve current modulation capabilities for CuI TFTs. The CuIBr films exhibit a uniform surface morphology and good crystalline quality. The on/off current (ION/IOFF) ratio of CuIBr TFTs increased from 103 to 106 with an increase in the Br doping ratio from 0 to 15%. Furthermore, the performance and operational stability of CuIBr TFTs are significantly enhanced by indium tin oxide (ITO) surface charge-transfer doping. The results obtained from the first-principles calculations well explain the electron-doping effect of ITO overlayer in CuIBr TFT. Eventually, the CuIBr TFT with 15% Br content exhibits a high ION/IOFF ratio of 3 × 106 and a high hole field-effect mobility (μFE) of 7.0 cm2 V-1 s-1. The band-like charge transport in CuIBr TFT is confirmed by the temperature-dependent measurement. This study paves the way for the realization of transparent complementary circuits and wearable electronics.

Derivatives of Br-doped metal-organic framework for improved acetaldehyde adsorption-photocatalytic oxidation

Different Br-doped metal-organic frameworks (MOFs) derived (Brx@UiO-66) have been prepared by heat treatment using UiO-66 as the precursor. The experimental results showed that Br0.2@UiO-66 exhibited the best photocatalytic oxidation and adsorption performances toward acetaldehyde. In the dynamic system, the acetaldehyde removal rate and adsorption capacity of Br0.2@UiO-66 were 93.2 % and 230.59 mg/g, respectively. The improvement of the photocatalytic performance can be attributed to the presence of Br ions and CBr bonds, which facilitated the rapid separation of electrons and holes and the production of •O2−. In addition, Br0.2@UiO-66 had a better adsorption performance than 300UiO-66, mainly because of the increased Lewis acidity of the metal active sites due to Br doping. Radical capture experiments indicated that •O2− and e- were the primary active substances in acetaldehyde oxidation, and allowed establishing the possible mechanism of acetaldehyde oxidation. This work shows that MOFs can have high catalytic oxidation performances toward volatile organic compounds (VOCs) while retaining their adsorption capacity, and can be used for practical applications in the adsorption-catalytic integrated degradation of VOCs.

Anion/Cation Co-Doping to Improve the Thermoelectric Performance of Sn-Enriched n-Type SnSe Polycrystals with Suppressed Lattice Thermal Conductivity.

Enhancing the thermoelectric performance of n-type polycrystalline SnSe is essential, addressing challenges posed by elevated thermal conductivity and compromised power factor inherent in its intrinsic p-type characteristics. This investigation utilized solid-state reactions and spark plasma sintering techniques for the synthesis of n-type SnSe. A significant improvement in the figure of merit (ZT) is achieved through strategic reduction in Se concentration and optimization of crystal orientation. The co-doping with Br and Ge further improves the material; Br amplifies carrier concentration, enhancing electrical conductivity, while Ge introduces effective phonon scattering centers. In the Br/Ge co-doped SnSe sample, thermal conductivity dropped to 0.38Wm⁻¹K⁻¹, yielding a remarkable power factor of 662µWmK- 2 at 773K, culminating in a ZT of 1.34. This signifies a noteworthy 605% improvement over the pristine sample, underscoring the pivotal role of Ge doping in enhancing n-type material thermoelectric properties. The enhancement is attributed to Br doping introducing additional electronic states near the valence band, and Ge doping modifying the band structure, fostering resonant states near the conduction band. The Br/Ge co-doping further transforms the band structure, influencing electrical conductivity, Seebeck coefficient, and thermal conductivity, advancing the understanding and application of n-type SnSe materials for superior thermoelectric performance.

Charge redistribution on NiCo-P hybrid nanoneedle via Br doping enables highly HER

Designing and manufacturing a catalyst with promoted activity and robust stability plays a great role in hydrogen production through electrocatalytic water splitting, but it still remains a great challenge. Herein, this paper reports a porous Br doping NiCoP nanoneedles grown onto the coarsen nickel foam (NF/Ni@Br-NiCoP NNs) through a sequential process of electrodeposition, hydrothermal, and thermal phosphorization. The characterization demonstrates that Br enhanced the electric conductivity and regulated the electron structure, thus leading to a proper H absorption energy (ΔGH*) of –0.13 eV. As a sequence, the NF/Ni@Br-NiCoP NNs only needs 35 (170 mV) to reach 10 (100 mA cm−2) for HER. In addition, the NF/Ni@Br-NiCoP NNs exhibits long-term durability for HER, which the overpotential increased by approximately 3.84 % post 100 h at 50 mA cm−2. Additionally, the KSCN poisoning experiment and first-principle density function theory (DFT) calculation reveal that the Co served as the active site due to the most proper ΔGH*. Moreover, the in-situ Raman spectroscopies characterization indicates that the Ni(OH)2 and α-Co(OH)2 were generated in HER. Hence, this study not only demonstrates a facile synthesis route to prepare HER catalysts, but also establishes a detailed understanding of the interaction between crystal structure, morphology, and electrocatalytic activity.

Br doping-induced evolution of the electronic band structure in dimorphic and hexagonal SnSe2 thermoelectric materials.

SnSe2 with its layered structure is a promising thermoelectric material with intrinsically low lattice thermal conductivity. However, its poor electronic transport properties have motivated extensive doping studies. Br doping effectively improves the power factor and converts the dimorphic SnSe2 to a fully hexagonal structure. To understand the mechanisms underlying the power factor improvement of Br-doped SnSe2, the electronic band parameters of Br-doped dimorphic and hexagonal SnSe2 should be evaluated separately. Using the single parabolic band model, we estimate the intrinsic mobility and effective mass of the Br-doped dimorphic and hexagonal SnSe2. While Br doping significantly improves the mobility of dimorphic SnSe2 (with the dominant hexagonal phase), it results in a combination of band convergence and band flattening in fully hexagonal SnSe2. Br-doped dimorphic SnSe2 is predicted to exhibit higher thermoelectric performance (zT ∼0.23 at 300 K) than Br-doped fully hexagonal SnSe2 (zT ∼0.19 at 300 K). Characterisation of the other, currently unidentified, structural phases of dimorphic SnSe2 will enable us to tailor the thermoelectric properties of Br-doped SnSe2.

Unveiling the bifunctional modulation evoked by bromine doping of CoP towards efficient hydrolytic hydrogen generation

Developing efficient and economical catalysts for hydrolytic hydrogen production from chemical hydrogen storage materials such as ammonia borane and NaBH4 is highly desirable but challenging. Herein, Br doped CoP nanoparticles in a carbon−based polyhedron with controllable morphology were developed as such an efficient hydrogen generation catalyst, and the bifunctional modulation of Br doping was explored. Firstly, regulating the doping content of Br results in the formation of more and larger nanopores in the CoP polyhedron, exposing more accessible active sites. Secondly, Co vacancies are introduced via Br doping, which significantly optimizes the electronic structure of Co atom, thus boosting AB and water dissociation, i.e., the rate−determining step (RDS). Therefore, the Br1 −CoP@C catalyst with optimal composition exhibited a superb turnover frequency (TOF) of 67.3 min−1, implying an astonishing over 3 −fold improvement compared with CoP@C. These findings showcase a novel and promising approach to build high−efficiency nanocatalysts for hydrogen production and beyond.

A comprehensive study of mechanically stacked tandem photovoltaic devices: Materials selection and efficiency analysis using SCAPS

To advance the photovoltaic industry, highly efficient solar modules with reduced manufacturing and installation costs are needed amidst rapid market growth. To surpass the performance limitations of single-junction solar cells, multijunction configurations have been the focus of rigorous study. The current work showcases a comprehensive investigation into the development and optimization of four terminal tandem solar cell architectures, with a focus on exploring the most technologically viable impactful, and promising combinations of top cell materials (CdTe, GaAs, MAPbI3, and MASnI3) and bottom cell options (c-Si and CIGS). Through numerical simulations using the Solar Cell Capacitance Simulator SCAPS and meticulous analysis, considering crucial parameters such as bandgap, charge carrier mobility, and defect densities, this study aims to identify the most promising material combinations for achieving high-efficiency tandem devices. The findings reveal that when c-Si is used as the bottom cell absorber, the tandem device as a whole produces a higher power conversion efficiency than when CIGS is used. The top cell options, namely CdTe, GaAs, MAPbI3, and MASnI3 in conjunction with c-Si as the bottom cell, achieve maximum efficiencies of 27.23%, 29.31%, 31.66%, and 15.64% respectively. In contrast, when paired with CIGS as the bottom cell, the efficiencies slightly decrease to 23.76%, 26.43%, 28.45%, and 12.83%. Notably, the investigation involving 25%, 50%, and 75% Br-doped MASnI3 alongside c-Si reveals efficiencies of 16.59%, 14.94%, and 14.28% respectively. In the case of CIGS, the corresponding efficiencies for 25%, 50%, and 75% Br doping are slightly lowered to 13.78%, 12.17%, and 11.43%. The obtained results offer valuable insights that can guide future research endeavors and foster the development of more efficient and commercially viable solar energy conversion technologies in the field of tandem photovoltaics.

Enhanced stability and optoelectronic properties of double perovskite Cs2AgSbI6 by Br doping for solar cells

Lead halide perovskite photovoltaic cells offer much higher energy conversion efficiency. However, new non-toxic semiconductor compounds are being sought due to instability and lead toxicity. The stable double perovskite Cs2AgSbI6 is the base material for this investigation since it has been demonstrated to be an effective and ecologically replacement for lead halide perovskites. In this study, the cubic space phase of the bromine alloy double inorganic halide perovskite Cs2AgSb(I1−xBrx)6 was analyzed using density functional theory (DFT). The band gap was widened with increasing percentages of Br doping, and theoretical calculations were used to determine the best structures for these compounds. Theoretically, its optoelectronic characteristics are computed using the GGA-PBE and GGA-TB-mBJ approximations. We found that Cs2AgSb(I1−xBrx)6 is stable under typical conditions with a band gap below 2 eV. Thus, it is advised to utilize Cs2AgSb(I1−xBrx)6 for solar cell applications. The spectroscopic limited maximum efficiency (SLME) technique was used to analyze theoretical efficiency (η), with the gap energy, absorption coefficient, and absorption estimated from the typical AM1.5G solar spectrum at 25 °C serving as key input factors. We attained an η of 18 % for Cs2AgSb(I0.50Br0.50)6 at a thickness of 800 nm.

Mechano-chemical solution process for Li3PS4 solid electrolyte using dibromomethane for enhanced conductivity and cyclability in all-solid-state batteries

Increasing conductivity and stability is one of the essential and ultimate goals for electrolyte research. For sulfide solid-state electrolytes (SSEs), elemental doping is often suggested for this purpose. A typical doping method for sulfide SSE is an energy intensive and non-uniform solid-state reaction, because most solvents react with sulfide SSEs. Here, we have demonstrated that highly efficient Br-doping into lithium thiophosphate Li3PS4 (LPS) can be achieved through a solution-based strategy using dibromomethane (DBM) as Br-source and solvent in a ball-milling process. In this “mechano-chemical” process, simultaneous pulverization of large LPS particles and Br-doping occur, achieving remarkably improved Li+ ion conductivity (1.3 mS cm−1) which is eight times higher than that of the pristine LPS at only 1.14 at. % Br doping. This conductivity is one of the highest for LPS SSE, especially at this low doping level. The LPS to DBM ratio critically affects the efficiency of these chemical and physical modifications. In all-solid-state lithium-metal-batteries, the modified LPS exhibited exceptional cycling stability with reduced overpotential. The Li-Li symmetric cell demonstrated extremely stable Li deposition and stripping for over 1350 h, and the full cell with the Li anode and Li[Ni0.8Co0.1Mn0.1]O2 cathode retained 83 % of its initial capacity after 100 cycles. With possible application toward the slurry fabrication of LPS SSEs, the proposed approach provides a new and effective strategy for fabricating high-performance sulfide SSEs for large-scale applications.

Study on Cs2AgIn(Cl1−xBrx)6 perovskite based on the balance of stability and optical absorption properties

The Cs2AgIn(Cl1−xBrx)6 (x = 0, 1/6, 1/3, 1/2, 2/3, 5/6, 1) lead-free perovskites show great advantages as a stable and non-toxic alternative to lead halide perovskite. In this study, Cs2AgIn(Cl1−xBrx)6 are treated by replacing Cl with Br in a stepwise manner to balance its stability and optical properties. Density functional theory is used to investigate the structural, electronic, and optical properties of Cs2AgIn(Cl1−xBrx)6. The results show that the doping of Br make the average bond length of metal-halides longer, resulting in an increase in volume. The value of the bandgap decreases from 3.168 eV to 2.095 eV. The decomposition energy (−92.3365 to −70.4435 meV/atom) of the material gradually increases, the stability decreases gently (−92.3365 to −90.934 meV/atom, Δ0–1/2 = 0.4675) when the amount of Br doping is less than 1/2, and it decreases significantly (−90.934 to −70.4435 meV/atom, Δ1/2–1 = 6.83) when it exceeds 1/2. The partial density of states reveal that the electronic contribution is mainly related to the [AgX6]5- (X = Cl, Br) octahedral. The analysis of charge density indicates that partially or completely replacing Cl with Br is beneficial for the generation of free electrons, which may improve its photoelectric performance. The analysis of the complex dielectric function and the optical absorption coefficient shows a more significant increase in the absorption coefficient when half of the Br is incorporated compared to full substitution. According to our results, adjusting x in Cs2AgIn(Cl1−xBrx)6 can expand the material's range of spectroscopic applications. Based on the trade-off between stability and light absorbance, Cs2AgInCl3Br3 exhibits the best overall performance.

Br doping promotes the transform of Cu2O (100) to Cu2O (111) and facilitates efficient photocatalytic degradation of tetracycline

The activity of single-crystal catalysts with different crystal faces varies greatly, and the construction of catalysts with highly exposed active facets is essential for the improvement of photocatalytic performance. In this paper, Cu2O (100) crystal facets were transformed into high degrade-active Cu2O (111) crystal facets by doping with halogen atoms Br for the photocatalytic degradation of tetracycline. The effect of the optimal Br/Cu2O ratio on the degradation activity was investigated by adjusting the amount of Br. Meanwhile, based on photocatalytic degradation performance tests, photoelectric performance characterization and theoretical calculations, it was found that the doped Br-Cu2O introduced impurity energy levels, reduced the band gap, broadened the absorption range of the photocatalyst under visible light, and enhanced the oxidation capacity and the rate of photogenerated electron leap. In addition, the highly active Cu2O (111) crystal surface facilitates the adsorption of oxygen to generate superoxide radicals and promote the photocatalytic reaction. The synergistic effect of these two aspects promotes the efficient degradation of tetracycline by Br-Cu2O. This work provides a promising idea for the design and construction of highly efficient active surface highly exposed photocatalysts.

Performance Optimization of CsPb(I1–xBrx)3 Inorganic Perovskite Solar Cells with Gradient Bandgap

In recent years, inorganic perovskite solar cells (PSCs) based on CsPbI3 have made significant progress in stability compared to hybrid organic–inorganic PSCs by substituting the volatile organic component with Cs cations. However, the cubic perovskite structure of α-CsPbI3 changes to the orthorhombic non-perovskite phase at room temperature resulting in efficiency degradation. The partial substitution of an I ion with Br ion benefits for perovskite phase stability. Unfortunately, the substitution of Br ion would enlarge bandgap reducing the absorption spectrum range. To optimize the balance between band gap and stability, introducing and optimizing the spatial bandgap gradation configuration is an effective method to broaden the light absorption and benefit the perovskite phase stability. As the bandgap of the CsPb(I1–xBrx)3 perovskite layer can be adjusted by I-Br composition engineering, the performance of CsPb(I1–xBrx)3 based PSCs with three different spatial variation Br doping composition profiles were investigated. The effects of uniform doping and gradient doping on the performance of PSCs were investigated. The results show that bandgap (Eg) and electron affinity(χ) attributed to an appropriate energy band offset, have the most important effects on PSCs performance. With a positive conduction band offset (CBO) of 0.2 eV at the electron translate layer (ETL)/perovskite interface, and a positive valence band offset (VBO) of 0.24 eV at the hole translate layer (HTL)/perovskite interface, the highest power conversion efficiency (PCE) of 22.90% with open–circuit voltage (VOC) of 1.39 V, short–circuit current (JSC) of 20.22 mA/cm2 and filling factor (FF) of 81.61% was obtained in uniform doping CsPb(I1–xBrx)3 based PSCs with x = 0.09. By carrying out a further optimization of the uniform doping configuration, the evaluation of a single band gap gradation configuration was investigated. By introducing a back gradation of band gap directed towards the back contact, an optimized band offset (front interface CBO = 0.18 eV, back interface VBO = 0.15 eV) was obtained, increasing the efficiency to 23.03%. Finally, the double gradient doping structure was further evaluated. The highest PCE is 23.18% with VOC close to 1.44 V, JSC changes to 19.37 mA/cm2 and an FF of 83.31% was obtained.

Effects of heavy bromine doping on the thermoelectric performance and dynamic stability of SnSe2 polycrystals

SnSe2 is a material with a layered crystal structure, which is abundant in the Earth's crust and is non-toxic. It exhibits anisotropic thermoelectric properties due to the anisotropy between its interlayer and intralayer electrical and thermal transport properties. However, its thermoelectric performance is intrinsically poor due to its lower electrical transport properties. In our study, we successfully synthesized n-type Bromine-doped SnSe2 polycrystals using a combined method of mechanical alloying (MA) and spark plasma sintering (SPS). Bromine (Br) acts as an electron donor, and its heavy doping has been achieved by substituting it with selenium (Se) atoms. This substitution results in a significant increase in carrier concentrations, thereby improving the thermoelectric performance of SnSe2. This Br doping has led to a notable improvement in the power factor, which increased to approximately 755 µWm−1K−2 at 573 K. The most significant anisotropy was observed in thermal conductivity, and Br doping led to an ultralow thermal conductivity of approximately 0.6 Wm−1K−1 at 748 K. Furthermore, density functional theory (DFT) was used to investigate the electronic structure and phonon dispersions. The results of our DFT calculations showed a shrinking bandgap and increased degeneracy, which supports the observed improvement in the thermoelectric performance of Bromine-doped SnSe2 polycrystals. Moreover, the absence of imaginary modes in the phonon dispersion confirmed the dynamical stability of the system after heavy Br doping. Finally, a maximum figure of merit (ZT) of 0.59 was obtained at 748 K for the SnSe1.95Br0.05 sample parallel to the SPS pressing direction, which is nearly sixfold higher than the value of pure SnSe2.

Enhanced quantum capacitance in Ti, V, Cr, Fe, Ga, Ge, Se, and Br doped arsenene: A first principles investigation

The present work systematically studied the quantum capacitance in 3d (Ti, V, Cr, Fe) and 3p (Ga, Ge, Se, Br) doped Arsenene using first-principles calculation. The calculated negative formation energy (EF) advocates the feasibility of such doping, with a large EF for 3d-Arsenene. Among the dopants, Ti was strongly embedded within the vicinity of the thinned monolayer. The HOMO-LUMO analysis confirms a strong interaction between the Ti-3d state and the Arsenene 4p-state. More importantly, semiconducting states resulted on Ti/Ga/Ge/Br doping, whereas metallic states took place from V/Cr/Fe/Se doping. Projected density of state (PDOS) also advocates these observations and predicts the 3d-state to play an important role in calculating the quantum capacitance (CQ) of 3d-Arsenene. It is found that 3d/4p doping significantly enhanced the quantum capacitances (CQ)/surface charges (Q) of Arsenene. Among 3d and 4p doping, Cr-Arsenene and Se-Arsenene, respectively, have the highest CQ of 345 µF/cm2 and 176 µF/cm2 in the positive and negative bias region, respectively. The finding recommends Cr and Se-doped Arsenene for asymmetric supercapacitors as anode and cathode materials, respectively. Also, Ti/V/Fe/Ga/Ge/Br-Arsenene show enhanced CQ and surface charge (Q), making them suitable for supercapacitor applications.

Electronic structure and optical properties of Br- and Cl-doped rutile TiO2 for application in self-cleaning and photovoltaic panel's coatings: first-principle calculations.

Development of novel self-cleaning technologies, especially those based on semiconductor photocatalysis system, is one of the most important research problems in environmental cleanup. Titanium dioxide (TiO2) is a well-known semiconductor photocatalyst that has a strong photocatalytic activity in the ultra-violet part of the spectrum while its photocatalytic efficiency is very limited within the visible range due to its large band gap. In the field of photocatalytic materials, doping is an efficient method to increase the spectral response and promote charge separation. However, the type of dopant is not the only important factor, but also its position in the material lattice. In the present study, we have carried out first-principle calculations based on density functional theory to explore how particular doping configuration, such as Br or Cl doping at an O site, may influence the electronic structure and the charge density distribution within rutile TiO2. Furthermore, optical properties such as the absorption coefficient, the transmittance, and reflectance spectra have also been derived from the calculated complex dielectric function and examined to see whether this doping configuration has any effect on the use of the material as a self-cleaning coating on photovoltaic panels.