Lower Valence Band Research Articles

Spin asymmetry of O 2p –related states in SrTiO3(001)

Atomically clean SrTiO3(001) is characterized by low energy electron diffraction, core level and valence band photoelectron spectroscopy, the latter also with spin resolution. Samples prepared by a sputtering-annealing procedure exhibited in-gap states in the valence band spectra, Ti3+ components in Ti 2p core level spectra and a noticeable spin asymmetry in the 3–9 eV binding energy range, which corresponds to valence states of mainly O 2p character. Upon annealing in oxygen, the spin asymmetry vanishes, accompanied by the intensity decrease of the contribution of titanium low ionization states and of in-gap states, indicating that these three phenomena are mutually connected. The observed spin asymmetry may be generated by indirect exchange mediated by the in-gap states between O 2p orbitals, or by the partial Ti 3d character of these states, which acquire non-zero spin in case of incomplete oxygen coordination.

Engineered Sn-TiO2@SnO2 and SnO2@Sn-TiO2 heterophotocatalysts for enhanced As(III) remediation: A comprehensive bulk and surface characterization and precise photocatalytic oxidation rates determination

Arsenite, As(III), is a highly toxic form of arsenic that poses a significant risk to human health if present in drinking water. Oxidation of As(III) to the less toxic As(V) using TiO2 as photocatalyst is an attractive solution in water treatment applications but challenged the high bandgap energy. In this study, we investigate the potential of doping TiO2 with Sn to reduce the bandgap and hence to improve the photocatalytic oxidation (PCO). To this end, we studied first the effect of varying Sn:TiO2 molar doping on the structure of the newly synthesized SnO2@TiO2 and Sn-TiO2@SnO2 hetero photocatalysts. We found that at low Sn:TiO2 doping ratios (0.1Sn:1TiO2), SnO2 tends to float on the surface and form a coat around the TiO2 (SnO2@Sn-TiO2), whereas at higher doping ratio (1Sn:1TiO2) a Sn-TiO2 coat forms alongside SnO2 clusters in the core of the catalyst (Sn-TiO2@SnO2). We assessed the PCO and observed significant shifts to lower conduction and valence band edge energies and a reduction of the bandgap at higher doping ratios. The smallest bandgap was 2.87 eV with a doping ratio of 1Sn:1TiO2. Sn-TiO2@SnO2 and as SnO2@Sn-TiO2 improved the PCO of TiO2 by ∼30 and 46 %, respectively. We finally determined the rate constant (k) for the As(III) oxidation using a combination of spectrochemical and surface sensitive techniques and determined for a 1Sn:1TiO2 (i.e. Sn-TiO2@SnO2) catalyst a value of 0.055 ±0.002 min−1, i.e., 78 folds faster than using only TiO2. We conclude that Sn doping of TiO2 is a very promising approach for improving the PCO of As(III) in water treatment.

Engineering Facet‐Dependent Interface Charge Transfer in Liquid Metal‐Embraced BiVO4 Photoelectrodes for Efficient Photoelectrochemical Water Splitting

AbstractCrystal facet‐dependent photogenerated charge transfer at the semiconductor/current collector interface of photoelectrodes is equally important compared to that at the semiconductor/liquid interface for efficient photoelectrochemical (PEC) water splitting, which, however, is difficult to explore due to the rigid solid/solid interface in conventional photoelectrodes. Here, the facet‐dependent charge transfer at both semiconductor/liquid and semiconductor/collector interfaces in liquid metal‐embraced photoelectrodes is systematically investigated using faceted BiVO4 micro‐particles with different ratios of {110} and {010} facets as model materials. The results from the photo(electro)chemical and photophysical characterizations reveal that {010} facets outperform {110} facets at the semiconductor/liquid interface in triggering water oxidation due to the lower valence band maximum (VBM) of {010} facets, while {110} facets are more efficient at the semiconductor/metal interface for the collection of photogenerated electrons due to their higher conduction band minimum (CBM). Consequently, the photoelectrodes of liquid metal‐embraced BiVO4 particles exposing 53% {110} facets yield the best PEC performance for water splitting due to the well‐balanced photogenerated charge transfer at the interfaces of semiconductor/metal and semiconductor/liquid.

A systematic computational study of novel SrTrCu3Se4 (Tr = Al, Ga) direct band gap materials: Probing electronic, optical, and thermoelectric nature

Aluminum and gallium-based quaternary semiconductors have unique features, like tunable optical response and high thermoelectric stability. Using well-known density functional theory here the intricate relation in the structural, optoelectronic, and transport properties of new direct band gap SrTrCu3Se4 (Tr = Al, Ga) quaternary semiconductors. These materials exhibit a direct energy gap behavior at the respective Г-point. According to density of state estimates, the upper valence band is predominantly composed of Cu-d states, whereas the lower valence band is composed of Se-p states. To determine the potential use in optoelectronic applications, the complex dielectric constant, along with significant optical constants, were researched and studied. The investigated materials are suitable for thermoelectric applications, as evidenced by significant and noteworthy thermoelectric properties. The current work can establish their possible use in advanced optoelectronic devices and pave the way for a variety of technologies.

Internal structure of metal vacancies in cubic carbides

A combinatorial approach is employed to investigate the atomic and electronic structures of a metal vacancy in titanium carbide. It turns out that the usual relaxed geometry of the vacancy is just a metastable state representing a local energy minimum. Using calculations and by systematically searching through the configurational space of a Ti monovacancy, we identify a multitude of local minima with reconstructed geometry that are lower in energy. Among them, there is a planar configuration with two displaced carbons forming a dimer inside the vacancy. This structure has the optimal number and order of C–C bonds making it the global minimum. Further calculations show that this reconstructed geometry is also the ground state of metal vacancies in other carbides such as ZrC, HfC, and VC. The reconstructed metal vacancies are characterized by localized electron states due to the relatively short C–C bonds. The defect states lie just below the upper and lower valence bands. The existence of reconstructed vacancy configurations is essential for understanding the mechanism of metal self-diffusion in transition-metal carbides. Published by the American Physical Society 2024

Mechanism of p-Type Heteroatom Doping of Lithium Stannate for the Photodegradation of 2,4-Dichlorophenol: Enhanced Hole Oxidative Capability and Concentrations.

A systematic evaluation of enhancing photocatalysis via aliovalent cation doping is conducted. Cation In3+, being p-type-doped, was chosen to substitute the Sn site (Sn4+) in Li2SnO3, and the photodegradation of 2,4-dichlorophenol was applied as a model reaction. Specifically, Li2Sn0.90In0.10O3 exhibited superior catalytic performance; the photodegradation efficiency reached about 100% within only 12 min. This efficiency is far greater than that of pure Li2SnO3 under identical conditions. Density functional theory calculations reveal that introducing In3+ increased the electron mobility, yet decreased the hole mobility, leading to photogenerated carrier separation. However, photoluminescence and time-resolved photoluminescence suggest that In3+ induced nonradiative coupling in the matrix, reducing the photogenerated carrier separation ratio compared with that of Li2SnO3. The optical band gap of Li2Sn0.90In0.10O3 was almost unchanged compared with that of Li2SnO3 via ultraviolet-visible absorption. The increased photocatalytic efficiency was ascribed to the lower valence band position and enhanced hole concentrations by valence band X-ray photoelectron spectroscopy and electrochemical measurements. Finally, a 2,4-dichlorophenol degradation pathway, an intermediate toxicity assessment, and a photocatalytic mechanism were proposed. This work offers insights into designing and optimizing semiconductor photocatalysts with high performance.

Promising thermoelectric performance in p-type AgBiSe2 doping with alkaline-earth metals

P-type AgBiSe2 is a promising thermoelectric material because of its intrinsic low lattice thermal conductivity and multiple valence band behavior. However, realizing high performance in p-type AgBiSe2 is challenging due to the doping bottleneck. In this work, the enhancement of thermoelectric performance for p-type AgBiSe2 has been successfully realized by adding an excess amount of Se and doping with alkaline-earth metals. We show that Ca or Mg doping at the Bi site effectively increases the room-temperature hole concentration and improves the electrical transport properties of p-type AgBiSe2. Combined with the intrinsic lower thermal conductivity, the maximum zT values of ∼0.74 and ∼0.63 at 448 K were achieved in AgBi0.98Ca0.02Se2 and AgBi0.98Mg0.02Se2, respectively. This work demonstrates a crucial strategy for improving the thermoelectric properties of p-type AgBiSe2-based materials.

Surface restructuring Ni0.85Se/ZnSe catalyst shows large boosting electrocatalytic and photoelectrochemical performance

Catalytic performance is often affected by electronic band structure. Here, it is demonstrated that though loading ZnSe on the surface of Ni0.85Se to build Ni0.85Se/ZnSe heterojunction catalysts. The electronic band structure of Ni0.85Se/ZnSe heterojunction can be adjusted by the loading ZnSe, which largely affects the electrocatalytic and photoelectrochemical performance. Compared with pristine Ni0.85Se (1.49 eV) and ZnSe (2.50 eV), the bandgap of Ni0.85Se/ZnSe change from 1.28 to 1.60 eV, which is even lower than that of Ni0.85Se and ZnSe. Meanwhile, the positions of the conduction and valence bands of composites also show unusual changes: NZS2 has the highest conduction band of −0.78 eV which is higher than that of Ni0.85Se (−0.62 eV) and ZnSe (−0.66 eV) while NZS3 shows the lowest valence band of 0.88 eV which is also little lower than that of Ni0.85Se (0.87 eV). The characteristics of this adjustable electronic band structure bring obvious changes in catalytic performance. In the hydrogen evolution reaction tests, NZS2 has the lowest overvoltage of 209 mV and Tafel slope of 56 mV/dec, and NZS3 shows the lowest overvoltage of 318 mV and Tafel slope of 89 mV/dec in the oxygen evolution reaction. As compared, the Ni0.85Se has an overvoltage of 247 mV and Tafel slope of 77 mV/dec in hydrogen evolution reaction, and cannot achieve current density of 10 mA/cm2 in oxygen evolution reaction. It is considered that the higher conduction band is beneficial for reduction reaction and lower valence band means higher oxidation capacity. Moreover, the loading of ZnSe enhances the carrier's separation efficiency which causes higher photoelectrochemical performance.

Effect of structural optimization of magnetic MnFe2O4@Bi24O31Br10/Bi5O7I with core-shell structure on its enhanced photocatalytic activity to remove pharmaceuticals

Pharmaceutical contamination spreading across the aquatic environment has resulted in great disturbance to ecosystem and severe menace to human health. Magnetic photocatalysts have achieved great attention due to their magnetic separation capacity, recycling usage and low risk for secondary pollution. However, their practical applications to solve pollution problem are limited due to the insufficient photocatalytic activity, which is caused by their low valence band potentials and fast recombination of photo-generated carriers. In our research, by involvements of layer-structured bismuth-rich oxyhalides (BixOyXz, X = Cl, Br, I), optimizations for the microstructure and band structure of magnetic MnFe2O4 were applied to improve its photocatalytic activity for effectively removing pharmaceuticals residues. With the assistance of Bi24O31Br10 and Bi5O7I, MnFe2O4 nanoparticles (NPs) was gradually optimized to core-discontinuous shell structure of MnFe2O4@Bi24O31Br10 (M@B) and multi-layer entire core-shell structure of MnFe2O4@Bi24O31Br10/Bi5O7I (M@B/B). The optimized microstructures of M@B and M@B/B provide tight contact between components and promote the separation and utilization rates of carriers in photocatalytic process. For ternary M@B/B, tight contact between the components permits the working of optimized band structure, where double-Z scheme is formed and a favorable electron transfer mode is allowed. The production rates of active radicals from CB of Bi5O7I and VB of MnFe2O4 and Bi24O31Br10 are promoted and their redox abilities are strengthened. The synergy of improved utilization rate of carriers and their strengthened redox ability endows M@B/B with superior photocatalytic performance for removing pharmaceuticals with high concentrations. The removal efficiencies of M@B/B are determined to be 93.2%, 95.0% and 87.8% in 100 min for levofloxacin (LVFX, 20 mg L−1), tetracycline (TC, 50 mg L−1) and triclosan (TCS, 100 mg L−1), respectively. Our research provides a novel and effective channel to improve the photocatalytic activity of magnetic materials by involvements of BixOyXz compounds. According to its enhanced photocatalytic performance, suitable magnetic separation capacity and recycling usage, the practical applications of MnFe2O4 magnetic composites to treat real pharmaceuticals wastewater are reasonable and realistic.

Facile Synthesis of TiO2 with a Narrow Bandgap and Low Valence Band for Efficient Visible-Light Photocatalytic Degradation of Various Phenols

Facile Synthesis of TiO₂ with a Narrow Bandgap and Low Valence Band for Efficient Visible-Light Photocatalytic Degradation of Various Phenols

Selective photocatalytic oxidation of furfural to C4 compounds with metal-TS-1 zeolite

A series of metal-TS-1 zeolite catalysts were designed to selectively catalyze the photo oxidation of furfural to C4 carboxylic acid derivatives at ambient temperature and pressure. The photocatalytic preparation of malic acid from furfural was realized for the first time. The selective distribution of products could be controlled by adjusting the physical and chemical characteristics of the catalyst. Smaller pore size prevented the further conversion of maleic acid to malic acid; moderate acidity was beneficial for the preparation of malic acid; lower valence band was in favor of maleic acid production while higher valence band tended to form malic acid. The synergistic effect of pore structure, acidity and energy band structure of catalysts affected the product distribution. The yield of maleic acid reached as high as 40% over Fe-TS-1, meanwhile, the yield of malic acid reached as high as 63% over Ni-TS-1. The doping of metal was believed to be an effective procedure to adjust the structure and physicochemical properties of zeolite. Matel-TS-1 zeolite was also expected to be widely used in photocatalytic system to achieve more selective reactions.

Influence of silver introduction into (Ag,Cu)(In,Ga)S2 thin films on their physical properties

Silver was introduced into pure-sulfide Cu(In,Ga)S2 (CIGS) to form (Ag,Cu)(In,Ga)S2 (ACIGS) compound. The impact of the Ag addition on physical properties and photovoltaic performances was therefore examined to determine suitable Ag amount in ACIGS solar cells. The ACIGS thin films with different Ag/(Ag + Cu) (AAC) compositional ratios were formed through the sulfurization of the In/Cu/Ga/Ag stacked precursors. It is disclosed that the AAC is obviously increased from 0 to 0.18 under the increase in the Ag precursor thickness from 0 to 80 nm. Moreover, under the suitable Ag introduction (ACC of 0.04), the quality of ACIGS absorbers is improved with low Urbach energy (EU) and the enlargement of crystal grain size. The decreased conduction band offset between the absorber and CdS buffer layers under Ag addition is realized with lower valence band maximum value of the ACIGS absorbers, thus feasibly increasing the hole barrier. Additionally, the band alignment between absorber and CdS buffer layers was disclosed with the varied ACC based on photoemission yield spectroscopy. Ultimately, the short-circuit current density of the ACIGS solar cell is clearly increased by 2 mA/cm2 under suitable ACC of 0.04.

Co3O4 anchored on sepiolite surface grooves for superior adsorption of tetracycline from wastewater

Due to the low valence band maximum value, Co3O4 is an outstanding catalyst, but its utilization in adsorption needs to be addressed. In this study, we proposed a novel method for loading aggregation-prone Co3O4 onto sepiolite (Sep) to facilitate tetracycline (TC) adsorption. The XRD, TEM, and FTIR analyses demonstrated that the highly dispersed Co3O4 was successfully anchored on the sepiolite grooves via the Si-OH on the sepiolite surface’s grooves to the cobalt site in Co3O4. We firstly proposed a view of how metal oxide aggregates are confined to the grooves on the surface of sepiolite (via Si-OH at the edges of the grooves on the sepiolite surface). The ultra-high sorption capacity of Co3O4-Sep is 219.53 mg/g for TC, which is three times that of Sep (70.75 mg/g) and Co3O4 (85.29 mg/g). The kinetic and isotherm results fitting suggested that the adsorption of TC on Co3O4-Sep mainly contributed to the multilayer chemisorption adsorption process. Thermodynamic investigations revealed the spontaneous endothermic reaction of TC adsorption on Co3O4-Sep. Co3O4 strengthened the complexation between the composite and functional groups of TC, significantly increasing TC adsorption capacity. In addition, the Co3O4-Sep retained an extraordinary adsorption capacity with the presence of competing ions, at strongly acidic and alkaline pH values and after three cycles. Therefore, this study offers new perspectives on applying cobalt-based materials and demonstrates the potential for antibiotic adsorption in the prepared composites.

Mid-wave infrared optical receiver based on an InAsSb-nBn photodetector using the barrier doping engineering technique for low-power satellite optical wireless communication.

This paper proposes a new nBn photodetector (nBn-PD) based on InAsSb with a barrier doping engineering technique [core-shell doped barrier (CSD-B) nBn-PD] for utilization as a low-power receiver in satellite optical wireless communication (Sat-OWC) systems. In the proposed structure, the absorber layer is selected from an I n A s 1-x S b x (x=0.17) ternary compound semiconductor. The difference between this structure and other nBn structures is the placement of the top and bottom contacts in the form of a PN junction, which increases the efficiency of the proposed device through the creation of a built-in electric field. Also, a barrier layer is placed from the AlSb binary compound. The presence of the CSD-B layer with the high conduction band offset and very low valence band offset improves the performance of the proposed device compared to conventional PN and avalanche photodiode detectors. By applying -0.1V bias at 125K, the dark current is demonstrated at 4.31×10-5 A/c m 2 by assuming high-level traps and defect conditions. Examining the figure of merit parameters under back-side illumination with a 50% cutoff wavelength of 4.6µm shows that at 150K, the responsivity of the CSD-B nBn-PD device reaches about 1.8A/W under 0.05W/c m 2 light intensity. Regarding the great importance of using low-noise receivers in Sat-OWC systems, the results indicate that the noise, noise equivalent power, and noise equivalent irradiance are calculated as 9.98×10-15 A H z -1/2, 9.21×10-15 W H z 1/2, and 1.02×10-9 W/c m 2, respectively, at -0.5V bias voltage and 4µm laser illumination with the influence of shot-thermal noise. Also, D ∗ obtains 3.26×1011 c m H z 1/2/W without using the anti-reflection coating layer. In addition, since the bit error rate (BER) plays an essential role in the Sat-OWC systems, the effect of different modulations on the BER sensitivity of the proposed receiver is investigated. The results represent that the pulse position modulation and return zero on-off keying modulations create the lowest BER. Attenuation is also investigated as a factor that significantly affects BER sensitivity. The results clearly express that the proposed detector provides the knowledge to achieve a high-quality Sat-OWC system.

The Application of GaN/ZnO Heterojunction in Water Splitting

Different morphology of ZnO were deposited on GaN substrate using magnetron sputtering method by changing deposition conditions. The ZnO and GaN can form II-type heterojunction due to its higher conduction and lower valence band compared to GaN. The electric field generated by space charge region can separate the photo generated carriers more promptly. In the photocatalytic test, the best performance of GaN/ZnO photoanode with fine crystal quality is about 1.39 times compared to planar GaN. Our research paves a new way for the application of GaN in water splitting performance.

A Strategy to Optimize Nickel Oxide/Crystalline Silicon Heterocontact of HJT Solar Cells

NiOx is a p-type semiconductor material with wide band-gap (3.6 ∼ 4.0 eV), good thermal and chemical stability. In terms of energy band structure, NiOx/n-Si possesses low valence band offset to allow hole and high conduction band offset to block electron, NiOx is thus a promising hole-selective layer for n-type c-Si based heterojunction (HJT) solar cells. However, intrinsic NiOx suffers from low carrier concentration and poor conductivity, which severely limits its development in photovoltaics. This study aimed to obtain Ag-doped NiOx film with high carrier concentration and low resistivity by co-sputtering using high-purity Ag and NiOx target for high efficiency solar cells. The results show that appropriate Ag doping can increase the acceptor concentration of the film, promote the tunnelling effect, reduce interface recombination, and thus improve the device efficiency. When Ag content is 2.4%, the fill factor of Al/ITO/NiOx:Ag/SiOx/c-Si/SiOx/Al solar cell is increased from 52.97% to 68.42%, and the power conversion efficiency reaches 9.11%. Combined with the analysis of AFORS-HET simulation, the mechanism how Ag doping works in the hetrojunction is revealed.

α-Fe2O3/g-C3N4 Z-Scheme Heterojunction Photocathode to Enhance Microbial Electrosynthesis of Acetate from CO2

A visible-light responsive photocathode microbial electrosynthesis (MES) is an attractive method for CO2 fixation via a microbial electrochemical process. Here, an α-Fe2O3/g-C3N4 formed a Z-scheme heterojunction structure and exhibits high photogenerated electron–hole separation ability under visible light. The low valence band potential of α-Fe2O3 makes binding electrons transferred from the anode easier for photogenerated holes, providing an additional driving force to improve MES performance. Furthermore, the introduction of α-Fe2O3 can promote electron transfer between the electrode and microorganisms. α-Fe2O3/g-C3N4 achieved an acetate production rate of 0.33 g L–1 d–1, which increased by 3-fold compared to a carbon felt cathode. This work provides new opportunities for constructing a highly efficient photocathode for MES.

Highly selective nitrate reduction to ammonia on CoO/Cu foam via constructing interfacial electric field to tune adsorption of reactants

Electrochemical reduction of nitrate to ammonia (ERNA) is a new process to recycle nitrogen resource from nitrate polluted wastewater. Nevertheless, how to optimize active sites on electrode to improve activity is a key challenge. Here, we proposed that building interfacial electric field could enhance ERNA. XPS analysis, DFT calculations and in-situ electrochemical measurements confirmed that high Fermi level of Cu (1.09 eV) and low valence band maximum of CoO (−0.23 eV) formed interfacial electric field in CoO/Cu electrode to transfer electron from Cu to CoO, resulting in positively charged Cu (+0.01 eV) increase nitrate adsorption, whereas negatively charged CoO (−0.007 eV) decrease NO adsorption, improving removal and selectivity greatly for boosting ERNA. Eventually, CoO/Cu foam (Co/Cu ratio of 3.05) achieved the highest ammonia yield of 4.3 mg cm−2 h−1 with faradic efficiency of 96.7 %, surpassing Cu foam (1.2 mg cm−2 h−1) and CoO/Ni foam (1.3 mg cm−2 h−1) electrodes.

Developing Subthreshold-Swing Limit of PEALD In–Sn–Ga–O Transistor via Atomic-Scaled Sn Control

The In–Sn–Ga–O (ITGO) thin-film transistor (TFT) is promising in that it possesses enhanced electrical characteristics and stability because the tin (Sn) has large spherical s orbitals and a high binding energy with oxygen (O). Recently, there have been several reports of ITGO material fabricated via sputtering. Therefore, studies that control Sn composition to achieve unique characteristics and obtain conformal films have been limited. For these reasons, we evaluated plasma-enhanced atomic layer deposition (PEALD)-derived ITGO materials with varied Sn composition. The electrical characteristics are enhanced with the Sn subcycle ratio from 1 to 5 in the ITGO films (carrier concentration: 6.4 × 1020 to 2.2 × 1021 cm–3, resistivity: 8.6 × 10–4 to 6.1 × 10–4 Ω cm). These results are due to carrier generation by the Sn, a decrease in oxygen-related defects (22.9% to 19.5%), and suppressed indium-oxide (In2O3) crystallinity. To demonstrate their applicability to practical devices, the ITGO films were applied to TFTs as active channel layers. The ITGO TFTs with increasing Sn content show a decrease then increase of subthreshold swing (S.S.) characteristics, while the field-effect mobility (μFE) slightly increases. In addition, the ITGO TFTs show improved negative bias illumination stress (NBIS) stability with increasing Sn content, while the turnaround point is observed in the Sn 5 subcycle. As a result, the ITGO TFT with the Sn 3 subcycle shows an extremely low S.S. of 64.8 ± 1.9 mV/decade and an NBIS result of −0.5 V. The outstanding performance of the ITGO TFT with Sn 3 subcycle is attributed to its low number of oxygen-related defects, amorphous structure, and low valence band maximum (VBM) level. Therefore, the ITGO TFTs with optimized Sn content have the advantages of low power consumption and resistance to an environment with illumination.

Large tunable Rashba spin splitting and piezoelectric response in Janus chromium dichalcogenide monolayers

A mirror asymmetric Janus structure induces Rashba spin splitting (RSS) and a piezoelectric response. Inspired by the recently synthesized layered material CrSSe [Yang, Shi, Wang, Yue, Zheng, Zhang, Gu, Yang, Shadike, Li, and Fu, J. Mater. Chem. A 8, 25739 (2020)], we use first-principles calculations to systematically study the Rashba effect and piezoelectricity of Janus chromium dichalcogenide monolayers $\mathrm{Cr}XY$ ($X\ensuremath{\ne}Y=\text{S,}\phantom{\rule{4.pt}{0ex}}\text{Se,}\phantom{\rule{4.pt}{0ex}}\text{Te}$), as well as their regulation with biaxial strain. Our results reveal that spin-orbit coupling (SOC) plays an important role in the electronic properties (such as the semiconductor type, RSS, and valley polarization) of a $\mathrm{Cr}XY$ monolayer. Due to the mirror symmetry break and strong SOC, the strain-free $\mathrm{Cr}XY$ exhibits large Rashba parameters. Specifically, the Rashba parameter of CrSeTe is as high as 1.23 eV \AA{}. Due to the ${\mathit{k}}^{3}$ term in the valence-band edge, the CrSeTe exhibits a strong hexagonal warping effect along with a nonzero out-of-plane spin polarization ${\mathit{S}}_{z}$, which can also be found in the CrSSe and CrSTe monolayers in the lower energy valence bands. Moreover, the Janus $\mathrm{Cr}XY$ monolayer exhibits superior intrinsic piezoelectric responses (${\mathit{d}}_{31}$ = $0.4--0.83$ pm/V), which are orders of magnitude larger than those of the $\mathrm{Mo}XY$ monolayer. Furthermore, we reveal in detail the modulation of the band structure, RSS, and piezoelectric properties with biaxial strain. Tensile strain suppresses the band gap, whereas compressive strain increases the band gap. Thus, strain engineering can effectively tune the band structures resulting in semiconductor-metal and indirect-direct transitions. In addition, the strain has opposite effects on the RSS and the piezoelectricity; that is, unlike compressive strain-enhanced RSS, the tensile strain can significantly elevate the piezoelectric coefficients. Our results indicate that a Janus $\mathrm{Cr}XY$ monolayer has coexisting large intrinsic RSS and piezoelectricity, which can be efficiently regulated by strain engineering, opening opportunities for applications in spintronic and piezoelectric devices.