Lead-free Halide Double Perovskites Research Articles

DFT calculations on physical properties of the lead-free halide-based double perovskite compound Cs2CdZnCl6

Lead-free halide double perovskite materials have recently attracted considerable interest from the scientific community due to their vast potential in optoelectronic applications without toxicity issues. Herein, we report a new lead-free halide double perovskite, namely Cs2CdZnCl6, based on DFT calculations. We found that Cs2CdZnCl6 is mechanically stable in the cubic nonmagnetic phase. The Electronic band structure calculations revealed that this compound exhibits a direct semiconductor band gap of 1.43 eV. The dielectric function ε, reflectivity R, refractive index n, absorption coefficient α, and optical conductivity σ are analyzed up to 13.0 eV. Furthermore, it is found that the studied compound has a significant photoresponse in the ultraviolet light region. Finally, the findings suggest that Cs2CdZnCl6 is a promising material for optoelectronic applications.

Tunable and Efficient Photoluminescence of Lanthanide-Doped Cs2NaScCl6 Double Perovskite Single Crystals toward Multifunctional Light-Emitting Diode Applications.

Lead-free halide double perovskite, as one of the promising candidates for lead halide perovskite materials, shows great potential in light-emitting diodes (LEDs), benefiting from its environmental friendliness and high chemical stability. However, the poor regulation of the emission spectra severely limits its application range. Herein, various lanthanide ions were successfully doped in Cs2NaScCl6 double perovskite single crystals (DPSCs) to yield effective and stable emissions spanning from visible to near-infrared (NIR) regions. Notably, efficient energy transfer from the host to the dopants enables tunable emissions with good chromaticity, which is rarely reported in the field of lead-free double perovskite. Moreover, density functional theory calculations reveal that the high local electron density around the [LnCl6]3- octahedron in DPSCs plays a key role in the improvement of photoluminescence quantum yields (PLQYs). The optimal PLQYs are up to 84%, which increases around 3 times over that of the undoped sample. Finally, multicolor and NIR LEDs based on Ln3+-doped Cs2NaScCl6 DPSCs were fabricated and had different application functions. Specifically, the single-composite white LED shows adjustable coordinates and correlated color temperatures, while the NIR LED shows good night vision imaging. This work provides new inspiration for the application of efficient multifunctional LEDs based on lead-free double perovskite materials.

Enhanced CO2 Reduction with Cs2AgBiBr6-gC3N4 Heterojunction Photocatalysts Prepared by Green Synthesis

Halide perovskites are increasingly explored for CO2 photoreduction to carbonaceous products and fuels. However, multistep solution-based perovskite synthesis not only poses significant safety concerns but also introduces trap states in the perovskite, negatively impacting its properties/activities. In this work, we develop Cs2AgBiBr6-xGCN heterojunction (GCN, graphitic carbon nitride) by an environmentally nonhazardous hand-grinding method. The photocatalytic CO2 reduction activity of these hybrid catalysts is investigated in isopropyl alcohol using a 250 W mercury vapor lamp as an irradiation source. A high average CO and CH4 yield of 12.14 and 8.85 μmol/g/h is achieved for Cs2AgBiBr6-1GCN. These results exhibit 3- and 9.8-fold improvement in CO and CH4 production compared to pristine Cs2AgBiBr6. Space charge limited current and XPS measurements prove that GCN incorporation reduces the trap density, increases the carrier mobility, and induces strain in the perovskite. The interfacial defect passivation at the heterojunction ensures a faster and smoother charge transport, as confirmed by EIS Nyquist plots, suggesting enhanced CO2 photoconversion activity. These results extend the use of lead-free halide double perovskites in the photocatalysis field for solar fuels, leveraging a solvent-free dry synthesis route to diversify the utilization of perovskite heterostructure photocatalysts.

Cs2AgBiCl6: a novel, high-efficient and stable visible-light photocatalyst for degradation of organic dyes.

In the past decades, great efforts have been made to develop novel visible-light photocatalysts to achieve high photocatalytic efficiency by utilizing visible light, the largest proportion of solar energy. As a new type of photocatalyst materials, all-inorganic lead-free halide double perovskites have begun to attract widespread interest. Herein, double perovskite Cs2AgBiCl6 was developed into a visible-light photocatalyst for degrading organic dyes. Cs2AgBiCl6 was prepared by the hydrochloric acid precipitation and anti-solvent recrystallization methods, respectively, and was used to degrade organic dyes under visible light. Samples prepared by the anti-solvent recrystallization method are smaller than those prepared by the hydrochloric acid precipitation method, which can degrade 95.7% of Sudan III in 10 min and show excellent photocatalytic activity. The cyclic experiments demonstrate that Cs2AgBiCl6 has a good cycle stability. Moreover, Cs2AgBiCl6-AS also exhibits good photocatalytic degradation ability for Methyl red and Malachite green. These distinctive results indicate that Cs2AgBiCl6 may be a promising material for developing novel, high-efficient and stable visible-light photocatalysts.

A high-temperature double perovskite molecule-based antiferroelectric with excellent anti-breakdown capacity for energy storage

Halide double perovskites have recently emerged as an environmentally green candidate toward electronic and optoelectronic applications owing to their non-toxicity and versatile physical merits, whereas study on high-temperature antiferroelectric (AFE) with excellent anti-breakdown property remains a huge blank in this booming family. Herein, we present the first high-temperature AFE of the lead-free halide double perovskites, (CHMA)2CsAgBiBr7 (1, where CHMA+ is cyclohexylmethylammonium), by incorporating a flexible organic spacer cation. The typical double P-E hysteresis loops and J-E curves reveal its concrete high-temperature AFE behaviors, giving large polarizations of ~4.2 μC/cm2 and a high Curie temperature of 378 K. Such merits are on the highest level of molecular AFE materials. Particularly, the dynamic motional ordering of CHMA+ cation contributes to the formation of antipolar alignment and high electric breakdown field strength up to ~205 kV/cm with fatigue endurance over 104 cycles, almost outperforming the vast majority of molecule counterparts. This is the first demonstration of high-temperature AFE properties in the halide double perovskites, which will promote the exploration of new “green” candidates for anti-breakdown energy storage capacitor.

Bromide ions substitution-induced photoluminescence tuning in Cs2NaInCl6:Sb3+ double perovskite

Compositional tune and doping/alloying routes have become the research focus for tailoring optical features of lead-free metal halide double perovskites to advance the development of solid-state lighting and display applications. Cs2NaInCl6 double perovskite is receiving tremendous attention owing to its excellent optical properties. In this paper, we have successfully obtained the lead-free Cs2NaInCl6-xBrx:Sb3+ perovskites using the hydrothermal method. Via the substitution of bromine ions for chloride ions in Cs2NaInCl6:Sb3+, a tunable emission from 445 nm to 480 nm was realized. The X-ray diffraction, scanning electron microscope, UV–vis absorption spectra, PL spectra, TRPL spectra, air stability and thermal stability were investigated in detail. The sample shows an admirable air stability and excellent thermal stability. The results demonstrate that the cyan-emitting Cs2NaInCl6-xBrx:Sb3+ perovskites can be applied to white LEDs, especially for the full-spectrum LED illumination.

Lead-Free Solid State Mechanochemical Synthesis of Cs2NaBi1-xFexCl6 Double Perovskite: Reduces Band Gap and Enhances Optical Properties.

Efficient and stable lead-free halide double perovskites (DPs) have attracted great attention for the future generation of electronic devices. Herein, we have developed a doping approach to incorporate Fe3+ ions into the Cs2NaBiCl6 crystal unit and reveal a crystallographic and optoelectronic study of the Cs2NaBi1-xFexCl6 double perovskite. We report a simple solid-state mechanochemical method that has a solvent-free, one-step, green chemistry approach for the synthesis of Cs2NaBi1-xFexCl6 phosphor. The analysis of powder X-ray diffraction (XRD) data determines the contraction of the lattice due to the incorporation of Fe3+ cations, and this effect is well supported by X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), Raman spectroscopy, and solid-state nuclear magnetic resonance spectroscopy (ss-NMR). The band gap is reduced with increasing Fe content owing to the strong overlap of the Fe-3d orbitals with Cl-3p orbitals and shift of the valence band maxima (VBM) toward higher energies, as confirmed by ultraviolet photoelectron spectroscopy (UPS) and density functional theory (DFT) analyses. Photoluminescence (PL) studies of Cs2NaBi1-xFexCl6 phosphors exhibit a large Stokes shift, broadband emission, and increased PL intensity more than ten times for 15% of Fe content phosphor with enhancement in the average decay lifetimes (up to 38 ns) compared to pristine Cs2NaBiCl6 DP. These results indicate that the transition of dark self-trapping of excitons (STEs) into bright STEs enhances yellow emission. XRD, UV, and thermo-gravimetric analysis (TGA) confirmed that the Cs2NaB1-xFexCl6 DPs have good structural and thermal stabilities. Our findings indicate that the doping of Fe3+ cations into the Cs2NaBiCl6 lattice is a constructive strategy to enhance significantly the optoelectronic properties of these phosphors.

Triangulating Dopant-Level Mn(II) Insertion in a Cs2NaBiCl6Double Perovskite Using Magnetic Resonance Spectroscopy

Lead-free metal halide double perovskites are gaining increasing attention for optoelectronic applications. Specifically, doping metal halide double perovskites using transition metals enables broadband tailorability of the optical bandgap for these emerging semiconducting materials. One candidate material is Mn(II)-doped Cs2NaBiCl6, but the nature of Mn(II) insertion on chemical structure is poorly understood due to low Mn loading. It is critical to determine the atomic-level structure at the site of Mn(II) incorporation in doped perovskites to better understand the structure-property relationships in these materials and thus to advance their applicability to optoelectronic applications. Magnetic resonance spectroscopy is uniquely qualified to address this, and thus a comprehensive three-pronged strategy, involving solid-state nuclear magnetic resonance (NMR), high-field dynamic nuclear polarization (DNP), and electron paramagnetic resonance (EPR) spectroscopies, is used to identify the location of Mn(II) insertion in Cs2NaBiCl6. Multinuclear (23Na, 35Cl, 133Cs, and 209Bi) one-dimensional (1D) magnetic resonance spectra reveal a low level of Mn(II) incorporation, with select spins affected by paramagnetic relaxation enhancement (PRE) induced by Mn(II) neighbors. EPR measurements confirm the oxidation state, octahedral symmetry, and low doping levels of the Mn(II) centers. Complementary EPR and NMR measurements confirm that the cubic structure is maintained with Mn(II) incorporation at room temperature, but the structure deviates slightly from cubic symmetry at low temperatures (<30 K). HYperfine Sublevel CORrelation (HYSCORE) EPR spectroscopy explores the electron-nuclear correlations of Mn(II) with 23Na, 133Cs, and 35Cl. The absence of 209Bi correlations suggests that Bi centers are replaced by Mn(II). Endogenous DNP NMR measurements from Mn(II) → 133Cs (<30 K) reveal that the solid effect is the dominant mechanism for DNP transfer and supports that Mn(II) is homogeneously distributed within the double-perovskite structure.

Efficient Charge Transfer and Effective Active Sites in Lead-Free Halide Double Perovskite S-Scheme Heterojunctions for Photocatalytic H2 Evolution.

The practical application of lead-free double perovskite Cs2 AgBiBr6 in photocatalytic H2 evolution is still restricted due to the low activity and poor stability. The rational design of lead-free halide double perovskites heterojunctions with efficient charge transfer and effective active sites is a potential route to achieve the ideal prospect. Herein, in this work an S-scheme heterojunction of Cs2 AgBiBr6 with enriched Br-vacancies and WO3 nanorods (VBr -Cs2 AgBiBr6 /WO3 ) obtaining excellent visible-light responsive photocatalytic H2 evolution performance and durable stability is reported. The S-scheme heterojunction driven by the unaligned Fermi levels of these two semiconductors ensures the efficient charge transfer at the interface, and density functional theory calculations reveal the enriched Br vacancies on Cs2 AgBiBr6 (022) surfaces introduced by atom thermal vibration provide effective active sites for hydrogen evolution. The optimized VBr -Cs2 AgBiBr6 /WO3 S-scheme photocatalyst exhibits the photocatalytic hydrogen evolution rate of 364.89µmol g-1 h-1 which is 4.9-fold of bare VBr -Cs2 AgBiBr6 (74.44µmol g-1 h-1 ) and presents long-term stability of 12h continuous photocatalytic reaction. This work provides deep insights into the photocatalytic mechanism of VBr -Cs2 AgBiBr6 /WO3 S-scheme heterojunctions, which emerges a new strategy in the applications of perovskite-based photocatalysts.

Two-dimensional semiconducting Cu(I)/Sb(III) bimetallic hybrid iodides with a double perovskite structure and photocurrent response.

Stable lead-free hybrid halide double perovskites have sparked widespread interest as a new kind of photoelectric material. Herein, for the first time, we successfully incorporated copper(I) and antimony(III) into two two-dimensional (2D) hybrid bimetallic double perovskite iodides, namely (NH3C6H11)4CuSbI8·H2O (CuSbI-1) and (NH3C6H10NH3)2CuSbI8·0.5H2O (CuSbI-2), using cyclohexylamine and 1,4-cyclohexanediamine as organic components. The band gaps for CuSbI-1 and CuSbI-2 were determined to be 2.22(2) eV and 2.21(2) eV, respectively. Furthermore, these two layered perovskites were readily dissolved in an organic solvent (1 mL DMF can dissolve 1 g sample for each compound) and could form smooth, pinhole-free, and uniform thin films through a facile spin-coating method. Photocurrent experiments with xenon lamp irradiation revealed the obvious photoelectric responses for both 2D double perovskites. The ratio of the photocurrent to the dark current (Ilight/Idark) for CuSbI-1 and CuSbI-2 is about 23 and 10, respectively, further suggesting their potential to be applied as light harvesters or light detectors. More importantly, these 2D double perovskite iodides show high moisture and thermal stabilities, indicating their potential for optoelectronic applications.

Understanding the polaron behavior in Cs2CuSbCl6 halide double perovskite.

Lead-free halide double perovskites A2MM'X6 (A = Rb+, Cs+, etc.; M = Ag+, K+, Li+; M' = Sb3+, In3+ or Bi3+ and X = I-, Br- or Cl-) have recently been suggested as an alternative to lead-based halide perovskites for optoelectronic and photovoltaic applications. While a great deal of effort has been put into device engineering to improve the performance of photovoltaic and optoelectronic devices that are based on A2MM'X6 double perovskites, there has been relatively little attention given to their inherent photophysical properties. The current research demonstrates that small polaron formation under photoexcitation and polaron localization limit the carrier dynamics in the Cs2CuSbCl6 double halide perovskite. In addition, temperature-dependent AC conductivity measurements indicate that single polaron hopping is the primary conduction mechanism. The ultrafast transient absorption spectroscopy results revealed that the formation of small polarons, which function as self-trapped states (STSs) and result in the ultrafast trapping of charge carriers, are caused by a distorted lattice under photoexcitation. These findings provide a thorough understanding of the intrinsic restrictions of Cs2CuSbCl6 perovskite and could have relevance for other antimony-based semiconductors.

First-principles study on the role of anion in the physical properties of lead-free halide double perovskites

Lead-free halide double perovskite (HDP) materials have received increased attention in the field of perovskite solar due to their non-toxic nature, structural stability and enhanced optical properties. In this work, we performed the density functional theory calculations to investigate the role of halide ion (X = Cl, Br, I) substitution in the lead-free Cs2AgSbX6 compound as a prototype structure. The results revealed that the halogen ions play a crucial role in changing the physical properties of Cs2AgSbX6. The halide ions play a major role in light harvesting as absorption of light mainly involves optical transitions from the p- to s-orbitals of the halide ions. Cs2AgSbX6 (X = C1, Br, I) exhibits enhanced light absorbance α (ω) and less reflectivity n(ω) in the near infra-red to the visible region of the solar spectrum which clearly indicated that the efficiency of solar cells can be enhanced. Moreover, the material showed an indirect bandgap of 1.38 0.88, and 0.395 eV (Cl, Br, and I). This study is a valuable reference for single-junction solar cells and tandem solar cells for enhancing the power conversion efficiency.

Structural, optical and charge density investigations on lead free Mn2+ doped Cs2NaBiCl6 double perovskite microcrystals

Improved ambient stability and the non-toxicity of lead-free halide double perovskites have rendered them tremendous research focus in the recent years. However, their large indirect bandgap’s limit their optoelectronic applications. Introduction of activator transition metal ion such as Mn 2+ in their lattices modifies their absorption and emission spectrum. In this article, we have successfully synthesized Mn 2+ doped Cs 2 B′B′′Cl 6 (B′= Na + , B′′=Bi 3+ ) microcrystals by chemical reflux method. Crystallinity and morphological analysis were studied using X-ray diffraction and scanning electron microscopy respectively. The elemental analysis was carried out using Energy dispersive X-ray (EDS) and X-ray photoelectron spectroscopy. A prominent emission at 585 nm in tune with the 4 T 1 → 6 A 1 transition of the Mn 2+ ions is observed from the photoluminescence studies and carrier recombination dynamics was analysed using time resolved photoluminescence spectroscopy. Electron density distribution studies were also carried out using Maximum entropy method to understand the nature of bonding in Mn 2+ :Cs 2 NaBiCl 6 double perovskites. • Orange-red emission at 585 nm corresponding to Mn 2+ transitions. • Energy transferred from Cs 2 NaBiCl 6 to dopant Mn 2+ ions. • Mn 2+ doping preserves the cubic symmetry. • Mn 2+ acts as both sensitizer and activator. • Non-toxic, environment friendly, thermally stable, lead free double perovskite.

Origin of ultralow phonon transport and strong anharmonicity in lead-free halide perovskites

All-inorganic lead-free halide double perovskites offer a promising avenue toward non-toxic, stable optoelectronic materials, properties that are missing in their prominent lead-containing counterparts. Their large thermopowers and high carrier mobilities also make them promising for thermoelectric applications. Here, we present a first-principles study of the lattice vibrations and thermal transport behaviors of Cs2SnI6 and γ-CsSnI3, two prototypical compounds in this materials class. We show that conventional static zero temperature density functional theory (DFT) calculations severely underestimate the lattice thermal conductivities (κl) of these compounds, indicating the importance of dynamical effects. By calculating anharmonic renormalized phonon dispersions, we show that some optic phonons significantly harden with increasing temperature (T), which reduces the scattering of heat carrying phonons and enhances calculated κl values when compared with standard zero temperature DFT. Furthermore, we demonstrate that coherence contributions to κl, arising from wave like phonon tunneling, are important in both compounds. Overall, calculated κl with temperature-dependent interatomic force constants, built from particle and coherence contributions, are in good agreement with available measured data, for both magnitude and temperature dependence. Large anharmonicity combined with low phonon group velocities yield ultralow κl values, with room temperature values of 0.26 W/m-K and 0.72 W/m-K predicted for Cs2SnI6 and γ-CsSnI3, respectively. We further show that the lattice dynamics of these compounds are highly anharmonic, largely mediated by rotation of the SnI6 octahedra and localized modes originating from Cs rattling motion. These thermal characteristics combined with their previously computed excellent electronic properties make these perovskites promising candidates for optoelectronic and room temperature thermoelectric applications.

Theoretical Understanding of thermoelectric energy conversion efficiency in Lead-Free halide double perovskites showing intrinsic defect tolerance

Thermoelectric devices based on the Seebeck effect can directly convert waste heat to electricity, but the demand for better thermoelectric materials remains unfulfilled. The lead-free halide double perovskites have recently shown promises for their stability and environment-friendly nature, but impacts from intrinsic defects (vacancies and anti-sites) on their thermoelectric performance remains elusive. Combing first-principle calculations, the Boltzmann transport theory, and the defect formation theory, we investigate the thermoelectric properties of lead-free double perovskite Cs2NaInCl6, taking the intrinsic defects into consideration. Our results demonstrate that the pristine Cs2NaInCl6 presents thermodynamic, mechanical, and dynamic stability. The band edges are mainly comprised of the electrons from In and Cl atoms. Furthermore, the double perovskite has an ultra-low lattice thermal conductivity and a high Seebeck coefficient, while showing a small charge carrier relaxation time and electric conductivity. Promisingly, the maximum ZT values can reach as high as ∼ 1.36 and ∼ 1.44 at 800 K temperature, respectively, with optimal extrinsic carrier concentrations of ∼ 1.9 × 1019 and 5.8 × 1020 cm−3 for N- and P-type carriers (holes and electrons), and the maximum power generation efficiency can reach ∼ 14% (for P-type) when the hot-side temperature is 800 K. Among various intrinsic defect types, we determine the preferable defect types in Cs2NaInCl6 based on the minimal defect formation energy criteria. The free carriers can be switched from N- to P-type under these two preferable defects, respectively, with Cl and Na vacancies. Even under a very high defect concentration of 2.1 × 1019/cm3 considered here, the extra carrier concentrations induced by the defects are only ∼ 1017 cm−3 at 800 K, showing strong defect tolerance in carrier concentration. This work suggests that lead-free halide double perovskites are promising thermoelectric materials, and they show strong intrinsic defect tolerance that prevents a negative impact on the extrinsic doping-controlled carrier concentrations.

Improved charge extraction and atmospheric stability of all-inorganic Cs2AgBiBr6 perovskite solar cells by MoS2 nanoflakes

Among lead-free halide double perovskites, Cs 2 AgBiBr 6 is a potential alternative to substitute toxic and unstable organic-inorganic lead-based halide perovskites. However, the film forming ability and wide indirect bandgap have impeded its applications. Herein, we investigate to use MoS 2 nanoflakes as a hole transport interlayer to improve the crystallinity of Cs 2 AgBiBr 6 , tailor energy level alignments and enhance the stability of solar cells. With the addition of the MoS 2 nanoflakes, the Cs 2 AgBiBr 6 -based solar cell has a power conversion efficiency of 4.17% with an open circuit voltage of 1.10 V and short-circuit current of 6.12 mA cm −2 . This work would provide a new approach for developing all inorganic lead-free Cs 2 AgBiBr 6 -based solar cells with high power conversion efficiency and good stability. • MoS 2 can tailor the energy level of Cs 2 AgBiBr 6 to enhance hole extraction. • The power conversion efficiency of the device with MoS 2 nanoflakes is up to 4.17%. • The devices with MoS 2 remain 90% efficiency up to 23 days under ambient conditions.

High-Efficiency and Wavelength-Tunable Near-Infrared Emission of Lanthanide Ions Doped Lead-Free Halide Double Perovskite Nanocrystals toward Fluorescence Imaging.

Near-infrared (NIR) fluorescent materials show unique photophysical properties, which make them widely used in optical communication, night vision imaging, biomedicine, and other applications. However, the development of high-efficiency and wavelength-tunable NIR nanomaterials is still a challenge. Herein, a series of lanthanide ions doped Cs2AgIn0.99Bi0.01Cl6 double perovskite nanocrystals (DPNCs) with wavelength-tunable NIR light emission (800-1600 nm) have been synthesized. The optimal photoluminescence quantum yield (PLQY) of the DPNCs reaches 66.7%, which is a record value for DPNCs. It is mainly attributed to the contribution of NIR emission of lanthanide ions doped into DPNCs. More importantly, the series of NIR emission wavelengths of lanthanide ions doped Cs2AgIn0.99Bi0.01Cl6 DPNCs include not only shorter-wavelength NIR light (≤900 nm) but also longer-wavelength NIR light (>900 nm), which are more appropriate for foodstuff analysis and medical diagnosis applications. Furthermore, 11.2% Nd3+ doped Cs2AgIn0.99Bi0.01Cl6 DPNCs with the optimal PLQY were embedded in a polymethyl methacrylate (PMMA) polymer matrix (DPNCs@PMMA), and the stability of DPNCs modified by PMMA has been greatly improved. Finally, the 11.2% Nd3+ ions doped Cs2AgIn0.99Bi0.01Cl6 DPNCs@PMMA based NIR LEDs have demonstrated good night vision and human tissue penetration. This work indicates that lanthanide ions doped DPNCs have a potential in NIR light applications and could inspire future research to explore novel lanthanide ions doped semiconductor NCs based NIR LEDs.

In-situ assembling 0D/2D Z-scheme heterojunction of Lead-free Cs2AgBiBr6/Bi2WO6 for enhanced photocatalytic CO2 reduction

All-inorganic lead-free halide double perovskites have emerged as rising star photocatalysts to substitute the toxic lead-based hailed perovskites (LHPs) owing to their unique photophysical properties. Nevertheless, their photocatalytic activities toward CO2 reduction are still far from comparable with the LHPs, associated with severe charge recombination and sluggish surface catalytic reaction. Herein, a delicate 0D/2D heterojunction of Cs2AgBiBr6/Bi2WO6 (CABB/BWO) was assembled by in-situ growing cubic CABB nanocrystals on the flat surface of BWO nanosheets via a facile hot-injection method. Density functional theory (DFT) calculations disclose that the work function and Fermi level difference between CABB and BWO give rise to charge redistribution at the interface upon the formation of the heterojunction, creating an internal electric field (IEF). Upon light irradiation, the IEF enables the photogenerated electron transfer from BWO to CABB via direct Z-scheme electron transfer mode with striking spatial charge separation as verified by in-situ X-ray photoelectron (XPS) and electron spin resonance (ESR) spectra. Consequently, the CABB/BWO heterojunction realizes 7-fold higher photocatalytic activity than pristine CABB with significant electron consumption rate of 87.66 µmol g-1h−1 under simulated solar light (AM 1.5G).

DFT study of structural, mechanical, and opto-electronic properties of scadium-based halide double perovskite Cs2ScInBr6 for optoelectronic applications

A complete and compressive first-principles investigation of the physical characteristics of a lead-free halide double perovskites Cs2ScInBr6, has been reported. Cs2ScInBr6 has a small and direct bandgap at L-point, as predicted from the band structure profile. The band structure were calculated using GGA and GGA + mBJ potential and it shows the same trend in both exchange-correlation potential. The calculated value of bandgap using GGA potential is 0.73 eV, while using mBJ it has 0.81 eV. The lattice stability reported in this study was in good agreement with previously synthesised, and analyzed double perovskites Cs2AgBiBr6. Similarly, from elastic analysis results show that the material under investigation is mechanically stable, and ductile in nature. Optical properties like absorption coefficients, refractive index, optical conductivity and reflectivity, electron energy loss, and extinction coefficients are computed and studied over an energy range of 0–4 eV. The analysis of small and direct band gaps, as well as optical properties such as absorption coefficients, show that Cs2ScInBr6 is suitable for infrared device applications. Also, the findings of current study would be useful for future experimental investigations to assess Cs2ScInBr6 for optoelectronic applications.

Reactive Physical Vapor Deposition of Yb-Doped Lead-Free Double Perovskite Cs2AgBiBr6 with 95% Photoluminescence Quantum Yield

Yb-doped Cs2AgBiBr6 is a promising lead-free halide double perovskite that can be used as a downconverting coating on silicon solar cells to redshift UV and blue photons to the near-infrared where the quantum efficiencies are larger. Herein, we show that photoluminescence quantum yield (PLQY) of Yb-doped Cs2AgBiBr6 thin films synthesized via physical vapor deposition depends strongly on how the substrate temperature changes during deposition, which determines the amount of Bi incorporated into the film. Yb-doped Cs2AgBiBr6 films with PLQY as high as 95% were deposited with excess BiBr3 and by ramping substrate temperature during the deposition. Ramping the substrate temperature reduces BiBr3 loss from the film by promoting reactions that form Cs2AgBiBr6. As a result, the films formed have high PLQY and retain 93% of their initial PLQY values after 1 month.